Semiconductor Laser Amplifier Research Articles

1.3 μm MQW semiconductor optical amplifiers with high gain and output power

1.3 μm BH semiconductor laser amplifiers are described with MQW active layers. A single pass gain of 31dB is achieved with a 1000 μm long device. A 500 μm long device is realised with a spectral bandwidth of 110 nm and saturated output power of 25 mW.

Optical bistability and set-reset operation of a Fabry-Perot semiconductor laser amplifier with two detuned light injections

Optical bistability in a Fabry-Perot semiconductor laser amplifier when two optical inputs detuned from the resonant wavelength of a semiconductor laser amplifier are injected is discussed. A split branch is found in the optical output versus input characteristics in addition to conventional optical bistability behavior. It is shown analytically and experimentally that set and reset can be achieved in the optical output of the semiconductor laser amplifier for each wavelength by applying two detuned optical pulses and using the split branch. >

Theory of signal degradation in semiconductor laser amplifiers with finite 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new structure for high-power TW-SLA (Travelling wave semiconductor laser amplifier)

A structure utilizing an exponential tapered active layer to improve the saturation output power and quantum efficiency of a traveling-wave semiconductor laser amplifier is discussed. Both the spatial distributions of the carrier density and the optical field are considered in the analysis. It is shown that an optimum taper geometry for maximizing the efficiency exists and that this structure provides simultaneous improvement in the saturation output power (7 dB) and the quantum efficiency (1.5 times) compared to a conventional device.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modulation of picosecond pulses using semiconductor laser amplifiers

Semiconductor laser amplifiers are studied as modulators of picosecond pulses. A new hybrid laser amplifier model is described which is used to investigate ultrashort pulse amplification in both modulated and non-modulated amplifiers. Novel shaping of chirped pulses is demonstrated experimentally and theoretically using a continuously driven amplifier. Modelling of electrically modulated amplifiers shows that direct amplifier modulation may be possible up to a frequency of 5 GHz to provide pulse gating or enhanced pulse train amplification.

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. >

Power scaling in quantum-well laser amplifiers

The effects of increasing excitation on the performance of quantum-well semiconductor laser amplifiers were investigated. Amplified spontaneous emission (ASE) and gain roll over at high injected carrier densities are two limitations to the power scaling of these devices. A Rigrod analysis was used to study the effects of these limitations on the gain, ratio of signal to ASE power, and efficiency for different values of injection current, facet reflectivity, and input laser intensity. Comparisons are made with an equivalent amplifier operating with a bulk semiconductor gain medium. This analysis suggests that quantum-well semiconductor amplifier performance improves with a double-pass configuration. >

High-gain polarization-insensitive optical amplifier

A polarization-insensitive optical amplifier (PIOA) consisting of two serial semiconductor laser amplifiers (SLAs) is studied theoretically and experimentally. A polarization-insensitive isolator (PII) inserted between the two SLAs serves not only to eliminate the coupling cavity, but also to rotate any polarized forward light by 90 degrees . Experimental results show a maximum fiber-to-fiber gain of 29 dB. PIOA gain deviation for the input polarization launch angle is just 0.6 dB compared to an original value of 5-6 dB in a single SLA. A theoretical analysis shows that it is necessary to achieve a PII rotation design error of less than 0.5 degrees in order to suppress deviation below 0.1 dB. PIOA noise figure deviation, for the input signal polarization launch angle, was only 0.1 dB from both the experimental and theoretical results even though there was a rotation error of 2 degrees . >

Long-haul coherent optical fiber communication systems using optical amplifiers

Studies on long-haul coherent optical fiber communication systems with in-line optical amplifier repeaters are made theoretically and experimentally. By theoretical calculation it was found that coherent systems can achieve wider dynamic range for an amplifier input power as compared with the intensity-modulation direct-detection (IM-DD) systems. The feasibility of such systems using traveling-wave semiconductor laser amplifiers (TWSLAs) and erbium-doped fiber amplifiers (EDFAs) was investigated, and 546 km, 140 Mb/s CPFSK transmission using TWSLAs and 1028-km, 560-Mb/s CPFSK transmission using EDFAs were successfully demonstrated. >

A scheme of picosecond pulse shaping using gain saturation characteristics of semiconductor laser amplifiers

To obtain high power, well shaped picosecond pulses from gain-switched semiconductor lasers, the use of dynamic gain saturation characteristics of semiconductor laser amplifiers was investigated theoretically and experimentally. A configuration of a reflected-wave amplifier (RWA) with single-side external coupling is introduced for pulse shaping, which is found to be suitable for enhancing dynamic gain saturation. By a combination of a distributed feedback laser oscillator at 1.3 mu m in wavelength and a reflected-wave amplifier of 400 mu m cavity length with asymmetric facet reflectivities of 0.01% and 30%, single-mode optical pulses with almost no tailing, full width at half maximum of 15 ps, and peak power exceeding 50 mW were obtained without pulse broadening, despite the considerable tail structure of the incident pulse.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dual-function semiconductor laser amplifier in a broad-band subcarrier multiplexed system

A near-traveling-wave semiconductor laser amplifier (SLA) has been used as a dual-function device to simultaneously perform optical amplification and receive baseband network control data in a multichannel subcarrier-multiplexed system. The dual-function SLA receives 100-Mb/s baseband signal from the electrical terminal with an error rate of less than 10/sup -9/ and improves the system power budget by 11 dB for five FSK channels (100-Mb/s each) in the 2 to 3-GHz band. Using SLAs as dual-function or multiple-function devices in broadband networks is an attractive means to enhance network functionality and performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

All-optical loop mirror switch employing an asymmetric amplifier/attenuator combination

For the first time a report is made on a loop mirror switch containing the nonreciprocal combination of a semiconductor laser amplifier and an optical attenuator. Self-routing of optical pulses has been demonstrated on 10 ns pulses with powers of <250 μW, within a 17 m loop. The model predicts the form of the switching.

Low noise characteristics of a GaAs-AlGaAs multiple-quantum-well semiconductor laser amplifier

Low noise characteristics are experimentally demonstrated in a multiple-quantum-well laser amplifier. The measured noise figure of a GaAs-AlGaAs traveling-wave laser amplifier at a 20 dB signal gain was found to be 4.6 dB. This is the smallest value reported for semiconductor laser amplifiers. A signal gain of 20 dB was obtained at a low bias current of 23.5 mA. >

Polarisation insensitive configuration of semiconductor laser amplifier

A new polarisation insensitive configuration of a semiconductor laser amplifier is presented. This configuration achieves polarisation insensitive gain by a bi-directional pass of the split polarised light waves through a laser amplifier. The experiments demonstrate a reduction of the gain difference from 5dB to 0.1dB while attaining a high fibre-to-fibre gain of 12dB and a high saturation fibre output power of +6dBm.

High peak power picosecond pulse generation from AlGaAs external cavity mode-locked semiconductor laser and traveling-wave amplifier

Thin active region single stripe aluminum gallium arsenide traveling-wave amplifiers have been used to generate and amplify 15 ps optical pulses to nearly 50 mW average powers and to peak powers in excess of 3 W. No appreciable temporal pulse distortion is observed after amplification. These peak power levels should prove to be sufficient to induce nonlinear optical effects in fibers.

Nonlinearity difference in the two passbands of a distributed-feedback semiconductor laser amplifier

The nonlinearity difference in the two passbands of a distributed-feedback semiconductor laser amplifier was studied experimentally. A theoretical explanation was given by using the transmission matrix approach. The difference of nonlinearity in the two passbands was found to be enhanced greatly by the mechanism of asymmetric facet reflection.

Low residual reflectivity of angled-facet semiconductor laser amplifiers

Ridge-waveguide angled-facet semiconductor laser amplifiers for the 1.5 mu m band have been fabricated with facet angles of 7 degrees and 10 degrees . Gain measurements performed with a stable, computer-controlled setup have revealed gain ripples as low as 0.025 dB at 22 dB gain for a 10 degrees device. This corresponds to a residual reflectivity of 1*10/sup -5/. Results demonstrate that the residual reflectivity of angled devices with one-layer antireflection coatings can be as low as that for normal facet devices with highly controlled double-layer antireflection coatings.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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>

Prediction of the gain versus injection-current characteristic of individual semiconductor laser amplifiers

A method of calculating the gain versus current characteristic of an individual laser amplifier is presented. The method applies to traveling-wave amplifiers that are derived from semiconductor lasers by antireflectively coating both facets. It relies on a knowledge of certain general parameters, the power versus current characteristics of the laser before and after the first coating has been applied, and a measurement of the residual reflectivity of the first coating. These measurements are normally done during the coating process and therefore require no additional experimental effort. It is found that four parameters, along with a set of fixed general parameters, are sufficient to provide good agreement between calculated and measured results for different lasers. >

Automatic gain control of semiconductor laser amplifiers

Abstract A new approach to automatic gain control has been demonstrated and a signal polarization independent operation over a 35-nm wavelength range at a gain level of 17 dB has been obtained.