Showing papers on "Semiconductor optical gain published in 1991"

Well-barrier hole burning in quantum well lasers

Abstract: The reported wide variations in the damping behavior of quantum well lasers are explained by a novel theory of nonlinear gain, well-barrier hole burning. In the model a spatial hole develops perpendicular to the active region involving carriers moving between the wells and the barrier/confinement layers. The modified rate equations describing well-barrier hole burning are presented. An analytical approximation for the nonlinear gain coefficient epsilon , valid only under certain conditions, is given. A numerical solution is given for the case of high photon densities and large capture-times. It is shown how well-barrier hole burning explains the measurements of the increased spontaneous emission from the barrier/confinement region above threshold. Various higher-than-expected damping rates reported in some quantum well lasers are shown to be consistent with the model. >

Nonlinear gain suppression in semiconductor lasers due to carrier heating

Abstract: A simple model is presented for carrier heating in semiconductor lasers from which the temperature dynamics of the electron and hole distributions can be calculated. Analytical expressions for two new contributions to the nonlinear gain coefficient, in are derived, which reflect carrier heating due to stimulated emission and free carrier absorption. In typical cases, carrier heating and spectral holeburning are found to give comparable contributions to nonlinear gain suppression. The results are in good agreement with recent measurements on InGaAsP laser diodes. >

Spectral characteristics of vertical-cavity surface-emitting lasers with external optical feedback

Abstract: The measurement of the effects of external optical feedback on the spectra of VCSELs (vertical-cavity surface-emitting lasers) is reported. It is surprising that VCSELs have a sensitivity to optical feedback comparable to that of conventional edge-emitting lasers such as DFBs despite their significantly different structures. This is because the extremely short cavity length of VCSELs negates the effects of their highly reflective output mirrors. As in edge-emitting lasers, VCSELs exhibit well-defined regimes of feedback effects in their spectra. Since optical isolators cannot be easily applied to VCSELs due to their array structure, these lasers may be most useful in applications which are not sensitive to the spectral qualities of the light source. >

Physics of semiconductor lasers

Abstract: 1. Preface. 2. Physical principles of the operation of semiconductor lasers. 3. Basic techniques for fabricating semiconductor lasers. 4. The design and basic characteristics of semiconductor lasers. 5. Review of the structures and properties of Fabry Perot cavity junction lasers. 6. Structures of distributed feedback lasers. 7. Dynamic properties of junction lasers and methods for improving their frequency discrimination. 8. Thermal effects occurring in semiconductor lasers. 9. Principles of modelling the physical phenomena in junction lasers. 10. Reliability of LEDs and junction lasers. References. Subject Index. List of main symbols. List of abbreviations.

Measurement of carrier lifetime and linewidth enhancement factor for 1.5- mu m ridge-waveguide laser amplifier

Abstract: Semiconductor optical amplifiers are used for investigation of the effective carrier lifetime and the linewidth enhancement factor. Contrary to semiconductor lasers, semiconductor optical amplifiers allow measurement at high levels of injected carrier density. The carrier lifetime and the linewidth enhancement factor are measured with a simple dynamic self-heterodyne method. Carrier lifetimes of 750 ps at the threshold current for the SOA without antireflection coating and 200 ps at high injection have been found. The linewidth enhancement factor is measured to be between 4 and 17 which fits with a simple empirical expression. >

Oscillation wavelength and laser structure dependence of nonlinear damping effect in semiconductor lasers

Abstract: For the first time, the oscillation wavelength and the laser structure dependence of the K factor and of the nonlinear gain suppression coefficient e in semiconductor lasers were systematically investigated. As a result, we suggest that the nonlinear gain effect can be explained by the spectral hole burning theory.

Improved performance due to suppression of spontaneous emission in tensile-strain semiconductor lasers

Abstract: It is shown that application of biaxial tension to the active region of a bulk or quantum well semiconductor laser can significantly enhance TM gain compared to TE gain and reduce the threshold current density, due to suppression of spontaneous emission polarised in the growth plane of the laser structure. The differential gain is enhanced compared to unstrained structures and a larger peak gain can be achieved than in comparable structures under biaxial compression.

A new density matrix theory for semiconductor lasers, including non-Markovian intraband relaxation and its application to nonlinear gain

Abstract: A density matrix equation for semiconductor lasers is derived from the microscopic equation of motion for electrons using a projection operator method. The effect on non-Markovian intraband relaxation is described by the autocorrelation functions of electron scattering terms in the microscopic interaction Hamiltonian. The obtained density matrix equation provides a systematic treatment for dynamical properties of semiconductor lasers, and the treatment can be performed by calculating the autocorrelation functions from available material parameters. A gain formula for arbitrary light output power is derived from a single-mode steady-state nonperturbative solution. A simplified estimation using a stochastic model shows that non-Markovian intraband relaxation enhances both linear gain and nonlinear gain. The reduction of nonlinear gain effects is discussed. >

A new structure for high-power TW-SLA (Travelling wave semiconductor laser amplifier)

Abstract: A structure utilizing an exponential tapered active layer to improve the saturation output power and quantum efficiency of a traveling-wave semiconductor laser amplifier is discussed. Both the spatial distributions of the carrier density and the optical field are considered in the analysis. It is shown that an optimum taper geometry for maximizing the efficiency exists and that this structure provides simultaneous improvement in the saturation output power (7 dB) and the quantum efficiency (1.5 times) compared to a conventional device. >

Gain saturation coefficients of strained-layer multiple quantum-well distributed feedback lasers

Abstract: The gain saturation coefficients were measured for strained and unstrained multiple quantum-well distributed feedback (MQW-DFB) lasers. The gain saturation coefficient depends on the deviation of the laser's transverse-magnetic (TM) mode gain peak wavelength from its transverse-electric (TE) mode gain peak wavelength delta lambda , which is related to the strain on the active-layer wells. The gain saturation coefficient epsilon increased with increasing compressed strain on the active-layer wells. The coefficient epsilon of the unstrained MQW DFB laser with a wavelength deviation delta lambda of -350 AA was 2.45 x 10/sup -17/ cm/sup 3/, and epsilon increased up to 12.6 x 10/sup -17/ cm/sup 3/ in the SL-MQW DFB laser with a wavelength difference delta lambda of -890 AA.

Statistics for the transient response of single-mode semiconductor laser gain switching.

Abstract: For a gain-switched semiconductor laser we study the statistics of the time at which the laser intensity first reaches a threshold level and also the laser intensity fluctuations in the nonlinear regime. The dispersion in the maximum value of the laser intensity at the first peak of the relaxation oscillations is calculated. A simple relation between this maximum value and the passage time for each individual switch-on event is found.

Second harmonic generator using a laser as a fundamental wave source

Abstract: A second harmonic generator has a semiconductor laser for a fundamental wave light source. The laser includes a semiconductor laser chip and a quasi-phase matching element optically coupled together in series. The semiconductor laser chip can lase utilizing feedback of a light from the quasi-phase matching element. The quasi-phase matching element receives a laser emitted from the semiconductor laser chip and generates a second harmonic light using the laser beam as a fundamental wave light.

Semiconductor laser pump source

Abstract: A laser source for pumping an optical device which requires for its operation a significant amount of light power, the source comprising a semiconductor array (11) for providing a plurality of spaced apart light beams at different wavelengths, an optical assembly (14, 15, 16) for focussing the light beams into an optical waveguide (19), the optical waveguide (19) being coupled to the optical device.

Spontaneous emission and gain in GaAlAs quantum well lasers

Abstract: Measurements of spontaneous emission from GaAlAs single quantum well lasers over a wide range of carrier densities are discussed. From these measurements, the optical gain, refractive index, and linewidth enhancement factor are determined, all of which contribute to the overall performance of a semiconductor laser. In addition, a simple model which adequately describes the important features in the spontaneous emission (and therefore the gain) data is presented. With this model, quantitative information about the carrier density-dependent bandgap shrinkage, lifetime broadening, and the shape of the broadening functions is obtained. >

Semiconductor laser device with plural active layers and changing optical properties

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.

Method for characterization of intrinsic and extrinsic components of semiconductor laser diode circuit model

Abstract: A simple method for the characterization of the intrinsic and extrinsic parameters of a semiconductor laser diode has been described. This method is based on the measurement of intensity noise, small-signal modulation response and input reflection coefficient of the device. The intrinsic 3-dB-modulation bandwidth and the extrinsic parasitic components associated with the device can be readily determined by using the analytical expressions presented. It has been shown that the major limitation of the 3-dB-modulation bandwidth can be attributed to the device chip RC time constant. >

A GaInAsP/InP tapered-waveguide semiconductor laser amplifier integrated with a 1.5 mu m distributed feedback laser

Abstract: A GaInAsP/InP index-guided type tapered-waveguide traveling-wave semiconductor laser amplifier (TTW-SLA) with exponential taper structure was realized for the first time and its integration with a 1.5 mu m wavelength phase adjusted DFB laser was demonstrated. A reasonable amount of the single-pass gain, which was limited by the residual reflectivity at the output end of the amplifier region, was obtained with no serious problem with the lasing spectrum. A narrow beam divergence of FWHM=5.5 degrees and stable longitudinal mode operation were obtained with the output waveguide width of 20 mu m by adopting both a window structure and 7 degrees angled facets. This value agrees well with the theoretically calculated one and proves that single transverse-mode propagation can be attained by an exponentially tapered TTW-SLA with a very wide output end. >

Nonlinear external cavity modelocked laser

Abstract: Modelocking of a solid state laser such as a Ti:Al₂O₃ laser (101) is achieved by employing an external cavity defined by spatially separated reflective elements (104,107) wherein at least one of the reflective elements (107) exhibits a nonlinear characteristic in response to an impinging light beam. Exemplary nonlinear reflective elements are described using bulk semiconductor material or semiconductor quantum well structures integrated with a rear reflector such as a stack of quarter-wave thick dielectric or semiconductor material. Tuning control of the nonlinear reflective element may be introduced with temperature control arrangements and with mechanical translation arrangements in conjunction with lateral band gap engineering of the semiconductor material.

Model of the spectral output of gain-guided and index-guided semiconductor diode lasers

Abstract: A model for predicting the longitudinal-mode spectra of semiconductor diode lasers is presented. The model considers the effects of experimentally observed scattering, which exists in or near the active region. By changing the amount of scattered light and the location of the scattering center, one can predict theoretical longitudinal-mode spectra to be multimode, single mode, asymmetric, or double gain peak. Thus the model, coupled with the observed scattering properties of index-guided and gain-guided lasers, provides an explanation of why gain-guided lasers tend to operate more multilongitudinal-mode than do index-guided lasers.

Encyclopedia of lasers and optical technology

Abstract: Chemical lasers, W.C.Solomon colour centre lasers, C.R.Pollock colour, science of, R.M.Boynton diffraction, optical, S.Solimeno electrodynamics, quantum, W.P.Healy free-electron lasers, H.P.Freund and R.K.Parker gas lasers, W.W.Duley holography, C.C.Guest interferometry, optical, P.Hariharan laser cooling and trapping of atomsl, J.E.Bjorkholm lasers - materials interactions, M.Bass laser pulsations, dynamical, N.Abraham lasers, W.T.Silfvast light sources, J.F.Waymouth luminescence, J.N.Demas and S.E.Demas micro-optics, K.Iga mode-locking of lasers, P.W.Smith and A.M.Weiner nonimaging concentrators (optics), R.Winston and J.O'Gallagher nonlinear optical processes, J.F.Reintjes nuclear pumped lasers, D.A.McArthur optical circuitry, H.M.Gibbs, et al optical fibre communications, B.K.Tariyal and A.H.Cherin optical fibre techniques (medicine), A.Katzir optical fibres, drawing and coating, L.L. Blyler, Jr and F.V.DiMarcello optical information processing, M.M.Mirsalehi optical phase conjugation, R.A.Fisher optical systems design, R.E.Fischer quantum optics, J.H.Eberly and P.W.Milonni rare gas-halide lasers, M.Obara and F.Kannari semiconductor injection lasers, P.J.Delfyett and C.H.Lee speckle interferometry, H.A.McAlister switching, optical, S.C.Gratze telescopes, optical, L.D.Barr tunable dye lasers, T.F.Johnston, Jr ultra-fast laser technology, P.J.Delfyett, et al ultrashort laser pulse chemistry and spectroscopy, J.L.Knee.

Sensitivity to external feedback for gain-coupled DFB semiconductor lasers

Abstract: Performances of DFB semiconductor lasers with both index and gain spatial modulation are theoretically analysed in terms of threshold gain, emission wavelength, modal discrimination and sensitivity to external optical feedback. It is found that gain coupling provides low threshold gain, high spectral selection in favour of the mode oscillating at the Bragg wavelength with a relative immunity from facet reflection, and the sensitivity to external feedback is not significantly reduced in comparison with the case of pure index coupling.

Numerical investigation of ultrahigh frequency polarization self-modulation in semiconductor lasers

Abstract: Numerical simulations performed show that polarization self-modulation in suitably designed semiconductor lasers into the tens of GHz frequency region should be possible. The calculations are based on a simple model developed to describe polarization self-modulation in a ring laser cavity with a traveling-wave semiconductor laser amplifier as the gain medium. A set of difference-differential equations is derived and numerically solved. Periodic oscillations in the two polarization modes are obtained as previously reported experimentally. An examination of the various parameters and their roles in maintaining this instability is also conducted. The results indicate that, in an appropriately designed semiconductor laser with a monolithically integrated intracavity TE-TM mode converter, ultrahigh frequency polarization self-modulation to at least 50 GHz should be possible. >

Differential gain of GaAs/AlGaAs quantum well and modulation‐doped quantum well lasers

Abstract: The differential gain which is an important parameter for modulation dynamics in semiconductor lasers is evaluated experimentally by measuring the gain coefficient and the carrier lifetime in GaAs/AlGaAs double‐heterostructure (DH) lasers, quantum well (QW) lasers, and p‐modulation‐doped quantum well (p‐MDQW) lasers. The results indicate that the differential gain of the QW laser is 2.4 times as high as that of the DH laser, which is consistent with the theory. In addition, it is found that improvement of the differential gain using the p‐MDQW structure is not so large as that expected by the theory. This result suggests that enhanced energy broadening due to the reduction of the equivalent dephasing time τeqin, which includes both the dephasing time τin due to the intraband relaxation and the band tailing effects, significantly affects the gain spectra in the p‐MDQW lasers, which is confirmed by the measurement of the spontaneous emission spectra.

Semiconductor laser device and a method for producing the same

Abstract: A semiconductor laser device is provided which is constituted by semiconductor materials so as to emit laser light from a cavity end facet, the laser light being excited in a waveguide within an active layer sandwiched between a pair of cladding layers, wherein a window layer made of a semiconductor material having a band gap greater than that of the active layer is formed on the cavity end facet from which the laser light is emitted, so as to have a thickness sufficient to prevent local generation of crystal defects by lattice mismatching between the semiconductor material of the window layer and the semiconductor materials at the cavity end facet. There is also provided a method for producing such a semiconductor laser device with high efficiency.

Strain and scattering related spectral output of 1.3-μm InGaAsP semiconductor diode lasers

Abstract: A correlation between the spectral output of 1.3 μm InGaAsP semiconductor diode lasers and the distribution along the length and width of the active region of strain and scattering centers is reported. The strain and scattering center distributions in the active region were obtained by measuring and analyzing the spatially resolved and polarization resolved electroluminescence along the active region of the lasers. Measurements were made on gain-guided, planar buried heterostructure, and arrowhead buried crescent lasers. The results suggest that the material properties of the laser structure affect the longitudinal mode spectrum.