Quantum-well Semiconductor Lasers Research Articles

Peculiarities of electron spectrum rearrangement for the double-well heterostructure GaAs/AlGaAs with a variable dimensionality of electronic states in an external electric field

Peculiarities of the electron spectrum rearrangement for the double-well heterostructure GaAs/AlGaAs with a variable dimensionality of electronic states in an external electric field are investigated theoretically and experimentally. The structure is an important part of the active element of a quantum-well unipolar semiconductor laser proposed by the authors earlier. The possibility of controlling the dimensionality of the lower laser subband in such an active element by an external electric field is demonstrated.

A theoretical investigation of the characteristic temperature T/sub 0/ for semiconductor lasers

The temperature dependence of the characteristic temperature T/sub 0/ of semiconductor quantum-well lasers is investigated using detailed simulations. The critical-temperature-dependent processes are the optical gain and the nonradiative recombination. The gain model is based on k /spl middot/ p theory with the multiple quantum wells in the active layer represented by a superlattice. The Auger process is assumed to be thermally activated. It is shown that, with inclusion of the continuum state filling and interband mixing, the most important features experimentally observed in the temperature dependence of the T/sub 0/ value can be explained. The continuum state filling and band nonparabolicity cause a significant deviation from the ideal linear carrier density versus temperature relation for quantum wells. The results are compared to experiment for broad area devices lasing at 980 nm and 1.3, and 1.55 μm, and show good agreement over a broad range of temperature.

Mode locking in Fabry-Perot semiconductor lasers

Passive mode-locking (ML) operation in semiconductor quantum-well (QW) lasers with Fabry-Perot (FP) cavities is investigated theoretically and experimentally. Structural and operational conditions for a semiconductor QW laser to exhibit ``amplitude modulation (AM)'' or ``frequency modulation'' ML operations are investigated by numerical analysis based on a semiclassical laser model. It is shown experimentally that clear AM ML pulses self-build and persist under continuous current injection in ${\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}\mathrm{As}/{\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}{\mathrm{As}}_{y}{\mathrm{P}}_{1\ensuremath{-}y}/\mathrm{InP}$-based FP QW lasers with cavity lengths of $300\ensuremath{-}600 \ensuremath{\mu}\mathrm{m}.$ The observed ML features are explained in terms of the laser model.

Energy States of Particles and Quasi-Particles in Active Region of InGaSa/InP Injection Semiconductor Quantum-Well Laser

Energy States of Particles and Quasi-Particles in Active Region of InGaSa/InP Injection Semiconductor Quantum-Well Laser

Anomalous dispersion, differential gain, and dispersion of the α-factor in InGaAs/AlGaAs/GaAs strained quantum-well semiconductor lasers

A new procedure for the experimental determination of the differential gain and dispersion of the amplitude-phase coupling coefficient in semiconductor injection lasers was proposed and implemented. The α-factor and differential gain for InGaAs/AlGaAs/GaAs single quantum well (QW) semiconductor lasers were determined using this procedure in a wide spectral range (from 957 to 996 nm) at various pumping current densities (from 280 to 850 A/cm2). The factor which characterizes the dispersion of the group velocity and restricts the minimum duration of the lasing pulse at the level of 10−13 s was experimentally determined for InGaAs lasers for the first time.

Relative intensity noise characteristics of injection-locked semiconductor lasers

An experimental and theoretical study of relative intensity noise (RIN) spectra of side-mode injection-locked Fabry–Pérot semiconductor lasers is reported. It is shown that the injection-locking technique effectively increases the relaxation oscillation frequency from 4.5 GHz (free-running mode) to 12 GHz (injection-locked mode) and enhances relaxation peaks of the slave laser RIN spectra. Results from our theoretical model, which include the key parameters for semiconductor quantum-well lasers, such as the linewidth enhancement factor, the nonlinear gain saturation coefficients, and optical confinement factor, show good agreement with our experimental results.

Selective excitation and photoinduced bleaching of defects in InAlGaAs/GaAs high-power diode lasers

Mounting-induced defects in semiconductor quantum-well (QW) lasers are investigated by photocurrent spectroscopy. The defects are located in the laser waveguides and give rise to an absorption band below the QW band gap with a maximum absorption cross section of σ=2×10−15 cm2. We observe a nonlinear fully reversible photobleaching of the defects and a resulting increase of QW photocurrent upon continuous wave irradiation of the devices, demonstrating a direct interaction between quantum-confined carriers and a defect level.

Polarization-dependent gain saturations in quantum-well lasers

Theoretical analyses of polarization-dependent optical gain saturation are given for semiconductor quantum-well (QW) lasers to investigate the conditions of polarization switching and bistable operations. Nonlinear susceptibilities, which give saturation coefficients, are obtained in the perturbative analyses of density matrices, where the relevant electronic states in the QW are calculated by diagonalizing Luttinger's Hamiltonian, thus including valence band mixing. The present formulation is applied to InGaAsP QW lasers with edge-emitting and vertical-cavity surface-emitting laser (VCSEL) structures, and the self- and cross-saturation coefficients with parallel and orthogonal optical polarizations are numerically calculated, which are compared with those of bulk lasers. For the edge-emitting case, the saturation coefficients are strongly dependent on the photon energies, and the bistable operation condition is not satisfied in the gain peak, different from a bulk laser which showed only a slight energy dependence. In a VCSEL, the saturation coefficients are also dependent on the photon energies but the bistable operation condition is always satisfied.

The effect of substrate orientation on the modal gain of quantum-well semiconductor lasers

The properties of In1−xGaxAsyP1−y–In1−xGaxAsyP1−y were studied as a function of substrate orientation. The Luttinger–Kohn formalism was used for holes, and a simple effective mass equation was used for conduction electrons. A novel method to calculate the TE optical modal gain was used. It was found that the modal gain is strongly dependent on the substrate orientation. At carrier concentrations less than 3.5×10cm−3, it has its largest value for the (111) growth direction. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 27: 407–410, 2000.

Influence of effective mass and energy band splittings on the radiative characteristics of QW lasers at transparency

The effect of degenerate light- and heavy-hole bands on the carrier and current density and the differential gain are studied and compared with the nondegenerate case in semiconductor quantum-well (QW) lasers. It is demonstrated that the presence of the degenerate bands at the valence band (VB) maximum will always lead to an increased threshold radiative current density compared to the case where only one band is significantly populated. When the valence bands are separated by an energy E s, the current density decreases rapidly with increasing E s, with greater reductions being achieved for a given tensile than compressive strain. The effect of the second subband becomes less important with increasing E s, and the radiative current density reverts to that of the one VB case, demonstrating the importance of maximising the subband energy separation to optimize laser characteristics.

Stability analysis of quantum-well semiconductor lasers with carrier transport effects

We have formulated a coupled-mode theory with the inclusion of carrier transport effects and used it to analyze dynamics of laser arrays. Special attention has been paid to high-frequency behavior and carrier transport limitations imposed on in-phase mode. General theory has been illustrated for two laterally coupled lasers. Stability analysis had been performed and it was found that the inclusion of the carrier transport effects modifies the stability diagram for /spl theta/=/spl pi/, where /spl theta/ is the difference between electric field phases of the two lasers.

The effect of carrier capture and escape on the optical gain of quantum-well semiconductor lasers

Effects of the carrier capture and escape on the optical gain of a quantum-well system are introduced and analyzed. The analysis is based on the density matrix time evolution equation solved in the linear approximation. It has been found that the capture and escape effects modify the broadening function and, as a consequence, reduce the optical and differential gain. The temperature dependence of the gain peak resulting from the inclusion of carrier capture/escape processes has been found.PACS Nos.: 42.55.P, 78.66

Clamping of the linewidth enhancement factor in narrow quantum-well semiconductor lasers

The linewidth enhancement factor in single quantum-well graded index separate confinement heterostructure semiconductor lasers is investigated theoretically and experimentally. For thin wells, a small linewidth enhancement factor is obtained which clamps with increasing carrier density, in contrast to the monotonous increase observed for thicker wells. Microscopic many-body calculations reproduce the experimental observations attributing the clamping to excitation dependent gain shifts and the influence of the population of off-resonant states on the refractive index.

The effect of carrier capture and escape on the optical gain of quantum-well semiconductor lasers

The effect of carrier capture and escape on the optical gain of quantum-well semiconductor lasers

Ultra-sensitive all-optical sampling at 1.5 [micro sign]m using waveguide two-photon absorption

Ultra-sensitive all-optical sampling at 1.5 µm using two-photon-absorption in a commercial 1.3 µm quantum-well semiconductor laser has been demonstrated. Using only direct detection of the unamplified two photon absorption photocurrent, a temporal resolution of ~2 ps and a sensitivity of less than 2 mW2 have been achieved.

QUANTUM STATE ENGINEERING BASED ON ELECTROMAGNETIC ANALOGIES AND NUMERICAL METHODS FOR SEMICONDUCTOR INTERSUBBAND LASERS

The design of semiconductor intersubband lasers using quantum state engineering based on electromagnetic analogies is a relatively new area. There has been little systematic effort in this direction as yet. The use of these analogies allows laser researchers to apply tools and methodologies found in the mature field of electromagnetic optics. The purpose of this paper is to describe the procedures by which intersubband quantum-well semiconductor lasers (or detectores) may be designed using these methodologies.

Microscopic modeling of vertical-cavity surface-emitting lasers: many-body interaction, plasma heating, and transverse dynamics

A microscopic theory for the interaction between semiconductor quantum-well structures and laser fields based on the semiconductor Bloch equations is applied to vertical-cavity surface-emitting lasers (VCSELs) with the inclusion of plasma heating. The semiconductor Bloch equations are reduced to a set of equations for the first and second moments of the carrier distribution functions. Plasma heating and many-body effects are then studied by solving this set of equations in steady state under the approximation of a single transverse and longitudinal mode. The transverse- and longitudinal-mode dynamics of VCSELs is analyzed by solving the full space-time-dependent problem.

Superradiant generation of femtosecond pulses in quantum-well heterostructures

We propose a new type of accessible source of ultra-short pulses based on the phenomenon of collective coherent recombination (superradiance) of electrons and holes in semiconductor heterostructures. We find and analyse a novel regime of ultra-fast operation of quantum-well semiconductor lasers in which a quasiperiodic sequence of femtosecond superradiant pulses is emitted under continuous pumping. According to our calculations for AlGaAs - GaAs heterostructures, the coherent optical pulses of duration 30 fs and peak intensity can be generated in a low-Q cavity of length .

Simple analytical approximations for the gain and refractive index spectra in quantum-well lasers

An analytical expression for the low-temperature optical susceptibility of quantum-well semiconductor lasers is presented based on a simple parabolic band model. The optical susceptibility obtained keeps the nonlinear dependence on the carrier density, providing both a broad gain spectrum and a dispersion curve, so it can be used to analyze the dynamics of multimode devices or devices with large carrier density variations. The resulting peak gain, differential peak gain, and linewidth enhancement factor are discussed. cw operation of a single-mode laser is studied as a function of the frequency of the cavity resonance. An analytical approximation to the finite-temperature gain spectrum is also presented, although the refractive index spectrum must be determined numerically.

Experimental analysis of temperature dependence of oscillation wavelength in quantum-well FP semiconductor lasers

We experimentally evaluated the temperature dependence of the oscillation wavelength in 1.3-/spl mu/m GaInAsP-InP strained multiple-quantum-well (MQW) semiconductor lasers compared to bulk lasers. The temperature dependence of the oscillation wavelength can be characterized by two newly introduced coefficients /spl alpha//sub 1/ and /spl alpha//sub 2/ which are the gain peak wavelength shift coefficients under the constant current condition and under the constant temperature condition, respectively. These two coefficients of various MQW structure lasers are the same as those of bulk lasers. This result means that the oscillation wavelength shift coefficient d/spl lambda//dT is only a function of the characteristic temperature T/sub 0/. The higher T/sub 0/ induces the large temperature dependence of the oscillation wavelength, When the characteristic temperature T/sub 0/ is equal to the characteristic temperature T/sub ltr/ of the transparency current I/sub tr/, the oscillation wavelength shift coefficient d/spl lambda//dT takes the maximum value which is determined by the thermally induced bandgap narrowing effect d/spl lambda//sub g//dT. One possibility to solve the paradox between a high characteristic temperature T/sub 0/ and the small temperature dependence of the oscillation wavelength is the introduction of the temperature-independent leakage current.