Semiconductor Laser Medium Research Articles

On a Multiple-Scales Analysis of Multilateral Phenomena in Semiconductor Lasers

A mathematical model describing the coupling of electrical and optical effects in the active region of a realistic semiconductor laser medium is introduced. The weakly nonlinear analysis which follows gives rise to a leading-order problem describing three lateral modes. At the next order, the secularity conditions exhibit competition for photons and modal interaction. By making further assumptions, a partially lumped model is deduced which has no counterpart in the existing literature; this simplified system consists of one parabolic and six first-order hyperbolic partial differential equations. Predictions of this partially lumped model are compared with experimental observations.

Simple annular-beam generator with a laser-diode-pumped axially off-set power build-up cavity

We have developed a novel, compact-mode selective annular-beam generator that employs a laser-diode (LD)-pumped, passively locked power build-up cavity (PBC). The PBC functions as a flexible and compact light source that is capable of producing TEM 0n high-order Hermite-Gaussian (HG) beams. The generated HG beams can then be converted to LG modes, particularly to annular-beams, using two cylindrical lenses. The system was theoretically studied and a mode-matching condition was derived. The tailoring position of the active semiconductor laser medium relative to the external cavity of the PBC enabled the production of single high-order HG modes. The optimum position was calculated by model calculations of the mode-coupling efficiency. The desired TEM 0n modes of HG beams were generated by translating the axial position of the external cavity of the PBC in increments of ∼100 μm relative to the LD emission surface. High quality TEM 01 to TEM 015 of the HG beams and their conversion to the desired LG modes having powers of the order of 1 mW was successfully demonstrated. This system is suitable for optical tweezers.

In-line interferometer for direction-sensitive displacement measurements by optical feedback detection

We demonstrate a compact in-line interferometer for direction-sensitive displacement measurement by optical feedback detection with a semiconductor laser (SL) light source. Two reflected beams from a semitransparent reference mirror and a reflecting test object interfere in the SL medium, causing a variation in its output power. The reference mirror is located between the SL output facet and the test object. The performance of the interferometer is investigated numerically and experimentally to determine its optimal operating conditions. We have verified the operating conditions where the behavior of the SL output power profile could indicate accurately the displacement magnitude and direction of the moving test object. The profile behavior is robust against variations in optical feedback and scale of the interferometer configuration.

Nonlinear gain and carrier temperature dynamics in semiconductor laser media

The macroscopic behavior of a semiconductor laser medium is described by use of modified rate equations. The model, valid on time scales greater than 10-13 s, explicitly treats carrier temperature as a dynamic variable and includes the nonlinear dependence of the gain function on carrier density and temperature. Gain suppression that is due to carrier heating is a natural consequence of the model and gives a qualitative explanation of subpicosecond gain dynamics experiments without introducing gain nonlinearity phenomenologically. We demonstrate the temperature behavior of the laser during transient dynamics near and well above threshold. By including carrier temperature as a dynamic variable we show that the laser response to an external perturbation exhibits a noticeable change in the damped oscillations of the photon density compared with that in models without temperature dynamics. Variation in the evolution of the gain function for different external pulse energies is also demonstrated.

Carrier correlation effects in a quantum-well semiconductor laser medium

This paper describes the results of a microscopic treatment of carrier-carrier scattering effects in the optical gain and refractive index spectra of a quantum-well semiconductor laser structure. The approach uses the Semiconductor Maxwell Bloch equations to describe the interaction between the carriers and the laser field, in the presence of many-body Coulomb interactions. Coulomb correlation effects are treated at the level of quantum kinetic theory in the Markovian limit. This approach shows the presence of nondiagonal Coulomb correlation contributions, in addition to the familiar diagonal contributions giving rise to polarization dephasing.

Picosecond and sub-picosecond pulse generation in semiconductor lasers

Generation of short optical pulses in semiconductor lasers is of practical interest for an increasing number of applications. It is also of fundamental interest because of its tight relation with the field of semiconductor laser dynamics. After an introductory review, we compare the performances of gain-switching, Q-switching and mode-locking techniques. The comparison is illustrated by experimental results as well as by laser modelling, some of which are new. A special emphasis is given on the aspects of phase modulation in the semiconductor laser medium. Finally, we discuss some perspectives for further developments.

Many-body treatment on the modulation response in a strained quantum well semiconductor laser medium

The carrier density modulation response of a semiconductor laser medium is analyzed. The differential gain and linewidth enhancement factor are computed as functions of strain and threshold gain. The example of InGaAs/InP with different InAs content is used to illustrate the situations of zero, tensile and compressive strain.

Side-mode gain in semiconductor lasers

Side-mode gain and coupling coefficients in semiconductor laser media are calculated with the use of a multimode Fourier technique valid both for mode spacings that are small compared with the carrier–carrier relaxation rates and for spacings comparable with these rates as predicted by the Boltzmann theory of Binder et al. [ Phys. Rev. B45, 1107 ( 1992)]. The medium is described by a free-carrier model that provides for carrierprobability pulsations around quasi-equilibrium Fermi–Dirac values. We find that population pulsations play just as important a role as spectral hole burning for mode spacings comparable with the intraband relaxation rates. For the carrier–carrier relaxation rates of Binder et al., side-mode gain is predicted to be smaller than the main-mode gain, leading to single-mode operation. However, for somewhat smaller intraband relaxation rates, side-mode gain is readily found that exceeds the single-mode gain, which would encourage multimode operation. In addition, we find that the gain and coupling coefficient spectra are sensitive to the k dependence of the carrier—carrier relaxation rates and might provide a useful way to measure these rates. We are also able to explain the asymmetric side-mode gain spectra for small beat frequencies in terms of the rapid decrease of the quasi-equilibrium Fermi–Dirac electron distribution just above the gain region.

Multiwave mixing in semiconductor laser media.

This paper analyzes the interaction of a strong wave and one or two probe waves with an intrinsic semiconductor medium which is partially inverted by an injection current. The many-body interactions of the electron-hole excitations are described using recently developed generalized Bloch equations for semiconductors. Coupled-mode equations for the different light fields are derived and solved, and predict that the gain and the coupling coefficients experience asymmetric dips. These dips are generated by scattering of the strong field off carrier-density pulsations induced by the pump-probe interference.

Four-wave mixing and phase conjugation in semiconductor laser media

A theory of four-wave mixing in semiconductor laser media is developed by considering the contributions of both the gain and index gratings created by the carrier-density modulation occurring at the beat frequency of the pump and the probe waves. The general formalism can be applied to semiconductor lasers operating below or above threshold. As an illustration, we consider the case in which the semiconductor laser is operated as a traveling-wave amplifier. The results show that the dominant contribution to the four-wave mixing process comes from the index grating. Further, the index grating makes the probe transmission asymmetric with respect to the pump-probe detuning.