Showing papers on "Semiconductor optical gain published in 1990"

A simple analytic expression for the stable operation range of laser diodes with optical feedback

Abstract: A simple analytic expression for the critical feedback level, above which a semiconductor laser becomes unstable, is derived This tolerable feedback level increases with increasing damping of the relaxation oscillations Good agreement is found between the analytic expression and numerical evaluations of the rate equations >

Optical gain and gain suppression of quantum-well lasers with valence band mixing

Abstract: The effects of valence band mixing on the nonlinear gains of quantum-well lasers are studied theoretically for the first time. The analysis is based on the multiband effective-mass theory and the density matrix formalism with intraband relaxation taken into account. The gain and the gain-suppression coefficient of a quantum-well laser are calculated from the complex optical susceptibility obtained by the density matrix formulation with the theoretical dipole moments obtained from the multiband effective-mass theory. The calculated gain spectrum shows that there are differences (both in peak amplitude and spectral shape) between this model with valence band mixing and the conventional parabolic band model. The shape of the gain spectrum calculated by the new model becomes more symmetric due to intraband relaxation together with nonparabolic energy dispersions. Optical intensity in the GaAs active region is estimated by solving rate equations for the stationary states with nonlinear gain suppression. >

Effect of gain and index nonlinearities on single-mode dynamics in semiconductor lasers

Abstract: The finite intraband relaxation time in semiconductor lasers leads to gain saturation at high laser powers. The nonperturbative solution of the single-mode density-matrix equations shows that both the optical gain and the refractive index become intensity dependent as a result of intraband relaxation dynamics. Gain and index nonlinearities are included in the rate equations, and how the modulation response and noise characteristics of semiconductor lasers are affected by such nonlinearities is studied. The intensity dependence of the frequency and the damping rate of relaxation oscillations leads to a fundamental limit imposed on the small-signal modulation bandwidth; the analysis provides an expression for the ultimate modulation bandwidth in terms of the material parameters. >

Theory of hot carrier effects on nonlinear gain in GaAs-GaAlAs lasers and amplifiers

Abstract: A concise and straightforward model of nonlinear grain based on the carrier heating effect in semiconductor lasers is presented. The problem is formulated using the density matrix approach and includes a priori the effect of free-carrier absorption. Coupled field-medium equations involving photon densities, carrier densities, and carrier temperatures are derived using the results of the density matrix method. The propagation of ultrashort pulses in laser amplifiers is studied and a qualitatively new model along with results on the transient gain recovery dynamics are presented. The model accounts for the wavelength dependence of the asymmetric part of the nonlinear gain observed in direct mixing experiments observed in semiconductor lasers. >

Monolithic high density arrays of independently addressable offset semiconductor laser sources

Abstract: Monolithic high density arrays of independently addressable offset semiconductor laser emitters or elements are able to be placed in close center-to-center proximity, e.g., on 3-10 μm centers, without experiencing any undesirable phase locking and with minimal amount of electrical and thermal interaction or crosstalk occurring between the independently addressed lasing elements and their independent operation in ROS printer applications. With a proper offset in the laser emitters, interlace scanning relative to an image bearing surface, which is required with other multiple emitter lasers in ROS printer applications, is eliminated thereby permitting adjacent line scanning of an image bearing surface without complicated optics and electronics.

Locking range, phase noise and power spectrum of an injection-locked semiconductor laser

Abstract: The locking range of an optically injected semiconductor laser is discussed, including the spectral hole burning and lateral carrier diffusion effects. These effects are modelled with a gain suppression coefficient. In addition, an expression for the mean square phase jitter of an injection-locked semiconductor laser is derived when these effects are insignificant. The power spectrum of a locked laser is obtained and compared with experimental results.

Semiconductor laser device capable of controlling wavelength shift

Abstract: A wavelength-tunable semiconductor laser device presenting a large wavelength-tunable range or a very-high-speed modulating semiconductor laser device having a distributed feedback structure including a diffraction grating as in the case of a DBR laser or a DFB laser incorporates therein a plurality of active layers differing from one another in constituent elements or composition ratio or thickness for reducing spectral line widths, while improving single-mode spectral oscillation characteristics.

Vertical cavity semiconductor lasers

Abstract: In a vertical cavity laser, such as an InP based vertical laser, the energy bandgap in the active region can be made equal to or larger than the bandgap in a semiconductor mirror stack by virtue of degenerate doping in the stack sufficient to suppress electronic band-to-band optical absorption. For example, the active region of an InP based laser can be lattice-matched GaInAs, GaInAsP, or a multiple quantum well structure composed of layers of InP and GaInAs--with the mirror stack composed of alternating layers of InP and degenerately doped n-type lattice-matched GaInAs or GaInAsP.

Gain characteristics of an Er/sup 3+/-doped multicomponent glass single-mode optical fiber

Abstract: Experimental results on gain characteristics of an Er/sup 3+/-doped multicomponent glass single-mode optical-fiber amplifier are reported. This amplifier shows a gain spectrum with twin gain peaks of 1.535 and 1.543 mu m, providing a broadened gain bandwidth. The apparent 6-dB gain bandwidth is 12 nm. Furthermore, the signal gain of 17 dB and 15-mW pump power is realized at a signal wavelength of 1.536 mu m, and a signal gain coefficient of 1.4 dB/mW is achieved. >

External cavity semiconductor laser

Abstract: An external cavity semiconductor laser comprising a resonance cavity coupled to a diode laser. The cavity may contain a lens or lens system or may be constructed as an optical waveguide. The external cavity may also contain a nonlinear optical material to produce light of a frequency which is higher than that produced by the semiconductor laser. The use of an external cavity insures the single mode and/or single frequency operation of the semiconductor laser.

Observation of a two-photon gain feature in the strong-probe absorption spectrum of driven two-level atoms.

Abstract: A feature associated with continuous-wave two-photon optical gain has been observed in the absorption spectrum of an ensemble of barium atoms driven by a strong near-resonant optical field. In the dressed-atom picture, the observed gain is attributable to inverted two-photon transitions with nearly resonant intermediate states. A cw optical two-photon laser utilizing this gain appears feasible.

Frequency-tunable semiconductor lasers

Abstract: Recent advances in frequency-tunable semiconductor lasers are reviewed. They are classified into hybrid and monolithic tunable lasers. Monolithic tunable lasers based on distributed Bragg reflector or distributed feedback laser structures are most attractive for practical applications. The device structures and the tuning characteristics are described, with emphasis on the tuning range, spectral linewidth and frequency-switching time. Recent system experiments using monolithic tunable lasers in an optical communication area are also described.

Frequency conversion by nearly-degenerate four-wave mixing in travelling-wave semiconductor laser amplifiers

Abstract: The paper describes a scheme for frequency conversion of optical data signals with use of NDFWM in travelling wave semiconductor laser amplifiers. The frequency conversion range is limited by the gain bandwidth of the optical amplifier, which is about 4000 GHz in the considered case. The experimental arrangement of the conversion scheme is described and a theoretical analysis is presented. Finally the advantages and disadvantages of this scheme are discussed.

On the linewidth enhancement factor in semiconductor lasers

Abstract: The linewidth enhancement factor α is known to have an important impact on semiconductor laser frequency stability. We determine under what general circumstances the value of α for a semiconductor laser may depend upon the longitudinal laser structure. A longitudinal modulation of the modal refractive index is shown not to have any influence on α, while our results indicate that a longitudinal modulation of the modal gain such as would be used in a gain‐coupled laser will in general change the linewidth enhancement factor.

Simultaneous measurement of spontaneous emission rate, nonlinear gain coefficient, and carrier lifetime in semiconductor lasers using a parasitic‐free optical modulation technique

Abstract: An optical modulation technique is used to determine three important parameters for 1.3 μm InGaAsP diode lasers: the rate of spontaneous emission into the guided modes, the nonlinear gain coefficient, and the carrier lifetime at threshold. These results are unaffected by electrical parasitics, and are essential to understanding the noise and modulation properties of diode lasers.

Length dependence of the saturation characteristics in 1.5- mu m multiple quantum well optical amplifiers

Abstract: The dependence on amplifier length of gain and gain saturation characteristics in 1.5- mu m multiple-quantum-well optical amplifiers is reported. Gain measurements are presented for amplifiers with lengths of 200 mu m to 1 mm, and a simple model is introduced which relates gain and saturation characteristics to the amplifier length. The 1-mm-long device has superb properties, with a gain of 25.2 dB and a saturation output power of 40 mW. >

Partial-integration method for analysis of mode-locked semiconductor lasers.

Abstract: A new, computationally efficient semiconductor-laser model has been developed for subpicosecond mode-locked laser analysis. It consists of a set of infinitesimal laser sections resulting from longitudinal integration of the laser rate equations. The model is used to predict the response of an actively mode-locked semiconductor laser for various pulsed-current drives.

Vertical cavity semiconductor laser with lattice-mismatched mirror stack

Abstract: In a vertical semiconductor laser, the top mirror is composed of alternating layers of lattice-mismatched semiconductors. Quantum reflections and other charge transport barriers for majority carriers at the interface, and hence electrical resistance and power dissipation, are reduced by choosing the lattice-mismatched semiconductor materials in such a manner as to align their band edges for majority carriers. On the other hand, the semiconductor materials are selected to supply relatively large refractive index differences, and hence relatively large optical reflections, at their interfaces. The lattice-mismatching may also produce vertical thread dislocations through the stack, which increase the electrical conductivity.

Two‐dimensional simulation of quantum well lasers

Abstract: A versatile two-dimensional simulator for various types of semiconductor lasers for both steady state and transients has been developed. The simulator is capable of spectral analysis of quantum-well semiconductor lasers, such as gain-spectrum analysis, as well as analysis of the two-dimensional current flow and optical intensity patterns. The simulator is based on the drift-diffusion model with full Fermi-Dirac statistics for the transport equations as well as for the Poisson equation. Simulation of the thermionic emission current is required at the abrupt heterointerfaces of the quantum well. For the spectral analysis of quantum-well lasers, we have used the photon rate equation for each Fabry-Perot mode. For the optical intensity pattern, we have solved the two-dimensional Helmholtz eigenvalue equation using the subspace iteration method. The transient simulation is done by the full backward-Euler method in conjunction with the full Newton approach for the entire semiconductor equations. To demonstrate the simulator, a model GaAs-AIGaAs graded-index-separate-confinement-heterostructure buried-quantum-well laser is analyzed.

The effects of electron-hole Coulomb interaction in semiconductor lasers

Abstract: A recent many-body theory is applied to investigate the corrections to semiconductor laser gain and carrier-induced refractive index. The results show nonnegligible modifications to these quantities and demonstrate the importance of band-gap renormalization and Coulomb enhancement. The many-body Coulomb corrections also result in a different prediction of filamentation effects in semiconductor lasers. >

Nonlinear optical pulse propagation in a semiconductor medium in the transient regime. I. Temporal and spectral effects

Abstract: The propagation of optical pulses in a semiconductor medium is modeled in the limit where the optical pulse width is assumed to be shorter than the interband recombination time of the semiconductor. Intense pulses cause saturation of the optical transitions, leading to transient changes in absorption and refractive index of the semiconductor. The changes in absorption and refractive index lead to distortions in the spectra of the pulses. >

Gain nonlinearities in semiconductor lasers and amplifiers

Abstract: A concise and fundamentally straightforward physical model that accounts for the nonlinear gain in both semiconductor amplifiers and lasers is presented. Calculations based on this model yield results that agree very well with observed transient gain recovery dynamics in semiconductor laser amplifiers. The value of the symmetric steady‐state gain suppression factor is found to be β=1.67×10−23 m3 in good agreement with experiment. The model accounts for a wavelength dependence of the asymmetric part of the nonlinear gain observed in direct mixing experiments observed in semiconductor lasers.

Semiconductor laser excited solid laser device

Abstract: A semiconductor laser excited solid laser device of side light excited type in which the excitation region is well matched with the mode volume of the laser oscillation mode, for providing high output and high efficiency. The semiconductor laser excited solid laser device comprises a diffraction grating for diffracting the output light beams of the semiconductor lasers in a direction of formation of the laser resonator mode in application of the output light beams to the solid laser medium.

Calculation of the propagation constant of optical modes in multiquantum-well structures

Abstract: A simple mathematical formalism is used to calculate the propagation constant beta for optical modes (TE/sub 0/, TM/sub 0/) in multiquantum-well semiconductor laser structures. The energy correction due to narrow quantum wells, the energy dependence of the refractive indexes, and the energy dependence of electron and hole masses are taken into account. The data show that there is a considerable difference between the calculated values and the averaged values for beta , especially for a small number of narrow quantum wells. >

Time-dependent simulation of a semiconductor laser amplifier: pulse compression in a ring configuration and dynamic optical bistability

Abstract: A dynamic theory for a semiconductor laser amplifier with time-dependent optical input signal and driving injection current is presented. Previous treatments are extended by including a carrier density-dependent refractive index, a frequency-dependent gain, and multimode operation. The simulation yields optical bi- and tristability strongly depending on the speed at which the optical input-output characteristic is scanned. Tristability can be found in case of high pumping and large linewidth enhancement factor only. Applying the theory to a ring laser configuration, asymptotic pulse compression, which can lead to the emission of a stable sequence of short pulses with widths down to about 6 ps is found. >

Nonlinear gain effects in strained-layer lasers

Abstract: The effects of nonlinear gain on the dynamics of a semiconductor laser in which the active region consists of a strained-layer structure are presented. Gain suppression is enhanced in the presence of strain, thus reducing the relaxation oscillation frequency in strained-layer lasers at very high optical powers compared with equivalent unstrained structures.

Method for non-destructive identification for electronic inhomogeneities in semiconductor layers

Abstract: A semiconductor layer is irradiated with an intensity-modulated laser emission to induce a modulated optical reflectivity which is a valid measure for the density of the electronic inhomogeneities in the semiconductor layer. The use of a test laser beam having a wavelength in a range of 200-345 nm makes exact measurements possible in the entire range of application and is particularly enabling for identification of low and high implantation doses and the identification of residual damage in crystalline semiconductor layers.

Method and apparatus for stabilizing frequency of semiconductor laser

Abstract: A method of stabilizing the frequency of a semiconductor laser comprises stabilizing a time-dependent frequency fluctuation by utilizing an optical energy absorption medium including an isotope acetylene gas molecule. An apparatus for stabilizing the frequency of a semiconductor laser, comprises a semiconductor laser, an optical energy absorption medium, a photodetector and a control circuit as essential elements. The optical energy absorption medium includes an isotope acetylene molecule.