P.D. Greene

Bio: P.D. Greene is an academic researcher. The author has contributed to research in topics: Quantum well & Semiconductor laser theory. The author has an hindex of 4, co-authored 4 publications receiving 63 citations.

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

Abstract: 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.

Linewidth enhancement factor and carrier‐induced differential index in InGaAs separate confinement multi‐quantum‐well lasers

Abstract: Quantum‐well lasers can achieve a low spectral linewidth because of their high differential gain, leading to a lower linewidth enhancement factor α than for bulk lasers. The differential refractive index and the gain of InGaAs separate confinement multi‐quantum‐well lasers with two different quaternary barrier layers, have been determined from the spontaneous emission spectra below threshold. The measured value of the α factor is about 2.8 up to 3.5 at the gain maximum for both laser structures. The refractive index and the gain spectra are connected via the Kramers–Kronig relation. Therefore, the differential refractive index and the α factor have been deduced from calculated gain spectra with an additional contribution of the intraband transitions of the free carriers.

High power operation of GaInAsP/GaInAs MQW ridge lasers emitting at 1.48 mu m

Abstract: Multi-quantum-well (MQW) ridge lasers have been produced with CW light outputs in excess of 100 mW at 500 mA. The wavelength of operation is 1480 nm and the lasers are suitable for pumping erbium-doped-fibre amplifiers. These are the highest power ridge lasers yet produced in the 1500 nm wavelength region.

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

Abstract: 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. >

Long-wavelength monolithic mode-locked diode lasers

Abstract: 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.

Dynamics of monolithic passively mode-locked semiconductor lasers

Abstract: Monolithic colliding pulse mode-locking (CPM) in semiconductor lasers is compared with self colliding pulse mode-locking (SCPM) through a large signal dynamic computer model which incorporates most of the significant features of semiconductor lasers. These include gain saturation, spontaneous emission, the gain-frequency relation, and the line-width enhancement factor. This new model replicates many of the published experimental results and also gives additional insight into the internal operation of the device. In particular, gain saturation combined with the standing waves created by colliding pulses within the saturable absorber produce a transient gain grating. This is found to have significant effects in locking either the even or the odd modes together in CPM. A performance comparison between CPM and SCPM is completed and some key design parameters of both configurations are explored. >

On the semiconductor laser logarithmic gain-current density relation

Abstract: The simplified relation, alpha =G/sub 0/ In ( eta /sub i/J/J/sub 0/), between material gain alpha and current density J is shown to be a very good shape approximation, for quantum wells and bulk materials, essentially independent of the type of recombination processes present. Simulations show that for a given material system, G/sub 0/ decreases by only about 30% from pure electron-hole-recombination-dominated to pure Auger-recombination-dominated. A generic quantum-well situation is explored to reveal the density of states and recombination coefficient dependence of G/sub 0/ and to formulate simple estimates for G/sub 0/. The results were tested against published data for eight quantum-well diode lasers. The predicted values of G/sub 0/ were generally found to be in agreement with experiments only for the wider gap diodes. The discrepancies were attributed in part to carrier induced absorption, and it is shown that the formalism can be modified in selected cases to incorporate this without changing the basic form of the gain. A new expression which relates the temperature dependence of the measured parameters to the characteristic temperature, T/sub 0/, is provided. >

Analytical formulas for the optical gain of quantum wells

Abstract: Analytical expressions for the quantized energy levels in quantum wells, the optical gain, the differential optical gain, and the linewidth enhancement factor are presented based on a simple parabolic-band gain model. Explicit formulas show clearly the dependence of these factors on well width, doping, and photon energy. The optical gain in the form of g=g/sub 0/ In(N/N/sub 0/) is derived using explicit approximations in the Fermi functions, where g/sub 0/ is the proportionality constant, N is the injected carrier density, and N/sub 0/ is the transparency carrier density. The approximate formulas are shown to provide not only an efficient way of computing the gain-related parameters but also a convenient way of getting physical insights into the overall interplay of quantum well parameters.