InGaAsP/InP 1.3-µm wavelength surface-emitting LED's for high-speed short-haul optical communication systems

Performance and reliability for InGaAsP/InP 1.3-µm wavelength high-speed surface-emitting DH light emitting diodes (LED's) have been investigated. High-speed and high-radiance performances were obtained by the optimal design of both structural parameters and LED driving circuit. Rise and fall times were both 350 ps and peak optical power coupled to a 50-µm core 0.20 NA graded-index fiber at the 100-mA pulse current was - 15.8 dBm with 6-dB optical ON/OFF ratio. A 2-Gbit/s non-return-to-zero (NRZ) pulse transmission over a 500-m span was carried out, Feasibility of using surface-emitting LED's in a high-speed optical communication system has been confirmed. Accelerated aging tests on high-speed LED's were carried out. The half-power lifetimes have been estimated to be more than 1 × 10⁸h at 50°C ambient temperature.     

Optical receivers for lightwave communication systems

As long-wavelength optical telecommunications systems are now being installed in countries throughout the world, this is an opportune time to review the successful developments in detectors and receivers for this application. We given prominence to receivers using p-i-n and avalanche photodiodes, describing in some detail the principles of their operation as well as the details of their development. However, we also consider bipolar phototransistors, photoconductive detectors, and the receiver requirements for coherent optical systems, concluding with a broad comparison of the various receiver designs.     

Optical receivers for lightwave communication systems

As long-wavelength optical telecommunications systems are now being installed in countries throughout the world, this is an opportune time to review the successful developments in detectors and receivers for this application. We given prominence to receivers using p-i-n and avalanche photodiodes, describing in some detail the principles of their operation as well as the details of their development. However, we also consider bipolar phototransistors, photoconductive detectors, and the receiver requirements for coherent optical systems, concluding with a broad comparison of the Various receiver designs.     

Recent advances in coherent optical fiber communication systems

Research and development of coherent optical fiber communications have been accelerated mainly because of the possibility of receiver sensitivity improvement reaching 20 dB, and partly because of the possibility of frequency-division multiplexing (FDM) with very fine frequency separation. In this paper, recent advances in the research on coherent optical fiber communication systems are reviewed, with emphasis on those reported in the past two years. The bit-error rate measurements so far reported are classified and investigated in four categories: PCM-ASK, PCM-FSK, PCM-PSK, and PCM-DPSK. The states-of-the-art of polarization-state stabilization techniques is also discussed.     

Power and modulation bandwidth of gaAs-AlGaAs high-radiance LED's for optical communication systems

We present an analytical model for GaAs-AlGaAs double heterostructure high-radiance LED's intended for use in optical communication systems. This model takes all the important device and material parameters, such as self absorption, heterointerfacial recombination, doping concentration, active-layer width, injection carrier density, and carrier confinement into account. A theoretical discussion of the effect of these parameters on LED output power and modulation bandwidth is given along with experimental results which are in good agreement with the model. The best high-output 50-μm LED's (biased near saturation) emitted 15 mW into the air with a radiance of 200 W/cm². sr (highest ever reported for a surface emitter LED) and a modulation bandwidth of 17 MHz; the highest bandwidth obtained was 170 MHz at 2-mW output.     

Recent advances in theory and applications of scrambling techniquesfor lightwave transmission

This paper discusses recent advances in the theory and applications of scrambling techniques for digital lightwave transmission. It introduces the theories of sequence space and shift register generator (SRG) space which enable systematic analysis and mathematical manipulation of the behavior of sequences in general and the related SRG's. It discusses the behavior and realization of frame synchronous scrambling (FSS) and distributed sample scrambling (DSS) with emphasis on parallel sequences and the related parallel SRG's (PSRG). In addition, it describes self synchronous scrambling (SSS). Then the paper applies the theories to today's lightwave transmission systems by demonstrating practical parallel designs of FSS for SDH/SONET transmission, DSS for cell-based ATM transmission, and SSS for SDH-based ATM transmission. It finally considers how DSS can be used for scrambling of mixed isochronous and nonisochronous data in future high-speed data networks. The paper employs various new concepts and terminology, such as PSRG engine, generating vector discrimination matrix, (M,N) PSRG, sampling vector, correction vector, correction matrix, predictable scrambling concurrent sampling, and immediate correction     

Effects of TE-TM mode kinks on the performance of semiconductor lasers in lightwave communication systems

Effects of kinks in 1.3-μm InGaAsP etch-mesa-buried-heterostructure lasers on their performance in lightwave communications systems are studied through bit-error rate measurements. These kinks are due to the onset of TM modes in the light emission. Noise associated with kinks is observed when the lasers are operated above the kink region. This noise associated with kinks leads to a noise floor in the bit-error rate curves. The magnitude of the noise associated with these kinks is deduced by fitting the experimental bit-error-rate curves using computer simulations.     

Performance characteristics and extended lifetime data for InGaAsP/InP LED's

The performance and lifetest results of InGaAsP/InP LED's emitting at 1.27 µm are described. At a current density of 10 kA/cm², 40 µW of optical power is coupled into a 63 µm core, 0.21 NA optical fiber, and the projected lifetime at room temperature is approximately estimated to be 8 × 10¹⁰hours.     

High-power InGaAsP edge-emitting LEDs for single-mode optical communication systems

The letter describes 1.3 ?m InGaAsP edge-emitting LEDs which couple 40 to 60 ?W into a single-mode fibre. The 1.0 ns rise times and 30 to 45 nm spectral widths of these LEDs make suitable for optical communication systems operating at data rates as high as 400 Mbit/s.     

Band-to-band Auger effect on the output power saturation in InGaAsP LED's

Band-to-band Auger effect on output power saturation in InGaAsP light emitting diodes is studied theoretically. The CHSH-type Auger transition rate is calculated using an approximation formula which involves a weak degeneracy effect. Calculated carrier lifetime and radiance versus current density for 1.3 μm LED's agree with reported experimental results. Band-to-band Auger recombination of the CHSH process greatly affects the radiance saturation in InGaAsP LED's.     

Recent advances in long-wavelength semiconductor lasers for opticalfiber communication

A brief history of the semiconductor laser and a short tutorial on its basic operating principles are given. Some key criteria for semiconductor lasers to be used in advanced systems are discussed. Various advanced laser structures (including single-frequency, high-speed and wavelength tunable lasers, laser transmitter optoelectronic integrated circuits, and coherent receiver photonic integrated circuits) are presented together with their performance characteristics     

Recent advances in DSP systems

Some of the advances that have contributed to the realization of communication systems with programmable digital signal processors (DSPs) are described. DSP architectures are examined, covering the performance improvements resulting from advances in circuitry as well as in architecture. Architectural advances discussed are parallel processing, function generation, integrating analog circuits, and sigma-delta analog-to-digital conversion. DSP applications to high-speed modems, trellis-coded modulation, and echo cancellation are examined. The DSP implementation of a V.32 modem is described     

AM/OFDM混合光传输系统误码特性

本文分析了在限幅噪声和高斯噪声环境下,在ＨＦＣ网中混合传输ＡＭ／ＯＦＤＭ信号时的误码特性,并与单载波ＡＭ／ＱＡＭ系统进行比较,结果表明ＯＦＤＭ系统由于多个子通道的稀释作用,其抗限幅噪声性能比单载波系统好。     

Modification of cutsets for reliability evaluation of communication systems

A general and simple technique for the evaluation of symbolic reliability expression in the case of practical systems such as a communication system having fixed channel capacities of its various communicating links, a computer communication network allowing a fixed amount of data exchange amongst different terminals of various computer centres and a power distribution system having limited power ratings of its various power lines, is presented. A system is considered reliable only if it successfully transmits at least the required system capacity from the transmitter to the receiver station. In this method, the various branch sets are obtained which completely disrupt the communication path, i.e. ensure system failure. It is observed that these branch sets are not necessarily the cutsets in the usual graph theoretic sense. The unreliability expression is then determined by adopting an existing method for making various terms disjoint. Two typical examples are solved by this method. It is observed that the method is computationally fast and efficient.     

Silicon MOS amplifier operation in the integrate and dump mode forgigahertz band lightwave communication systems

The operation of a MOS amplifier in the integrate and dump mode is discussed. This mode of operation results in the suppression of the input load resistor noise while retaining the advantages of a large dynamic range and no equalization requirement. The technique is useful in improving the receiver sensitivity in circuit topologies such as the nonintegrating front. Several aspects of its MOS implementation are presented, along with test results     

Optimization and characterization of high-radiance (Al,Ga)As double-heterostructure LED's for optical communication systems

Phenomenological models for Burrus-type high-radiance double-heterostructure LED's are described which make it possible to calculate the maximum optical power emitted from a diode chip, the equilibrium optical power coupled into an optical fiber of a given numerical aperture NA and core diameter, and the transient response of the spontaneous emission of the LED, and afford criteria for optimization of these devices. Measured values of power and rise time are found to agree with theory to a useful degree of approximation. Reliability data for optimized LED's are presented.     

Recent advances in memory consistency models for hardware sharedmemory systems

The memory consistency model of a shared memory system determines the order in which memory operations will appear to execute to the programmer. The memory consistency model for a system typically involves a tradeoff between performance and programmability. The paper provides an overview of recent advances in hardware optimizations; compiler optimizations, and programming environments relevant to memory consistency models of hardware distributed shared memory systems. We discuss recent hardware and compiler optimizations that exploit the observation that it is sufficient to only appear as if the ordering rules of the consistency model are obeyed. These optimizations substantially improve the performance of the strictest consistency model, making it more attractive for its programmability. Recent concurrent programming languages and environments, on the other hand, support more relaxed consistency models. We discuss several such environments, including POSIX threads, Java, and OpenMP     

Large signal circuit model for LED's used in optical communication

A new lumped equivalent circuit for light emitting diodes (LED's) is presented which models the electrical and optical performance incorporating linear and nonlinear recombination mechanisms. Most of the model parameters can be determined from electrical measurements. The model is tested by experiments with different types of LED's and its use in connection with SCEPTRE is demonstrated by a simulation of a 200 Mbits/s pulse code modulation (PCM) pulse train. Special attention is devoted to the electrical reverse recovery behavior of LED's.     

Effect of reliability on the efficiency of communication systems

Reliability consideration of performance systems is an important problem of today. The results obtained by using the well known theoretical foundations of reliability are not sufficient. Therefore a new reliability concept for performance systems is developed. A main aspect of this concept is to use the reliability as an independent variable while system efficiency is used as a dependent variable. The introduced concept is illustrated with the help of a parallel structure as well as a nonseries parallel structure.