Theory of signal degradation in semiconductor laser amplifiers withfinite facet reflectivities

An analytic expression is derived for the output signal spectrum from a semiconductor laser amplifier (SCLA) using an approach analogous to the Langevin equations of laser noise analysis. The authors present an analysis of the line broadening effects of SCLAs taking into account the effect of facet reflectivities. The signal linewidth is shown to increase with input linewidth and amplifier gain. There is an optimum facet reflectivity which gives the smallest linewidth increase. The results have significant implications in weakly coherent systems utilizing cascades of optical amplifiers     

Recent progress in semiconductor laser amplifiers

Recent progress in semiconductor laser amplifiers (SLAs), mainly GaInAsP traveling-wave semiconductor laser amplifiers (TWAs) for use in optical fiber transmission systems, is discussed. The status of antireflection coating on laser-diode facets which are indispensable for TWAs is discussed. Reported data on small-signal gain, signal-gain saturation, and noise are summarized and discussed in relation to active-layer parameters. Common amplification using SLAs for the amplification of various multiplexed signals, including interchannel crosstalk, is also described. A thick, short active-layer structure for a broadband high-output-power low-noise TWA with polarization-insensitive signal gain is proposed     

Noise characteristics of semiconductor laser amplifiers

Noise characteristics of Fabry-Perot (FP) cavity type AlGaAs laser amplifiers are studied theoretically and experimentally. Noise power dependencies on pumping rate and input signal level are measured. Multimode rate equations with McCumber's fluctuation operator are solved for the parabolic band and the exponential bandtail models, both with the no k-selection rule. Experimental results are in good agreement with theoretical predictions.     

Four-wave mixing in traveling-wave semiconductor laser amplifiers

Nondegenerate four-wave mixing (NDFWM) effects on simultaneous amplification of copropagating and counterpropagating waves with a frequency spacing of a few gigahertz in a 1.5-μm nonresonant near traveling-wave semiconductor laser amplifier are discussed. Experimental results are in qualitative agreement with a theoretical model assuming the NDFWM process is mainly due to carrier pulsation produced by the beating of copropagating waves in the amplifier. The amplification of a phase-modulated wave is considered. Time-reversal properties of four-wave mixing are demonstrated     

Packaged double-pass travelling-wave semiconductor laser amplifiers

A novel travelling-wave semiconductor laser amplifier (TW-SLA) proposed previously (1990) was experimentally achieved. The input and output optical signals were transmitted through a single piece of monomode optical fibre which is coupled to the chip of the TW-SLA. An optical circulator was used to separate the two signals.<>     

Simultaneous optical amplification, detection, and transmissionusing in-line semiconductor laser amplifiers

It is demonstrated that in broadband networks inline semiconductor laser amplifiers (SLAs) that provide system gain can also be used as simultaneous transceivers for additional channels at higher frequencies. In the experiment, an SLA in a 622-Mb/s baseband system provided a 6.5-dB fiber-to-fiber gain and served simultaneously as a receiver and a transmitter for two frequency-shift-keying (FSK) channels (each carrying 10 Mb/s) at 755 and 1075 MHz, respectively. Such optical amplifiers/transceivers are potentially useful in broadband digital networks with out-of-band signaling channels or in subcarrier multiple-access networks     

Noise and error rate performance of semiconductor laser amplifiers in PCM-IM optical transmission systems

Applications of semiconductor laser amplifiers in intensity modulated digital optical transmission systems were studied theoretically. An optical linear amplifier repeater between electronically regenerating terminal repeaters and an optical linear preamplifier in front of a photodetector in an electronically regenerating repeater are discussed. Both traveling-wave type and Fabry-Perot cavity type laser amplifiers are considered. The noise and error rate performance in these systems are evaluated using formulations for semiconductor laser amplifiers. The mean and variance in the optical amplifier output photons calculated by the photon master equation [1] is used to obtain the worst case variance in the equalized output voltage [2] for these systems. The required receiving power reduction from direct detection scheme by a preamplifier system and the repeater spacing expansion between two electronically regenerating terminals by an optical linear amplifier repeater system are delineated.     

Time slot interchanging using semiconductor laser amplifiers

A four-channel optical time slot interchange switching experiment operating at 2.5 Gbit/s is reported. The system is based on a parallel switch fabric incorporating semiconductor laser amplifier gates and fibre delay lines. A sensitivity penalty of 0.2 dB for straight through operation, and 0.7 dB for fully interchanged time slots was observed.<>     

All-optical signal processing based on semiconductor optical amplifiers

In this paper,we review the recent progress in the optical signal processing based on the nonlinearity of semiconductor optical amplifiers (SOAs).The four important optical signal processing functional blocks in optical switching are presented,i.e.,optical wavelength conversion,optical regeneration,optical logic,and optical format conversion.We present a brief overview of optical wavelength conversion,and focus on various schemes to suppress the slow gain recovery of the SOA and improve the operating speed of the SOA-based optical switches.Optical regeneration including re-amplification,re-shaping and re-timing is also presented.Optical clock recovery that is essential for optical regeneration is reviewed.We also report the recent advances in optical logic and optical format conversion,respectively.After reviewing the four important optical signal processing functional blocks,the review concludes with the future research directions and photonic integration.     

Noise in semiconductor laser amplifiers with quantum box structure

The low-noise properties of a quantum-box traveling-wave semiconductor laser amplifier (QB-TW-SLA) are discussed. The gain and population-inversion parameter of a quantum-box structure are precisely expressed using density matrix theory. Due to sharp gain characteristics as well as a small population inversion parameter, dominant two-beat noise is significantly reduced, even in a solitary device without a narrow bandpass filter. The noise figure can be reduced to 3.5 dB     

GaInAsP semiconductor laser amplifiers for single-mode fiber communications

Gain, polarization sensitivity, saturation power, and noise characteristics of quaternary semiconductor laser amplifiers of the Fabry-Perot (FP) and traveling-wave (TW) types are reviewed. The status of antireflection coatings for TW amplifiers is presented. New results concerning the polarization sensitivity and output saturation power of a 1.5-μm buried-heterostructure (BH) amplifier are reported. A theoretical model is presented concerning the influence of the waveguide structure on the maximum internal gain of a CW-operating 1.5- μm BH amplifier, including thermal effects, and a comparison of this model with recent experimental results is reported. The influence of nonresonant losses on the noise factor of 1.5-μm amplifiers is discussed.     

半导体激光放大器的理论与实验研究

从理论与实验上研究了1.3μm的法布里-珀罗放大器(FP-SLA)与行波放大器(TW-SLA).分析了半导体激光器的增益特性,指出了“准”行波放大器的优越性.     

Gain saturation in traveling-wave ridge waveguide semiconductor laser amplifiers

The saturation behavior of traveling-wave ridge waveguide diode amplifiers is studied both numerically and analytically. It is shown that an 'effective saturation power' can be used to characterize the saturation of these devices by up to 4 dB. The effective saturation power, which is sensitive to device geometry, carrier density, and operating wavelength, is useful in the design of the ridge waveguide optical amplifiers.<>     

Physics and applications of optical bistability in semiconductor laser amplifiers

This contribution is intended as a review of the use of semiconductor laser amplifiers as non-linear and bistable elements, and their potential for applications in optical logic and signal processing. The basic physics of the optical non-linearity occurring in these devices is discussed both intuitively and in a more rigorous theoretical manner, and a survey is given of the experimental results reported to date. Bistable amplifiers are found to switch at input powers of order 1 μW and in times as short as a few nanoseconds. The resulting optical energy requirement of order femtojoules is a prime feature which, when combined with the ready availability of lasers, their inherent optical gain, and the wavelength compatibility with existing optical transmission systems, make amplifiers extremely attractive for applications where limited amounts of signal processing are required. Potential applications for these devices are discussed.     

Temperature dependence of polarization characteristics in buriedfacet semiconductor laser amplifiers

The temperature dependence of gain and amplified spontaneous power for both TE and TM modes in semiconductor laser amplifiers are measured. Experiments are performed on three selected amplifier types, with higher TE, higher TM, and equal TE-TM gains, respectively. The gain differences are significantly reduced at higher temperature for the TE-dominant and TM-dominant amplifiers. For amplifiers with equal TE-TM gains, the TE and TM gains remain equal at high temperature. The measurements of the amplified spontaneous power show similar similar characteristics. More importantly, less polarization-sensitive gain characteristics can be obtained with some decrease in maximum gain by raising the operating temperature. The experimental results are explained by using the gain equations of the semiconductor laser amplifier     

Carrier-induced group-velocity dispersion and pulse compression in semiconductor laser amplifiers

The effect of gain dispersion on pulse amplification in semiconductor laser amplifiers is investigated theoretically. A novel phenomenon, referred to as carrier-induced group-velocity dispersion, is shown to influence considerably the amplified pulse. Chirped input pulses are predicted to be compressed in the presence of carrier-induced dispersion even when the amplifier operates far below saturation. The dependence of the compression factor on device parameters such as the pulse width, the amplifier gain, and the linewidth enhancement factor are studied using a simple analytic model. The results are important for optical communication systems as they imply that semiconductor laser amplifiers can be used to compensate simultaneously for the effects of both fibre loss and fibre dispersion when used as in-line amplifiers.<>     

Strained-layer InGaAs(P) quantum well semiconductor lasers and semiconductor laser amplifiers

Progress in long-wavelength strained (compressive and tensile) InGaAs(P) quantum well semiconductor lasers and amplifiers for applications in optical fibre communication systems is reviewed. By the application of grown-in strain, device performance is considerably improved to such an extent that conventional bulk and unstrained quantum well active-layer devices are outperformed, while high reliability, similar to that of unstrained devices, is maintained.     

A theoretical and experimental investigation of Fabry-Perot semiconductor laser amplifiers

A simple model for the characteristics of Fabry-Perot type semiconductor laser amplifiers is developed, the model leads to several simple analytic expressions. The theoretical results have been compared with measurements using a 1.3 μm laser as an amplifier. Our results are compared to those of other authors, and we indicate how the model can be used to optimize the amplifier performance.     

Analysis of antireflection coatings on angled facet semiconductor laser amplifiers

An analysis of the modal reflectivity of antireflection coated semiconductor laser amplifiers is presented. The effect of an angle between the facet normal and the amplifier axis is shown to lead to less stringent tolerances on coating index and thickness, and reflectivities of less than 10/sup -4/ can be achieved with a 7 degrees facet angle for TE and TM modes simultaneously.<>