Semiconductor Laser Amplifier Research Articles

Sensitivity and power penalty considerations for laser preamplified direct detection optical receivers

The paper presents a theoretical analysis of the performance of direct detection optical receivers incorporating semiconductor laser amplifiers (SLAs) prior to the photodetector, and places an emphasis on achievable sensitivity, considering in particular the influence of various system impairments. Illustrative results are included based on amplifier material and device structural parameters. Important specific issues addressed in detail include the influence of residual facet reflectivity, the extinction ratio associated with the incoming optical signal, input and output laser amplifier coupling losses, and the frequency mismatch between the signal and the amplifier peak gain. The results show that little further improvement in receiver sensitivity can be obtained by reducing facet reflectivity below 0.1%, or by inserting an optical filter with bandwidth greater than 50 nm. The authors found that these new laser preamplifier receivers can be more sensitive to the input signal extinction ratio compared with conventional pin or APD receivers, especially when a narrow bandwidth filter is used. In addition, any deviation in the signal frequency from the amplifier central mode frequency will significantly degrade receiver performance, especially when the amplifier gain is high, as one would expect. The analyses presented in the paper aim to provide useful guidelines for the design of wideband high sensitivity optical receivers.

The properties of a GaAs-GaAlAs traveling-wave laser amplifier

Abstract The reflectivity of the cavity mirrors of a GaAs-GaAlAs DH semiconductor laser are reduced to 1∗10−4 by sputtering a film Si3N4. The gain of traveling-wave laser amplifiers is measured. The highest gain is about 25 dB. The dependence of gain on the injection current is measured. The measured frequency bandwidth shows the great advantage over other types of semiconductor laser amplifiers.

Performance of a dual-stage semiconductor laser amplifier for optical transmission repeater system

Performance of a dual-stage semiconductor laser amplifier for optical transmission repeater system

Influence of nondegenerate four-wave mixing on coherent transmission system using in-line semiconductor laser amplifiers

Three-channel coherent frequency-shift-keying (FSK) transmission experiments using in-line semiconductor laser amplifiers under the influence of nondegenerate four-wave mixing in laser amplifiers are discussed. The experiments show that the effect of four-wave mixing is reduced by applying modulation to the interfering carriers and enlarging the frequency separation of each carrier. However, transmission quality degradation becomes serious in multistage amplifier systems. >

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.

Theory of Ultrashort Pulse Generation and Amplification by Gain‐Switched Semiconductor Lasers

AbstractA theory of the nonlinear ultrashort dynamic response of unbiased gain‐switched semiconductor laser amplifiers is presented. For suitable time delays between the incident laser pulse and the injection current pulse driving the laser amplifier, optical pulse compression due to self‐induced gain depletion is found. The finestructure of the emitted pulse resulting from multiple reflections is shown to depend crucially upon the detuning off cavity resonances and upon the ratio of input signal width to cavity round‐trip time.

A comparison between Fabry-Perot and travelling wave laser amplifiers in an 8 Gbps repeatered optical system using a time domain model

A time domain model is used to investigate the use of semiconductor laser amplifiers in repeatered communication systems. This is based on the transmission line laser model and allows modelling over a wide optical bandwidth. Simulations show that the travelling wave laser amplifier provides a high gain and large dynamic and optical bandwidths, whereas the Fabry-Perot device has a smaller gain and optical bandwidth. The filtering action of the Fabry-Perot device is shown to distort the signal in both the time and frequency domains.

Analytical model for semiconductor laser amplifiers in coherent optical systems

A model based on a full travelling-wave analysis of a semiconductor laser amplifier is applied to calculate the increase in spectral linewidth of an unmodulated optical carrier passing through the amplifier. This linewidth can then be used in system performance calculations for a coherent optical transmission system employing laser amplifiers along the fibre link.

Polarisation-independent configuration optical amplifier

A new polarisation independent semiconductor laser amplifier is presented. By using a regular semiconductor amplifier in a double pass configuration, polarisation independent gain is achieved. Experiments demonstrate a reduction in the gain difference between TE and TM waves from 4dB to 0.2 dB.

The tilted waveguide semiconductor laser amplifier

The performance of a tilted waveguide semiconductor laser amplifier is shown to be affected by tilt-induced intermode coupling at the mirrors of the device. We find that, for some device parameters, higher-order gain-guided modes can dominate the output field pattern of the amplifier even when the gain of the fundamental mode is greater than that of the higher-order modes. A simple coupled-mode analysis is presented to explain these observations, and the observed far-field intensity distribution of a laser amplifier is compared with the calculated results.

Transfer matrix analysis of the amplified spontaneous emission of DFB semiconductor laser amplifiers

Analytical expressions are derived for the amplified spontaneous emission of a DFB (distributed-feedback) semiconductor laser amplifier with reflective cavity ends. The analysis is extended to a multisection DFB structure including a phase-shifted DFB semiconductor laser amplifier. It is shown that the spontaneous emission power per unit frequency bandwidth emitted from one facet is proportional to the transmission gain and to a quantity which at threshold becomes the inverse of the differential quantum efficiency of the other facet. The analysis is applied to two practical cases: (1) calculation of emission spectra of a DFB semiconductor laser biased below the threshold, and (2) assessment of the signal-to-noise ratio performance of DFB semiconductor laser amplifiers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Wavelength selection with nanosecond switching times using distributed-feedback laser amplifiers

Wavelength selection with 1 ns switching times is demonstrated using DFB semiconductor laser amplifiers with net gain of 10 dB. Dynamic selection of packets from two wavelength-multiplexed 1.2 Gbit/s channels, separated by 0.23 nm, is demonstrated with BER &lt; 10−9.

Resonantly enhanced two-wave mixing via population pulsations in semiconductor laser amplifiers

Demonstrates theoretically the existence of enhanced probe gain via population pulsations in nearly degenerate two-wave mixing in a semiconductor amplifier. The enhancement arises from the injection current modulation frequency coinciding with the pump/probe detuning. Probe saturation is shown to occur in less than 10 mu m cavity length.

Gain-switched semiconductor laser amplifier as an ultrafast dynamical optical gate

A gain-switched semiconductor laser is shown to act as an optical gate with picosecond resolution and amplification for light pulses from another laser source. The amplification mechanism and the gate width change qualitatively when the gate laser undergoes a transition from a pumping rate slightly below the dynamic laser threshold to slightly above the dynamic threshold. If the gate laser is pumped below but close to its dynamical threshold, unsaturated amplification of an external signal pulse occurs over a delay time range between the external optical pulse and the electrical driving pulse of about 100–200 ps which is equivalent to the optical gate width. The signal amplification is observed to increase by two orders of magnitude and the gate width decreases by one order of magnitude if the gate laser is pumped slightly above the dynamical threshold. Amplification then occurs for input signals injected much earlier. A detailed theory of coherent, time-dependent amplification including the nonlinear dynamics of the semiconductor laser is shown to account for the observations. Both amplification regimes, below and above threshold, are reproduced in the numerical simulations. The extremely short and highly sensitive gate range above threshold is identified as being due to the gain maximum related with the first relaxation oscillation of the laser.

Ultra-low reflectivity 1.5μm semiconductor laser preamplifier

Reports travelling-wave 1.5 mu m semiconductor laser amplifiers with very low gain ripple. The average facet reflectivity is less than 5*10/sup -5/ over a 170 AA interval. The minimum gain ripple is below the measurement accuracy, 0.2 dB, at 27.5 dB gain. When used as an optical preamplifier in a 4 Gbit/s receiver, a sensitivity of -34.3 dBm is achieved.< >

Cascaded inline semiconductor laser amplifiers in a coherent optical fibre transmission system

A coherent optical transmission system with two broadband inline optical amplifiers was investigated. The main cause of system degradation was the generation of an interfering signal owing to backward scattered waves in the amplifier chain. The perturbation was eliminated by an isolator or sufficient attenuation between both amplifiers. It is possible to convert the effective 30 dB gain of both amplifiers fully into an increase of the transmission span.

Crosstalk in a two-channel coherent fibre-optic ASK system using an optical amplifier and non-negligible linewidth lasers

We present measurements of crosstalk penalties in a two-channel ASK system using 1.55μm DFB lasers and a semiconductor laser amplifier. The amplifier was operated well below gain saturation. No additional receiver sensitivity penalty due to the amplifier was observed for single channel operation. However, the additional crosstalk in the amplifier required a 10% increase of the channel spacing compared to the spacing in the nonamplifier system.

Semiconductor laser optical amplifiers for use in future fiber systems

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 amplifier as an optically controlled switch

The application of a semiconductor-laser amplifier with reduced facet reflectivity as all-optical switch is described. An optical data signal is switched on and off with an extinction ratio of 10 dB when an optical control signal is turned on and off. The two optical signals are polarized perpendicularly to each other. The device was operated up to 100 MHz.

Instability Thresholds in General Nonlinear Ring Resonators

Abstract By considering a passive ring cavity with linear absorption in the dispersive limit, a unified analysis is presented for tuning-optimized minimum instability thresholds; the treatment is general, allowing consideration of arbitrary material response times, cavity tuning and finesse. In the adiabatic limit (τ → 0) the results reduce to the usual Ikeda map. The case of long medium-response time (τ → ∞) is treated in some detail in the high-finesse limit; these conditions being of particular relevance to semiconductor laser amplifiers. It is found analytically that in the high-finesse limit, both optical bistability and self-pulsing instabilities should exhibit the same low-threshold behaviour. An analytical expression is derived for the ‘instability threshold curve’, A 2 B against B for minimum A 2, in the mapping limit.