Fiber-optic communication systems using semiconductor laser amplifiers are investigated theoretically and experimentally. The noise and bit-error-rate characteristics of lightwave systems with optical amplifiers are calculated and the dependence of system performance on amplifier characteristics such as optical bandwidth, noise figure, gain, etc., is shown. Experimental results for both a 4-Gb/s optical preamplifier as well as coherent and direct detection systems with four inline amplifiers are presented. >

Lightwave systems with optical amplifiers

Semiconductor optical amplifiers are useful building blocks for all-optical gates as wavelength converters and OTDM demultiplexers. The paper reviews the progress from simple gates using cross-gain modulation and four-wave mixing to the integrated interferometric gates using cross-phase modulation. These gates are very efficient for high-speed signal processing and open up interesting new areas, such as all-optical regeneration and high-speed all-optical logic functions.

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Semiconductor optical amplifier-based all-optical gates for high-speed optical processing

A theory of spontaneous emission noise is presented based on classical electromagnetic theory. Unlike conventional theories of laser noise, this presentation is valid for open resonators. A local Langevin force is added to the wave equation to account for spontaneous emission. A general expression is found relating the diffusion coefficient of this force to the imaginary part of the dielectric function. The fields of lasers and amplifiers are found by solving the wave equation by the Green's function method. The lasing mode is a resonant state associated with a pole in Green's function. In this way, noise in lasers and amplifiers is treated by a unified approach that is valid for either gain guiding or index guiding. The Langevin rate equations for the laser are derived. The theory is illustrated with applications to traveling wave and Fabry-Perot amplifiers and Fabry-Perot lasers. Several new results are found: optical amplifier noise increases inversely with quantum efficiency; spontaneous emission into the lasing mode is enhanced in lasers with low facet reflectivities; and the linewidth of a Fabry-Perot laser with a passive section decreases as the square of the fraction of the cavity optical length that is active.

Theory of spontaneous emission noise in open resonators and its application to lasers and optical amplifiers

The application of semiconductor laser amplifiers to long-wavelength optical fiber systems is discussed. The basic equations defining laser amplifier characteristics are presented together with experimental results. Linear and nonlinear modes of operation are considered; the former includes use as an optical gain block, a linear repeater, and a preamplifier, while the latter includes use as a bistable element, an electrically controlled optical switch, and an injection-locked amplifier. >

Semiconductor laser optical amplifiers for use in future fiber systems

Photonic packet switches offer high speed, data rate and format transparency, and flexibility required by future computer communications and cell-based telecommunications networks. In this paper, we review experimental progress in state-of-the-art photonic packet switches with an emphasis on all-optical guided-wave systems. The term all-optical implies that the data portion of a packet remains in optical format from the source to the destination. While the data remain all-optical, both optical and optoelectronic techniques have been used to process packet routing functions based on extremely simple routing protocols. An overview of the design issues for all-optical photonic packet switching is given and contrasted with electronic packet switch implementations. Low-level functions that have been experimentally implemented include routing, contention resolution, synchronization, and header regeneration. System level demonstrations, including centralized photonic switching and distributed all-optical multihop networks, will be reviewed. >

Photonic packet switches: architectures and experimental implementations

The recent advent of very low loss single mode optical fibers (< 0.2 dB/km at the 1.55μπι wavelength) opens the possibility for very long distance, high information bandwidth (^1 Gbit/s) communication systems, as transoceanic cable links or trunk networks. With such fibers, especially when chromatic dispersion is negligible, the range is only limited by attenuation, so there would be no need for complete signal regeneration (pulse shaping, timing, etc...). In these conditions, direct light amplifiers would be very attractive as \"on-line\" amplifiers as an alternative to sophisticated optoelectronic repeaters; they could also be used in a receiver as low noise preamplifiers, in combination with a pinphotodiode, especially at the 1.3 ... 1.55 μη wavelength, where avalanche photodiodes (APD) are more \"noisy\" than silicon APDs. It is our purpose to discuss the possibility for semiconductor laser amplifiers to be used in a single mode fiber communication system. We shall first derive the power budget improvement due to the insertion of a laser amplifier in a digital optical communication system. A review of semiconductor laser amplifiers (SCLA) characteristics of the traveling-wave type (TW), Fabry-Perot type (FP) and injection locked laser type (ILL) will then be presented, with emphasis on recent experimental results. Finally, possible applications of these devices in single mode fiber communication systems will be discussed. 2 Noise characteristics of a laser amplifier in an optical communication system

J. C. Simon

Papers

Semiconductor Laser Amplifier for Single Mode Optical Fiber Communications