The objective of this paper is to present an overview of topics related to one of the fundamental parameters for semiconductor lasers-the linewidth broadening factor α that describes the coupling between carrier-concentration-induced variations of real and imaginary parts of susceptibility. After introducing the definition of α and discussing its dependence on carrier concentration, photon energy, and temperature, we give a short historical summary on how the concept of α evolved over the past two decades. This is followed by a discussion of α dependence on device structure in gain-guided and subdimensional lasers (quantum wells and quantum wires). The bulk of the paper is devoted to a detailed review of laser properties influenced by α and of associated methods of estimating the value of α. Results of measurements reported to date are collected and the most reliable methods are indicated.

Linewidth broadening factor in semiconductor lasers--An overview

WASPNET is an EPSRC-funded collaboration between three British Universities: the University of Strathclyde, Essex University, and Bristol University, supported by a number of industrial institutions. The project which is investigating a novel packet-based optical WDM transport network-involves determining the management, systems, and devices ramifications of a new network control scheme, SCWP, which is flexible and simplifies optical hardware requirements. The principal objective of the project is to understand the advantages and potential of optical packet switching compared to the conventional electronic approach. Several schemes for packet header implementation are described, using subcarrier multiplexing, separate wave lengths, and serial transmission. A novel node design is introduced, based on wavelength router devices, which reduce loss, hence reducing booster amplifier gain and concomitant ASE noise. The fabrication of these devices, and also wavelength converters, are described. A photonic packet switching testbed is detailed which will allow the ideas developed within WASPNET to be tested in practice, permitting the practical problems of their implementation to be determined.

WASPNET: a wavelength switched packet network

In this paper, we have developed a relatively simple algorithm to calculate the large-signal dynamic response of DFB lasers by solving the time-dependent coupled wave equations directly in the time domain. The spontaneous emission noise, longitudinal variations of carrier (hole burning) and photon densities as well as that of the refractive index are taken into consideration. To demonstrate the power of this straightforward algorithm, the model shows how the side-mode suppression ratio in devices with high /spl kappa/L and a /spl lambda4: phase shift is significantly affected by the radiation in the second-order DFB laser. The time-dependent radiation pattern in grating-coupled surface-emitting lasers is also calculated for the first time. >

Dynamic analysis of radiation and side-mode suppression in a second-order DFB laser using time-domain large-signal traveling wave model

The progress in long-wavelength compressively and tensile-strained InGaAs(P) quantum-well semiconductor lasers and amplifiers is reviewed. By the application of grown-in strain, the device performance is considerably improved such that conventional bulk and unstrained quantum-well active-layer devices are outperformed, while a high reliability is maintained. >

Progress in long-wavelength strained-layer InGaAs(P) quantum-well semiconductor lasers and amplifiers

A detailed study of the design issues relevant to long-wavelength monolithic mode-locked lasers is presented. Following a detailed review of the field, we have devised a validated travelling wave model to explore the limits of mode-locking in monolithic laser diodes, not only in terms of pulse duration and repetition rate, but also in terms of stability. It is shown that fast absorber recovery is crucial for short pulse width, that the ratio of gain to absorption saturation is key in accessing ultrashort pulses and that low alpha factors give only modest benefit. Finally, optimized contact layouts are shown to greatly enhance pulse stability and the overall operational success. The design rules show high levels of consistency with published experimental data.

https://iopscience.iop.org/article/10.1088/1367-2630/6/1/179/pdf

Long-wavelength monolithic mode-locked diode lasers

A detailed nonlinear model of the performance of single-frequency laser structures operating both below and above threshold is discussed. Arbitrary series combinations of uniform pitch grating, linearly-chirped pitch grating and plane guide sections can be analyzed-taking longitudinal-mode spatial hole burning into account. The material properties of each section of a device structure can be specified. The output power from each end of the laser and the emission wavelength, and the longitudinal intensity, carrier density, and relative permittivity profiles are predicted as a function of drive current above threshold for each lasing mode. The linewidth is also estimated while allowing for the nonuniform longitudinal distribution of spontaneous emission into the mode in a physical manner. The model was used to provide the data with which to trade off the numerous interacting performance parameters of a lambda /4 phase-shifted DFB (distributed-feedback) laser. The design options are then summarized. >

The design assessment of lambda /4 phase-shifted DFB laser structures

The influence of longitudinal mode spatial hole burning (LMSHB) on the performance of distributed feedback (DFB) laser structures is examined in detail. A comprehensive model has been used to interpret the experimental results and to construct a theoretical framework that was utilized to develop more advanced device designs. An increasing side mode intensity with output power, movement of the lasing mode relative to the stopband, and curvature of the light-current characteristic at low power can all be manifestations of the influence of LMSHB on the static device performance. The dynamic behavior can also be affected, with extended wavelength chirp and amplitude patterning effects on the timescale of the effective carrier recombination time being particularly important. >

The static and dynamic characteristics of single and multiple phase-shifted DFB laser structures

The threshold current density of InGaAs/InGaAIAs/InP SCH MQW lasers with various cavity lengths and numbers of wells has been measured. The gain of each well depends logarithmically on current density from 200 to at least 2000 A cm−2. Curves are presented for optimising the number of wells. Comparisons are made with GaAs/AIGaAs MQW lasers.

Logarithmic gain/current-density characteristic of InGaAs/InGaAlAs/InP multi-quantum-well separate-confinement-heterostructure lasers

A 13-wavelength channel 10-GHz pulse source is demonstrated using a novel scheme incorporating a dispersion-imbalanced fiber loop mirror and an arrayed waveguide grating. The output high-quality pulses are 5 ps wide with the pedestal suppression in excess of 25 dB.

Multiwavelength pulse source for OTDM/WDM applications based on arrayed waveguide grating

A model has been developed of the zero-order supermode stability with drive current for real index-guided laser arrays allowing for the effect of injected carriers on the active-layer dielectric constant. It is difficult to design simultaneously for a high output power capability and zero-order supermode stability over the full dynamic range of the array.

J.E.A. Whiteaway

Papers

The design assessment of lambda /4 phase-shifted DFB laser structures

The static and dynamic characteristics of single and multiple phase-shifted DFB laser structures

Logarithmic gain/current-density characteristic of InGaAs/InGaAlAs/InP multi-quantum-well separate-confinement-heterostructure lasers

Multiwavelength pulse source for OTDM/WDM applications based on arrayed waveguide grating

Mode stability in real index-guided semiconductor laser arrays