Optically transparent time-division multiplexors and switches can be used to create terabit packet-switched networks. Cascaded optical delay (COD) multiplexors are modular, buffered 2:1 statistical packet multiplexors build from 'smart' crossbars and fiber delay lines. We have implemented the fundamental unit of COD multiplexors, a memoryless 2:1 packet multiplexor. It accepts fixed-length packets. It is designed to handle slotted and unslotted traffic, so it does not require network synchronization. This multiplexor has been built using off-the-shelf components. We demonstrate its switching characteristics for 340 ns packets, as well as present its measured packet loss rate. It can be used to make larger, buffered multiplexors with improved packet loss rates. We present the statistical insertion los distribution associated with buffered COD multiplexors. Furthermore, we outline a method of optical loss compensation which eliminates the insertion loss distribution.

Recently, optical ATM switches, composed of optical switches, fiber delay lines and other devices, have been proposed by researchers world-wide as a way of overcoming the EMI, pinout and interconnection problems that would be encountered in future large electronic switch cores. Attaining the size of buffers in optical ATM fabrics that would be required in practice is a major problem; in this paper, an architectural solution is presented. A technique is introduced for cascading many small switches to form a bigger switch with a larger buffer depth. A special feature of this scheme is that the number of cascaded switches is proportional to the logarithm of the buffer depth, providing an economical and feasible hardware solution. Architectural concepts are discussed and justified mathematically, and an electronic control scheme is introduced. Cell loss and delay performance, and buffer dimensioning are considered. The performance in terms of crosstalk and noise will be covered in a companion paper. In conclusion, it is clear that optical switching elements, with a buffer depth of several hundred required for bursty traffic, can be constructed using fewer components than other schemes, and, by implication, better noise and crosstalk performance.

Frequency chirp in modulator devices is of increasing importance at higher bit rates and increased transmission distances. The chirping behavior of reflective, resonant electroabsorptive optical modulators is analyzed and compared to the non-resonant case for a Framz-Keldysh effect based device. The chirp is found to display oscillatory behavior which is explained by the interaction of the electric field induced changes in complex refractive index with the cavity. The effect of a front face reflectivity lower than that for matching is shown to be poorer modulation and chirping performance. If the front face reflectivity is greater than that needed to match then negative chirp is possible but the insertion loss is greater than 8 dB. By fine tuning the length of the device it is shown that this can be reduced to 3 dB producing a contrast ratio of 4.5 dB and -500 MHz chirp for 400 ps, 15V pulses.

We present the design and realization of two optical front- ends in the bandwidth 0.5-10 GHz and with a transimpedance gain greater than 60 dB. The two amplifiers implement a lossy matching architecture with an interstage matching and a matched feedback architecture with a frequency controlled local feedback. We realized two hybrid circuits on an alumina substrate. A p-i-n photodiode has been placed on a ceramic substrate together with the three stage amplifier block. We propose a comparison between the two architecture taking into account the effects of the photodiode hybrid assembly. The parasitic link effects on the expected performances of the different architectures. We firstly measured on the photodiode hybrid circuit to verify its model: the response was not as flat as expected from the datasheet. Therefore we had to equalize the photodiode frequency response by means of an input reactive network.

A novel proposal to integrate the filter necessary in optically preamplified systems with a photodiode is described. The concepts involved in accurate analysis of optically preamplified receivers are introduced. This is followed by a description and analysis of resonant photodiodes which have been demonstrated in recent years. Such diodes possess the filtering capabilities required for spontaneous noise reduction and so eliminate the need for an external filter device. Preliminary analysis of the performance of resonant diodes with optical amplifiers is presented and an indication of the design parameters concerned given. The conditions for optimum bit error rates are discussed and indications given of substantial further work both in the optimization of device characteristics and the improvement of calculation methods.

This paper considers the design of a common collector common emitter PPM PIN-BJT receiver to achieve a good sensitivity improvement in the indoor infrared wireless communication system. The system operates at a bit rate of 10 Mbit/s and (lambda) equals 0.85 micrometers . The results demonstrate a low noise current for the receiver of about 2.7 pA/ (root)Hz. Original results are presented illustrating the systems to achieve a sensitivity of -50.5 dBm at an error rate of 10^-9 representing an improvement of 9.8 dB over a comparable ON OFF keying PIN-BJT system. The sensitivity enhancement has significant impact on the optical wireless network where the maximum allowed transmitted power is limited by safety issues. Moreover, the use of PPM offers other advantages such as the low average power which is suited for battery operation and a high peak power that aids detection.

This paper considers the design and performance of a tuned front-end receiver for use in a free-space optical video systems system. The use of front-end tuning is advantageous as it enables large area optical collectors to be employed, it reduces receiver noise and it eliminates the problematic L.F. emissions that emanate from typical lighting sources. Results are presented that show the receiver produced enables a 50 dB weighted SNR to be achieved at a received optical power of -32.7 dBm and threshold to be achieved at a received optical power of -39.5 dBm. It is concluded that with such a receiver a 50dB SNR could be provided in a cell having diameter of 10m with a source that emits 181mW/Str. With the same source a useful SNR of 45 dB would be achieved within a cell having a diameter of 15m and threshold would occur at the edge of a 19m diameter cell. The above results are not significantly affected by typical ambient lighting conditions.

Subcarrier multiplexed (SCM) optical network s offer a near to medium term alternative solution over high cost, evolving digital technology to distribute broadband services. Majority of existing systems are based on analogue optical transmission techniques and their principle disadvantage is the sensitivity to noise and system nonlinearities. Therefore, conventional SCM systems impose stringent noise and linearity requirements and as a result their performance is limited. A simple and attractive solution is to introduce an appropriate second stage modulator in order to improve the receiver sensitivity, hence the system performance.In this paper a SCM optical transmission system employing pulse position modulation as a second stage modulator, for transmission of video, audio and data channels is reported. Signal to noise ratio measurements obtained shows an improvement in optical receiver sensitivity compared with standard SCM systems.

Direct intensity modulation of semiconductor lasers in subcarrier multiplexed (SCM) optical fiber communication systems is of interest because of its simplicity and the possibility of integration of the drive electronics with the laser diode. Direct modulation also produces distortion which degrades system performance. In this paper, we extend a static numerical simulation method for multi-carrier SCM systems to a dynamic simulation employing rate equations. We first show that the results of our simulation agree with analytical results for multi-carrier SCM systems obtained from perturbation theory in the absence of optical reflection into the semiconductor laser. We proceed with the calculation of distortion in the presence of weak reflections. We show that the distortion is lower than what is expected from previous analytical considerations for two subcarriers. Our simulation can also take into account the effect of overmodulation in a dynamic manner. However, our simulation does not take into account the distortion due to device imperfections.

Pulse position modulation (PPM) is a format that can potentially offer several advantages when deployed over the optical wireless channel. PPM is characterized by low average power which suits laser operation and elongates battery life in mobile terminals. PPM also offers high sensitivity which is desirable in view of the limited transmitter power as governed by eye safety regulations. The performance of PPM can be significantly impaired by timing jitter. This contribution evaluates the performance and optimal filtering of PPM under timing jitter.

A novel digital pulse interval modulation scheme, a new form of pulse time modulation format, suitable for optical communication systems has been proposed. In this paper we present equations for the probability of error as a function of carrier-to-noise ratio for direct detection scheme along with theoretical and practical results illustrating the potential of this new modulation technique for optical fiber communication systems.

This paper details the design and testing of an optical wireless Ethernet system. This system is a demonstration unit that grants the user of a mobile computer access to network services usually only available to wired users. The system operates at the full Ethernet rate of 10Mbit/s and has a range of approximately four meters in a typical office environment. Issues concerning the safety of the transmitters has been presented along with details of how the commercial LEDs used in the transmitter were switched at the high speeds and powers required. Also the transmitter/receiver link has been modeled and simulated. These simulations compare well to measurements taken in a test room, the layout of which matches that of a typical office environment.

In this conference, we demonstrate a new communication system exhibiting a double security level. Information coding is based on differential phase shift keying of the light emitted from a highly coherent CW source. An imbalanced Mach-Zehnder interferometer whose time delay matches the bit duration is used to decode the data. Since the optical power is constant in the transmission link, security levels comparable with those obtained in coherence modulation may be achieved. To further enhance the security, a low coherent source is used to send false data down the transmission link. The discrimination between real and false signal is based on common mode rejection. A study of the signal to noise ratio achieved with this system is also discussed in this manuscript.

In this presentation, we discuss the security aspect of coherence modulation for telecommunications. Recently, we demonstrated a simple technique for decoding the signal without any decoder interferometer. We now demonstrate a secure alternative method based on the corruption of the interferometer's optical path difference. Experimental results at low bit rate using fiber interferometers as well as transmission at high bit rates using large-imbalanced integrated optic interferometers are presented. Considerations about the polarization state of the light are also discussed.

An optically preamplified pulse position modulation (PPM) system operating at 622 Mbit/s and (lambda) equals 1.53 micrometers is analyzed and shown to offer a sensitivity benefit of 9.2 dB over an equivalent OOK system. Fiber chromatic dispersion is taken into account and is used to estimate the received pulse shape. Pulse dispersion can potentially induce a significant performance penalty in PPM systems due to the temporal nature of the PPM format. The results show that for a transmitted pulse of duration 80 ps, the received pulses have full width half maximum of 160 ps and 320 ps for fiber lengths equaling 120 km and 240 km respectively. The system sensitivity degradation due to dispersion is explicitly evaluated. It is shown that a sensitivity penalty of up to 5 dB can be incurred over the transmission spans considered.

Recent study shows that optical code-division multiple- access (CDMA) networks cannot be evaluated or designed by only considering the performance of the optical pseudo- orthogonal codes selected. The structures of optical encoders and decoders are another important factor to consider and are needed to coordinate with the selected optical codes as much as possible. As a result, a 'serial' coding architecture for optical CDMA has been introduced. This new architecture is found particularly attractive for ultrafast optical processing and waveguide implementation for the future high-capacity, low-loss, all-optical CDMA networks. Since the optical encoder is made of a serial combination of 2 by 2 optical switches with n of them being biased to a 'mix-split' state, the generated OOC's, so- called 2ⁿ codes, pose with a symmetric delay- distribution property. In this paper, we first experimentally demonstrate the serial coding architecture. Afterwards, some techniques for algebraically constructing 2ⁿ codes of weight 4 are presented.

Architectural and algorithmic principles of the common planar multistage interconnection network are reviewed. For the purpose of its proper operation in the circuit switching mode the enlarged planar network and the multiple planar network are introduced. Additionally, a novel planar 4 X 4-switch is presented and applied to two planar architectures with switches of size >= 4 X 4.

Space, time and polarization photonic switching process in nonlinear Kerr-like media is described by the system of coupled nonlinear Schrodinger equations. New analytical solutions to these equations were obtained by means of modification of inverse scattering transform (IST) method. Matrix modification of the IST method is used to solve the problem of two-frequency spatial and temporal solitons. Some 'soliton spectral flashes' at sum and difference frequencies are discovered. It is shown that if the nearest sum and difference frequencies lie in the transmission region then bit-rate capability of optical fiber soliton information superhighways can be increased. When soliton pulses propagate in the optical fiber with loss and inserted optical amplifiers, the main difficulty is that after amplification the soliton lose their ideal soliton shape and nonsoliton radiation appears. A topic of particular interest is the development of the methods of the theory of optimal control of distributed media for the nonlinear equations solvable by the IST method. Novel ideas and results obtained in this paper include distributed optimal control formulation of the IST method. Obtained solution to the problem describe the amplification of the solitons by the optimal manner without formation of nonsoliton radiation.

This paper is a study of routing in optical WDM grid networks, these being chosen since they represent good idealizations of less regular networks, suggest hypotheses about them, can be used for local area and computer networks, and are analytically tractable. Due to performance, cost, and physical effects in the fibers, it will be necessary to have several fibers between each pari of connected nodes supporting some small number of wavelengths on each. This is modeled analytically and compared with simulation for a variety of cases. It is shown that the simplified analytical routing compares well with the heuristic simulation algorithm, and that when multiple fiber links are used, wavelength conversion offers little reduction in network requirements.

The WDM/OFDM-networks of the paper are multigraphs. Transformations of these graph models are presented and applied to WDM/OFDM-networks for their later analysis and optimization. The paper concentrates on two transformations, the complement and the dual of WDM/OFDM-networks. However, the complement exists only for simple graphs whereas WDM/OFDM-networks are multigraphs with multiple edges between two nodes. The computation of the dual is simple only for planar graphs and for regular graphs in terms of hypergraphs. Throughout the paper, the dual and the complement of nonregular simple graphs/networks are computed by means of computer programs. However, the aim of the ongoing work is to compute the dual and the complement of multigraphs. By means of the dual of multigraphs the topologically equivalent simple graph and in turn the complement may be obtained which both are aimed to extend the range of analysis and design concepts of WDM/OFDM- networks. Various examples are presented which explain the applied concepts.

Scheduling all-to-al connections in a network of limited physical connectivity provides a way to trade bandwidth for reduced routing control as well as deterministic connection latency. In this paper, we consider the problem of scheduling all-to-all connections in a WDM ring. For a given number of wavelengths, K, and a given number of transmitter/receiver pairs per node, T, we determine the theoretical lower bound (TLB) on the scheduling length. A basic scheduling strategy called complementary assembly with dual strides (CADS) is proposed. In a special case when K equals 1 and T equals 1, the TLB can be achieved based on CADS. Heuristic algorithms based on either homogeneous or heterogeneous CADS are then proposed for the case when K > 1, and near minimum scheduling length can be achieved for any T. Our analysis also indicate that there is an optimal value of T for a given K such that neither T nor K would become the performance bottleneck. Impact of wavelength-tuning delay, ring propagation delay, laser array fabrication especially wavelength drift of the WDM sources on the scheduling method is also discussed.

To reduce four-wave-mixing crosstalk in long-haul wavelength-division multiplexing (WDM) lightwave systems, the use of unequally spaced channels has recently been proposed. Instead of being solved y integer linear programming, the unequal-spaced channel-allocation problem is here treated as constructing suitable optical orthogonal codes in optical code-division multiple-access (CDMA). Three 'algebraic' algorithms on finding the frequency locations of unequally spaced WDM channels are reported. The constructions are based on generating optical CDMA codewords with a predetermined pulse separation and 'aperiodic' autocorrelation sidelobes no greater than one. The algorithms potentially provide a fast and simple alternative to solve the problem, besides the recently reported computer-search method.

This paper presents different architectures for high split, wide range bidirectional SuperPONs.One of the ways to achieve such SuperPONs is by the introduction of erbium- doped-fiber-amplifiers or semiconductor optical amplifiers (SOA) in order to overcome the strongly increased power budgets in comparison to conventional PONs. This will however present new challenges in overcoming the 'noise- funneling' effect caused by the parallel amplifiers. Four different approaches are studied: 1) using of on/off switchable semiconductor optical amplifiers, 2) using parallel erbium-doped-fiber amplifiers, 3) using electro- optic regeneration, and 4) using conventional SDH, ATM and APON technology. A description is given of each architecture, including advantages and drawbacks. These architectures serve as input to further studies performed by the ACTS-PLANET consortium. The power-budget studies showed that it is technically feasible to develop a SuperPON with a 2048 split and a 70-100 km range.

All optical network is creating a paradigm shift in the way communication network is designed, comparable to analog to digital transition. This paper focuses on architecture design methods for all optical network. Its primary focus is on the restoration of these networks, as the impact of failure is many magnitudes higher than traditional transmission systems. The paper also has sections related to the key element of all optical network, namely the size of optical cross-connects, as the economics of all optical network heavily depends on the cross-connect size. Capability of multiplexing wavelengths created the ability to transmit high bandwidths and technology leaps in optical amplifier resulted in longer express system. The economic benefits of such architecture are also discussed. Managing wavelengths is another key element in the all optical network. This paper discusses benefits of wavelength switching. Last but not the least, the performance requirement of optical network is discussed. Performance during failure scenarios are discussed. The paper also discusses, at a high level, a typical modeling approach with evaluation criterion for good network design.

An enhanced multistage optically amplified passive optical network (PON) known as SuperPON is presently being investigated by the ACTS-PLANET consortium as a possible future solution for broadband access networks. As it is extremely probable that user bandwidth requirements will continue to increase substantially in the short to medium term it is highly pertinent to consider the upgradeability of SuperPON topologies. In this paper capacity upgrades in the wavelength, space and time domains for both the downstream and upstream directions are discussed with reference to a particular basic SuperPON.

Most telecommunication operators are currently deciding on how to respond to customers' needs stimulated by the synergy between compression coding of multimedia and the emergence of broadband digital networks. This paper describes a range of broadband access architectures under consideration in the full services access network initiative. All architectures have a common requirement for a broadband ATM PON. A common broadband PON applicable to many operators increases the world-wide market for the product. With greater production volumes manufacturers' costs reduce because of the experience curve effect making broadband access systems economic.

Developments in optical amplifiers and the tendency towards fewer and larger switching stages made feasible and desirable the concept of SuperPONs with a range of 100km. Up to 15000 residential customers can share the SuperPON on a TDMA basis lowering the cost of access to B-ISDN services. Tree PONs require a MAC protocol to arbitrate the access to upstream slots among the competing customer ATM cells in a dynamic and efficient way. The protocol presented in this work combines different access mechanisms according to service quality requirements. All bursty traffic is manipulated transparently using a reservation approach with closed loop control so as to handle the unpredictability of arrivals. In contrast, voice, N-ISDN and other delay sensitive services are provided with unsolicited access permits. In addition, composite cells offered quasi- synchronous permits are used to support STM legacy traffic without echo-cancellers. So, ABR traffic which is delay tolerant and more cost sensitive, can and should be concentrated with full exploitation of multiplexing gain prospects. The permit distribution algorithm focuses on cell spacing, control of CDV, almost jitter free access for synchronous traffic and efficiency for ABR traffic.

This paper is concerned with the development of a long range, wide splitting passive optical network (PON) for deployment in the access network, termed SuperPON. Such a network requires careful attention at the medium access control (MAC) layer in order to provide for the high round trip delay. In particular the paper deals development and testing of a software simulation platform which may be used to investigate the performance of potential SuperPON MAC layer protocols. Furthermore, a new MAC protocol developed for operation on a SuperPON is simulated and its performance characteristics are discussed. In addition for purposes of comparison a previously utilized PON protocol is also modeled on the SuperPON and hence the benefits of the new SuperPON protocol are demonstrated.

This paper proposes a MAC protocol for 2D grid networks, termed slotted grid protocol (SGP), for high speed LANs/MANs. To support high speed transmission and all- optical operation, intermediate routing and buffering is avoided. SGP combines the linear optical network concepts with 2D grid topology. It employs prefixed slotting and routing mechanisms, consequently resulting in scalable, all- optical or almost-all-optical techniques that results in high performance. SGP consists of two layers. The lower layer is slotted ring based protocol which employs two uni- directional trains to transport the packets along each of the merged rings which connect a group of nodes in the network. The upper layer is a token driven protocol which is to control the merging process so that al nodes are involved in the transmission simultaneously and every node can get a chance to work as a merging node. Multiple-queue strategy is adapted to realize the one-cycle full inter-connection on a unidirection ring. The multiple-queue strategy makes also the benefits for balancing the traffic load of the network, and for eliminating the head-queue effects. Consequently extendable capacity of the network and wider effective traffic load range are achieved based on the same node configuration and network configuration as that of the linear protocol, such as DQDB. The primary properties of the SGP are modeled and analyzed based on polling system principles. Simulation results are presented in this paper, which includes the comparison of the performance of SGP with that of DQDB.