Traveling-wave Semiconductor Laser Amplifier Research Articles

Optical carrier linewidth broadening in a traveling wave semiconductor laser amplifier

The powerful spectral densities of the phase, intensity, and electron density noise derived in a previous paper are used to calculate the linewidth broadening of an optical carrier as it propagates through a traveling-wave semiconductor laser amplifier. It is found that the amount of broadening is dependent upon the input linewidth as well as amplifier parameters. The effect of saturation due to high input power is considered, as well as the operational regime where intensity, rather than phase, noise determines the amplifier output line shape. An example system calculation is used to demonstrate the impact of amplifier line broadening on system design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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- mu m 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Detuning characteristics and conversion efficiency of nearly degenerate four-wave mixing in a 1.5- mu m traveling-wave semiconductor laser amplifier

The optical nonlinearity in a semiconductor laser gain medium is investigated through copropagating nearly degenerate four-wave mixing (NDFWM) in a 1.5- mu m InGaAsP traveling-wave laser amplifier (TWA). The FWM signal output powers vary symmetrically with the sign of probe detuning with respect to the pump frequency, while the pump and probe output powers vary asymmetrically. The NDFWM conversion efficiency from the probe input to the FWM signal output is a maximum of 8.3 dB around zero detuning and has positive gain in the range of +or-6 GHz. This demonstrates highly efficient nonlinear interaction due to both large optical gain and large third-order susceptibility. The NDFWM efficiency is also investigated in connection with the TWA gain saturation characteristics and is found to be a maximum for operation around the saturation intensity of the TWA. >

565 Mbit/s 219 km transmission experiment using four gain controlled packaged semiconductor laser amplifiers

A 565 Mbit/s 219 km optical transmission system is investigated, using four gain controlled travelling wave semiconductor laser amplifier packages. The addition of gain control caused little deterioration in system performance, and allowed stabler operation against changes in signal polarisation and device temperature. Residual system output power fluctuations of less than 0•5 dB were observed over a 7 degree temperature range

Frequency conversion by nearly-degenerate four-wave mixing in traveling-wave semiconductor laser amplifiers

The paper describes a scheme for frequency conversion of optical data signals with use of NDFWM in travelling wave semiconductor laser amplifiers. The frequency conversion range is limited by the gain bandwidth of the optical amplifier, which is about 4000 GHz in the considered case. The experimental arrangement of the conversion scheme is described and a theoretical analysis is presented. Finally the advantages and disadvantages of this scheme are discussed.

Gain saturation characteristics of traveling-wave semiconductor laser amplifiers in short optical pulse amplification

The gain saturation characteristics of traveling-wave semiconductor laser amplifiers (TWAs) are theoretically and experimentally investigated. In the amplification of an isolated pulse whose repetition period is short compared to the carrier lifetime, the gain saturation is related through the carrier lifetime to the gain saturation in CW amplification. When the output pulse energy is smaller than the saturation energy, short optical pulses can be amplified without pulse shape distortion, whereas high-energy pulses suffer from pulse shape distortion due to the temporal gain variation during the pulse radiation. FWHM pulse duration variation in amplification by TWAs depends on the input pulse shape. The pulse energy gain saturation was experimentally confirmed to be independent of pulse durations and to be determined only by the pulse energy. In extremely-high-repetition-rate pulse amplification, the saturation of the pulse energy gain is determined by the average signal power. >

Effects of multiple wave mixing and gain saturation in an ideal traveling wave semiconductor laser amplifier

Nonlinear distortions induced by four-wave mixing and gain saturation in a semiconductor laser amplifier can affect the overall performance of lightwave systems using such devices. A model which includes both types of distortion in a three-channel optical transmission system is presented. Large-signal analysis is used to calculate distortion in amplifiers operating near saturation. The technique provides more realistic predictions than the small-signal rate equation analysis used in previous theoretical studies of four-wave mixing in optical amplifiers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pulse energy gain saturation in subpico- and picosecond pulse amplification by a traveling-wave semiconductor laser amplifier

Optical pulses with durations ranging from 0.49 to 21 ps are amplified by a traveling-wave semiconductor laser amplifier. The pulse energy gain is determined by pulse energy only. The dependence of pulse energy gain on output pulse energy does not change in the pulse duration range. The saturation characteristics are successfully explained by a four-level system model. >

Direct optical phase modulation in semiconductor laser amplifier

Efficient optical phase modulation in a nearly travelling-wave semiconductor laser amplifier, via modulation of the amplifier injection current, is proposed and demonstrated. Using a 500 mu m-long GaInAsP buried heterostructure amplifier and a 1530 nm optical carrier, phase deviations of the order of 0.1 rad/mA are obtained for modulation frequencies in the range 100 MHz to 2 GHz. >

Four-wave mixing in travelling-wave semiconductor laser amplifier

Experiments on codirectional nondegencrate four-wave mixing in a 1.52µm travelling-wave semiconductor laser amplifier are presented. Estimations for the spontaneous carrier lifetime and linewidth enhancement factor are derived from comparison between experimental and calculated results from theory based on signal-induced carrier-density modulation.

A model for noise processes in semiconductor laser amplifiers, part 1: the travelling-wave semiconductor laser amplifier

A model for noise processes in semiconductor laser amplifiers, part 1: the travelling-wave semiconductor laser amplifier

Application of communications theory to analyse carrier density modulation effects in travelling-wave semiconductor laser amplifiers

It is shown that standard communications phase modulation theory can be used to analyse the carrier density modulation caused by interchannel beat powers. Also, it is shown that spontaneous lifetime produces a phase shift which causes an interchange of power between channels.

Wavelength dependence of noise figure of a travelling-wave GaInAsP/InP laser amplifier

Heterodyne noise measurements on a travelling-wave semiconductor laser amplifier show that the excess noise factor decreases with increasing wavelength. When the signal wave-length is changed from 1.48 μm to 1.55 μm the noise figure decreases from 10.5 dB to 6.0 dB.

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. >

Nearly degenerate four-wave mixing in a traveling-wave semiconductor laser amplifier

Nearly degenerate four-wave mixing (NDFWM) in a traveling-wave semiconductor laser amplifier is demonstrated by simultaneously injecting two lights of slightly different frequencies in the same direction. A new frequency light at an expected frequency for NDFWM is observed with the same order of output as that of the injected light. The output power ratio of the three beams is strongly dependent on the sign of the frequency detuning. Theoretical analysis, in which the carrier rate equation is coupled with nonlinear Maxwell’s equations, explains the experimental results well. The observed behaviors are attributed to a unique third-order nonlinearity stemming from saturation-induced refractive index change in the semiconductor gain medium.

Picosecond pulse response of a travelling-wave semiconductor laser amplifier

The dynamic pulse response of a travelling-wave semiconductor laser amplifier has been investigated. Peak output powers greater than 100 mW, with a fibre-to-fibre gain of 10 dB, have been observed for narrow pulses (&lt;50ps FWHM) at low repetition rates. The dynamic bandwidth of the amplifier has been shown to be at least 50 GHz.

Gain saturation dependence on signal wavelength in a travelling-wave semiconductor laser amplifier

Gain saturation dependence on signal wavelength in a 1.5 μm InGaAsP travelling-wave semiconductor laser amplifier is experimentally studied. Saturation output powers were 6.9dBm, 8.3dBm and 10.6dBm for signal wavelengths of 1490 nm, 1510 nm and 1540 nm, respectively. This saturation dependence on wavelength, i.e. higher saturation output power for longer signal wavelength, results from signal gain peak shift towards longer wavelength with increasing input power.

Recombination, gain and bandwidth characteristics of 1.3-µm semiconductor laser amplifiers

The influence of the spontaneous recombination mechanism and the temperature- and wavelength-dependent material gain on the performance of 1.3-μm InGaAsP traveling-wave semiconductor laser amplifiers is analyzed. Measurements of signal gain are presented. Frequency detuning and optical bandwidth characteristics are discussed. By considering the trade-off between optical bandwidth and resonant signal gain, guidelines for the requirements to the facet reflectivity are given.