Leonid G. Kazovsky

CORD: contention resolution by delay lines

The implementation of optical packet-switched networks requires that the problems of resource contention, signalling and local and global synchronization be resolved. A possible optical solution to resource contention is based on the use of switching matrices suitably connected with optical delay lines. Signalling could be dealt with using subcarrier multiplexing of packet headers. Synchronization could take advantage of clock tone multiplexing techniques, digital processing for ultra-fast clock recovery, and new distributed techniques for global packet-slot alignment. To explore the practical feasibility and effectiveness of these key techniques, a consortium was formed among the University of Massachusetts, Stanford University, and GTE Laboratories. The consortium, funded by ARPA, has three main goals: investigating networking issues involved in optical contention resolution (University of Massachusetts), constructing an experimental contention-resolution optical (CRO) device (GTE Laboratories), and building a packet-switched optical network prototype employing a CRO and novel signaling/synchronization techniques (Stanford University). This paper describes the details of the project and provides an overview of the main results obtained so far.

Optical Fiber Communication Systems

The Communications Toolbox: Introduction. Probability and Random Variables. Some Important Probability Distributions. Signals and Systems. Random Processes. Spectral Analysis. Narrowband Signals and Systems. Elements of Detection Theory. From Light to Signals. Basic Optical Fiber Communications Components: Introduction. The Refractive Index and the Laws of Reflection and Refraction. Total Internal Refraction. Step Index Fibers and Slab Waveguides. Maxwells Equations in the Slab Waveguide. Even Propagation Modes. Odd Propagation Modes. Number of Modes and Single-Mode Fibers. Phase Velocity. Group Velocity. Attenuation and Dispersion. Dispersion-Shifted and Dispersion-Flattened Fibers. Polarization-Maintaining and Single-Polarization Fibers. The P-N Junction. Single Heterostructure. Double Heterostructure. LED Physical Structure. The LED Rate Equation. LED Output Spectrum. LED Modulation Response. The Fabry-Perot Resonator. Semiconductor Laser Physical Structure. Laser Output Spectrum--Spectral Width and Linewidth. Bragg Reflections. Distributed Feedback (DFB) and Distributed Bragg Reflection (DBR) Lasers. Rate Equations. The Steady-State Solution to the Rate Equations. Laser Modulation--Step Response. Laser Modulation--Sinusoidal Frequency Response. Relative Intensity Noise (RIN), Phase and Frequency Noise, Chirp. Laser Package. The PIN Photodiode. The Avalanche Photodiode, ADP. Basic Binary Optical Communication System: Introduction. System Description. Performance Evaluation. Coherent Systems: Motivations and Basics. Fundamental Receiver Sensitivity--Homodyne Systems. Heterodyne Systems--Synchronous Detection. Heterodyne Systems--Asynchronous Detection. Heterodyne Systems--Weakly Synchronous Detection. Summary and Comparison of Fundamental Sensitivities. Optical Hybrids. Phase Noise and Linewidth. Synchronous Systems. Asynchronous Systems. Weakly Synchronous Systems. How to Deal with Phase Noise--Summary. Polarization Fluctuations. Appendix A--Statistics of Phase Noise to Amplitude Conversion. Appendix B--Evaluation of Averages by Quadrature Rules. Optical Amplifiers: Introduction. Semiconductor Amplifiers. Erbium-Doped Fiber Amplifier. Comparison of Major SOA and EDFA Characteristics. Other Fiber Amplifiers. Soliton Systems: Intuitive Explanation of Solitons. Advantages of Solitons for Long Distance Transmission. Derivation of Solitons. Amplitude, Duration, Energy, and Power. Higher-Order Solitons. Qualitative Physical Explanation of Solitons. Estimation of Peak Pulse Power Required for Solitons. Fiber Loss and its Compensation. Lumped Amplifiers in Soliton Systems. Polarization Dispersion. Amplified Spontaneous Emission Noise in Soliton Systems. Error Rates in Soliton Systems. Soliton Experiments. Using Recirculating Loops. Wavelength Division Multiplexing with Solitons. Bidirectional Soliton Systems. Sources of Soliton Pulses. Beyond the Gordon-Haus Limit. Multichannel Systems: Introduction. Time-Division Multiplexing (TDM). Wavelength-Division Multiplexing. Subcarrier Multiplexing. Code-Division Multiplexing. Space-Division Multiplexing. Network Issues.

SUCCESS: a next-generation hybrid WDM/TDM optical access network architecture

In this paper, the authors propose a next-generation hybrid WDM/TDM optical access network architecture called Stanford University aCCESS or SUCCESS. This architecture provides practical migration steps from current-generation time-division multiplexing (TDM)-passive optical network (PONs) to future WDM optical access networks. The architecture is backward compatible for users on existing TDM-PONs, while simultaneously capable of providing upgraded high-bandwidth services to new users on DWDM-PONs through advanced WDM techniques. The SUCCESS architecture is based on a collector ring and several distribution stars connecting the CO and the users. A semipassive configuration of the Remote Nodes (RNs) enables protection and restoration, making the network resilient to power failures. A novel design of the OLT and DWDM-PON ONUs minimizes the system cost considerably: 1) tunable lasers and receivers at the OLT are shared by all ONUs on the network to reduce the transceiver count and 2) the fast tunable lasers not only generate downstream data traffic but also provide DWDM-PON ONUs with optical CW bursts for their upstream data transmission. Results from an experimental system testbed support the feasibility of the proposed SUCCESS architecture. Also, simulation results of the first SUCCESS DWDM-PON MAC protocol verify that it can efficiently provide bidirectional transmission between the OLT and ONUs over multiple wavelengths with a small number of tunable transmitters and receivers.

BROADBAND FIBER OPTICAL PARAMETRIC AMPLIFIERS

The bandwidth of a single-pump fiber optical parametric amplifier is governed by the even orders of fiber dispersion at the pump wavelength. The amplifier can exhibit gain over a wide wavelength range when operated near the fibers zero-dispersion wavelength. It can also be used for broadband wavelength conversion,with gain. We have experimentally obtained gain of 10-18 dB as the signal wavelength was tuned over a 35-nm bandwidth near 1560 nm.

Sleep Mode for Energy Saving PONs: Advantages and Drawbacks

A common approach to reduce energy consumption in communication networks is to allow network elements to switch to sleep mode. While this technique has been widely utilized in wireless networks, recent studies have proposed to exploit sleep mode in wired networks to conserve energy as well. This paper focuses on some feasible implementations of sleep mode in passive optical networks (PONs). In particular, ONU sleep mode is considered. The paper first outlines the ONU wake-up process using current time division multiplexing (TDM) PON protocols. Current and novel optical network unit (ONU) architectures that selectively switch-off some elements are then described. Their advantages in terms of energy savings are analytically computed under different traffic scenarios. Using the proposed architectures, analytical results show more than 50% energy saving under realistic TDM traffic. Finally, possible drawbacks in terms of new scheduling challenges are also discussed and potential solutions are presented.

Wide-band tuning of the gain spectra of one-pump fiber optical parametric amplifiers

By suitably choosing the fiber properties, and by tuning the pump wavelength near the fiber zero-dispersion wavelength, one can in principle generate a wide variety of one-pump fiber optical parametric amplifier gain spectra. These can range from a very wide single region to two symmetric narrow gain regions far away from the pump. We have experimentally verified these predictions. With a highly nonlinear fiber, we have inferred the existence of gain over a single 400-nm region and measured a maximum on-off gain of 65 dB. With a common dispersion-shifted fiber, we have obtained tunable gain regions less than 1 nm wide, up to 200 nm from the pump; we have also shifted these by several nanometers by lowering the fiber temperature to 0/spl deg/C.

Phase- and polarization-diversity coherent optical techniques

Progress in phase- and polarization-diversity coherent optical techniques has led to impressive receivers able to tolerate wide laser linewidth and large polarization fluctuations. The advantages and the drawbacks of diversity receivers, and recent experimental and theoretical research results are discussed. >

Cross-phase modulation in fiber links with multiple optical amplifiers and dispersion compensators

We have theoretically and experimentally investigated the cross-phase modulation (XPM) effect in optical fiber links with multiple optical amplifiers and dispersion compensators. Our theory suggests that the XPM effect can be modeled as a phase modulator with inputs from the intensity of copropagating waves. The frequency response of the phase modulator corresponding to each copropagating wave depends on fiber dispersion, wavelength separation, and fiber length. The total XPM-induced phase shift is the integral of the phase shift contributions from all frequency components of copropagating waves. In nondispersive fibers, XPM is frequency-independent; in dispersive fibers, XPMs frequency response is approximately inversely proportional to the product of frequency, fiber dispersion, and wavelength separation. In an N-segment amplified link, the frequency response of XPM is increased N-fold, but only in very narrow frequency bands. In most other frequency bands, the amount of increase is limited and almost independent of N. However, in an N-segment amplified link with dispersion compensators, the frequency response of XPM is increased N-fold at all frequencies if the dispersion is compensated for within each fiber segment. Thus, the XPM-induced phase shift is smaller in systems employing lumped dispersion compensation than in systems employing distributed dispersion compensation.

200-nm-bandwidth fiber optical amplifier combining parametric and Raman gain

Theory shows that the gain bandwidth of a one-pump fiber optical parametric amplifier (OPA) using highly nonlinear fiber (HNLF) could be more than 200 nm. Under these circumstances, the OPA gain would overlap the pump-induced Raman gain. We have studied the combined effects of OPA and Raman gain theoretically and experimentally. The experimental results demonstrate a 200-nm bandwidth from a single fiber-optical amplifier and also verify that the influence of the Raman effect is relatively small, as predicted by the theory.

A summary of the HORNET project: a next-generation metropolitan area network

Metropolitan area networks are currently undergoing an evolution aimed at more efficiently transport of data-oriented traffic. However, the incoming generation of metro networks is based on conventional technology, which prevents them scaling cost-effectively to ultrahigh capacities. We have developed a new architecture and set of protocols for the next generation of metro networks. The architecture, named HORNET (hybrid optoelectronic ring network), is a packet-over-wavelength-division multiplexing ring network that utilizes fast-tunable packet transmitters and wavelength routing to enable it to scale cost-effectively to ultrahigh capacities. A control-channel-based media access control (MAC) protocol enables the network nodes to share the bandwidth of the network while preventing collisions. The MAC protocol is designed to transport variable-sized packets and to provide fairness control to all network end users. The efficiency and the fairness of the MAC protocol is demonstrated with custom-designed simulations. The implementation of the MAC protocol and the survivability of the network have been demonstrated in a laboratory experimental testbed. The article summarizes the accomplishments of the HORNET project, including the design, analysis, and demonstration of a metro architecture and a set of protocols. The HORNET architecture is an excellent candidate for next-generation high-capacity metro networks.