We report a new type of high-performance RF-lightwave transmitter, which can provide >10 dB RF insertion gain at <0 dBm optical power with high spur-free dynamic range and low noise in analog fiber links.

A wavelength-shift-keying (WSK) proof-of-concept experiment was demonstrated by using tunable laser and wavelength discriminator with both 2-level and 3-level modulations. Basic applications of this new technology have been discussed. The WSK could potentially be a high-speed and flexible transmission technology for future optical networks.

With OC-192 communications systems now being commercially available and higher bit rate systems in development, prudent telecommunications network administrators are testing their installed fiber to determine if it can be successfully used at 10 Gb/s and higher. Together with NBTe1, we have tested various installed fibers and cables for their losses at wavelengths of 1244, 1310, 1550 and 1625 nm, as well as for strain and polarization mode dispersion (PMD). Aging effects on different fiber types have been studied. Experimental data has been analyzed to determine the relationships, if any, between loss, strain, weather, fiber age, fiber type and PMD. The suitability of these fibers for high speed systems has been analyzed. Some of the results of this analysis are presented.

This paper proposes and demonstrates a scheme for generating pseudo-random wavelength hopping sequences in semiconductor lasers by using chaotic dynamics. The system consists of a wavelength tunable light source, a nonlinear wavelength element, and a delayed opto-electric feedback. By feeding back the filter output signal to the light source to control the lasing wavelength, it is possible to achieve periodic or chaotic wavelength variation patterns with a wide variation range covering several longitudinal modes. In experiments, wavelength hopping among up to 10 modes was observed with the hopping frequency about 100 MHz. Synchronization of the wavelength hopping in two separate lasers is performed by coupling part of the feedback signal of one laser into the feedback of a second laser. Synchronization was observed between the on-off intensity modulation patterns of each pair of corresponding longitudinal laser modes.

We propose an all-optical parallel interface based on the HIPPI-6400 protocol [1]. WDM techniques and optical switches asawellas buffers are used to implement the parallel interface. Optical switches can switch all wavelengths in one switching operation, so the switch fabrics can be simplified. Since the information is kept in the optical domain, the cost and latency can be reduced. Through the optical transparency, variable bit rates of data micropackets can be used in different connections.

Optical packet networks have the advantages of high efficiency and transparency. It can take care of a heterogeneous mix of traffic. We demonstrated bit-rate and signal-format transparent operations of an all-optical packet-switched network.

A time domain system model is developed for studying the performance of a FO-CDMA LAN (i) with non-ideal network parameters and (ii) in the presence of multi-user interference (MUI). We examine the effect of chirping in a laser diode on its spectral response. Effects of changes in laser device parameters on its output are studied. Error performance of the complete system, including non-idealities of laser source, optical fiber channel and the APD detector is studied using our time domain simulation model, in the presence of MUI. The effect of having two hard-limiters on the system performance is studied. Our simulation result is verified with the help of an analytical model.

In this work, the optimization of level spacing in terms of the extinction ratio variation in quaternary optical communication systems is investigated, for signal-dependent noise dominance. It is shown that the performance of optically preamplified quaternary communication systems can be optimized in terms of levels spacing using very simple formulas, also derived in this work. For the null extinction ratio, sensitivity improvements of about 6 dB can be achieved by proper location of signal levels in comparison with the sensitivity of equally spaced levels. At high extinction ratio, this improvement is not so significant.

The gain of an EDFA (erbium doped fiber amplifier) is in general wavelength-dependent, leading to different amplification levels among WDM (wavelength division multiplexing) channels. The use of Optical FFH-CDMA (fast frequency hopped code division multiple access) offers a natural diversity of wavelength, and therefore gain, thus eliminating the requirement of an equalization stage to achieve flat gain on all channels. Computer simulations are developed to analyze and compare equalization performance of these two transmission approaches (CDM and WDM) in EDFAs, especially in situations where the EDFA operating point is subject to change (i.e., variable input traffic). We find that WDM requires an equalization stage that fails when packetized traffic characteristics shift, whereas optical FFH-CDMA presents the advantage of more robust, hence truly dynamic, gain equalization.

In this paper, an optical bufferless interconnection network is proposed. Due to its modular architecture and the use of the advanced wavelength-division-multiplexing technology, the proposed optical interconnection network can be scaled up in the range ofterabit per second. In this paper, we present its architecture and component complexity as a function ofthe number of wavelengths. In addition, we also analyse its power budget, and evaluate the crosstalk caused by the finite ON-OFF ratio of optical switching gates. Bit error rate with respect to different ON-OFF ratios and extinction ratios are evaluated by simulations. The results show that it is feasible to construct a 256x256 optical interconnection network with existing state of the technology.

In this paper, a transparent 24-node WDM bi-directional wavelength path switched ring (BWPSR) network with high transmission capacity is presented by using recently developed wavelength division multiplexing (WDM) and fiber Bragg grating (FBG) technologies to support logical full-meshed topology. The wavelength assignment algorithm for any size ring network is proposed. We also propose a new node structure, and develop numerical simulation model to study the effects of the accumulated amplified spontaneous emission (ASE) noise, insertion losses, and dispersion losses in large-scale BWPSR network.

In this paper we describe a phasar-based packet WDM network architecture. The main characteristics and trade-offs are explained and simulation results of three different network architectures for IP and ATM protocols are presented.

Large data processing environments in use today can require multi-gigabyte or terabyte capacity in the data communication infrastructure; these requirements are being driven by storage area networks with access to petabyte data bases, new architecture for parallel processing which require high bandwidth optical links, and rapidly growing network applications such as electronic commerce over the Internet or virtual private networks. These datacom applications require high availability, fault tolerance, security, and the capacity to recover from any single point of failure without relying on traditional SONET-based networking. These requirements, coupled with fiber exhaust in metropolitan areas, are driving the introduction of dense optical wavelength division multiplexing (DWDM) in data communication systems, particularly for large enterprise servers or mainframes. In this paper, we examine the technical requirements for emerging nextgeneration DWDM systems. Protocols for storage area networks and computer architectures such as Parallel Sysplex are presented, including their fiber bandwidth requirements. We then describe two commercially available DWDM solutions, a first generation 10 channel system and a recently announced next generation 32 channel system. Technical requirements, network management and security, fault tolerant network designs, new network topologies enabled by DWDM, and the role of time division multiplexing in the network are all discussed. Finally, we present a description of testing conducted on these networks and future directions for this technology.

The application of optic and photonic technology in electric networks in many cases is subject to constraints that differ from telecommunication or commercial applications. Starting by an overview of the quality of service (QoS) needed, in the first part of this paper we summarise some issues that confronted Hydro-Quebec in applying fibre optic technologies to its network. We explore by presenting lab and field trials some issues related to optical ground wires (OPGW) design and network architecture. We present temperature, vibration, ageing and short circuit current effects. We submit the results and analysis of a first field trial of and OC-48 link over a 265 km OPGW line, PMD measurements and an overview of the final design that is being implemented presently using Raman amplification. In the last section of the paper, we will discuss shortly of non-conventional photonic based technologies, local and distributed sensors and optical phenomenon that are used or have been discovered in utilities optical networks.

This paper describes the evolution of future WDM networks that use multi-wavelengths to realize several network functions. together with the implications of technology enhancements.

In this paper, a novel dual-bus WDM ring network is proposed, its medium access protocol is discussed, and the system performance is analyzed. Compared with some existing network architecture and protocols, the proposed network can achieve high throughput with moderate delays. We also proposed a slightly revised 10Gb/s WDM Ethernet using the ringshaped dual bus with 4 wavelength channels. Simulation result shows that the proposed 10Gb/s WDM Ethernet has a better throughput and delay performance than a conventional Ethernet based on CSMA.

A scalable transparent fiber-based microcellular system is proposed. Optical coherent detection is used in both MSC and antenna unit. The user units access the antenna by time division multiplexing access technology

Multiple Bragg gratings are written in a single fibre strand with accurate positioning to achieve predetermined time delays between optical channels. Applications of fibre Bragg grating arrays include encoders/decoders with series of identical gratings for optical code-division multiple access.

Fiber-optic Bragg gratings are fabricated in hydrogen-loaded communications-grade optical fibers using 244 nm continuous wave light. The fiber-buffer is only partially stripped to allow the ultraviolet grating writing beam to enter the fiber. This light is completely absorbed by the buffer behind the fiber. The absorption of ultraviolet light by the buffer significantly increases the rate of formation of Bragg gratings. This is explained as being due to the heating effect on fiber due to the absorption of ultraviolet light.

Electric discharge and CO2 laser exposure can produce long period gratings in standard telecommunication fibers. These two fabrication techniques are examined and compared to the UV laser exposure technique. Cladding modes involved in these gratings have been measured and identified using a computer simulation based on coupled mode equations. Fundamental mechanisms of the gratings production are also examined.

Using a recently developed inverse scattering layer-peeling algorithm and a modified stroboscopic grating writing technique, we have designed and successfully demonstrated novel grating devices, such as 50GHz-bandwidth dispersion compensators and square dispersionless filters, suitable for future high performance DWDM optical systems.

Fused fibre 2 x 2 couplers are key components for telecommunication networks. The fusion and tapering technique is the preferred technique because fused couplers are easy to manufacture, low cost and low loss devices. They also are the basic elements of a number of more complex components which are as well essential parts of the networks. However before entering the production process they must be carefully designed and it is one of the role of the the Fiber Optic Laboratonj which acquired over the years an expertise and a know-how which led to commecially available products.

An interferometric technique for the measurement of chromatic dispersion and length of long single mode fiber is demonstrated using a novel asymmetrically modulated Sagnac interferometer. The mterferometer incorporates a phase modulator and a test fiber, so that dispersion and length can be determined from the interference fringe that is available at the Outut when a sweep RF signal is applied to the modulator. This technique measures dispersion with high temporal resolution, requires no fast test equipment and is suitable for installed fibers over a wide range of lengths.

A review is presented of state-of-the-art optical planar waveguide demultiplexers (DEMUXes); that is, phasars (arrayed waveguide - AWG) and etched grating devices designed for dense wavelength division multiplexing (WDM) systems. The advances made in their performance are reviewed and ultimate limitations, set by physical principles and technological constraints, are considered. Finally, the advantages and disadvantages of etched grating and phasar planar waveguide DEMUXes are discussed.

Bent waveguides are a very important structure in integrated optics [1]. They are used to change the propagation of the light guided in optoelectronic devices. The inherent limitation of bent waveguide structures is that its associated radiation loss increases with branching angle [2]. To reduce the radiation loss, a bent waveguide with small branching angle must be reluctantly constructed due to the sacrifice of dimensional compactness. To achieve compact integrated optical devices and modules with low loss, a variety of low-loss and wide-angle bent waveguide structures have been reported [3]-[8]. Among of them, the microprism-type bent structure is a promising one for practical application [4]-[8J. In a conventional bent waveguide, phase compensation rule was used to design microprism-type structures. To tilt the entire phase front of the guided eigen mode wave, a microprism was designed to compensate for the phase difference between phase fronts in front of and behind the bent region. However, for the conventional design, only the innermost and outmost optical paths of the microprism were considered for phase compensation. Since the other optical paths are ignored, the designed microprism was trangular. To avoid the compensation error, the whole optical paths propagating through microprism must be considered. Since the optical path changes its direction gradually and continuously within bent or tapered region [9], instead of abrupt change as assumption of conventional analysis, a curved path is adopted to simulate more actual situation. The systematic design and analysis of the so-called full phase compensation microprism-type bent waveguides are investigated. It is very difficult to construct the ideal microprism configuration in practical fabrication process due to inevitable fabrication tolerances. For example, the vertices of the designed microprism shape are distorted and flattened, referred as "flattened-vertex" tolerance, during practical photolithography processes. Besides, the accurate refractive indices of the designed structure are unattainable in practical deposition, referred as "Variant-index" tolerance. For the pattern alignment during the photolithography process, the microprism pattern may be tilted from exact position, referred as "pattern-tilt" tolerance. All of the dependences of the transmission efficiency on these tolerances in fabrication processes are studied.

Numerically simulated performance of a new type of bandpass filter, based on discontinuity-assisted ring resonator (DARR) loaded couplers is presented. The operating characteristics of the device are similar to those of a long grating with a centered cavity or a photonic crystal with a defect. The filter is tuned by varying the length or the refractive index of the cavity. Selectivity and tuning range is controlled by the coupling coefficient of the couplers and by the reflection coefficient of the discontinuities. A design procedure and the effect of loss are also presented.

Integrated power splitters with high performances in a very broad spectral region are key components in Passive Optical Networks (PON). In this paper we present the design and experimental characterization of several power splitters with division ratios ranging from 1x8 to 1x32 and using an innovative layout architecture that allows a sensible reduction of the device occupation with a simultaneous improvement in the device performance. The measurements show that all the devices have a uniform response well within specifications and, thanks to the ion exchange in glass substrate fabrication technology, very low insertion losses and Polarization Dependent Losses (PDL).

The increasing diffusion of WDM communication systems requires low cost and efficient optical add-drop devices to add or drop channels at predefined wavelengths with reduced insertion loss and cross-interference. Although many fiber based devices have already been proposed, the integrated solution is very attractive since it allows an increase in the compactness and in the mechanical stability. In this paper we propose an innovative integrated OADM based on a grating assisted coupler that exhibit a theoretically null back-reflection at all the ports and does not require a critical grating longitudinal positioning. Simulations done assuming a glass on silica technology show the excellent performances of the proposed device.

An integrated optical demultiplexer is an ideal device for the measurement of the effect of strain (or, equivalently, stress) on birefringence. We fabricated optical demultiplexers from silicon oxynitride optical waveguides and measured the strain dependence of the passband wavelengths. From the shift in the passband wavelength, we determined the strain dependence of the effective index for the silicon oxynitride waveguide.

The design, packaging, and performance of a novel 32 channel, 100GHz dense wavelength division demultiplexer (DWDM) using the 22w' diffraction order of an Echelle grating is described. A fully packaged prototype operating in the 1 .54 to 1 .57-rim spectral range is built and tested. The insertion losses of all 32 channels are within -3.0±0.2 dB. The crosstalk between adjacent channels for all the 32 channels is in the neighborhood of -30dB, and average 1dB optical pass band is O.256nm. Key words: Wavelength division demultiplexing, Echelle grating, dispersion ability, DWDM packaging

Dense wavelength division multiplexing at high data rate is believed to be a viable solution to the growing demand for large bandwidth optical communication. Such development requires a wide range of active and passive optical components. Semiconductor laser with high power and diffraction-limited output beam are important light sources for a number of applications including pump source for EDFA and Raman amplifiers, as well as free space optical communications. One of the most promising designs to obtain high brightness lasers is the so-called tapered cavity laser, which consists of a ridge and a tapered gain section [1]. In order to achieve single mode with circular emission, we developed curved grating coupled surface-emitting tapered lasers [2]. Figure 1 shows a schematic view of our laser. The lasers were fabricated on a strained InGaAs/GaAs/A1GaAs triple-quantum well GRINSCH structure. The 3-jim wide ridge is designed to only support the fundamental lateral mode. The ridge length is 400-jim. The function of the spoiling groove is to prevent any feedback from the tapered section to the unpumped region in the ridge side. Therefore the ridge and spoiling grooves promote fundamental mode operation and suppress high order lateral modes. Connected to the ridge is the tapered section, which provides most part of the gain needed for lasing. The length of the tapered section is 1 800-jim with a full angle of about 7 degrees, which is designed to accommodate the free diffraction of the beam inside the tapered section. The feedback mirrors consist of a cleaved facet on the ridge side and a curved second-order Bragg grating on the tapered side. The curvature of the grating is designed to approximately match the phase front of the forward propagating beam, in this case, the center of curvature is located at 1800 jim from the tapered end. This will make the output beam to be collimated and has a small divergence angle.

Photonic techniques offer several advantages in microwave systems and applications. Optical method of generating time delay of a microwave signal for beam forming and beam steering an antenna array has been an important application.1 The advantages are in terms of higher resolutions and bandwidth. In this paper we present an optical integrated circuit that forms a part of optical true time delay network. The circuit consists of different segments of curved optical waveguides selected by electro-optic switching on a lithium niobate substrate. The design is for a 16-element antenna array with 4-bit beam forming resolution. Optimisation of delay time lengths with respect to time delay is done. Also analysis of errors in beam steering angle and time delay due to variations in curved waveguide arc lengths and cross talk in optical directional coupler switches are also presented.

We are studying the frequency selective properties of a tapered silica capillary for applications in multiwavelength optical communications. The 22-nm wall thickness capillary presents Fabry-Perot resonances at 6.4 THz intervals in the 1500-nm band. With resonances as sharp as 1 .5 nm such capillaries could serve as stable inexpensive fibered Fabry-Perot reference filters.

There is a need for integrating various active and passive devices on a single substrate to increase the functionality of optical modules [1-4]. One of the methods is to use regrowth for creating a low-loss passive waveguide butt-coupled to the active waveguide [1]. Besides being a complex technology, issues like low-loss coupling over multiple runs is still a challenge. A second technique used for integration is selective area growth [2]. In general, this technology does not allow for freedom in the design of the various layer thickness and bandgaps of the integrated waveguides. Quantum well interdiffusion [3] has also been used for integration by altering the bandgaps of the waveguides but also suffers from a lack of freedom in waveguide design and in the selection of the proper bandgaps.

A two-dimensional self-consistent time-dependent simulation technique has been used to investigate electron-hole transport processes in the active region of metal-semiconductor-metal photodiode structures (MSM-PD) and to analyze their high-speed response at different energy levels of the optical illumination. Charge accumulation and screening of the dark electric field at high optical excitation levels greatly modify the drift conditions of the photogenerated electrons and holes in the active region of the MSM-PD. This effect gives rise to impulse response distortion and reduced bandwidth and efficiency. Several ways of improving the high-speed response of the MSM-PD are analyzed and discussed. The conditions under which screening of the internal field has no effect on the MSM-PD response are formulated. Modeling data are compared with experimental results.

Exploiting the unique properties of holographic optical elements, a novel design for the receiver optical subsystem used in Multi-Spot Diffusing Configuration (MSDC) is proposed. With a holographic spherical mirror (HSM) as an optical front-end, the receiver would achieve significant improvements in the electrical signal-to-noise ratio compared to a bare photodetector. Though better performance could be achieved using other types of optical concentrators, the multifunctionality of the HSM, its small size, light weight, and low-cost make it a promising candidate for a user's portable equipment in broadband indoor wireless multimedia access.

A new formulation of the vectorial-BPM with Perfectly Matched Layer absorbing boundary conditions of coordinate stretching-type has been developed. It is shown that, if the resulting wave equations are discretized by a Fourier series expansion method based on the Galerkin's strategy, the obtained results are clearly superior to those obtained with the classical FFT-BPM (based on the collocation strategy). Both the formulation and the proposed discretization scheme were tested in 2D situations, homogeneous and guided-wave media, showing in all cases excellent results. Also, in this work, a variable transformed Fourier series expansion method is used to analyze the propagation in 2D structures and the problems involved with reflections in the transformed coordinates are pointed out.

A key issue in hybrid integration of optical waveguidc devices such as plU)todiOdes, modulators or semiconductor optical amplifiers is efficient coupling of light from a fiber into (lie waveguide device. Typically, a coupling loss of 7dB occurs when a cleaved single mode fiber (SME) is used for direct coupling toa waveguide device. This large value arises from the fact that the circular modal spot (diameter about I Op iii) of the SME I Op iii is poorly matched to the small (I —3pm) elliptical mode profile of a semiconductor wavcguide structure Major improvements can he achieved by introduction of mode profile transformers such as integrated spot size converter (SSC) Ij, the employment of micro lenses 121, or tapered fibers 31. Among these approaches, the most straightforward solution to increase the coupling efficiency is to employ tapered or lcnsed SMEs is spot size reducer. 'Ibis technique neither requires sophisticated fabrication techniques nor additional lcnses. In this paper. we report on the fabrication of low—loss tapered SMI"s will] mode field diameters( MFDs) as small as 0.8 pm. Improved coupling efficiency up to 80 (3 has been achieved when coupling 1 .55piii light from tapered fibers into I .55 pm InGaAsP/InP waveguide modulators and photodetectors

The crosstalk performance of an arrayed-waveguide grating (AWG) multi-/demultiplexer is primarily caused by random optical phase errors introduced in the arrayed-waveguides. Since the layout of waveguides on a wafer is patterned by photomask through photolithography process, the resolution of a photomask has a direct influence on the phase errors of an AWG. This paper presents a theoretical analysis on the phase error caused by photomask resolution along with other basic design parameters. Both calculation and measurement results show that a high-resolution photomask (better than 25 nm) is a critical requirement to produce low-crosstalk (less than -30 dB) AWG demultiplexers. We also investigated the non-ideal power distribution in the array waveguides since it contributes considerable phase errors when material impurity is not well controlled during wafer fabrication. Basic criteria of power profile truncation, number of grating waveguides, and material index variation are summarized in this paper as well.

The National Institute of Standards and Technology (NIST) has recently administered two interlaboratory comparisons, coordinated within the Fiber Optics Committees ofthe Telecommunications Industry Association (TIA), of measurements on single-mode optical fibers. The first dealt with Effective Area (Aeff) but also included Mode-Field Diameter (MFD) measurements; the second concerned Nonlinear Coefficient (n2/Aeff). The Aeff comparison included five participants. Standard deviations, per fiber, for all participants' measurements, ranged from 0.4 % to 0.7 % for MFD and from 1.3 % to 3.9 % for Ae. The fl2/Aeff comparison included data from six participants. Differences in measurement test sets required different participants to use wide ranges of specimen lengths and input powers. Standard deviations, per fiber, for all participants' measurements of n2/A ranged from 9.6 % to 18.7 %.

The response of a fiber to a sinusoidally modulated input which models an alternating hit sequence is studied to analyze the cross-phase modulation penalty in a WDM system. The derived expression shows good agreement with numerical results in conventional single-mode fiber systems over a wide range of channel spacing. JJ and in dispersion-shifted fiber systenis when 4f> 100GHz.

In a dynamic WDM-OXC, due to the various available paths for an incoming signal, there exits a special kind of samewavelength crosstalk, termed same-source crosstalk. Its impact on the system is more severe than that of other kinds of crosstalk under the worst case. This paper also points out that, by introducing light path differences between different channel, one can distinctly reduce the impact of the same-source crosstalk with simple and minimum hardware cost.

Recently, lightwave systems have attracted great interest not only for digital optical communication but also for the distribution of microwave and mm-wave signals in wireless applications. Future wireless communication networks are expected to offer broadband multimedia services to a large number of subscribers. As a consequence, the radio frequency is expected to be within the mm-wave band where a sufficient bandwidth for the large number of broadband channels is available. Since the electrical transmission of the mm-wave radio signals over long distances is not feasible, fiber-wireless systems have attracted great interest. They are considered to form the backbone of future broadband mm-wave wireless communication systems. Obviously, the successful implementation of mm-wave wireless communication networks in mass-market applications strongly depends on the costs of the infrastructure. In that respect, specially the cost of each single base station (BS) is a very critical factor since future wireless networks are expected to support a large number of remote BSs. Consequently, it is of great interest to reduce the base station complexity and cost. In this paper, we present a novel photonic transceiver component and discuss its application in mm-wave fiber-wireless systems. In detail, an InP-based 1 .55im waveguide electroabsorption transceiver (EATs) is presented that serves as a modulator and a photodetector simultaneously. Besides the basic device concept and its properties, the employment of high-speed EAT in 60GHz millimeter-wave (mm-wave) fiber-wireless applications is experimentally demonstrated. For the first time, full-duplex broadband (155.52Mbit/s) fiber-optic transmission in the 60GHz band has been achieved in a point-to-point link. Furthermore, a point-to-multipoint fiber-ring network architecture employing EAT is presented and in a first experiment full-duplex point-to-multipoint operation in the 60GHz band is experimentally demonstrated.

A novel structure for an electro-optic (e-o) polymer based Mach-Zehnder modulator is proposed and its anticipated device performance is detailed. The modulator is designed using commercially available materials and makes usc of wellcharacterized electrical and optical structures. The modulator is designed to be competitive with the pertrmance of LiNbO based modulators. The results of the analysis predict a bandwidth of 20 GHz, V of 8-10 V, optical insertion loss of S d13, and a contrast ratio of approximately 13 dB.

Fiberoptic transmission systems are based on the transmission and reception of intensity-modulated optical signals. Within these networks, optical amplifiers are deployed to compensate for fiber propagation and optical splitting losses1. Both high-speed digital and CATV transmission are used placing significant demands on the fidelity of the transmission network. Optical amplification of intensity-modulated signals also imparts intensity noise which degrades the signal-to-noise ratio at the amplifier output terminals. The importance of intensity noise is illustrated in Figure 1 by the figures of merit describing signal or transmission quality that are based on intensity measurements. Figure 1 shows how Q, bit-error rate (BER), relative intensity noise (kIN), and received signal-to-noise ratio (SNR) all depend on measurable intensity noise. In this paper we will discuss how the SNR degradation after passage through an optical device such as an amplifier is quantified in terms of its noise figure17. In particular, we will focus on the direct-detection noise figure that is applicable to the direct-detection optical communications systems in place or being contemplated for deployment. The noise figure is used to compare the noise-generating nature of amplifiers allowing (along with data on gain, bandwidth, power etc.) a basis for selection of an amplifier for a particular application. We will also discuss some of the noise mechanisms contributing to the intensity noise along 'with a review of measurement methods used for the characterization of amplifier noise figure. The theory presented here applies to both active and passive optical components.

Erbium-doped fiber amplifiers noise figure reduction using ioop mirror filter is demonstrated. At least O.6-dB noise figure reduction is. The insertion loss of the device is less than 2-dB.

In this paper, we present a new method to equalize the optical signal-to-noise ratio (OSNR) of all wavelength division multiplexed channels at the end of a cascade of several erbium-doped fiber amplifiers (EDFAs), by use of pre-emphasis and the proper choice of EDFA design parameters. Identical OSNR at the end of the cascade ensures better signal detection and quality of service

We analyzed the key design parameters of semiconductor optical amplifiers (SOAs) based wavelength converters. Simple analytical equations to calculate the rise and fall time of the converted signals in a long SOA (>5OOim) are derived.

A serious problem facing wavelength division multiplexed (WDM) networks with fiber amplifier cascades is transient cross saturation or gain dynamics of fiber amplifiers. Attention has been focused primarily on circuit-switched scenarios. When the number of WDM channels transmitted through a circuit-switching network varies, channel addition/removal will tend to perturb signals at the surviving channels that share all or part of the route. Even more serious bit error rate deterioration can arise in WDM packet switched burst mode networks. In this contribution we present experimental results demonstrating the effect of fast power transients in erbium-doped fiber amplifiers (EDFAs) on packetized traffic transmitted through a chain of five EDFAs. Traffic of a LAN has been transmitted over one channel, the effect of EDFA cross gain saturation due to the bursteness of the traffic has been observed in a cw channel. The stabilizing effect of gain clamping the first EDFA in the cascade has been investigated.

WDM systems require some means to lock the gain of surviving channels when one or several channels are added or dropped. The pump loss method is particularly interesting but, to our knowledge, has not been applied to multiplestage amplifiers. This paper reports on a modified pump loss technique for the gain locking of dual-stage amplifiers.

Gain equalization of an amplifier is performed by introducing spectrally designed Bragg gratings in the mid-stage of a dual-stage erbium-doped fiber amplifier. The long-haul performances of the amplifier are evaluated using a 50 km recirculating loop. The results show a clear improvement of the transmission quality when equalizing the gain.

Design criteria for two-stage gain-shifted erbium-doped fiber amplifiers (GS-EDFAs) determined for multiwavelength operation at the 1580 nm wavelength band are presented. In order to achieve a flat gain and low noise figure, special care must be taken when selecting erbium-doped fiber lengths, pump configuration and pump powers.

A generalized defmition ofprincipal states ofpolarization (PSPs) for an optical pulse is given from this work for a fiber with both polarization mode dispersion (PMD) and polarization dependence loss (PDL). As a result, the two PSPs of a pulse are generally non-orthogonal. The effective PDL of the pulse strongly depends on input pulse width. For a multi-section fiber, the effective PDL can be smaller than the minimum differences ofthe individual fiber section's PDL. The narrowest output pulse width can be smaller than the input pulse width in the presence of PDL.

An algorithm capable of finding the input and output states ofpolarization for maximum pulse narrowing at the output of an optical fiber with polarization mode dispersion (PMD) is analytically presented and numerically solved. It is always possible to obtain output pulses which are narrower than the input pulses when PMD is compensated by controlling both the input polarization as well as the receiver polarization states. This anomalous effect was shown to be exclusively due to PMD as no chromatic dispersion or polarization dependent losses were assumed. We report the detailed study for the cases in which the fiber consists oftwo, three and five hundred segments ofhighly-birefringent (Hi-Bi) fiber. The solution shows the existence of two orthogonal input and output states ofpolanzation (different from those introduced by Poole et. al.) under which the integrity of the pulse is preserved and the pulsewidth at the output is the narrowest possible. The cost to be paid for this improvement is a reduction ofthe optical power in the output pulse.

A study of the group delay responses in fibre Bragg dispersion compensators due to chromatic dispersion and first-order PMD is characterised at different optical modulation frequencies using a system based on a modified phase-shift method. A simple theoretical model has been constructed to account for the interdependency of the chromatic dispersion and PMD and to explain the effect of the modulation frequency on the group delay responses and the PDL. Measurement results and conclusions are presented.

The new Polarization-OTDR (Optical Time-Domain Reflectometry) technique theoretically and numerically described in this paper is based on the fact that the polarization state evolution ofthe backscattered signal gives information about the distribution of the fibre birefringence along its length. The knowledge of full polarization properties of a singlemode optical fibre can be very useful for determining the Polarization Mode Dispersion (PMD), which has become an important limiting factor in high capacity optical communications systems. Another interesting application is the possible realisation of fully-distributed optical-fibre sensor (FDOFS). Simulations have been done and gave promising results.

In a 4Ogbit/sec transmission test through 240 km of a TrueWave Classic fiber, with dispersion compensated by a high-order mode Dispersion Management Device, the bit error ratio was under 10b0 across the band of 1530nm through 1560nm. In a stimulated Brillouin scattering test, a light power of up to 22dBm was launched into the high-order mode Dispersion Management Device without detecting the SBS threshold. These tests and others indicate that the high-order mode Dispersion Management Device enables high transmission rates in long-haul networks.

In this paper, we show that Bragg gratings can greatly contribute to enhance the performances of today's optical amplifiers. some of the applications of Bragg gratings in optical amplifiers such as gain equalization, gain stabilization and dispersion compensation will thus be reviewed.

The variation in system performance ofmulti-span lightwave systems that use a cascade ofdispersion compensating gratings is characterized in terms of the maximum peak to peak group delay ripple over the -1 dB bandwidth of the grating. Results are presented that specify the requirement for the group delay ripple in order for the system performance to remain within a specified penalty.

The variational method is used to model output pulse widths in concatenated fiber links designed for dispersion compensation. The expressions for the output widths are given in analytical form with explicit dependence on the key parameters of initial width and chirp, the dispersion constant ofeach fiber section and the length of each section. In the ideal linear case, perfect compensation occurs when the sum ofthe dispersion-distance products of the two links is zero. However, in the presence ofnonlinearities a new relationship is found to govern many operating systems. Specifically, the dispersion-distance product ofthe second link should equal minus one-half the dispersion-distance product ofthe first link.

The main source of bit errors in multi-mode fibers (MMF) transmission systems is the inter-symbol interference (ISI) caused by the differential mode dispersion (DMD) generated multi-path effects. The DMD creates inter-symbol interference and limits the transmission distance-bandwidth product of a MMF to 3OO MHz-km. Hence, at 10 Gb/s data rate, the transmission distance is only -3O meters, which is not very useful for networking. In this work, we propose to utilize the adaptive equalization technique to combat the DMD and increase the transmission distance to almost the desired length. With this technique, we not only obtain MMF-based 10 Gb/s gigabit Ethernets (GE) but also upgrade all the already installed MMFs (OC-3 backbones) to higher-speed pipes. We present simulation results that show the success of our proposed adaptive equalization approach in canceling the DMD generated multi-path effect in MMF transmissions.

Dispersion management is analyzed with a regular perturbative method where the nonlinear effects are considered as a small perturbation when compared with the high local dispersion. In the spectral domain, a master integral equation is obtained that describes the stroboscopic evolution of a pulse along a periodic dispersion map. Functional analysis is used to find analytical approximations concerning the profile ofdispersion-managed solitons.

We derive approximate expressions to predict the chirp and peak power of a pulse propagating through a given dispersion map with lumped amplifiers. We use second-order moments to derive expressions for the evolution of the root-mean-square (RMS) width and chirp parameters within one period of the map. Numerical simulations confirm the accuracy of the analytical model.

This paper investigates, through semi-analytical simulation, the feasibility of the application of the dispersion supported transmission technique in the normal dispersion regime for the first time. It is shown that, in case of normal propagation regime, the dispersion supported transmission technique operated at 4OGbit/s can improve the system sensitivity by about 7dB relative to anomalous propagation regime. This improvement is achieved due to a significant increase of eye diagram opening, which happens at lower total fiber dispersion, and with greater -3dB bandwidth frequency of first order equalizer filter at receiver than in the anomalous regime. It is shown that these conclusions are consistent with analysis performed utilizing the amplitude and delay distortions of the system transfer function.

This paper investigates the influence of laser phase noise in dispersion supported transmission systems performance. It is shown that the relative intensity noise enhancement at fiber output due to fiber nonlinearity, observed in the anomalous propagation regime, can reduce considerably the maximum transmission distance achievable by dispersion supported transmission systems operated at 2OGbit/s. The results indicate that for a power at fiber input of 10mW, the maximum transmission distance achievable by dispersion supported transmission systems operated at 2OGbitJs is reduced from about 70km to 48km when the influence of laser phase noise is taken into account. The influence of laser phase noise in intensity modulated with direct detection systems performance operated at 2OGbit/s is also assessed and compared with the correspondent dispersion supported transmission systems operated at the same bit rate. The results indicate that dispersion supported transmission systems are much more sensitive to laser phase noise, than the intensity modulated with direct detection systems.

A new quantum-well intermixing process in InGaAs-InGaAsP structures, based on controlled low energy phosphorus (P) ion implantation, has been employed in the fabrication of multiple wavelength selective channel electroabsorption (EA) intensity modulators. These modulators, fabricated on a single chip, have an intensity modulation depth as high as -1 1 dB for voltage swings as low as -6 V.

The importance of renewable energy sources is currently attracting widespread attention due to the limited availability of fuels and major environmental impacts. A great deal of effort is put our days on the development of new efficient solar energy collectors either by quantum or thermal conversion. On this communication we will focus on the roughness and microtopographic inspection of surface thin films and spectrally selective coatings for these types of applications. Physically Vapour Deposited (PVD) coatings like sputter deposited metal oxide and nitride thin multilayered and graded ones can be used in spectrally selective surfaces for thermal collectors and energy-efficient windows. The efficiency of Cr-Cr2O3 cermet solar absorbers for both static and dynamic control of radiative heat transfer through absorbing surfaces will depend Ofl the chemical and physical structural characteristics and related optical properties like reflectance, emittance, absorbance and transmittance. The topographic characteristics of the produced coatings will greatly condition its relevant properties. A careful integral evaluation of the micro-relief structure of these Cr-Cr203 cermet coatings needs to be performed in a nondestructive, non-invasive way. Two optical inspection system suitable for the type of surfaces and range of roughness involved were employed: the MICROTOP.03.MFC an active optical triangulation sensor developed by the principal author at the Universidade do Minho; and, the Rodenstock' RM1 00 focus sensing based system. Not only the roughness values and roughness regimes of the surfaces are meaningful but also all other microtopographic characteristics including lay and form. The Fourier analysis of the different obtained profiles was performed and frequency filtering and extracting applied as a major source of meaningful microtopographic information.

Silica based planar technology on silicon has been identified as a very serious source of devices for optical communication s:ystems. Low temperature fabrication of passive and active structures is of special interest as it allows monolithic integration with temperature sensitive semiconductor components on a common silicon platform. Standard PEC\'D (Plasma Enhanced Chemical Vapour Deposition) processing for fabrication of silica based optical waveguides has been investigated to optimize the process parameters. We chose a high power process regime with high ratio between nitrous oxide and silane gas flows as the best conditions. Significant improvement in optical properties of silica-on-silicon planar waveguides for optical communication in the 1.50 -1 .55 tmwavelength range has been obtained.

Epitaxial metastable (GaAs)1x(Ge2)x thin films throughout most of the full compositional x range were studied by Raman scattering. Two optical modes were present near the allowed longitudinal optic (LO) and forbidden transverse optical (TO) modes of GaAs. We get direct evidence for the zinc-blend to diamond structural transition (ZB-D transition), which is observed to occur at x-O.35, from the features observed in the compositional dependence of the ratio of the f lower energy to rb higher energy half widths at half maximum intensities rb ofthe LO like-mode and those of the integrated intensities of the forbidden TO like-mode and the allowed LU like-mode. Raman scattering data combined with X-ray diffraction results imply that the macroscopically averaged ZB-D transition has manifestation in microscopic sizes at the same concentration.

Epitaxial metastable (GaAs)1x(Ge2)x thin films have been grown on GaAs(100) in a rf planar magnetron sputtering system (MS), without As overpressure, throughout most of the full compositional x range. The structural and compositional properties are investigated by high resolution x-ray diffraction (HRXRD) and secondary ion mass spectrometry (SIMS). The SIMS depth profiles demonstrate good homogeneity of Ge concentration for all the samples. HRXRD measurements show that the lattice constant has a nonlinear dependence on the concentration x and that a transition between zmc-blende and diamond crystal structures occurs at x 0.35. The existence of interfacial layers and the interference between the scattered amplitudes for the epilayer and substrate are considered negligible effects on the lattice parameter determination, and computer simulations confirm this assumption. We propose, from SIMS, HRXRD measurements and X-ray profiles simulations, that the lattice constant behavior is influenced by the resultant As/Ga ratio in the film.

We propose to use the Bragg interference filter technology for fabrication of microrefrigerators. The idea of using superconductor-insulator-superconductor (SIS) or normal metal-insulator-superconductor (SIN) tunnel junctions as cooling elements in micro-refrigerators is attractive because of the absence of (micro-refrigerators operating below 150 K. There are corresponding experiments [1] on SIN tunnel junctions where an attached to the SIN tunnel junction membrane was cooled down. Theoretical approaches (both phenomenological [1] as well as microscopic [2] show that the cooling effect exists also in 515 tunnel junction. However this was not observed experimentally because of inefficient thermal contact between SIS tunnel junction and the membrane that must be cooled. The microscopic approach to cooling is based on the "phonon deficit effect" [2] in nonequilibrium regime of tunnel junctions. In some circumstances, when the applied voltage does not exceed the superconducting energy gap ( A ) the probability of phonon absorption from the heat-bath is higher than its emission in the nonequilibrium regime of tunnel junctions. There is an appropriate absorption window in the phonon emission spectra [2,3] and by absorbing these phonons from the heat bath the SIS or SIN tunnel junction can refrigerate its environment. This effect can be improved by use of phonon filters placed between the tunnel junction and the heath-bath [4]. Such a filter can be the Bragg interference superlattice (Bragg's grating) which is well studied for problems of optical communications. Bragg interference filters are used also for detection of phonons emitted by tunnel junctions [5]. Usually such filters cut low and high frequencies, and the used detector may detect well separated frequencies. In contrast, to enhance the refrigeration process one needs filters with very broad spectral transmission properties or a large transmission band with one or two narrow stop bands. The type of the needed filter will depend on the types of the used tunnel junction. Corresponding discussion is presented.

ZnSe/GaAs/GaAs heterostructures grown by Molecular Beam Epitaxy have been studied by Photoreflectance. From Franz-Keldysh oscillations we found the electric fields at ZnSe. It was observed that the electric field value decreases with the temperature. The calculated values (<58 kV/cm) are in agreement with the typical values in semiconductors and are higher than those at the interfacial GaAs. The electric field strength is conelated with the presence of superficial states due to defects such as dislocations.

ZnSe/GaAs/GaAs heterostructures grown by Molecular Beam Epitaxy have been studied by Photoreflectance. From Franz-Keldysh oscillations we found the electric fields at ZnSe. It was observed that the electric field value decreases with the temperature. The calculated values (<58 kV/cm) are in agreement with the typical values in semiconductors and are higher than those at the interfacial GaAs. The electric field strength is conelated with the presence of superficial states due to defects such as dislocations.

This paper deals with the non-linear parametric effects on both space charge waves (with phase velocity equal to the electron drift velocity) and electromagnetic waves (with phase velocity equal to c1 , where c is the permittivity) in GaAs semiconductors. If an external electric field is applied, a negative differential conductivity is obtained. Under these conditions, the electron velocity is a function of the electric field, which is given by E =E0 + E , where E0 is the constant part and is the variable part. The analysis of the parametric interaction of the waves in the GaAs semiconductor is realized considering both the Maxwell's equations and the velocity function. The one-dimensional model and the axis z, as the spreading wave direction, are chosen. The analyses of instabilities are realized -by using the Blombergen's Method. The instability efficiency is determined by the velocity, V0, the differential mobility, jiD; and the non-linear parameter, VD;by means of the temperature model of the Gunn Effect. The efficiency is good if the interaction parameters As and as, which are obtained from the system formed by the Maxwell's equations and the velocity function, are optimal. At the critical field value, Ecrit, the mobility changes its sign and becomes negative, as a result, there are obtained non-linear and linear parametric instabilities of the interactions at fields E2Ecrjt. The nonlinear parameter Vd obtains a maximum at the optimal value of electric field, where all linear processes are very effective.

GaAs at the ZnSe/GaAs and GaAs/GaAs interfaces of ZnSe/GaAs/GaAs heterostructures is studied by phase selective photoreflectance (PR) spectroscopy. Four samples with ZnSe layers of various thicknesses were examined. We unambiguously determined the origin of two different features observed in the PR spectra by combining in phase and out of phase measurements, with PR measurements employing excitation lasers with different wavelengths. These two features are found to originate at different regions of the heterostructure. One contributing transition is a bulk-like signal, resembling that of bare GaAs, which originates in a region that encompasses the buffer layer/substrate GaAs homointerface. A second contributing signal is attributed to a strained region adjacent to the ZnSe/GaAs heterointerface. Both this second signal and the bulk-like signal show Franz-Keldysh oscillations that allow us to determine the electric field strength at the ZnSe/GaAs and GaAs/GaAs interfaces. It is found that the electric field strength at the heteromterface is larger than that of the hcmointerface.

Self-assembled AI36Ino.As/AIo33Gao.67As quantum dots have been studied by single dot photoluminescence spectroscopy at T= 1.5 K. Emission from the biexciton state is observed, for which we find a binding energy of 5 meV, also, larger multi-exciton complexes are observed at higher excitation intensities. These artificial atoms are found to have an intersublevel spacing of7O meV. In magnetic field, we observe Zeeman splitting ofthe exciton and biexciton spectral lines.

Luminescence of Ga02A103As, highly doped with Si as an amphoteric impurity, was excited by an electron beam at liquid nitrogen temperature. Two luminescence bands with photon energies of about 1 .8 eV and 2. 1 eV are observed, showing peculiar intensity behavior when the external excitation current is switched between a high and a low value. While the highenergy luminescence band shows a common intensity dependence proportional to the exciting current, the low-energy luminescence band intensity diminishes when the beam current is increased. Such an opposite run of the cathodolurninescence intensity at preselected spectral lines just by incrementing or decrementmg the electron beam current implies optoelectronic switching properties. A study is carried out in order to determine the physical nature of the recombination transitions, and the process, which leads to the surprising intensity vs. excitation behavior. Experimental results are analyzed by using a set of rate equations for a free-to-bound and a donor-acceptor pair transition, whereby an AUGER impact ionization process between two occupied neighboring acceptors and a pair-forming donor is incorporated. Under the particular situation of highly doped and almost compensated semiconductors, a bound state may happen at high excitation levels, which involves a close donoracceptor pair and a neighboring second donor or acceptor. The de-excitation behavior of such a bound state resembles characteristics know from AUGER transitions, where an electron and a hole recombine and donate the annihilation energy to a third particle, either a hole or an electron. The consequence is quenching of the radiative recombmation efficiency of the first transition, and under certain circumstances an increase of the recombination intensity of a second channel, which incorporates the thus liberated third particle. Theoretical and experimental results are in good agreement.

Second Harmonic Generation (SHG) using counter-propagating Quasi Phase Matching (QPM) configuration often requires a fine non-linearity with a period of a fraction of a micrometer. The direct Electron Beam (EB) domain reversal technique seems to be promising to achieve gratings on LiNbO3 with such a small period compared to other current poling technologies as it is lithographic free and exhibits a very high theoretical resolution (5 mm). We present here, a preliminary study concerning the influence of EB irradiation conditions on domain inversion; SHG is also examined on a 6.58 j.tm inverted periodic domain grating in lithium niobate using a Nd-YaG laser light. It is well known that LiNbO3 is an attractive material for many optical applications because of its transparency over a large wavelength band (350 mm to 5000 mm) and its high nonlinear coefficients. EB irradiation is performed using a Scanning Electron Microscope (SEM) driven by a Computer Aided Design (CAD) application developed in our laboratory. Various structures such as periodic gratings can be written with the chosen period. The ferroelectric domain inversion is investigated as a function of the accelerating voltage of the electrons (10 to 30 kV), the scanning speed of the EB (0.97 to 7.76 mm/s) and the current received by the sample (1.6 to 14 nA). The inversion patterns have been revealed by chemical etching (HF) and they have been observed using SEM. It has been shown that the duty cycle is respected on the irradiated face. The SHG conversion efficiency is measured as a function of the temperature and the grating period is calculated (value of6.564 jim).

Understanding the physics of Ini..GaAsPi multiple quantum well (MQW) nanostructures is essential for the development of new photonic devices such as lasers, amplifiers and modulators. In this work, optical and structural properties as well as vertical transport of three different heterostructures grown by metalorganic vapor phase epitaxy and emitting at 1 .33 tm and 1 .55 jim have been studied using continuous wave and time-resolved photoluminescence (cw-PL and TRPL) and high resolution x-ray diffraction (HRXRD). Cw-PL measurements show an anomalous PL characteristics for the structure with a thicker active layer which is discussed in terms of electron-acceptor transitions, donor-acceptor pairs, and constraint relaxation and related structural defects. The overall observed red shift with increasing temperature is interpreted as resulting from two opposite and competitive processes: band-gap shrinkage (dominant) and blue shi:ft caused by fluctuations in the QW layer thickness across the lateral sample direction. In the observed full width at half maximum, we identified a component of 8 meV as a contribution from longitudinal optical phonons. At high excitation densities, it is shown that carrier spillover and Auger recombination may be the major mechanisms limiting the quantum efficiency. For TRPL measurements, carrier cooling rates are discussed in terms of concurrent and opposite scattering mechanisms. It is found that the rise times of the QWs and the confinement region increase slightly (''2 ps) on decreasing the excitation wavelength. The observed difference is attributed to a higher initial carrier temperature associated with the shorter excitation wavelength. Comparable times of 4 ps are observed for the carrier transport and relaxation time within the confinement region and the carrier capture time in the quantum wells.

Quasi phase-matched second-harmonic generation in the co-propagating geometry is demonstrated in an asymmetric quantum well waveguide. Modulation of the nonlinear susceptibility along the waveguide was achieved using a patterned quantum well intermixing process. Photoluminescence measurements ofthe quanturn well band edges indicated that a grating of alternating regions of intermixed and as-grown asymmetric quantum wells was produced for periods between 2 jtm and 12 jim . The variation of the second harmonic intensity generated by guided incident light between A=1480 nm and 1600 nm was measured. The resulting second-harmonic spectra show sharp quasi-phase matching resonances for grating periods near 3 pm , demonstrating that a periodic modulation of the quantum well nonlinear susceptibility was produced.

In this paper we report the development of a new and versatile ion implantation mask system which takes advantage of the high precision offered by recent deposition methods. A stack of alternate layers of two different materials which can be selectively etched is first deposited on the sample. Selective etching is then performed to remove a given number of layers from the stack in the various region of the sample. Owing to a high etching selectivity between the two materials, the thickness of the mask can be fixed very precisely in each region. During ion implantation, a different amount of ions will pass through the mask to reach the sample, according to mask thickness over each region. This method therefore provides a way to achieve a spatial control over the implantation dose, in a single implantation step. Thermal annealing can then be performed to induce quantum well intermixing in the underlying heterostructure, which brings about a blueshift of the emission wavelength. The results obtained with our method, which makes use of low energy ion implantation, for the fabrication ofsingle step graded blueshifting of InP/InGaAs/InGaAsP integrated laser heterostructures are presented. We also present a study of pairs of materials suitable for the mask fabrication, as well as the results of numerical simulations to determine the appropriate thickness ofthe mask layers.

In this paper we show that low energy ion implantation of lnP based heterostructures for quantum well intermixing is a promising technique for photonic integrated devices. In order to fabricate complex optoelectronic devices with a control of the bandgap profile of the heterostructure there is a list of requirements that have to be fulfilled. We have fhhricatcd high quality discrete blueshifted laser diodes to verify the capability of low energy ion implantation induced intermixing fbr integration. We also fabricated extended cavity lasers with this technique, which demonstrated a reduction of the propagation losses down to 5.3 cm' within the integrated passive waveguides.

The characteristics of thin BaTiO3 films deposited on Si and MgO substrates by employing the metal-organic deposition technique are studied. In the experiment, the commercial barium 2-ethyihexanoate and the synthesized titanium dimethoxy dineodecanoate are used as precursors for the formation of BaTiO3 films. The film characterization is performed by X-ray diffraction and the scanning electron microscopy. The obtained results show that the prepared films have nearly good stoichiometry and the obtained tetragonal structure properties of BaTiO3 indicates that these may fmd some possible optical/electrical applications in the field ofintegrated optics technology.

We study the reflection of two-dimensional spatial solitons at the nonlinear interface between a saturable nonlinear medium (photorefractive crystal) and a linear medium. Our study places emphasis on determining the experimental conditions under which the beam reflected by the nonlinear interface is still a spatial soliton.

Amplified spontaneous emission (travelling-wave lasing) was achieved for a series of arylene-vinylene polymers (PAy). Wave-guiding neat films on glass substrates were used. The samples were transversally pumped with picosecond laser pulses (wavelength 347. 1 5 nm, duration 35ps). The laser emission occurred in the wavelength region between 480 nm and 650 nm. The travelling-wave lasing was identified by spectral narrowing, temporal shortening, and threshold behavior of light emission.

A series of 5 conjugated aromatic polyimines (Schiff-base polymers), containing -C=N- linkages in the backbone and various side-group substitutions, has been synthesized, characterized, and used to investigate the effects of molecular structure on the electronic structure and properties of these polymers. In this paper we report the photophysical behaviour of the Schiff-base polymers and their diluted solutions in DMA. The fluorescence excitation and emission spectra of these compounds were measured. These compounds show no evidence of excimer formation under these conditions and their fluorescence exhibits in solid state and in solution first-order decay behaviour.

New polyethers have been obtained in the anionic polymerization of oxiranes containing carbazole andlor hydrazone groups in the substituent. Excitation and luminescence spectra of the novel polymers were measured in powder and in tetrahydrofuran solution. It allowed to conclude that in the absence of excimer trapping sites, only intermolecular energy migration will be encouraged in dilute solutions of the polymers. Some polyethers and their solutions in tetrahydrofuran showed blue fluorescence. That would have an application to electroluminescent materials, such as electroluminescence polymer diodes.

We investigate the dynamics ofholographic grating formation in methacrylate photopolymer films. Dual gratings consisting of surface relief and volume holograms are observed. The influence of such grating formation on temporal behavior of the diffiacted signal is discussed.

The quantum chemical investigations of the Disperse Orange 3 (D03) molecule isomerization through linear transition state has been assumed and investigated when -N=N- bond broken in the first excited state was not obtained. The one- and many electron energy diagrams have been drawn. It is shown that crossing between active one electron-state takes place. The many-electron diagram indicates that crossing between the closed shell state and the lowest open shell state is present.

A comparative investigation of the photochemical behavior of dichromated gelatin (DCG), dichromated polyacrylic acid (DCPAA) and dichromated polyvinylalcohol (DCPVA) gives evidence for the similarity of the photochemical behaviour involved when recording holograms in DCG and DCPVA. Chromium (V), the chromium species resulting from the photoredox process between the starting chromium (VI) (dichromate) and the polymeric chain, is stable, likely strongly complexed in gelatin and polyvinylalcohol. The quantum yields of the reaction are high and similar for both reactions. On the contrary, even though chromium (V) is also formed during the primary process in DCPAA, this species is quite unstable and disappears as soon s the irradiation is stopped. The behavior observed in DCG can be assigned to the presence of CM groups on the polymeric chain, these groups being the only groups present in polyvinylalcohol.

The nanosecond nonlinear absorption of organic molecules is a three-photon process, i.e. a two-photon initiating step followed by a transient absorption during the pulse duration. Order of magnitude calculations show that it is realistic to consider two-photon absorbing molecules for optical limiting applications at visible wavelengths. In this work we have investigated two molecular engineering approaches to optimize molecules: internal charge transfer molecules and conjugated oligomers. The oligomer approach is the most promising due the enhancement of nonlinearities that results from cooperative effects between monomers.

Our research was aimed at finding a photochromic compounds sensitive in the visible spectra. We have reported a new photochromic composite polymer materials consisting of carbazole-contained polymers, which are doped by spiropyran dyes. We have synthesized and experimentally characterized such photochromic polymers. The experimental measurements of its absorption characteristics are evaluated in conjunction with its potential applications for optical holography. Both recording and erasing procedures are possible using direct radiation from a blue line of an Ar laser (X=458nm). Also, simple diffraction gratings have been recorded by the use of two-color recording procedure ensuring artificial negativity in the visible spectra. Two structures of high-sensitive carbazole-contained photochromic compounds are proposed. Keywords: Holography, polymers, photochromic compounds, absorption spectra, diffraction efficiency

The photo excitations of Spiropyran-doped polymer films were studied. Cellulose acetate (CA), commercial ploy(methyl methacrylate) (PMMA) and PMMA prepared by radical polymerisation of MMA, were used as host polymer matrices. The open form of SP presents a maximum of absorption cantered at about 600 nm upon UV irradiation. We have determined the photoreaction rate constants, kuv and k15, for the coloring and bleaching processes. Reversible holographic recording in SPIPMMA films was studied and photochemical fatigue resistance was evaluated upon repeated UVfVisible irradiation cycles. We found a loss of 42, 53 and 74% respectively in PMMA by gravity deposition, PMMA (by polymerisation of MMA) and cellulose acetate films.

Polymers such as PMMA, PADC (commercially named CR39), BCB .. . under irradiation (gamma rays, ion beam. ..) have been widely studied. It has been shown that they undergo physical and particularly optical change. In the case of ion beam, an optical waveguiding is generated, due to a sufficient localized refractive index increase. In this work, an electron beam (EB) delivered by a Scanning Electron Microscope (SEM) is used. We show that this kind of irradiation also allows to create a guiding layer on the PADC polymer. Taking into account that the minimum spot size is 5 nm and that a specific Computer Aided Design (CAD) application, developed in the group, drives the SEM, we can expect to realize optical microstructures directly on the substrate, with an excellent lateral resolution. The first step of this study is the demonstration of the feasibility of optical waveguides in PADC by the EB techniques, with the aim to apply this method to the field ofinterconnect and optoelectronic devices for Telecommunications. The influence of the main irradiation parameters (energy of the electrons and electronic fluence) on optical characteristics is investigated. The CAD application driving the SEM allows to write various stmctures such as gratings, microguides, discs as well as any combinations ofthese elementary structures in order to achieve microoptical devices. We focused on a microguide structure which behavior is simulated with the intention of optimizing its dimensions and the required refractive index variation. Some modeling results giving the energy repartition in the structure are presented.

The peculiarities of holographic gratings recording in the thick layers of photopolymer self-processing materials have been investigated. It is shown the main reason of limit of gratings thicknesses and, consequently, their angular selectivity and diffraction efficiency is the dynamic amplification of holographic noises. The maximum diffraction efficiency and angular selectivity with the minimum noises are achieved with use of pre-polymerization of layer and the post-polymerizing self-amplification of holograms. This method allows to fabricate gratings with the thickness up to inmi and angular selectivity about 6'.

Microlenses, microlens arrays and diffraction gratings can be made by using polymer materials. These elements can work with mid-infrared light. The influence of some fabrication process variables in the fmal parameters of the elements is analyzed. The surface shapes of the fabricated elements were investigated by a surface analyzer and an interference microscope. The ability of microlenses to focus mid-infrared light and to form infrared images and a diffraction efficiency study of the gratings are shown.

Recently, the chalcogenide glasses (ChG) have attracted much attention in the field of optical communication and integrated optics. High transparency in the infrared spectral region, low phonon energy, high nonlinear properties, and high photosensitivity at near band-gap (Eg 2.35 eV, a 1-2 x iO cm1 at 5 14 nm) are important characteristics of these glasses. In particular, the photosensitive effects, among them photodarkening and giant photoexpansion (2-5%) [1], have been extensively studied and several holographic elements, such as microlenses, diffraction and Bragg gratings, and channel waveguides have been realized in fiber, bulk, and thin film forms of these materials [2-4]. In this work, we report for the first time to our knowledge, the observation and study of the strong polarization dependent photoinduced surface relief gratings in As2S3 thin films. A model to describe the observed phenomena is also presented.

The interaction of two coherent counterpropagating circu!ar po!arized beams (helicoida! standing wave) with cellu!ose acetate polymer fi!m doped with Disperse Red 1 (DR1) azo-dye is studied. Polarization properties of the recorded grating are simi!ar to cholecteric liquid crystals where the response ofthe system is different to left and right circularly polarized light.

Azobenzene containing amorphous polymers are used to fabricate thin films that can act as optical waveguides. Furthermore, stable surface relief structures such as gratings can be holographically inscribed onto the films using low and medium power lasers. The grating depth and spacing can easily be controlled with the depth varying from 15 nm to several hundred nanometers and spacing varying from 170 nm to 3 micrometers. These thin-film structures can then be designed to act as optical devices such as optical couplers, optical filters and birefringence films. We will describe the method of the fabrication ofthe surface relief structures and suinmarise the theories proposed for the mass polymer movement that produce these structures.

By means of real-time holographic recording, two important classes of photochromic compounds (spiropyrans and fulgides) have been characterized. For spiropyran molecules, important thickness and writing intensity effects were observed. Concerning fulgides molecules, photochemical fatigue resistance in different polymer hosts was investigated. After 10 irradiation cycles, the closed form lost 9, 1 1 , 13 and 35% of its initial absorbance respectively in PS, CA, PMMA and PVK. For the holographic study, diffraction efficiency in fulgide doped PMMA films was strongly dependent on the writing intensity: the rise time 'r takes values 25and 7s for respectively 2 and 8 mW/cm2. Optimum fulgide concentration and writing exposure have been obtained: diffraction efficiency is maximum with a concentration of 2% and an intensity of 4mW/cm2. Keywords:Photochromism, photosensitive materials, fulgides, spiropyrans, polymethylmetacrylate, polyvinylcarbazole, real-time spectrometry, photochemical fatigue resistance, holographic recording.

We present the design, development and characterization of MEMPLEX - a new photoreactive polymer that has widespread applications in holographic information storage and processing technology. The new polymer is characterized by its large M/# and, thus, large capacity for data storage (>Thit/5 inch diameter disk), good sensitivity in the visible, negligible shrinkage during recording, no wet chemical processing, and virtually unlimited storage time of information. MEMPLEX is inexpensive, completely self-supporting, can be fabricated to any size as required by the application, has excellent optical quality, is resistant to most chemicals, and has long shelf-life.

With the purpose of expansion of polymer materials in the area of fotonics and image registration we prepared, tested and investigated photopolymer photoresist layers from carbazolylalcylmethacrylats (CEM) with oktylmethacrylats (OMA) copolymers, having the high photosensitivity, adhesive and film forming properties. The photopolymer layers were made by pouring from solutions. The contents of iodophorm and other electron-acceptor additives was maintained within the limits of 5-10 weight % ofthe photopolymer. For all the photoresist layers the photographic sensitivity, factor of contrast, diffraction efficiency and resolution at holographic recording were studied. The numerous tests of the samples have shown, that complete crosslinking of copolymer CEM:OMA layers occurs during 10 - 15 s at (4,0 - 5,0) sm2/mWxs. The photographic sensitivity depends on the thickness of photopolymer layer. To examine the holographic characteristics of the layers, the growth kinetics of diffraction efficiency in dependence on the doze of exposure, the kinetics of diffraction efficiency in dependence on the duration and conditions of solvent treatment were investigated, the holographic sensitivity, resolution capability and optimal diffraction efficiency of the photoresist layers have been defmed. The diffraction efficiency more than 20% and the resolution capability up to 2500 irmiT1 were obtained for the developed photoresist layers based on CEM:OMA photopolymers.

With the purpose of expansion of polymer materials in the area of fotonics and image registration we prepared, tested and investigated photopolymer photoresist layers from carbazolylalcylmethacrylats (CEM) with oktylmethacrylats (OMA) copolymers, having the high photosensitivity, adhesive and film forming properties. The photopolymer layers were made by pouring from solutions. The contents of iodophorm and other electron-acceptor additives was maintained within the limits of 5-10 weight % ofthe photopolymer. For all the photoresist layers the photographic sensitivity, factor of contrast, diffraction efficiency and resolution at holographic recording were studied. The numerous tests of the samples have shown, that complete crosslinking of copolymer CEM:OMA layers occurs during 10 - 15 s at (4,0 - 5,0) sm2/mWxs. The photographic sensitivity depends on the thickness of photopolymer layer. To examine the holographic characteristics of the layers, the growth kinetics of diffraction efficiency in dependence on the doze of exposure, the kinetics of diffraction efficiency in dependence on the duration and conditions of solvent treatment were investigated, the holographic sensitivity, resolution capability and optimal diffraction efficiency of the photoresist layers have been defmed. The diffraction efficiency more than 20% and the resolution capability up to 2500 irmiT1 were obtained for the developed photoresist layers based on CEM:OMA photopolymers.

Two beam Coupling has been investigated in rhodamine 6G doped films of boric acid glass. A peizo-electric transducer has been used to shift the frequency of one of the interfering beams. The results have been interpreted as selfdiffraction in the directions of the input beams using a four level model of saturable absorbers. Good agreement between the experimental and the theoretical results has been observed.

We present experimental results showing that variable reflectivity gratings can be used to control the modal content, the spatial profile and the phase curvature of the beams emitted by solid-state lasers. The setup used to fabricate the apodized holographic gratings will be described; the gratings were recorded in photoresist materials with a Krypton ion laser operated at 413 nm. The results from the optical characterization of these elements will be presented. The holographic mirrors have been tested as output couplers in Littrow geometry for Nd :YAG lasers emitting at 1 .064 pm. Experiments have been made with several configurations of laser resonators. The most interesting results were obtained with positive branch confocal unstable resonators, where nearly diffraction-limited beams with output energy of up to 100 mJ were generated. To compensate for the astigmatic abenation due to the Littrow geometry, we developed an analytical model predicting the reflective properties of the holographic gratings ; from that model we found the conditions for which, in principle, the effects of the astigmatic aberration are completely eliminated. The degradation of photoresist materials by the environment and by high laser fluences is a factor limiting the applications of the holographic mirrors; to resolve that problem we are developing a new fabrication procedure through the replication of the holograms in epoxy materials that can withstand high laser powers.

Numerical simulations and experiments indicate that a graded reflectivity minor can improve the fundamental mode performance of moderate gain lasers operated with a stable resonator. Sizeable increases in TEM output power and far-field radiance are achievable.

We demonstrate a prototype of a laser-cooled 87Rb fountain clock and measure the frequency shift due to cold collisions. The shift is 30 times smaller than that in a laser-cooled Cs clock. We observe a density dependent pulling by the microwave cavity and use it to cancel the collision shift. We have also demonstrated a juggling atomic fountain to study cold collisions and we discuss the importance ofjuggling for future fountain clocks.

We show that lasers can be used as detectors. The experimental set-up consists in optically injecting a slave laser with a laser whose linewidth is smaller. Heterodyne technique allows us to detect signals as small as -1 17 dBm or 0.2 photon per correlation time. We explain the experiment by interpreting the laser as a nonlinear amplifier and filter.

A numerical propagation algorithm is presented that applies to a particular class of partially coherent beams. The algorithm relies on the azimutal decomposition of the cross-spectral density (or mutual intensity) of the field, which reduces the usual four-dimensional propagation integral into a series of two-dimensional integrals that can be treated using fast Hankel transform techniques.

The use of second harmonic generation as a technique for ultrashort optic pulse width measurement is analyzed to determine in detail the effect of group velocity mismatch (G\TM) between fundamental and second harmonic fields when considering different pulse shapes. We find that for interferometric autocorrelation and intensity autocorrelation, GVM has different effects versus different pulseshapes.

The e-AO FB radiative transition is investigated by the 10K PL measurements for the unintentionally doped MOCVD grown InGaAs. The intensity ratio of the e-AO FB transition to the BE exciton transition is found to be greatly larger in bulk material than that in the quantum well samples. In quantum well samples, this ratio is found to decrease rapidly as the well width decreases. A model is presented to calculate the oscillator strength of the e-AO recombination and the 1 1H excitonic recombination in quantum well, and this simulation can semi-quantitatively explain the experimental results.

Adiabatic mode expansion laser diodes (AME-LDs) with small beam divergence fabricated by selective area growth (SAG) are described. The AME-LDs have low thresholds of around 12 mA. The lateral and vertical far field angles (FWHM) are reduced from 25° and 300 to 8° and 14°, respectively. The measured alignment tolerance to a cleaved single mode fiber (SMF) is 3 pm.

We report preliminary results ofwidely tunable semiconductor laser materials using selective area growth techniques. This material has very broad gain profiles ofmore than 250 nm and is promising to be used as widely tunable laser diodes for future broadband wavelength division multiplexed (WDM) access networks.

The performance of an intensity modulated direct detection transmission system using an external cavity semiconductor laser (ECL) transmitter, for bit-rates of 2.5 and 5Gbit/s, predicted by using two ECL models is investigated. Results reveal that the transmission performances predicted by the two models can be remarkably different, even at bit rates as low as 2.5Gbit/s, and the discrepancies on the transmission performance are mainly due to the significantly different ECL frequency chirp predicted by each model. Since these discrepancies are attributed to the lowfrequency approximation used to derive the approximated model, the rigorous model must be used to assess more accurately the transmission performance of ECLs.

The steady-state stability of external-cavity semiconductor lasers (ECL) operating at the strong feedback regime is investigated. A simple analytical expression for the critical external power reflectivity, above which the ECL steadystate is stable, is presented and compared with other authors' results. The validity of this expression is discussed and compared with results obtained from accurate simulation of a set of improved differential nonlinear laser rate equations. It is shown that the steady-state bistability in the strong feedback regime can be first denounced by a kink in the L-I and frequency shift vs bias current characteristics which, after further reduction of the external feedback strength, is transformed into a hysteresis region.

We report new results on the generation and characterization of picosecond pulses from a self-mode-locked semiconductor diode laser. The active medium (InGaAs, 830-870 nm) is a semiconductor optical amplifier whose facets are cut at angle and AR coated. The amplifier is inserted in a three-minor ring cavity. Mode locking is purely passive; it takes place for specific alignment conditions. Trains of counterpropagating pulses are produced, with pulse duration varying from 1 .2 to 2 ps. The spectra of the counterpropagatmg pulses do not fully overlap; their central wavelengths differ by a few nm. The pulse repetition rate has been varied from 0.3 to 3 GHz. The pulses have been compressed to less than 500-fs duration with a grating pair. We discuss some of the potential physical mechanisms that could be involved in the dynamics of the mode-locked regime. Hysteresis in the LI curve has been observed. To characterize the pulses, we introduce the idea of a Pulse Quality Factor, where the pulse duration and spectral width are calculated from the second-order moments of the measured intensity autocorrelation and power spectral density.

The coherence properties of a widely tunable, multilongitudinal-mode erbium-doped fiber ring laser are investigated by means of an extremely long-arm scanning Michelson interferometer. A return of the coherence is observed at each integer multiple ofthe cavity length with a slowly decaying envelope over several kilometres.

In this paper, we report the numerical study of the synchronous soliton-like pulses generation in a multichannel fiber laser system, conformed by an array of 2 up to 7 coupled Erbium doped fibers, separately pumped. The pulse synchronous generation is obtained by means of an amplitude modulator inserted in one of the channels, and the energy interaction of evanescent waves between this channel and all the others.

In this paper, we report the development of an Er3-doped dual-wavelength fiber laser constructed from a quasi-ring structure incorporated with two cascaded fiber Bragg gratings (FBGs). A total output power of 8.5 dBm and a mode suppression ratio of more than 50 dB have been obtained in the cw operation case. The mode competition phenomenon for dual wavelengths lasing has been investigated by reducing the wavelength spacing of the two FBGs. With mode locking, switching from one wavelength to the other, and between single- and dual- wavelength lasing has been demonstrated by adjusting the rf frequency of an intensity modulator in the laser cavity.

Broadband discrete and continuous tuning of erbium-doped fiber lasers is demonstrated in this paper. First, an exact multiple of 100 GHz frequency step-tunable L band erbium-doped fiber ring laser is presented. Precise multiple of 100 GHz step-tunability is obtain by proper angle positioning of a 100 GHz Fabry-Perot micro etalon in the laser cavity. Secondly, continuous tuning over 90 nm is shown in a laser using gain-band switching between C and L band EDFAs. Lastly, a tunable laser design that uses a single gain medium to obtain 100 nm of tuning in the C and L bands is demonstrated.

re present a model for a 455 nm thulium-doped ZBLAN fiber laser co-pumped at 645, 684 and 1064 nm. This model calculates the blue laser output power using a rate equation analysis and takes into account the cross-relaxation and cooperative upconversion processes. We calculate the optimal pump wavelength for the case of a single visible pump wavelength, and then show the benefits of adding the second visible pump wavelength at 684 nm for a low 1064 nm pump power (120 mW). At high infrared pump powers (≥600 mW), we then show that adding the second pump does not increase the efficiency of the laser. These results are explained by studying the population densities of the energy levels of the thulium ions for each pumping configuration.

The operation of femtosecond lasers based on Kerr Lens Mode Locking is reviewed. We describe our home-made Ti:sapphire laser that produces pulses as short as 1 0 femtoseconds. Critical issues such as dispersion compensation and pulse measurement techniques will be addressed. We propose to characterize mode-locked laser pulses through a parameter that we call the "Pulse Quality Factor", in a way similar to the Beam Quality Factor used for optical beams. We show how the temporal second-order moments needed to evaluate the Pulse Quality Factor can be obtained directly from the autocorrelation trace and the spectral intensity distribution of a short laser pulse.

We present a new type of composite materials that we have designed for optical applications: sol-gel glasses highly doped with organic nanocrystals. The nanosized control of crystallization allows us to obtain optical grade samples with very high concentrations of active molecules. Here, we report on the optical limiting properties of bulk glasses doped with stilbene 3 nanocrystals, and on the second-harmonic generation of thin films doped with oriented nonlinear nanocrystals.

In this paper we report the linear and non-linear properties for PMMA films clusters with nanometrical Silver particles. These samples were prepared by bulk polymerization of methyl metacrylate solution of silver trifluoracetate and followed by post-heating. Varying the concentration ofparticles and using different thermal procedures shown different properties. Third-optical susceptibilities were measured

Development of a UV laser transmitter capable of operating from a space platform is a critical step in enabling global earth observations of aerosols and ozone at resolutions greater than current passive instrument capabilities. Tropospheric chemistry is well recognized as the next frontier for global atmospheric measurement. Moreover, global measurement of tropospheric ozone with high vertical resolution (2.5 km) from space were endorsed for the EX-1 Mission by NASA's Post2002 Mission Planning Workshop. At this workshop, held in Easton, Maryland, in August 1998, it was recognized that a space-based UV Differential Absorption Lidar (DIAL) system was necessary in order to obtain this high- resolution capability for measurements of ozone and aerosols. The results of this workshop can be found at http:llwww.hq.nasa.gov/office/ese/nra/RFldodgelPanelrev.html. For the EX-1 Mission, the UV DIAL measurement would be complemented with passive measurements of ozone precursor gases and pollutant tracer species. Langley Research Center (LaRC) and the Canadian Space Agency (CSA) have jointly studied the requirements for a satellite based, global ozone monitoring instrument. The study, called Ozone Research using Advanced Cooperative Lidar Experiment (ORACLE) has defined the DIAL instrument performance, weight and power, and configuration requirements for a space based measurement. In order to achieve the measurement resolution and acceptable signal-to-noise from lidar returns, 500mJ/pulse (10 Watts average power) is required at both, 308nm and 320nm wavelengths. These are consecutive pulses, in a 10 Hz, double-pulsed format. The two wavelengths are used as the on- and off-lines for the ozone DIAL measurement.1 5 NASA Langley is currently developing technology for a UV laser transmitter capable of meeting the ORACLE requirements; this development effort is focused on improving the efficiency of converting 1im laser energy to the 308 and 320nm energies needed for the DIAL measurement. Our approach includes making maximum use of existing, space-qualified optical components to reduce risk, cost and development time. Our experimental efforts to date have shown that our UV generation scheme is viable, and that energies greater than lOOmJ/pulse are possible. Future work will focus on improving efficiency and on addressing reliability, size and scalability issues. Our goal is to improve the optical conversion efficiency from the current state of the art, currently at 5%, to a minimum of 12%. We will accomplish this by using OPO/OPA and sum frequency mixing technology to generate the required UV wavelengths. The technology being developed has undergone an extensive peer review and down-select process from 20 possible UV generation schemes through in-house and industry trade studies and by experimental investigations. By using the selected technique and a diode pumped laser, a wall plug efficiency (electrical to optical) of greater than 2% is expected. In this paper, we will briefly discuss the study effort to date, the overall system design, and the down select process for the proposed laser design. We will describe UV laser technology that minimizes the total number of optical components (for enhanced reliability) as well as the number of UV coated optics required to transmit the light from the laser (for enhanced optical damage resistance). While the goal is to develop a laser that will produce 500 mJ of energy, we will describe an optional design that will produce output energies between 100-200mJ/unit and techniques for combining multiple laser modules in order to transmit a minimum of 500mJ of UV energy in each pulse of the on- and off-line pulse pairs. This modular laser approach provides redundancy and significantly reduces development time, risk and cost when compared to the development of a single, 500mJ double-pulsed laser subsystem. Finally, we will describe the common source for seeding the OPO's such that the absolute wavelength and linewidth of each transmitter module will be controlled and summarize the laser development effort to date, including results that include the highest known UV energy ever produced by a solid-state laser operating in this wavelength region.

Supercooled cloud and precipitation water droplets cause in-flight icing of aircraft lifting and control surfaces and thus constitute a safety hazard to aviation. There is a growing interest in the development of remote sensors to warn of the danger zones. A known characteristic of these zones is that they are spatially and temporally variable, hence the need for real time detection. We have tested in two coordinated field experiments the DREV multiple-fieldof- view (MFOV) lidar as a means of characterizing icing conditions. The required information is the temperature, the phase, the liquid water content arid the droplet size of clouds and precipitation. The last three quantities are obtainable, within limits, with the MFOV lidar. The paper briefly describes the MFOV measurement and solution methods, and reports on sample retrieval results of liquid water content and droplet effective diameter. These data are directly applicable to the remote characterization of in-flight icing conditions. The accuracy of these lidar solutions is currently estimated at 30-40%.

Currently, the commercial use of atmospheric lidar is limited to the measurement of cloud ceiling. However, very pertinent meteorological information (such as the structure and phase of clouds and precipitation) can be obtained by recording both polarization components of the returns while operating the lidar at a fixed repetition rate and scanning its axis at a constant angular elevation speed. We present results obtained with our dual-polarization scanning lidar system during two measurement campaigns: MWISP (Mount Washington Icing Sensors Project) in April 1999, and AIRS (Alliance Icing Research Study) in the 1999-2000 winter

A static polarization interference imaging spectrometer (SPIIS) was developed based on a single birefringent component. When it is launched on the satellite (or aeroplane), it will produce an interferogram and target s image in the spatial domain which is recorded using a 2D CCD camera with device s pushbroom.The spectrum of the target is reconstructed from the Fourier transform of the interferogram. The polarization interference imaging device has advantages of ultra-compact, static, wide field of view, high throughout. In laboratory, a series of images and interferogram are obtained using our principle device under module own pushbroom.

The quantization capabilities of a new passive FTIR method for the remote monitoring of chemical vapors are explored. The method is based on the use of a double beam interferometer-spectrometer optimized for optical subtraction.. The instrument is described with a particular emphasis on its capabilities for differential detection and background suppression. The algorithm developed for on-line detection and quantization of chemical vapor plume is also reviewed. The method has been successftilly used to map the integrated concentration and the temperature ofa plume ofmethanol vapor.

We present a simple scaling of the SNR plots for the minimum required SNRfor detecting the emission from an aerosol cloud. The required SNR for the detection of aerosol thermal emission is quite high, in the order of i03 to iO' (depends on the temperature difference and the depth of the cloud) but can be achieved with state of the art sensors equipped with large apertures and utilizing sufficient averaging.

In recent years, INO has developed an eye-safe, transportable industrial fiber lidar (IFL) for industrial applications of pollution control during handling of loose materials'2. However, it can also be used for other applications like urban particulates monitoring, cloud mapping, and unattended surveillance. The IPL is a compact and direct scanning lidar. It is based on 1140's diode pumped Erbium doped fiber laser, which delivers an energy of 1 .5microJoules in l2ns pulses with a high repetition rate of 10kHz at an eye-safe wavelength of 1.5microns. 1140's lidar system is composed of a lidar head containing the transmitter-receiver optics in a biaxial configuration mounted on a scanning platform. The lidar head is connected to the laser source and detector via optical fibers. A computer controls the scanning platform via an optical RS- 232 communication link. This allows remote operation since sensitive equipment like the laser and the computer can be located away from the surveillance site in an environmentally controlled room. The TEL characteristics and results obtained from monitoring in an urban area and field trials on surveillance of hard targets and transmission through obscurants will be detailed.

A laser Doppler anemometer for measuring wind speed ahead of wind turbines is under development. The anemometer is based on a CO2 laser. Three schemes for detecting the Doppler frequency of the back-scattered light have been compared with respect to compactness, robustness, signal strength, and cost. The autodyne scheme, where the backscattered light is collected through the same optical path as used for the transmitted beam and re-enters the laser cavity. The Doppler frequency is measured as perturbations of the laser power. The Michelson derived heterodyne system, where the Doppler frequency is measured as a beat frequency between the signal wave and a reference wave in a Michelson-like set-up. In an alternative system for detection by external mixing is the reference wave is established by reflecting a small fraction of the output beam back towards the detector by a partially reflecting window. Due to the response characteristics of the laser, an autodyne laser anemometer, based on a CO2 laser, is found to have an acceptable response only in a very narrow frequency range and is thus not useful the present application. It is decided to build the anemometer by using the alternative heterodyne mixing scheme. This system needs the fewest number of optical components and alignments.

We present a novel coronagraphic imaging technique and design for space-based telescopes. The Umbral Mission Blocking Radiating Astronomical Sources (UMBRAS) is a space mission design consisting of a free flying occulter, the Solar Powered Ion Driven Eclipsing Rover (SPIDER), and possibly one or two metrology platforms. The UMBRAS spacecraft operate in conjunction with a space-based telescope. The size of the occulting SPIDER is dictated by the size of the telescope with which it will work. The goal of UMBRAS is to provide "paleolithic" (i.e., non-focal plane) coronagraphic capability to enable direct imaging of extrasolar Jovian planets and other bright substellar companions such as brown dwarfs. We discuss two aspects of the operation of a free flying occulter: acquisition of targets and station keeping. Target acquisition is modeled after the onboard schemes used by Hubble Space Telescope (HST) science instruments. For UMBRAS, the onboard commanding sequences would include imaging the field using instruments on the telescope, locating the target and the occulter in the field, and accurately positioning the occulter over the target. Station keeping consists of actively maintaining the occulter position in the telescope line of sight to the target. Velocity matching of the c)cculter with the space-based telescope is essential to mission performance. An appropriate combination of solar electric and cold gas thrusters provide the ability to match velocities using position information derived from communication and from ranging data between telescope, occulter and any metrology stations. The accuracy requirements for target acquisition and station keeping depend upon the science requirements, the occultation geometry, and the sensitivity of the science to changes in occultation geometry during an exposure sequence. Observing modes other than the ideal centered occultation of a target will be discussed.

We have proposed and designed a photonic true-time delay (TTD) steered phased-array antenna system that can work at high RF frequency with high angular resolution. Several elementary techniques have been studied and developed, including an optical realization of the Blass matrix based on our substrate-guided wave fanout structure, switching operation of wideband MSM and PIN photodetectors, and heterodyne RF signal generation. A design for the system demonstration that has the bandwidth from 18 to 26GHz is reported.

This article describes work that has been undertaken at the Defence Research Establishment Valcartier (DREV) to integrate a number of electro-optics sensors into a modular mission configurable threat detection sensor suite (TDSS) demonstrator. The sensor suite is based on a series of plug and play detection heads networked together in the same fashion as a computer network. The architecture allows optimization of the detection capabilities according to a mission requirement. The TDSS demonstrator was developed to study different sensor configuration in order to establish the requirements to improve the protection of the military platforms. It is a good example showing how networking can help in adapting military systems to specific requirements. The paper gives an up to date description of the TDSS demonstrator. To our knowledge, it is the first time that this approach is used in the field of military detection sensors.

This paper updates progress on work1 in detecting bacterial auto-fluorescence against various food backgrounds using Laser-Induced Fluorescence (LIE). The fluorescence of bacteria and various meat products has been measured in order to find suitable excitation and detection wavelengths for discriminative imaging. The optical absorption of bacteria, meat and fish tissue was measured to provide a starting point for the fluorescence measurements. The bacteria measured was Escherichia Coli, and the food tissue products were, lamb, pork, chicken and fish. All absorption spectra have a peak around 400nm and most muscle tissue types have lower absorption around 325nm giving a good low contrast fluorescent background for the F. Coli. However, other tissue types such as fat, skin and bone skin have higher absorption levels and hence fluorescence. Three interference filters can be used to selectively sample the fluorescence spectra to generate a three point intensity ratio that can be used to discriminate between fluorescence of the various tissue types and E. Coli. The best fluorescence discrimination was achieved using the HeCd laser wavelength of 325nm. However in our current experimental setup there is not enough optical power at 325nm for direct laser imaging. We are currently working to increase UV laser excitation levels by using a dye laser to pump a frequency doubling crystal.

Optical sensing is one promising approach to monitor bioflims in an early stage. Generally, natural bioflims are quite inhomogeneous, therefore we start the investigation with suspensions of dead bacteria in water as a simple model for a bioflim. An experimental arrangement based on a white light fiber optic spectrometer is used for measuring the density of a thin film with a local resolution in the order of several tim. The method is applied with model biofilms. In a computer controlled procedure reflectance spectra may be recorded at different positions in the x-y plane. Scanning through thin suspension regions of bacteria between glass plates allows an estimation of the refractive index of bacteria. Taking advantage of the light collecting property of the glass substrate a simple measurement of the fluorescence with local resolution is demonstrated as well.

Medical therapeutic applications using lasers involves understanding the light tissue interaction, in particular the rate ofphotochemical and thermal reactions. Tissue is composed ofa mix ofturbid media. Light propagation in turbid media can be described by the so-called Equation of Radiative Transfer, an integro-differential equation where scattering, absorption and internal reflection are significant factors in determining the light distribution in tissue. The Equation of Radiative Transfer however can not commonly be solved analytically.' In order to visualize and simulate the effects of laser light on heart tissues (myocardium) in relation to the treatment of irregular heart rates or so called arrhythmias, a fast interactive computer program has been developed in Java.

Using a versatile system, transversal and longitudinal OCT images from the retina and skin are presented. Using stacks of transversal OCT images, 3D profiles ofretina and skin in vivo are constructed.

A system for fabricating integrating microfluidic and micro-optic systems is described. Microchannel walls and multimode waveguides are formed in UV-curable optical adhesive by moving the substrate under computer control in the focus of a HeCd laser beam. Optical properties of the system were measured and two system examples are presented.

The microfabrication of an on-chip capillary system using photolithography as well as etching and aligned bonding techniques is presented. Also the optical properties of the capillary waveguide are described. These are very satisfactory for hyper Rayleigh scattering (HRS) as measurements confirm.

Medical therapeutic applications using lasers involves understanding the light tissue interaction, in particular the rate ofphotochemical and thermal reactions. Tissue is composed ofa mix ofturbid media. Light propagation in turbid media can be described by the so-called Equation of Radiative Transfer, an integro-differential equation where scattering, absorption and internal reflection are significant factors in determining the light distribution in tissue. The Equation of Radiative Transfer however can not commonly be solved analytically.' In order to visualize and simulate the effects of laser light on heart tissues (myocardium) in relation to the treatment of irregular heart rates or so called arrhythmias, a fast interactive computer program has been developed in Java.

Photoelastic modulation (PEM) and synchronous detection of laser light scattered from an optically dense turbid medium can reveal the presence and topographical features of embedded targets invisible to naked-eye observation under ambient illumination, as well as provide a quantitative measure of the optical rotation, and therefore the concentration, of chiral constituents dissolved in a turbid fluid. A 544 nm helium-neon probe beam phase-modulated at f = 50 kHz was scanned across the front surface of a scattering cell containing an optically dense suspension of micron-sized polystyrene microspheres and different types of embedded targets. Backscattered light was analyzed for signals at the modulation frequency 1(f) and first harmonic I(2f), which gave nearly instantaneous measures (i.e. approximately over a modulation period T = 1 7 is) of the difference in intensities of orthogonal states of circular and linear polarizations, respectively. Examination of different targets showed sensitivity of polarimetnc imaging to edges, surface texture, and absorption. In another set of experiments the optical rotation and degree ofpolarization ofphase-modulated light was observed by forward, lateral, and back scattering from solutions of the enantiomer D-glucose containing a suspension of polystyrene microspheres. Optical rotations increased linearly with glucose concentration at a rate dependent on the microsphere concentration, and were large even at optical thicknesses sufficiently great to extinguish transmission of the incident beam. Applications of the techniques to remote viewing and biochemical analyses can be envisioned..

The confocal microscope with volume-holographic collector [1] utilizes Bragg selectivity in order to achieve depth sectioning. The volume hologram is recorded by the interference of two beams, one of which originates as a point source at a reference depth. When a reconstructing Qrobe) source is at the reference depth, it is Bragg-matched and causes a strong diffracted signal; sources at different depths are rejected because of Bragg mismatch. Therefore, the use of a pinhole in front of the detector (as in traditional confocal microscopes [2]) is not required. The arguments for use of a volume hologram instead of a pinhole to achieve depth sectioning are: (i) the depth resolution of the microscope is independent of its photon-collection performance; (ii) the hologram phase conjugates aberrations and other systematic phase distortions, and hence acts as an ideal matched filter to the reference source (unlike the ad hoc filtering function performed by the pinhole). In this paper we focus on the depth-resolving properties of volume diffraction when a turbulent (scattering) medium, emulating a biological tissue, is present in the path of the light entering the microscope. In particular, we compare the depth resolution of a microscope recorded with and without precompensation for the presence of the scatterer. Precompensation extends the matched filtering principle by use of a priori information (the thickness of the turbulent medium) during the recording phase of the hologram. Our experimental results (section 2) demonstrate that precompensation increases the scatterer thickness over which confocal imaging is possible.

In digital holography holograms are recorded by a CCD camera and image reconstruction is performed by a computer that calculates the diffraction from the hologram. In phase-shifting digital holography an in-line setup is employed in the recording to reduce the spatial frequency spectrum of the hologram, and the distribution of complex amplitude on the CCD is directly derived by means of phase-shifting of the reference beam and subsequent analysis of hologram patterns to suppress the conjugate image. It uses a simple optical setup and delivers distributions of complex amplitude including both amplitude and phase in three-dimensional space without mechanical focusing. We apply this method to microscopy and to surface contouring in which phase distributions resulting from two different angles of incidence at a diffuse object are compared to deliver surface height.