We present the theory and modeling of an all-optical device which realizes self-routing of waves at different wavelengths. The device exploits spatial soliton interaction in the Kerr-like nonlinear medium and can be used in WDM networks. Interaction is governed by four-wave mixing that produces the desired effects under suitable excitation conditions. We give the example of a device able to route ten wavelengths, with good spatial separation at the output and practically no loss.

We report that an optical wavelength converter can be constructed by combining a figure-8 laser and a nonlinear loop mirror (NOLM), all in fiber form. This forms a hybrid passively and actively mode-locked laser. The input signal pulse train is fed into the NOLM and the output wavelength- converted pulse train is obtained through a fiber coupler in the figure-8 laser.

In this paper, we propose a new traffic-balanced routing scheme for WDM networks based on the de Bruijn graphs. This scheme has the combined advantages of small number of hops, lower queuing delay and high throughput in packet-switched networks. We also analyze its blocking probability in circuit-switched all-optical networks and find that this probability is consistently lower than the Longest Path scheme.

Nonresonant-type Bi₂O₃-B₂O₃-SiO₂ glass containing high concentration of Bi₂O₃ was prepared by a melting method. Optical Kerr shutter switching and degenerated four wave mixing experiments for this glass were performed using femtosecond laser. This glass exhibited ultrafast response below 150 femtosecond in optical Kerr switching operation. Moreover, THz optical switching was successfully performed with this glass using 1.5 THz pulse train as the gate beam. Ultrafast response and high threshold for optical damage were also confirmed with this glass at the communication wavelength of 1.5 micrometers . These results indicate that high speed switching beyond THz can be realized using Bi₂O₃-glass.

High quality traveling-wave semiconductor optical amplifiers were designed and fabricated for all-optical switching applications. We obtained 21 dB small signal gain with 0.16 dB gain ripple. Measured residual reflectivity was 5 X 10^-5 and the 3-dB gain bandwidth as wide as 70 nm. Our results show careful wavelength selection is required in order to match the amplifiers gain peak wavelength to the desired operating wavelength of the optical switches.

We report a 4 X 4 hybrid-integrated optoelectronic switch that is capable of switching digital signals with bit rates up to 9.95 Gb/s (OC-192). The inherent analogue design of the switch, along with its high bandwidth, allows it to operate independently of the format and bit rate of the input signals. In addition, the modular design of the switch allows it to be connected in either an electrical- in/electrical-out or an optical-in/optical-out configuration.

Wavelength conversion in multi-wavelength networks offers resolution of wavelength contentions and distribution of network management. It is desired in such a network that wavelength converters can simultaneously convert multiple channels at the same time so that the resulting cross- connect can scale 'the degree of wavelength conversion' as the network evolution demands such as upgrade. In addition to the multi-channel conversion capability, the wavelength converters must offer polarization independent conversion efficiency and transparency to most of the signal formats and protocols. While numerous wavelength conversion techniques have been demonstrated to date, only difference- frequency-generation offers polarization independent, strictly transparent, and multi-channel wavelength conversion without significant crosstalk. The recent experimental results obtained in AlGaAs waveguides show 17 channel wavelength conversion with no measurable cross-talk and polarization-independent conversion efficiency. The linearity to signal power levels and the spectral inversion demonstrated by experiments also imply strict transparency of the conversion process. Successful bit-error-rate measurements were obtained at both 2.5 Gb/s and 10 Gb/s, and simultaneous conversion of both 2.5 Gb/s and 10 Gb/s showed extremely low bit-error-rate with negligible cross-talk. The impact of strictly transparent wavelength converting cross- connect in multi-wavelength networks will also be discussed.

A fused-tapered fiber coupler, which is fabricated by fusing and elongating two single-mode fibers, exhibits a nonlinear coupling characteristics when it is excited with an intense light, since an intensity-dependent index of refraction is induced in fiber couplers due to optical Kerr effect. An abrupt change of power transmission at coupled and through ports in the coupler can be observed at certain wavelength of incident light and it was found that the critical wavelength is shifted into a longer wavelength as the incident power increases. The experimental verification using a mode-locked Ti:sapphire laser that produces 50 femtosecond pulses at wavelengths of 800 - 850 nm with a repetition rate of 80 MHz is followed by the theory.

An optical fiber loop memory can be used in a packet switched optical network to resolve the contention problems and increase the system flexibility. We report a multi- wavelength optical fiber loop memory with in-loop waveguide grating router. Bit error rate of stored packets is analyzed both experimentally and theoretically. A new refreshable multi-wavelength loop memory configuration is proposed and experimentally demonstrated. With this refreshable optical memory, which works like a DRAM (dynamic random access memory), optical signal can be stored as long as system required.

In this paper we investigate the performance degradation in a wavelength division multiplexing network due to crosstalk in optical cross-connects. Worst-case analysis is carried out including in-band crosstalk components. In contrast with the approximate methods in the literature, all beat-noise terms are included, and both input signal hypotheses are considered. The results are obtained by using appropriate importance sampling strategies. The optimization of importance sampling parameters was done with new adaptive techniques based on stochastic Newton recursions, combined with a novel technique called the g-method. Accurate performance measures for practical system parameter values are obtained in short simulation run-times. Infinite and finite extinction ratios are considered. The results indicate that the detection threshold has a strong impact on the system performance. The importance sampling techniques are also useful for the optimization of this system parameter.

In this paper, a high-speed 4 X 4 optoelectronic switch with on-chip optical signal distribution is presented. The switching matrix integrates both metal-semiconductor-metal photodetectors and polyimide waveguides onto a monolithic structure. The bias-switched photodetectors are used to select which incident optical signals are to be detected and converted to electrical signals for distribution. The polyimide waveguides provide on-wafer distribution of the input optical signals to the detectors. This switch had an isolation of less than 48 dB at 1.0 GHz, a crosstalk of greater than -26 dB at 0.8 GHz, and a bandwidth between 4.3 to 6.5 GHz depending on the particular crosspoint being measured. This optoelectronic switch shows improved performance over a wider bandwidth compared to the 3 X 3 optoelectronic switch presented earlier. The current switching implementation is also easier to package because it does not require the precise alignment to discrete fibers over the photodetectors for optical distribution. Fabrication details, circuit configuration, and performance for the 4 X 4 optoelectronic switch will be discussed in greater detail in these proceedings.

In our laser neural network (LNN), previously reported, a laser diode with an extended cavity is used to provide all- optical neural action. The neurons of the network are the longitudinal cavity modes of the laser. Weighted inputs are provided to these neurons via an optical matrix vector multiplier placed in the external cavity. A setup that uses a fast liquid crystal display and a loop mirror is used to expand the capabilities of the LNN to data switching applications. Up to 32 neurons can be defined having up to 12 inputs. As an example a 1:16 data decoder is demonstrated.

A novel all-optical On/Off gate structure base on nonlinear channel waveguide grating is investigated in theory. The reflectivity of the grating to the signal, and thus the ON/OFF state of the device, is modified optically by the control light which has different wavelength with the signal. The simulation result of the performance of the device is given.

In this paper we present a scheme for integration of a number of key devices for WDM-networks based on three components. The elementary components, such as phased array demultiplexers, multi mode interference (MMI)-couplers and Mach-Zehnder Interferometer optical switches, are explained and experimental results are presented on integrated Multiwavelength (MW) add-drop multiplexers, MW-optical crossconnects. The integration of optical amplifiers and detectors to MW-sources and MW-receivers is briefly discussed.

We describe a novel technique for passband control and shaping of an arrayed-waveguide grating (AWG) by designing the output star coupler to exhibit a parabolic deviation from the standard Rowland circle geometry. Passband broadening from 1 nm to 12 nm is possible using this approach. In principle, the phase-apodization function is equivalent to incorporating a synthetic aperture within the AWG, so that the same effect can be achieved by positioning a suitable aspheric-shaped anomalous refractive-index region within the arrayed-waveguide section of the device.

The effect of optical confinement factor and gain constant (optical gain coefficient) on harmonic distortion in 1.55 micrometers semiconductor laser diodes are investigated by using a mathematical model based on multi-mode rate equations. The model can be extended and used to simulate the output of any direct modulated Fabry-Perot semiconductor laser in long wavelength by changing some of the parameters. Gain and spontaneous emission are included as spectrums, since each mode experiences different gain and spontaneous emission coupled to each mode is different. The important parameters such as Auger recombination, nonradiative recombination, spontaneous emission life time and gain saturation are included in the model. The second harmonic distortion levels are examined and computed graphically for different threshold levels.

Planar electrodes such as coplanar waveguides and coplanar strips are used in high-speed GaAs/AlGaAs traveling-wave electro-optic modulators. The modulation bandwidth of these modulators strongly depends on the microwave and optical velocity match and also on the microwave loss of the electrodes. The effect of substrate carrier concentration on the microwave loss of planar electrodes is experimentally investigated. Microwave losses were measured up to 40 GHz as a function of substrate carrier concentration over the range of 1 X 10⁸ cm^-3 to 2 X 10¹⁸ cm^-3 using both epitaxially grown and ion-implanted GaAs/AlGaAs substrates. It was found that a critical residual carrier density limit of 5 X 10¹⁴ cm^-3 exists, above which the microwave loss increases rapidly. These results were verified by growing a heterostructure optical waveguide with a carrier density of less than 5 X 10¹⁴ cm^-3 and measuring the microwave loss. A modulation bandwidth in excess of 22 GHz and a half-wave voltage of 30 V were measured for this structure.

The effects and characteristics of group delay ripple of chirped fiber gratings on the performance of a 10 Gb/s NRZ transmission system has been experimentally investigated. For the power penalty less than 1 dB at bit-error-rate of 10^-9, our experiment results show that the ripple magnitude of dispersion compensating gratings should be less than +/- 20 ps within its pass-band for 10 Gb/s systems.

The shape of the grooves of a diffraction grating can be designed to take advantage of total internal reflection. We demonstrated the effectiveness of the total internal reflection (TIR) grating numerically for the bulk optic case and experimentally for the integrated optic case. The results indicated that the efficiency of the retro- diffracted order is enhanced by about 10 dB when the TIR grating design is used in place of an echelle grating with no facet metalization. We demonstrate that a TIR grating can be integrated on a chip to demultiplex 120 optical channels that are transmitted in a dense wavelength division multiplexing (DWDM) application. The wavelengths of the channels had a 0.29 nm spacing and were within the 1550 nm wavelength band for DWDM applications.

The chirp and optical extinction ratio of multiple quantum well Mach-Zehnder modulators and electroabsorption modulators depend on the device design and the modulating voltage waveform. For transmission over non-dispersion shifted fiber, 10 Gb/s system performance is reviewed by considering joint optimization of the bias and modulation voltages. The implications of modulator design are examined taking into consideration group velocity dispersion and self-phase modulation arising from the Kerr nonlinearity. The results demonstrate that optimization of the bias and modulation voltages is effective for increasing the transmission distance, reducing the variation in performance obtained when Mach-Zehnder modulators of different designs are operated with maximum optical extinction ratio, and reducing the variation in performance obtained with different transmitted powers when electroabsorption modulators are operated with maximum optical extinction ratio.

In this study the effect of optical feedback in semiconductor laser diodes (LD) has been examined using small signal analysis. The transfer function of LD is given as H (j(omega) _m)_D and transfer function of external cavity LD is given as TF (j(omega) _m)_HD respectively. The investigated parameters of these transfer functions are external cavity length (L_ext), line-width enhancement factor ((alpha) ) and mirror power reflection coefficient (R). The gain change occurring due to optical feedback noise is shown by broadening the bandwidth and narrowing the frequency spectra and the state of chaos (coherence collapse) is determined in each case. By varying the level of reflected optical feedback power (f_ext) the optical feedback system of LD has been improved. In addition to that the system is driven out of chaos by finding reasonable levels for these variables.

We propose a new design to remove the undesirable sidelobes prevalent in fiber grating spectra. This method is based on the grating period variation according to the apodization function in order to maintain constant the Bragg condition along the structure.

A new optical encoder/decoder structure, named adjustable correlator, in optical CDMA networks is proposed. This adjustable correlator uses fiber-optical recirculating delay lines as programmable configuration and adapts only two electro-optical switches. Experiments were set up to measure the characteristics of a dynamic correlator and the experimental results show good agreements with theoretical model.

We have measured Polarization Mode Dispersion (PMD) and Polarization Dependent Loss (PDL) in chirped fiber Bragg gratings for dispersion compensation and in long-period fiber gratings for gain flattening. PMD and PDL were measured in reflection and in transmission by using a polarization analyzer and a tunable laser diode. Typical experimental results are presented for two grating devices.

For the generation of optical mm-waves many schemes have been investigated19 because of its increasing technical interest for the wireless local ioop. Simple beating of two different laser lines yields high flexibility, the excessive phase noise, however, is a drawback. Nearly all methods for pulse generation are based on RF injection into single or two mode DFB lasers or Fabry Perot lasers. The tunability ofthese mm-sources is rather limited. The RF power in some cases exceeds 25 dBm, so that the generation of the optical mm-waves becomes quite costly. Our method relies on two dc-biased DFB lasers. The output of one of them (master laser) is injected via an isolator into a second DFB laser (slave laser): Under these conditions output power oscillations ofthe slave laser can be created of nearly arbitrary repetition frequency up to the THz range with high modulation index, high output power and very low phase noise. The additional continuous tunability makes this method attractive for a very flexible and low cost optical mm-wave generation.

In this paper, we develop a multiple output laser with 14 outputs. The multiple output laser composes of an 8 X 8 arrayed waveguide grating (AWG) and a semiconductor optical amplifier. We combine these two elements to achieve a ring configuration in this experiment. The multiple output laser with AWG can provide multichannel of light sources simultaneously. The characteristics of all unconnected fiber arms of the 8 X 8 AWG multiplexer are measured.

By utilizing the gain decompression effect, nonlinear semiconductor-optical-amplifier devices are possible to operate at more than 100 Gb/s speeds. We study conditions how we can achieve such a high speed operation for ultrafast TDM applications.

A rigorous numerical method of solving the stochastic laser rate equations is investigated. Using this method, statistically correct numerical simulations of the relative intensity noise (RIN) spectrum at laser output are performed. The method is validated by comparison of the simulation results with analytical theoretical predictions. To estimate the RIN spectrum the periodogram technique is used. The impact of the number of periodograms, number of points, and time interval width on the RIN spectrum estimation is discussed. It is shown also that the usual methods of solving deterministic nonlinear differential equations should not be used to obtain by simulation the RIN at the laser output.

The trends in optoelectronic products are towards higher integration level of optics, electronics and mechanics. It means smaller dimensions and tighter packaging density. The precisions in component manufacturing and accuracies in module assemblings typically are in 10 to 50 micrometer range. Due to demands of the production in series of tens of thousands it means new type of know-how in production and assembling technologies.

In this study, static and dynamic behavior of a three cavity laser diode model have been analyzed and oscillation frequency shift under the dynamic structure is explained theoretically. In the analysis, the effect of both the laser facet and the external cavity reflectivities as well as the lengths on the threshold conditions are investigated theoretically. The results have shown that when the optical feedback is increased depending upon the phase of the reflected field, the threshold gain of the laser is decreased. The results indicate that strong optical feedback, AR coating of the laser facet and large external cavity lengths are effect for the frequency shift suppression.

Quantum well waveguide photodetectors that contain two inline segments have been used as wavelength monitors with sensitivities in the picometer range. Multi-segment detectors can also be configured as wavelength demultiplexers to separate up to four optical communications channels. We review recent work in this area and report on the use of a wavelength monitor for the 1.55 micrometers region in a fiber optic strain sensor application.

We investigated differential gain, refractive index and (alpha) -parameter in strongly index and gain guided broad- area semiconductor optical amplifiers. The measured linewidth enhancement factor is larger than the values reported for narrow-stripe lasers and is consistent with theoretical predictions.

Hybrid DBR lasers composed of a semiconductor Fabry-Perot laser diode and a fiber Bragg grating have been demonstrated. In our approach, we use a single-angled facet laser diode and a conically lensed grating to obtain stable single-longitudinal mode operation over more than 85 mA current range with high side mode suppression ratio and narrow linewidth.

Using a finite element formalism, the effects of an intensity dependent refractive index nonlinearity on the coupling coefficient and wavelength detuning of an index coupled multiple quantum well distributed-feedback laser structure are modeled. The associated nonlinear 1D guided wave equation is numerically solved for the effective index (eigenvalue) and the transverse field profile (eigenvector). Results are obtained for varying numbers of quantum wells and grating thickness. Changes in wavelength detuning and coupling coefficient for a given laser structure are shown to change linearly with increasing optical power.

In this paper, we present wide range tunable semiconductor lasers using multiple quantum wells of different widths. Conventional semiconductor-laser gain medium using the quantum-well structure for the wavelength near 0.8 micrometers has only 50 meV bandwidth. Using quantum wells of different widths could significantly broaden the gain bandwidth, so broadband tuning of the laser could be easily achieved. Two types of samples designed for broad bandwidth operation have been used in this experiment. In addition, unlike the past tuning experiments that suffer from serious ASE noise, this experiment demonstrates very high ASE suppression ratio (> 40 dB) over the entire tuning range by using a triangular ring cavity.

We have investigated optical parametric amplification and difference-frequency generation in the transverse-pumping geometry. For the amplification, when the pump power is set to the threshold, a very large gain is predicted if the input power for the signal is much lower than the threshold. However, as the input power increases, the gain decreases rapidly. On the other hand, for the difference-frequency generation, for each value of the pump power, there is an optimal input power at which the output power at the difference frequency reaches a maximum.

Results are presented of the spectrally resolved absolute measurements of the electroluminescence of reverse-biased silicon nanometer-scale diode-antifuses brought into breakdown. The emission spectrum of the diode-antifuses is measured in the energy range of 1.4 - 2.8 eV at different reverse currents. The dependence of the emission intensity on the current was evaluated to study the dominant emission processes. Also the stability of the diode-antifuses has been tested. Results indicate that the diode-antifuse is basically a high quality device. Furthermore due to the nanometer-scale dimensions of the diode-antifuse, very high electrical fields and current densities are possible at low power consumption. This makes the diode-antifuse an excellent candidate to be utilized as a light source in Si- based sensors and actuator applications.

This paper present a novel idea of integrating a photodetector and a light emitting diode (LED) for wavelength conversion. The detector of interest here responds in the 1.5 micrometers wavelength region and LED emits in the near infrared (e.g., 800 - 900 nm). A proof-of-the- concept experiment has been conducted and presented here. The eventual application is to use this device in a focal plane imaging format for up-converting a 1.5 micrometers image to the near infrared then captured by a Si CCD camera.

We have investigated second-harmonic generation in short- period periodically-poled bulk and waveguide potassium titanyl phosphate crystals to generate blue light using subpicosecond laser pulses. For the bulk, the maximum conversion efficiency is approximately equals 5.5%, which is about two orders of magnitude larger than that achieved previously. For the waveguide, the maximum conversion efficiency is approximately equals 32%, which is about a factor of 4 higher than that obtained before. These measured values are in good agreement with our theoretical results. We have observed saturation of conversion efficiency, which sets a limit to the maximum conversion efficiency that can be obtained.

The main features of a thulium-doped ZBLAN fiber laser are presented and compared to the results of a numerical analysis. Particularly, the problem of the photoinduced absorption arising from the formation of color-centers is addressed with special attention to its detrimental effects on laser operation. Practical solutions to this problem are also explored.

For the integration of optoelectronic components, like lasers, modulators, detectors or waveguides, materials with different band gaps are necessary, e.g. to avoid absorption in waveguides or to get optimal intensity contrast in modulators. By implantation induced thermal intermixing of semiconductor quantum film structures the band gap can be selectively changed and the band gap shift can be controlled by the implantation parameters. Focused ion beam technology additionally allows maskless patterning, which simplifies epitaxial overgrowth and makes in-situ processing possible. The paper gives an overview about highly spatially resolved quantum well intermixing by focused ion beam technology and how this technique can be applied for the definition of optoelectronic devices and components. By the high spatial resolution of the currently used focused ion beam systems the definition of first order gratings for wavelengths from the infrared to the visible spectrum were achieved. New approaches for the fabrication of gain coupled distributed feedback lasers based on implanted first order gratings for 1.0 and 1.55 micrometers emission wavelength are discussed and device results will be presented.

A comprehensive semiconductor laser model is used to analyze the first electrical derivative characteristic of long wavelength MQW semiconductor lasers. It is found that the charge neutrality condition and the continuity of the quasi- Fermi levels, usually assumed in the rate equation approach, need not be respected. The first electrical derivative characteristics of abrupt and GRINSCH MQW structures are presented. The effects of doping in the active region on the optical gain and on the first electrical derivative characteristic are also studied.

Modeling is used to show that interdiffusion can generate a polarization independent parabolic-like quantum well. Criteria to achieve the parabolic-like quantum wells by interdiffusion are discussed. The results indicated that interdiffused quantum wells can produce equal eigen-state spacing, polarization insensitive Stark shift and modulation characteristics similar to an ideal parabolic quantum well. The design process to obtain polarization insensitive ON- and OFF-states in the parabolic-like interdiffused quantum wells is discussed. The predicted modulation depth is comparable to those measured using parabolic quantum wells. The diffused quantum wells have the advantage of using an as-grown rectangular quantum well with post-growth annealing to tailor its confinement profile. These features suggest that the interdiffused quantum well structure can be used to product polarization insensitive electro-absorptive modulation.

An analytical expression is presented for light amplification by stimulated emission in arbitrary photonic crystals, which shows an enhancement due to small group velocity. This enhancement was evaluated quantitatively for a 2D crystal with a finite thickness composed of a square array of circular air-rods formed in a dielectric material. In addition to the enhancement at photonic band edges where the group velocity is equal to zero, an extremely large enhancement due to the group-velocity anomaly peculiar to 2- and 3-D crystals was found even for quite a thin structure.

A single gun He-Cd⁺ laser utilizes a He-Cd mixture as a laser medium and oscillates at seven spectral lines of three primary colors emitted from excited Cd⁺ simultaneously. Because the powers at the three primary colors are balanced, the composite output beam appears white. Hence the name `white light laser'. White light lasers have various applicability in the fields of science and technology such as medical diagnostics and surgery, photochemistry and isotope separation as an energy source, and for color display, color holography, color printers as a light source. In this report, we present conclusive evidence about the population mechanisms to produce excited Cd ions, especially for the green laser lines.

Time-resolved photoluminescence (PL), steady-state PL, and electro-luminescence techniques have been used to characterize the carrier relaxation processes and carrier escape mechanisms in a self-assembled AlInAs quantum dots (SAQD) p-i-n laser structure under reversed bias. The measurements were performed between 5 K and room temperature on a ring mesa sample as a function of bias. At 100 K, the PL decay time originating from the SAQD decreases with increasing reversed bias from approximately 450 ps under flat band condition to approximately 150 ps for biases of -4 V. The data can be explained by a simple model based on electron recombination in the quantum dots or escape our of the dots. The escape can occur by one of three possible routes: direct tunneling out of the distribution of electron excited state level, thermally assisted tunneling of ground state electrons through the upper electron excited states or thermionic emission to the wetting layer.

All optical logic and switching is one of the key issues of optical computing and addressing. This paper proposes a low power switching technology with which switching can be achieved with optical powers on the scale of a few mW/cm². This can be achieved by using a sensitive optical nonlinearity: the photorefractive effect. The drawback of the photorefractive effect sensitivity being its slow time response, this paper shows that this can be worked around by founding the switching technology on the transient photorefractive state rather than on its slow steady state.

Quantum Dot laser diodes have been made using InAs self- assembled quantum dots (QDs) in the active region of separate confinement heterostructures. The lasers grown by Molecular Beam Epitaxy (MBE) with stacked InAs QDs grown on GaAs gave record low thresholds of 13 A/cm² at 77 K and 82 A/cm² at 15 degree(s)C. On InP substrates, InAs QDs have been grown by Metal-Organic Chemical Vapor Deposition (MOCVD) with InP claddings, and by MBE in InGaAlAs separate confinement heterostructures. For the InAs/InP by MOCVD, the QD photoluminescence (PL) peaks between 1.51 micrometers and 1.57 micrometers at 77 K and close to 1.6 micrometers at 300 K. Transmission Electron Microscope analysis correlated with the PL results reveal that the QD density depends on the growth interrupt time which follows the InAs deposition. For the InAs/InGaAlAs by MBE, the QD electroluminescence peaks at approximately 1.42 micrometers at 300 K.

We present a study of a 2D photonic crystals composed of circular InGaAsP rods in air on an InP substrate for frequencies that span from the near-infrared to the far- ultraviolet. The crystal forms a square lattice and consists of infinitely long cylindrical rods. We use the transfer- matrix method and the multiple scattering formalism to calculate the transmission spectra as a function of the filling fraction, the incident angle of the wave, the compositions of Ga and As, the temperature and the impurity concentrations.

A novel Optical Decision Circuit (ODC) based on a Mach- Zehnder Interferometer with a Gain Clamped Semiconductor Optical Amplifier in each arm is proposed. Both its static and dynamic response from simulation results demonstrate that the ODC exhibits excellent reshaping capabilities. Also the high speed response of the ODC has been investigated.

The development of mid-infrared optoelectronic emitters and detectors is important for long-wave photonic applications. We report mid-IR emission spectra for three types of narrow- gap III-V light emitting diodes consisting of n^-/p^-InAs homojunctions and of n^-InAs_1-ySb_y/p^-InAs_1-ySb_y, and n^-InAs/p^-InAs_1-x-yP_xSb_y heterojunctions all grown by liquid phase epitaxy on InAs (100) substrates. Spectra were obtained under forward bias for photon energies between 300 and 425 meV (4.1 - 2.9 micrometers ), temperatures from 5 to 292 K, and bias currents from 20 (mu) A to 12 mA. Comparison are made with photoluminescence spectra from similar material.

We propose a simple, low cost, parallel optical data bus for CMOS to CMOS optical interconnects. At the light emission side, NRC-LEDs are chosen for their high external quantum efficiency at low currents (10 - 20% at sub-mA level), their expected high yield and temperature insensitive operation. Image Fiber Bundles (IFBs) are the medium of choice for conducting the high number of parallel light channels. IFBs are a mature product of glass technology, being at the same time flexible, low cost, low risk and highly efficient. Light is received directly in CMOS, using the concept of Spatially Modulated Light detection in combination with a Sense-Amplifier receiver at a bitrate of 180 Mbit/s.

A new method for fabricating Long Period Grating (LPG) using a microlens array is introduced. Instead of blocking the excimer laser beam, this new method convergences the UV laser beam into an intensity modulated profile and the writing efficiency is improved. This method enables shorter grating writing time and also suitable for batch production of LPGs, thus providing an efficient method with potential in the mass production of LPGs.

Polarization holographic gratings were inscribed in azobenzene side chain polymer films. The polarization gratings were produced using two orthogonally circularly polarized beams and the resulting stable transmission gratings were studied using a low power HeNe laser. The gratings were observed to efficiently separate left and right circularly polarized light from the probe beam and two generate two elliptically polarized beams in the first order diffraction direction.

A description of a new research facility for HOLOgraphy and Neutron Scattering (HOLONS) at the Geesthacht Neutron Facility, is given. It essentially consists of a light- optical holographic set-up inserted into a small-angle neutron scattering instrument of a beamline for cold neutrons. Among other possibilities, this facility permits to follow the buildup of holographic gratings during recording (i.e., in real time) by simultaneous light and neutron diffraction experiments. Thus it is especially suitable for the development of optically recorded diffraction elements for neutron scattering. The main features of this new facility will be described below and first results will be presented. In particular, we point out some interesting perspectives which became now open for investigation.

The use of fiber gratings is dispersion-based RF beamforming systems is reviewed. The relationship between the beamformer and grating parameters is discussed. Measurements on the RF characteristics of fiber gratings are presented, and their impact on beamformer performance is discussed.

After demonstration of a large variety of microoptic and optoelectronic components in many institutions world-wide, the main interest is focused on their hybrid integration into miniaturized systems. This concerns modules comprising lightsources, detectors, conventional and microoptical elements, like lenses, prisms, filters, and, for some applications, miniaturized actuators. A solution is described for replication of polymer microoptical elements on arbitrary substrates (semiconductor, glass). The replication is done on wafer scale level and includes the adjustment step between the optical elements and the substrate. Demonstrators are 90 degree(s) deflection prisms for the efficient coupling between monomode waveguides and photodiodes and various microlens-arrays. From the many different replication techniques, UV-reaction molding is chosen for this application. This technique has advantages against hot embossing and injection molding. Network polymers which are stable against temperature changes can be used. The replication is made in thin layers on a solid substrate resulting in high mechanical stability and very good flatness of the samples. There is neither mechanical stress nor thermal load on the substrate which can be a fully processed semiconductor wafer containing elements like diodes or VCSELs.

The effects of the local dielectric environment on the surface-plasmon resonances of annealed gold-island films are studied experimentally and modeled theoretically. Gold- island films were annealed at 600 degree(s)C to produce spheroidal shape particles which exhibit well-resolved resonances in polarized, angle-resolved, absorption spectra. These resonances are shifted in different amounts by the depolarization effect of the surrounding medium (liquids with various refraction indices). Cross-section calculations based upon non-retarded, single-particle, dielectric interaction for these various configurations are presented and found to be in good agreement with the experimental observations.

We present a focal plane terahertz (THz) ray imaging system through use of a big-size <100> oriented ZnTe electro- optic crystal plate. Some concealed living insects and moving objects have been directly imaged and the dynamic processes of the THz field distributions are clearly displayed, both in real-time model. We also discuss the maximum and minimum sizes of the available imaging objects in this THz imaging system, and give ways to improve them.

A possible approach to the synchronization of chaotic circuits is reported. It is based on an Optically Programmable Logic Cell and the signals are fully digital. A method to study the characteristics of the obtained chaos is reported as well as a new technique to compare the obtained chaos from an emitter and a receiver. This technique allows the synchronization of chaotic signals. The signals received at the receiver, composed by the addition of information and chaotic signals, are compared with the chaos generated there and a pure information signal can be detected. Its application to cryptography in Optical Communications comes directly from these properties. The model here presented is based on a computer simulation.

An electrically interconnected, linear array of photodetectors is a useful component for several optoelectronic systems applications. Traveling-wave concepts were employed in matching arrays of metal-semiconductor- metal photodetectors to a 50 (Omega) load, over a broad bandwidth. The photodetectors are embedded in a microstrip transmission line, to form a periodically loaded structure. The bias of each detector is independently controllable. Such periodic structures can be designed to exhibit specified characteristic impedance, and to be non-dispersive up to very high frequencies. With proper matching, each photodetector exhibits broadband response into an external load. Experimentally, a monolithic array of eight metal- semiconductor-metal photodetectors, attached to a microstrip bus, is shown to have uniform 12 GHz bandwidth. A model for the array is discussed, and theoretical and experimental results are in good agreement. Applications of broadband photodetector arrays are also discussed.

We report on two techniques developed at the University of Maryland, College Park for fabricating expanded mode laser arrays. Both of these techniques use single epitaxial growth and conventional fabrication techniques. The first of these techniques is based on adiabatic mode transformation from a tightly confined active waveguide to a loosely confined large underlying passive waveguide over a mode transmission region 500 micrometers long. The devices butt couple to a standard single mode fiber with a coupling loss of 3.6 dB and reduced farfield divergence angles of 22 degree(s) and 9 degree(s) in the transverse and lateral directions respectively. The excess mode transformation loss is 1.3 dB. The second device is based on a novel resonant coupling scheme between two waveguides of different dimensions and refractive indices. The mode is transformed over a taper length of 200 micrometers with excess mode transformation loss of 0.6 dB. Butt coupling efficiencies of 41% (3.8 dB coupling loss) is achieved to a standard single mode fiber. The farfield divergence angles achieved are 24 degree(s) and 13 degree(s) in the transverse and lateral directions respectively.

This report is on a new method of proton exchange that is much easier to use than current methods, is of equal optical quality, less substrate stress, and lends itself to large scale manufacturing. This process relates to annealed proton-exchanged guided wave devices in lithium niobate (LiNbO₃) and lithium tantalate (LiTaO₃) used in integrated optic circuits (IOC's). IOC's are useful in fiber optic gyros, photonic switching devices, and intensity/phase modulation systems. They have low optical loss, low voltage drive, high frequency bandwidth, and small size and weight.

The photolithographic and photosensitive fabrication processes of infrared sulfide chalcogenide glasses waveguides are presented. Integrated optical devices such as photoinduced waveguides and directional couplers are investigated and the propagation characteristics of the waveguides are reported.

Incorporation of active materials, such as Neodymium (Nd³⁺) and Erbium (Er³⁺) in suitable host media has potential applications in lasers and amplifiers. We have fabricated composite planar waveguides on glass substrates doped with Nd³⁺ and Er³⁺ ions using the sol-gel process. The composite sol-gel was prepared using polyvinylpyrrolidone as the organic part, while Tetraethyl orthosilicate and Titanium isopropoxide formed the inorganic part. The samples were prism coupled and it was found that they supported single mode at (lambda) equals 633 nm. Gain measurement of the Nd³⁺ samples have also been carried out.

Titanium (Ti) diffusion into lithium niobate (LiNbO₃) is often used to define waveguides for integrated optics devices which are now of considerable commercial importance. I report here on changes in the surface shape caused by titanium diffusion for fabricating (LiNbO₃) integrated optical devices. I found that the processing leaves surface ridges whose height and shape depend on mass flow of lithium niobate, thickness of titanium, hydrogen content of diffusion atmosphere, and time at temperature. I also describe the surface effects of a reaction between LiNbO₃ and quartz (silicon). To my knowledge the effects reported here have never before been reported in the open literature.

Integrated optical waveguides, as well as splitters and switches utilizing the principle of multimode interference have been realized in PECVD SiON/SiO₂ technology. The waveguide design has been optimized to meet a number of requirements, such as small device size, polarization- independent operation, and low-power active operation. The design, fabrication, and initial experimental results for these devices are discussed.

Influence of first order mode excitation in input/output waveguides of multimode interference couplers is analyzed. Emphasis in common mode rejection ratio penalty in 3-dB couplers as part of balance coherent detection receivers is encountered. Design analysis is carried out in InGaAsP/InP buried waveguides. Coupler behavior is modified basically when first order mode is excited at input waveguides. A drastically reduction of 25% couplers width tolerance is derived from first order mode partial presence (10% of full input optical power) in accessing waveguides. Some guidelines about width tolerance improvement in restricted interference couplers against general interference couplers is also reported. Couplers dependence on fabrication tolerance was described as a function of power distribution between different modes in multimode section.

We present a novel method for the analysis of the rectangular MQW waveguide. Preferentially 2D structure is transformed into 1D structure by using the effective index method. Then, the characteristic matrix of the resultant planar MQW waveguide is analyzed by the scanning angle method proposed in this paper. The effective index, modal field intensity, and confinement factor of rectangular MQW waveguide can be effectively obtained by this method. Our simulation results show excellent agreement with the accurate solutions based on the finite element method. We also introduce the approximation methods for the analysis of rectangular MQW waveguide and investigate their validity.

Selective area quantum well intermixing is used to create buried heterostructure narrow waveguides, which are shown to be effective waveguides for a narrow range of wavelengths near the lasing wavelength of the structure. Measurements on as-grown and uniformly intermixed slab waveguide are used to determine the refractive index of the two regions, and the net refractive index difference is used to predict modal behavior of the buried waveguides.

This work describes the implementation of all-optical switching in distributed-feedback single-mode waveguides having a non-linear multiple-quantum well core. The optical nonlinearity is due to variations of the excitonic optical properties induced by the presence of a carrier plasma, that is photogenerated using a pump beam. We summarize the theory and present results of both static and dynamic experiments, documenting pJ switching energies, bistability and pulse compression, at wavelength of interest to telecommunication applications.

Polarization controllable semiconductor optical waveguide material/devices have been design and studied using different type of strained quantum well heterostructures in the active region of the waveguide. A phase modulator devices has demonstrated a linear relative phase shift between the TE and TM polarizations with a V_(pi ) of approximately 4 V. Another electro-absorption waveguide modulator structure has shown a bias tunable polarization mode so that the polarization properties can be actively controlled. We are also developing a monolithic integration techniques using selective epitaxial growth to achieve band gap variation within the same wafer and therefore, fabric integrated passive and active waveguide systems without high cost regrowth or device coupling.

An improved variable transformed Fourier decomposition method to analyze nonlinear dielectric waveguides is presented in which, to increase the efficiency for nonsymmetrical and nonlinear situations, a new degree of freedom (the offset) is allowed in the tangent type variable transformation. Soundness of the method is provided by means of a new self-consistent algorithm to automatically find the numerical parameters of the variable transformation which allows blind detection of quasi-optimum values. This algorithm lies upon the fact that the optimum numerical parameters are those which minimize the variance of the spectrum of the functions to be approximated. The proposed method has been tested in a linear and nonlinear (Kerr type) graded-index waveguide of exponential profile for a great variety of situations showing excellent results.

We present design and fabrication considerations for a vertically integrated electro-optic polymer modulator. The hybrid design incorporates both passive and active core segments for optimized transmission and modulation of an optical signal. When compared to traditional structures, this vertically integrated modulator potentially reduces fiber coupling and propagation losses by more than 10 dB for a 6 cm structure while maintaining a minimized V_(pi ).

16 X 16 integrated optical star couplers were designed and fabricated using an ion exchange technique in glass substrates. The devices demonstrated a very good optical power distribution uniformity, low excess loss, low polarization sensitivity and excellent reproducibility.

Photonic IC is an attractive information processing means to fully utilize the enormous bandwidth carried by the optical signals. The full integration of photonics devices, such as tunable lasers, modulators and photodetectors have to be developed and which can be obtain by using the Quantum Well Intermixing technology. This paper will explore on the wavelength tunability using different Quantum Well Intermixing techniques, such as impurity induced diffusion and impurity-free vacancy diffusion. Emphasis will be put on the development of very recent innovations and applications.

The extensive efforts being devoted to integrated optics to enhance fiber system capabilities and to develop all-optical architectures will be addressed. The talk will highlight current research, mostly on InP-based components, to face the demand for new functions needed in high-bit-rate systems, wavelength-division-multiplexing and networking.

Mode conversion is used in a large refractive index difference tapered planar waveguide structure in order to obtain high negative dispersion (-1.5 to -200 ps/nm- cm) over 0.5 to 100 nm bandwidths. Light injected into a top silica core as a fast ARROW mode adiabatically converts into a slow conventional high-order mode of an underlying tapered silicon layer. The large differential velocity between the `redder' and the `bluer' spectral components of a pulse leads to dispersion compensation. Tailoring the profile of the silicon taper can compensate for higher-order dispersion in fibers.

Although silicon is the paramount material for the microelectronic industry, bulk Si is of little use for photonic devices owing to its indirect band-gap, which prevents the all-important direct optical transitions. However, a new type of luminescent Si has opened up its future for photonic applications. This new material is light-emitting SiO₂/Si superlattices, fabricated in our laboratory. Our theoretical calculations showed that the energy band within the silicon layer has direct bandgap character, a result of strong quantum-confinement caused by the large band-offset at the SiO₂/Si interface, so that the direct optical transition is not only possible but also vigorous. For a quantum-confined amorphous silicon, the breakdown of angular momentum will naturally make all optical transition possible. Our experiments have shown that SiO₂/Si superlattices can indeed emit bright light. Moreover, the band-gap or the wavelength can be tuned over the visible range by changing the Si layer thickness, in good agreement with quantum confinement theory. The luminescence intensity as a function of Si layer thickness is found to increase, reach a maximum, and then decrease. Theoretical studies show that this phenomena is caused by competition between an increased overlap of electron-hole wave functions in the normal direction to the quantum well and an increased exciton radius in the plane of the quantum well.

Thin films of lithium niobate are derived on SiO₂/Si substrate by the sol-gel method. The solution is prepared by mixing LiOC₂H₅ and Nb(OC₂H₅)₅. The films are deposited by spin coating and are annealed at different temperatures of 400 degree(s)C, 500 degree(s)C, 600 degree(s)C and 700 degree(s)C. The films are characterized by means of X-ray diffraction, atomic force microscopy and variable angle spectroscopic ellipsometry. The experimental results show that when the heat treatment temperature is about 500 degree(s)C, the films starts to crystallize and the desirable ferroelectric phase dominates. The crystalline size of the 500 degree(s)C annealed film ranges from 39 nm to 86 nm and the film is microscopically continuous and uniform. The refractive index of the film is found to be 1.83 at the wavelength of 633 nm. The nanocrystalline nature, the ferroelectric phase and the refractive index of the films make them potential candidates for active integrated optical component applications.

We report on simulated performance results obtained for resonant and lattice circuits, comprised of 2 X 2 couplers, waveguides, Bragg gratings and wavelength independent reflective elements. The range of operating wavelength depends on the type of components used and on the adequacy of the circuit model. A unified analysis allows the investigation of a large variety of network configurations by the same computer code. The method of analysis and the numerical results should be useful for the wavelength engineering of spectral filters, add/drop combiners, sensors, etc.

We report here the experimental results of pump-induced thermal effect in Er/Yb fibers. A 10-mm long fiber Bragg grating, written directly in a highly photosensitive B/Ge/Si annulus of a 12-mm long Er/Yb-P/Al/Si fiber, was employed for determining the temperature rise caused by nonradiative transitions in the Er/Yb fiber by measuring its Bragg wavelength shift. A temperature rise of 0.85 degree(s)C per mW of pump power was measured for the Er/Yb fiber. A fiber laser constructed with a FBG written directly in one end of the fiber and a mirror butt joined to the other end was investigated for the pump-induced thermal effect. Its lasing wavelength was shifted by 0.25 nm when the pump power was varying from 4 mW to 56 mW.

Optoelectronic devices are particularly sensitive to temperature changes induced by light absorption and current flow. In order to study the thermal issues arising in the Mach-Zehnder optical modulator manufactured by Nortel, a non-linear finite-element thermal model of the device was constructed, which computes the internal temperature as a function of the applied voltage and optical power in the waveguide. An experimental technique was also developed, in which liquid crystals are used to measure the temperature on the device surface. The model predictions and the experimental results were found to agree well over wide ranges of optical power and voltage. The model and the technique have produced evidence of a thermal cross-talk between an integrated laser and the modulator: the peak internal temperature inside the modulator is higher in integrated devices than in the stand-alone configuration for identical voltage and optical power. Because of the desire to integrate multiple devices on a common substrate and the continuous increase of the optical powers in optical fiber systems, thermal issues will only become more important in future systems.

Ultra-high speed optical time division multi-access networks, operating at single-stream data rates of 100 Gb/s, may offer unique advantages over wavelength division multiplexed systems. These advantages include providing integrated services, including packet service to high-end users, multiple quality of service levels and truly flexible bandwidth-on-demand. In this paper, we discuss architectures and technologies for implementing ultrafast TDMA networks. In addition, we discuss novel applications for the ultrafast technologies that have been developed.

We describe a three-stage wavelength-routed optical access network, utilizing coarse passband-flattened arrayed- waveguide grating routers. An N-dimensional addressing strategy enables 6912 customers to be bi-directionally addressed with multi-Gb/s data using only 24 wavelengths spaced by 1.6 nm. Coarse wavelength separation allows use of increased tolerance WDM components at the exchange and customer premises. The architecture is designed to map onto standard access network topologies, allowing elegant upgradability from legacy PON infrastructures at low cost. Passband-flattening of the routers is achieved through phase apodization.

We propose a new optical physical layer and protocol for optical Load Area Networks (LANs), which allow a large number of hosts to be connected while offering a large capacity and exhibiting a high degree of modularity and scalability. The physical layer of the optical LAN is first presented. It is based on a passive star topology and exploits the benefits of combining multichannel techniques together with coherent detection. It shows very simple emission and detection schemes requiring only one laser and one photodetector per node. The experimental setup of this physical layer has been implemented and is described. A new multichannel Ethernet protocol, tailored to the physical layer is also proposed and is presented in the second part of this paper. It results in a considerable improvement of the performance (transmission delay and packet loss), when compared to a single Fast Ethernet channel protocol with the same total capacity.

We propose a new architecture for an optical fast frequency- hop code division multiple access system using tunable Bragg gratings. Previously proposed architectures called for a series of in-fiber Bragg gratings, each independently tunable with a piezo-electric device. We propose a system where the entire fiber of multiple Bragg gratings uses one piezo-electric device to tune to a particular code. We introduce a new set of codes to take advantage of the new architecture and increase the bit rate of each user, as well as the total number of users and hence aggregate bit rate.

In this paper, we propose a single-hop TDMA optical network with throughput of several Tb/s. This high throughput is achieved by combining spectrum encoding and fast demultiplexing. Fast packet switching is accomplished by using a rapidly tunable delay line. The frequency domain DPSK modulation is adopted, which provides 3 dB improvement over FD-OOK. Finally, we discuss a scalable protocol that can be employed in a network with a large number of channels and users.

We investigate the performance of CDMA. systems with laser chirping effects, single mode fiber dispersion effect and by assuming a Poisson shot noise model for an APD receiver. We develop the time-domain simulation models for the functional blocks in CDMA LANs and evaluate the end-to-end system performance using these models. The use of direct sequence CDMA LANs attracts attention due to the improved usage of the bandwidth of the optical fiber [1] [2] . We investigate the effect of using non-ideal components (sources, medium, detectors) on the performance of such a CDMA fiber-optic LAN. In our simulation the system comprises of the following signal processing blocks—Data source (NRZ) , Electrically programmable encoder, Laser, Optical encoder and decoder, Single mode fiber and Receiver.

The current status of high speed 1300 nm optical transmission will be reviewed in this paper. In particular the activities within the collaborative ACTS Upgrade project will be presented comprising 10 Gbit/s field trials, an experimental 40 Gbit/s OTDM laboratory test bed and initial work on 40 Gbit/s WDM transmission.

Transmission of intensity noise along linear single-mode fiber taking into account the first- and second-order fiber dispersion is investigated theoretically and numerically. Excellent agreement between our theoretical predictions and accurate numerical simulations of intensity noise spectra after single-mode fiber transmission is obtained for different laser bias currents and fiber dispersion parameters. Our theoretical and simulation results show that the intensity noise spectrum at the fiber output is not dependent on the second-order fiber dispersion, and therefore it is determined solely by the first-order fiber dispersion. Accordingly, second-order dispersion effects on the intensity noise spectrum are proved to be irrelevant even for very long broadband optical communication systems operating near zero-dispersion wavelength.

The effect of RF phase noise and phase delay fluctuations on the performance of a Quadrature Amplitude Modulated fiber optic link is investigated. Plots showing the bit error rate against the phase noise for 16, 64 and 256 QAM systems are presented. Two techniques are used for evaluating the average error probability performance namely, numerical integration and Taylor series approximation. To alleviate the difficulties in the simulations, phase noise is assumed to have a zero mean Gaussian probability distribution function.

A practical co-network transmission system of Telecom and CATV over installed Telecom network is designed. The system, making use of WDM and other technologies, has undergone experiments and performance tests on the Public Switched Telephone Network, which illustrate that optical fiber telecommunication network could be thereby transformed into a unified broadband network integrating VOICE, DATA, and VEDIO expeditiously and conveniently.

The variational method is used to establish that the spectrum of a pulse in a nonlinear single-mode fiber asymptotes to a finite limit. The limiting pulse shape and RMS spectral width are calculated in closed form.

Optical duobinary coding is an attractive technique to increase the chromatic dispersion limit, to increase the spectral efficiency and even both. This topic has recently drawn considerable attention from various companies and universities.

A general small-signal theory for nonlinear dispersive optical fiber systems with in-line amplification is investigated and validated through numerical simulation for different dispersion propagation regimes, optical powers, and number of fiber segments. This theory allows for any arbitrary phase and intensity modulation at the transmission system input from which phase and intensity at the transmission system output are derived. It is shown that in case of anomalous dispersion regime the conversion factors between power and phase can be remarkably enhanced and their dips move towards higher frequencies as the number of fiber sections increases, even for moderate powers. In case of normal dispersion regime, all conversion factors can be significantly reduced and their dips move towards lower frequencies as the number of fiber sections increases.

Simple analytical expressions for determining the characteristic time of a single EDFA and evaluating the 1 dB time response of a cascade of EDFA are given in a form of a difference equation. It is shown that the expressions are in remarkable agreement with the results obtained through solving numerically the differential equations for chains of EDFAs. Simulations of the transient time response to channel drop/add are also included.

For 10 Gb/s and 40 Gb/s systems, the implications of the reflection and group delay spectra of a non-ideal dispersion compensating grating on the receiver sensitivity are examined. The range of fiber lengths for which a grating provides adequate compensation is determined.

The unprecedented growth in demand for network capacity, driven by the internet and data services in general, has motivated equipment manufacturers and service providers to fully exploit the bandwidth potential of single-mode optical fiber. In addition to the optical fiber itself, erbium-doped fiber amplifiers and dense wavelength division multiplexing components have enabled capacities approaching 1 Tb/s on a single fiber. Optical networking, in which signal routing and switching are at the optical layer, is currently a subject of active research and debate. This presentation summarizes many of the current activities working on the physical layer aspects of the optical network including system and component issues.

In optical transmission systems with in-line optical amplifiers, system performance degradation caused by random noise and optical path distortions are usually thought to be inseparable, which makes system performance evaluation complicated. We proposed to use an optical system eye-mask parameterization technique to separate noise from distortion in the system budgeting. The basic idea of this approach is to find the worst-case path distortion factor which is independent of the noise characteristics and system implementations. Both theoretical development and experimental verification are discussed.

Possible implementations of next generation high-capacity transport are presented and associated technical challenges are discussed. From the expected spectral efficiency of conventional modulation formats and based on substantial practical system integration experience, it is estimated that a practical transmission capacity for a single 1000 km fiber is between 2 and 5 Tb/s, assuming a 10 THz transmission window.

In this paper, we describe a demonstration using a Multiple Quantum Well modulator combined with an optical retroreflector which supported a high speed free space optical data link. Video images were transmitted over an 859 nanometer link at a rate of 460 kilo bits per second, where rate of modulation was limited by demonstration hardware, not the modulator. Reflection architectures for the modulator were used although transmission architectures have also been investigated but are not discussed in this paper. The modulator was a GaAs/Al_0.3Ga_0.7As quantum well which was designed and fabricated for use as a shutter at the Naval Research Laboratory. We believe these are the first results reported demonstrating a high speed free space optical data link using multiple quantum well shutters combined with retroreflectors for viable free space optical communications.

Composite second-order distortion (CSO) can significantly impair system performance of analog systems. Of the three mechanisms that contribute to the CSO level, namely, chromatic dispersion, PMD, and polarization-dependent loss (PDL), modeling and experimental results show that chromatic dispersion may be the main contributor if PMD from typical currently manufactured fibers are used. Because of this and due to the low variability of the chromatic dispersion values, levels higher than -70 dB of CSO can be accommodated. Using chirp values from current directly modulated lasers at 1310 nm, system lengths as long as 40 km are predicted to be achievable. Sixteen picoseconds of instantaneous PMD can be tolerated provided chromatic dispersion and PDL are reasonably controlled.

Recent results on echelle grating based InGaAsP/InP waveguide demultiplexers are presented. The effects of grating patterning defects on the crosstalk are analyzed theoretically and experimentally. The analysis suggests directions for further improvement as well as technological limitations.

In spectrum-sliced WDM systems with an optical preamplifier receiver there is an optimum m equals B_oT (B_o equals optical channel bandwidth, T equals bit duration) to minimize the average number of photons-per-bit (N_p) required at the receiver for a given error probability (P_e). These results, previously obtained for the case of rectangular filters and no interchannel interference, are extended to the case of practical filters. It is shown that interchannel interference increases the optimum m and the minimum N_p. Operating at this optimum, the total system throughput with first-order filters is maximized at a channel spacing-to- bandwidth ratio of 3.3, and this throughput is 31 Gbit/s when the total system bandwidth is 4.4 THz (35 nm).

This paper describes the implementation and investigation of an all-optical amplified ring network with Phased Array based optical add/drop multiplexers (OADMs). From crosstalk analysis follows that an OADM with a foldback-structure and 1 X 2-switches has an outstanding crosstalk performance. From the investigation of the dynamic behavior of Erbium doped fiber amplifiers (EDFAs) in a ring configuration we found that EDFAs in a ring-configuration require a faster gain-control when compared to a cascade-configuration.

Gain equalization of an EDFA is performed by introducing spectrally designed all-fiber filters in the mid-stage of a dual-stage fiber amplifier. Two types of filters are studied: a cascade of narrow-band Bragg gratings for discrete equalization of a finite number of channels and a wide-band Bragg grating performing equalization over the whole 1539 nm to 1557 nm range. In future work, it is planned to use the discrete Bragg grating configuration to simultaneously perform Dispersion compensation (D), Equalization (E) and Stabilization of gain (S) and Channel dropping (C) in a dual-stage EDFA. Integration of these functions will result in a high performance amplifier called the DESC-EDFA.

The effect of fiber chromatic dispersion on the performance of a multichannel optical coherent CPFSK system is analyzed including also the effects of shot and thermal noises and crosstalk interference. The sensitivity penalty is found to increase due to waveform distortion caused by chromatic dispersion. The channel frequency separation is, therefore, required to increase to overcome the dispersion effect. The channel spacing requirements become worse with increase in intermediate frequency (IF) and IF bandwidth.

A single-frequency fiber laser for frequency referencing in DWDM communication systems is presented. The frequency selective element is a sampled fiber Bragg grating and the laser can be step-tuned to exact multiples of 100 GHz over 16 lines between 192.0 and 193.5 THz.

A novel and simple design of all-optical encoder/decoder utilizing variable length orthogonal spreading sequences is proposed. The proposed encoder/decoder is applicable to fiber-optic WDMA/CDMA networks which combine wavelength division multiple access (WDMA) and code division multiple access (CDMA) techniques to provide large system capacity. Because when traffic is light, the subscriber can shorten the spreading sequence, and the utilization of network can be further increased.

We report a new generation switch, the data-block switch, which can greatly increase the capacity and reduce the complexity of the interconnect network of a parallel computing system. By using WDM techniques, parallel data can be multiplexed and transmitted through a single fiber. By using photonic switching techniques, we can switch a block of parallel data in one switch operation to any site desired. In this work, we demonstrate such an operation with our fabricated 1 X 2 semiconductor optical amplifier (SOA) switch. This integrated device is an active/passive Y- junction waveguide device with a passive waveguide region in the middle and 3 active waveguide regions at each end. The amplified spontaneous emission spectrum of the SOA shows that this broadband switch can easily cover a wavelength range of more than 64 ITU wavelength grids (100 GHz). The switch operation of multiple wavelengths and the switching speed of the device were studied. A switching time of around 400 ps was achieved.

This paper describes the evolution of future network which uses multi-wavelength as several network functions together with implication of technology enhancement, key issues to increase the number of wavelengths, and new 1580 nm band technology to extend transmission bandwidth.

A low cost and high performance 4-(lambda) WDM DFB laser array employing a new strong gain-coupling laser design and a novel compact package approach is developed for optical network application. The WDM4 laser array is capable of simultaneous operation with 2.5 Gb/s 100 km NDS fiber transmission.

Energy enhancement scaling for the quasi-stable soliton transmission in periodic dispersion-managed fiber links with arbitrary attenuation is proposed and discussed. Simulations show that the inclusion of the fiber loss has the effect of reducing the energy enhancement due to the dispersion variation.

This paper describes the development of numerical simulation models of soliton systems using a newly developed Fourier Series Analysis Technique to analyze the nonlinear Schrodinger equation of soliton propagation. Generation of sub-picosecond solitons in an active mode-locked fiber ring laser with amplitude and phase modulators and soliton pulse compression mechanisms using dispersion decreasing fiber are investigated.

Interest in obtaining useful light emission from silicon- based materials has never been greater. This is because there is a strong demand for optoelectronic devices based on silicon and also because there has recently been significant progress in materials engineering methods. Here we review the latest developments in this work, which is aimed at overcoming the indirect band gap limitations in light emission from silicon. One promising new approach, based on thin-layer Si/SiO₂ superlattices, is reviewed in detail. The incorporation of these different materials into devices is described and future device prospects are assessed.

Porous silicon (PS) is a promising but rather unstable photonic material. Plasma deposition of a protective amorphous hydrogenated carbon (a-C:H) coating was used to improve the stability of porous silicon's compositional and optical properties. a-C:H films, 0.2 - 0.5 micrometers thickness, were deposited on porous silicon at room temperature from a methane plasma generated in a five-electrode saddle-field glow-discharge chamber. Plasma-deposited films exhibited good adhesion, nano-scale smoothness, and excellent mechanical integrity. Photoluminescence, UV/VIS reflectance, SEM, and FTIR adsorption spectra of a-C:H/PS structures were measured. The a-C:H films were over 80% transparent in the 0.5 - 5 micrometers range and enhanced the stability of the luminescence of the light-emitting PS.

Nanocrystalline (nc)-Si/amorphous (a)-SiO₂ superlattices (SLs) have been studied by transmission electron microscopy, Auger elemental microanalysis (AEM), Raman spectroscopy and optical reflection spectroscopy. Recrystallized Si/SiO₂ SL is extremely stable under high temperature annealing (up to 1100 degree(s)C) and aggressive wet thermal oxidation: AEM and Raman spectroscopy of folded acoustic phonons show no changes in periodicity in the growth direction and the abruptness of the nc-Si/a-SiO₂ interfaces. Furthermore, Raman spectroscopy in the optical phonon range indicates that the annealing decreases the defect density in the Si nanocrystals, possibly due to Si-Si bond rearrangement accompanied by surface reconstruction and surface defect passivation by oxygen.

The use of second harmonic generation as a technique for ultrashort optical pulse width measurement is analyzed in detail to determine the effect of group velocity mismatch between fundamental and second harmonic fields. We find that for interferometric autocorrelation and intensity autocorrelation type II phase matching, GVM has an appreciable effect. While for intensity autocorrelation type I phase matching, the effect is less noticeable.

It is now well known that rhodium doped barium titanate (BaTiO3:Rh) exhibits a significant photorefractive response at near infrared wavelengths .We studied and characterized this crystal at 1 .06 jtm by two-wave mixing experiments. In a 45°-cut crystal with a low absorption (0.1 cm1), we measured a photorefractive gain F of 23 cm1 with cw illumination and 16.6 cm1 with nanosecond illumination. Using spectroscopic determinations of the photorefractive sites 2(Rh3+, Rh4+, RhS+), we demonstrated that the photorefractive properties of BaTiO3:Rh are well described by a three charge state model '. Internal parameters of the material were derived using these experimental characterizations which allowed to accurately predict its performances at 1 .06 tm. Comparative characterizations of several BaTiO3 :Rh samples proved that this material is now well reproducible. Reproducibility, high photorefractive gain, low absorption and accurate theoretical description make BaTiO3:Rh a good candidate for realization and optimization of non linear functions like optical phase conjugation. The application we are interested in, is the dynamic wavefront correction of nanosecond Nd:YAG master-oscillator power amplifier (MOPA) laser sources. We implemented a ring self-pumped phase conjugate mirror using a BaTiO3:Rh crystal . This geometry brings several advantages. The threshold in terms of "gain X interaction length" product, is low (F1=2) 6 This phase conjugate mirror does not require a source of long coherence length 7and the gratings involved in the four wave mixing process can be well controled. Moreover the phase conjugate beam can be efficiently selected among the backscattered light by inserting optical elements in the ring 8,9• Such a self-pumped mirror is self-starting and the four-wave mixing process is initiated by the beam-fanning. To avoid spurious internal oscillations in total reflection on the crystal faces that initially developed in several of our experiments and prevented phase conjugation we optimized the geometry of the crystal. Roof-cut, 45° orientation of the c axis and antireflection coatings of the crystal suppressed these internal oscillations and efficient phase conjugation was demonstrated.

An electrically addressed spatial light modulator is designed using poled polymers. Use of photonic crystals are proposed to increase nonlinearity. The contrast ratio of 70:1 was obtained at 1 kHz with 11 Vrms applied voltage.

Pockels and Kerr cells were fabricated by growing N-(4- nitrophenyl)-L-prolinol crystal films between two transparent fused quartz plates on which indium-tin-oxide layers were deposited. Both linear and quadratic electro- optic effects of the crystals with thickness of 5 and 10 micrometers were examined by an ac modulation method. Large modulation signals were observed with a low driving voltage, the figure of merit of the electro-optic phase retardation were estimated to be 8.0 X 10^-11 m/V. It is suggested that the electro-optic cells are promising for application because of their durability, relative easy manipulation during crystal growth and high figure of merit.

A method to control a 3D pulse shape is proposed. The three dimensions are two spatial dimensions and one temporal dimension. We use the new method to control pulses two dimensionally, and we introduce another new optical system which is the dimensionally extended former system with 2D spatial light modulator.

Dynamic holography and cross modulation techniques are used to study a new photosensitive polymeric material, cellulose acetate doped with the azo-dye DR1. This allowed the identification of the principal photophysical mechanisms involved in the resonant photoexcitation processes. Angular hole burning and reorientation mechanisms are used to write intensity and polarization holograms of comparable diffraction efficiency. Application of the material for the creation of polarization manipulation holographic elements is demonstrated.

Diffraction properties of phase relief gratings which can be photofabricated in dichromated poly(acrylic acid) films have been analyzed. The formation of these gratings which produce multiple diffracted waves takes place in darkness subsequent to the holographic illumination at a wavelength of 442 nm. The holographic surface relief gratings are obtained by self-development and without any chemical treatment or wet processing. Theoretical calculations of diffraction efficiencies and experimental results at a wavelength of 543.5 nm for a seven beam splitter are presented.

This work describes the development, characterization and optimization of materials for optical memory storage applications. The photorefractive polymers are designed to contain second-order nonlinear optical (NLO) chromophores and charge transporting (CT) molecules embedded in a polymer matrix. The necessary electrooptic response is achieved by subjecting samples to a strong dc electric fields in order to induce a non-centrosymmetric arrangement of the NLO chromophores. This paper presents work performed on the design of a new multifunctional NLO-CT polymer.

The paper presents a theoretical and experimental investigation of the self-focusing of a laser pulse in a photorefractive medium on a nanosecond time-scale. For times shorter than the dielectric recombination time, we analyze the space-charge field build-up with time and space and provide strong hints on the short time self-focusing of a narrow powerful beam. In order to validate our theoretical and numerical analysis, systematic investigations were performed on a Bi₁₂TiO₂₀ crystal, which show that under the influence of an applied electric field, a beam can be self-focused in a very short time.

Glasses based on TeO₂-BaO-MgO-ZnO-Na₂O have been made successfully. The Raman scattering and the transmission properties were measured, and the photoluminescence properties of Pr³⁺ doped tellurite glasses were studied. Tellurite glasses exhibit an IR transmission cut- off beyond approximately 6 micrometers . The maximum-phonon band is at 745 cm^-1. The emission from the Pr³⁺:¹G₄ yields ³H₅ transition is at 1.295 micrometers wavelength with a spectral bandwidth of 30 nm. Pr³⁺ doped tellurite glasses appear to be a promising candidate for waveguide amplifiers in the 1.3 micrometers telecommunication window.

Numerical studies of the interaction of KrF laser pulses with pulselengths ranging from 10 fs to 15 ns with aluminum have been carried out at intensities around the threshold for damage. These results are compared with experimental measurements of interactions with pulse lengths of picosecond to nanosecond duration. The calculated damage thresholds and ablation depths agree reasonably well with those from experiments. For a material irradiated by femtosecond and picosecond pulses the damage threshold is sensitive to the material's electron-phonon coupling constant. The value of electron-phonon coupling constant which gives good agreement is close to that calculated based on free electron theory.

Laser treatment of the 303 and 416 stainless steels with Ti precoating was studied. CW CO₂ and UV ArF excimer lasers were used. The TiN films were formed at a treatment velocity of 0.5 to 3 - 5 cm/sec and a power density of CO₂ laser at (3 - 5) 10⁴ W/cm². X-ray diffractometry, x-ray mapping and Auger electron spectroscopy techniques indicated a TiN phase on the surface with oxygen content 12 - 25 at%. The thickness of the TiN film was 0.3 - 0.4 micrometers after treatment of the 5 micrometers Ti coating and about 900 angstroms for the 0.3 micrometers coating. Some characteristics of TiN films were examined and features of the nitriding process are discussed.

Fluorescence and time-resolved degenerate-four-wave-mixing (DFWM) techniques have been used to characterize the optical properties of KNbO₃/KTaO₃ superlattice grown by pulsed laser deposition on a KTaO₃ substrate. The superlattice consisted of 8 layers with thicknesses of 40 nm (KTaO₃) and 30 nm (KNbO₃). In the fluorescence measurement a significant change of emission profile with the KNbO₃ thin films deposited on the substrate has been observed. In DFWM measurements the time-resolved spectrum is characterized by a sharp coherent response signal peaked at the time of zero delay followed by a build-up of a longer- lived signal. The third-order susceptibility (chi) ⁽³) was estimated to be dramatically increased by 2 orders of magnitude.

The development of second order nonlinear optical (NLO) polymers involves several important steps. The first step is the design, synthesis and characterization of second-order NLO chromophores followed by the identification of a suitable polymer matrix into which the chromophore can be incorporated either as a guest, as a side-chain or a main- chain group. Thin films of candidate polymers are then fabricated and studied by a number of spectroscopic and thermal analyses techniques in order to characterize their NLO properties such as EO coefficient (or (chi) ⁽²)), optical losses, and temporal stabilities of poling-induced chromophore alignment. This work describes the development, characterization and optimization of materials for second- order nonlinear optical applications. The second-order nonlinear optical materials are designed to possess large second-order nonlinearity by embedding 2^nd order NLO active chromophores in high glass transition temperature polyimide structures.

We investigated the role of the photovoltaic effect on the photorefractive grating formation under illumination of weak ultrashort light pulses whose duration is much shorter than the time constants of the carrier and compared it with the cw case. In our experiments using mode-locked picosecond and cw Nd:YAG lasers, the bulk photovoltaic current in an iron- doped lithium niobate crystal were confirmed to be in the same order of magnitude for both light sources. The evolution of photorefractive gratings was also essentially the same. The Glass expression for the bulk photovoltaic effect is not compatible with the scheme of the band transport model for a very fast response. Therefore we developed a model in which the bulk photovoltaic current was implemented as a spatial shift in the initial carrier distribution. The resultant expression agreed with that of the quasi-cw approximation in the limit of a small spatial shift.

The effective stimulated emission cross-section spectra of a para-phenylene-vinylene polymer and of two paraphenylene- ethynylene polymers are determined by a fluorescence amplification technique. For these luminescent polymers laser action has been achieved in solution. The effective stimulated emission cross-section spectra are found to be small compared to the stimulated emission cross-section spectra calculated from fluorescence quantum distribution and fluorescence lifetime measurements. The laser excitation of the polymer solutions seems to form lattice relaxed exciton conformations extending over a few monomer units which are thought to be responsible for upper-to-lower-state stimulated emission and lower-to-upper-state (excited-state) absorption.

The effects of (Gamma) X-valley mixing in (AlAs)_n(GaAs)_n (001) superlattices (SLs) on the electronic and optical properties are theoretically investigated versus the SL period (n equals 1.25) and the band offsets. The calculations are based on both the empirical sp³s^* tight-binding model and the surface Green-function-matching method. The results show that the top state of the valence band is always confined to the GaAs slabs, whereas the bottom state of the conduction band (CB) shows different behaviors as it is sensitive to band mixing and, therefore, can control the optical properties of the superlattice. For large values of n (n >= 9) the SL is found to have a direct bandgap at (Gamma) -point and, thus, forms of type-I heterostructure consisting of multiple quantum wells. Whereas for the ultrathin-layer SLs (n <EQ 8), the interaction between the wells becomes considerable and band mixing effects are important. The X-valley, attributed to the AlAs slabs, becomes the lowest state in the CB and therefore the SL forms a type-II heterostructure with an indirect bandgap. These valley-mixing effects are shown to be efficient only for small conduction band offsets (CBO <EQ 190 meV). As the SL bandgap energy varies from 2.1 to 1.6 eV when n changes from 1 to 25 respectively, and these former values do, indeed, lie within the energy spectrum of the visible light, we concluded that the studied SLs are suitable for photonic device applications when the layer thicknesses are L_GaAs >= L_AlAs >= 26 angstroms.

In this paper the results of detecting volatile organic compounds (VOC) employing surface plasmon-based sensors are presented. The initial step in preparing the sensing elements herein requires depositing Au degree(s) on a quartz slide. The sensing elements are based on either (1) freshly deposited Au degree(s) or (2) growth of a self assembled monolayer composite film (SAM) on to a freshly deposited Au degree(s) surface. The desired SAM is either (1) acid terminated using (omega) -mercaptoundecanoic acid (MUA-COOH) or (2) Cu²⁺ metal ion terminated yielding (omega) - mercaptoundecanoic acid-Cu²⁺ (MUA-Cu²⁺). The experimental apparatus shown here measures the reflectivity of the Au degree(s) surface as a function of time at a given angle. The response of this surface plasmon device to various VOC's is correlated to the composition of the SAM film.

The reflectivity of a polymer film on top of a thin metal layer is usually recorded for a fixed wavelength and the TM polarization as a function of the angle of incidence. This angular spectrum contains the surface plasmon resonance due to the metal layer and the leaky modes caused by the waveguide resonances of the polymer film. Here we investigated the reflectivity spectrum of such a multilayer for a white light source as a function of the wavelength at a constant angle of incidence. The leaky mode resonances on the wavelength scale have been detected. Dynamic measurements of the reflectivity of such a multilayer at constant angle and constant wavelength have been demonstrated for vapors of Toluene as an example. The realization of compact and simple devices using this technique is possible.

We report construction and operation of a multiplexed laser spectrometer, based on fiber coupled Distributed Feed-Back semiconductor diode lasers, for monitoring concentration of gases emitted from volcanoes. The main problems related to this particular application, as well as the way of operation of the apparatus are discussed. The first experimental data, recorded at the test site of Solfatara volcano, Naples, Italy are reported. To our knowledge, this is the first design of a small, low power consuming laser spectrometer for geochemical applications.

We investigate theoretically the limits to the resolution imposed by the fundamental optical noises in film-based chemical sensors interrogated by optical reflectometry. We suggest a dynamic reflectometry approach as a possible technique to achieve the ultimate resolution. We find that a theoretical resolution around 10¹⁰ absorbed analyte molecules/cm² is possible in different cases. In the case of conducting films appreciably lower values may be possible.

We demonstrate a high sensitivity detection in the weak magnetic-dipole band of molecular oxygen near 764 nm, using a high-finesse Fabry-Perot cavity to provide an equivalent path length of 980 meters.

Spectrocolorimetry in wines is analyzed within the context of the CIE recommendations and applicable standards in measurements and quality control (ISO 9 000). A methodology is presented for wine color measurements with traceability to the spectrocolorimetric scale. The concept of uncertainty in color measurements is emphasized as necessary to the intercomparison of measurements performed by different operators, at different times, different locations and with diverse instruments so that color communication is possible without misunderstanding. The layout of a norm is described involving all phases from concept to details on sample preparation. Applications on color of wine measurements in Port Wine are presented for model validation and to show the possibility of the study of the effects on influential parameters such as temperature, pH, sugar contend and aging. Reference to the application of the procedure to the control of wine color in blends is also described.