Semiconductor Laser Amplifier Research Articles

Properties of optical phase-locked loop based on four wave mixing in semiconductor laser amplifiers

In this paper, the properties of the optical phase-locked loop(PLL) based on the four-wave mixing in the semiconductor laser amplifiers (SLAs) are discussed. The components that achieve the function of detecting the bit phase of the input optical signal are concerned and discussed in detail together as a function module named as the optical bit phase detector referred to the general electronic PLL. Therefore, most of the properties of the optical PLL can be analyzed by applying the general phase-locked theory. Here the stability of the optical PLL is discussed. It's shown that the variance of input signal power in the practical application will cause optical PLL system unstable because of its long loop delay. The influence on the output phase jitter of the optical PLL is also investigated.

Modelling of semiconductor laser amplifier for the terahertz optical asymmetric demultiplexer

A semiconductor laser amplifier (SLA) may be used as a nonlinear element in ultrafast optical asymmetric demultiplexers. For demultiplexing to take place in the optical domain it is necessary to create a switching window by placing the SLA asymmetrically in an optical loop and saturating it with a short duration control pulse. The exact size of this window, for selecting the required pulse at the output port, depends mainly on the precise location of the SLA within the loop. In the paper a finite length model of an SLA, used as a switching gate within the loop, is presented and results for the carrier density, gain and phase time responses together with transmission (switching) windows are also given. The result obtained for the latter is compared with practical data.

Effect of chirped gratings on reflective optical bistability in DFB semiconductor laser amplifiers

We use spatial chirp of the built-in grating to improve optical bistability on reflection from distributed feedback semiconductor laser amplifiers. We show that improvements in the on-off switching ratio occur because spatial chirp greatly affects the saturation behavior of the reflectivity resonances, allowing access to states of low reflection during bistable switching. We also show that spatial chirp modifies the spectral range of the variety of hysteresis shapes that occur on reflection. In doing so, we discover a new type of hysteresis loop that reveals a qualitative difference between the loop-shaped hystereses occurring near the two edges of the stop band. With spatial chirp, the new hysteresis loop can exhibit an on-off switching ratio in excess of 100000.

Simultaneous amplification of terahertz difference frequencies by an injection-seeded semiconductor laser amplifier at 850 nm.

Two-frequency operation of an 850 nm semiconductor optical amplifier was achieved by simultaneously injection seeding it with two diode lasers. The two frequencies could be independently amplified without strong interference when they were separated by more than 10 GHz, and the spectral purity was preserved by the amplification process. At frequency differences below 10 GHz, unbalanced two-frequency output was observed, which can be explained by a two-mode interaction driven by the refractive index modulation at the beat frequency. The laser system is suitable for the difference-frequency generation of coherent terahertz radiation in ultra-fast photoconductors or nonlinear optical media.

Semiconductor Laser as High Speed Functional Device.

Research trends of semiconductor lasers as high speed functional device are reviewed. Enhanced nonlinear-optical response in the active region of semiconductor laser offers excellent functionality such as femtosecond pulse source, optical switch and wavelength converter. Specifically the research efforts on broad bandwidth anti-reflection coating for semiconductor laser amplifiers and external cavity mode-locked lasers are summarized. Bandwidth of 100 nm with reflectivity of 10-4 is expected.

Four-wave mixing mediated by the capture of electrons and holes in semiconductor quantum-well laser amplifiers

An experimental technique based on frequency-resolved four-wave mixing is proposed for the investigation of phonon-assisted capture of electrons and holes in electrically pumped semiconductor quantum wells. We show how this technique can be used to directly measure the intrinsic capture lifetime, with no need for involved numerical fits. We also present experimental results from an application of the technique to a multiquantum-well semiconductor optical amplifier. The possible impact of phase matching on the results is discussed.

Semiconductor laser amplifiers for ultrafast all-optical signal processing

Recent progress in the use of semiconductor laser amplifiers (SLA's) for high-speed all-optical switching is reviewed. We show that, despite SLA's having lifetimes of ⩾100 ps, they are, to date, the most promising material system for all-optical ultrafast signal processing. We highlight the role of SLA carrier dynamics, which permits switching rates faster than the recovery time. Experimental results are presented that imply that switching rates of as much as ∼100 GHz should be possible. Recent experiments are described in which SLA-based switches were incorporated into novel all-optical architectures.

Bi-directional switching based on semiconductor laser/amplifier with shallow-etched bending ridge waveguide

A new type of optical switching device is developed. For a semiconductor laser amplifier with a shallow-etched bending ridge waveguide, the laser beam could propagate along the bending direction or the straight direction. Switching between the two directions is characterized. With the device fabricated on the substrate with two quantum wells of different widths, switching characteristics are found to significantly depend on the spectral separation of the two lasing modes.

Modeling of an all-optical time-division demultiplexer

A model for the terahertz optical asymmetric demultiplexer (TOAD) is presented, and its performance is assessed. A numerical model of a semiconductor laser amplifier (SLA) used as a nonlinear element is also given. Results of SLA carrier density, switching window, pulse switching, and a comparison of phase modulation and power gain for a frame rate higher than the recombination are presented. Also investigated is the required optimum loop asymmetry for producing the desired switching window for channel selection, with reduced crosstalk, at the output port. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 380–384, 1997.

Photorefractive power transfer from parallel laser diode amplifiers into a single output beam

Photorefractive BaTiO(3):Ce was used to combine coherently a signal beam and two amplified pump beams at lambda=678 nm. The master laser beam was split and then amplified in two semiconductor laser amplifiers with gain of as much as 6. The amplifiers were made from quantum-well laser chips by use of antireflection coating. 40% of the power could be transferred to the signal beam without transferring the phase distortions of the pump beams.

Carrier dynamics model of fast refractive index changes in semiconductor laser amplifiers

Recent pump probe measurements of the fast optical response of semiconductor laser amplifiers are modelled using a density matrix approach in the relaxation approximation. The results obtained with the model in a variety of situations covering the three regimes below, at and above transparency are examined in terms of the optical response and the underlying carrier dynamics. The essential features of the optical response are explained using a simple physical picture and good qualitative agreement with experiment is demonstrated.

Subpicosecond heterodyne four-wave mixing experiments on InGaAsP semiconductor laser amplifiers

We give a detailed description of a recently proposed femtosecond heterodyne four-wave mixing experiment to investigate ultrafast coherent dynamics in waveguides and discuss similarities to femtosecond heterodyne pump-probe experiments. We demonstrate and discuss the potential and the limitations of the new technique on the basis of first experiments. Examples of measurements on an InGaAsP semiconductor amplifier are presented, that include transient four-wave mixing between pulses of the same and of orthogonal polarisations. Implications of our four-wave mixing results on the ultrafast dynamics in semiconductor amplifiers are discussed.

Integration of semiconductor laser amplifiers with sampled grating tunable lasers for WDM applications

A semiconductor laser amplifier is integrated with a sample grating distributed Bragg reflector (SGDBR) laser to act as an external modulator. The fabrication, characterization, and device characteristics of this integrated tunable transmitter are reported. The integrated tunable laser can have up to 75 nm of tuning range and more than 30 dB of side-mode suppression ratio (SMSR). The integrated amplifier can provide at most 8 dB of gain and more than 25 dB of contrast ratio for all the channels. Its RF modulation bandwidth can achieve 1.5 GHz, and the dynamic chirp is as good as a directly modulated laser. A simple model is proposed to explain the measured modulation responses and gain saturation is found to be the main cause of the resonant peaks in the dynamics.

The suppression of optical regenerator employing semiconductor laser amplifier loop mirror on the additive noise

In this paper, transmission properties of the regenerator employing a semiconductor laser amplifier loop mirror (SLALOM) are discussed. The ability of the regenerator to suppress the additive noise in the input data train is calculated. It’s shown that the regenerator can greatly suppress noise in communication system and improve their communication capacity by choosing suitable semiconductor laser amplifier(SLA) and the power of injected continuous wave.

Powerful, diffraction-limited semiconductor laser using photorefractive beam coupling

We use semiconductor laser amplifiers and a photorefractive crystal to generate a high-power, diffraction-limited laser beam at 860 nm. Using a single flared amplifier, we obtain 1.09 W in a diffraction-limited beam from 2.2 W of pump power. Using an array of flared amplifiers, we also demonstrate efficient beam coupling, showing that this technique is easily extended to semiconductor amplifier arrays.

Crosstalk of two-channel wavelength conversion using semiconductor nonlinearity

Crosstalk of two-channel wavelength conversion using four-wave-mixing through the nonlinearity of a semiconductor laser amplifier is studied. The maximum reductions of the conversion efficiencies caused by the crosstalk are numerically shown. The reductions decrease as signal powers decrease and pump power increases. In addition, it is found that there exists a phase-sensitive crosstalk which can be avoided by properly choosing the wavelength allocations or can be reduced using low signal power and high pump power.

SMALL SIGNAL ANALYSIS OF WAVELENGTH CONVERSION IN SEMICONDUCTOR LASER AMPLIFIERS BASED ON GAIN SATURATION

Wavelength conversion due to gain saturation in a semiconductor laser amplifier(SLA) is theoretically analyzed and also-studied experimentally based on small signal model.An analytic expression is developed describing the relationship between-conversion efficiency and characteristic parameters of SLA. The numerical simulation results show that the frequency response of the converter is not only limited to the carrier lifetime, but also affected by the saturation power, gain and waveguide internal loss of SLA.

Penalty-free wavelength conversion using cross-gain modulation in semiconductor laser amplifiers with no output filter

Penalty-free wavelength conversion at 622 Mbit/s and almost penalty-free conversion at 2.5 Gbit/s with very low residual input power levels have been achieved using cross-gain modulation in semiconductor laser amplifiers with no output filter. Theoretical simulations predict its concatenation performance.

Enhanced wide-bandwidth wavelength conversion via feedforward photomixing in semiconductor laser amplifiers

We have investigated a new technique for the enhancement of a wavelength conversion system based on nearly degenerate four wave mixing in a InGaAsP DFB semiconductor laser amplifier. We report enhanced wavelength conversion over 20 nm from 1.55 /spl mu/m to 1.53 /spl mu/m using feedforward photomixing from two independent source lasers to directly modulate the semiconductor laser amplifier. We find that the wavelength conversion efficiency is enhanced by 200% using this technique.

Transfer-matrix analysis of optical bistability in DFB semiconductor laser amplifiers with nonuniform gratings

We present a transfer-matrix method capable of simulating the effects of nonuniform gratings on the filtering, amplification, and bistability characteristics of distributed feedback (DFB) semiconductor laser amplifiers. The linewidth enhancement factor is incorporated in a way that allows direct gain-tuning of the bistability hysteresis. As an example, we compare a /spl lambda//4 phase-shifted DFB amplifier with and without spatial chirp. For amplifiers driven to yield the same unsaturated peak amplifier gain, positive linear chirp widens the spectral range of low-threshold switching and increases the switching contrast.