Showing papers on "Semiconductor optical gain published in 1998"

Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films

Abstract: A semiconductor laser whose cavities are “self-formed” due to strong optical scattering in highly disordered gain media is demonstrated. The lasers are made of zinc oxide polycrystalline films grown on amorphous fused silica substrates. Lasing occurs at an ultraviolet wavelength of ∼380 nm under optical pumping. Actual images of the microscopic laser cavities formed by multiple scattering have been captured. These results suggest the possibility of using disordered semiconductor microstructures as alternative sources of coherent light emission.

Hyperchaotic dynamics and synchronization of external-cavity semiconductor lasers

Abstract: Two unidirectionally coupled external cavity semiconductor lasers showing chaotic intensity fluctuations are studied by numerically solving the Lang-Kobayashi model equations [IEEE J. Quantum Electron. QE-16, 347 (1980)]. The systems are shown to synchronize when operating in the regime of low-frequency fluctuations, which is characterized by a very high-dimensional $(dg150)$ attractor. The influence of parameter differences between the two lasers on the synchronization quality is investigated.

3.8-THz wavelength conversion of picosecond pulses using a semiconductor delayed-interference signal-wavelength converter (DISC)

Abstract: A new all-optical semiconductor-band-filling-based wavelength converter, named delayed-interference signal-wavelength converter (DISC), is proposed. Its speed is not restricted by the carrier lifetime and its structure is very simple: it consists of only two essential components, namely, a semiconductor optical amplifier and a passive split-delay. Using this converter, 3.8-THz-shifted (from 1530 to 1560-nm) 14-ps-long pulses are generated from 1530-nm 140-fJ 0.7-ps pulses with high-conversion efficiency.

Polarization fluctuations in vertical-cavity semiconductor lasers

Abstract: We report, theoretically and experimentally, how polarization fluctuations in vertical-cavity semiconductor lasers are affected by optical anisotropies. We develop a spin-eliminated (class A) description of laser polarization and show how the various model parameters can be extracted from the experimental data. In practice, the linear anisotropies are often much stronger than the nonlinear anisotropies, so that the polarization modes defined by the linear anisotropies form a useful basis. For this case we derive a one-dimensional model for polarization noise, with simple expressions for the relative strength of the polarization fluctuations and the rate of polarization switches. For the other, more extreme, case where the nonlinear anisotropies are as strong (or even stronger) than the linear anisotropies, the spin-eliminated description remains valid. However, in this case the concept of polarization modes is shown to lose its meaning, as a strong four-wave-mixing peak appears in the optical spectrum and polarization fluctuations become highly nonuniform.

A multiwavelength semiconductor laser

Abstract: Many systems, such as atoms and molecules in gas mixtures, dye solutions and some solid-state materials, can exhibit simultaneous laser action at several wavelengths as a result of the excitation of several optical transitions1. But semiconductor lasers are usually monochromatic because the electronic levels are distributed in continuous energy bands2. In order to achieve simultaneous lasing at several well-separated wavelengths, researchers have proposed3 combining different semiconductors with distinct bandgap energies in the active material. However, the difficulty of pumping different regions and of absorption of the shorter-wavelength light could be resolved only by using separated multiple resonators or by multisection injection devices4,5,6,7. Here we report the realization of a single artificial semiconductor material with distinct optical transitions, which permits simultaneous multiwavelength laser action at mid-infrared wavelengths (6.6, 7.3 and 7.9 µm). This is achieved by tailoring the electronic states and electron relaxation times in the material, which is a superlattice layered structure. The laser has potential applications in sensors for trace-gas analysis.

Coexistence of low frequency fluctuations and stable emission on a single high-gain mode in semiconductor lasers with external optical feedback

Abstract: We present a systematic investigation of the dynamical behavior of semiconductor lasers subject to external optical feedback dependent on the injection current and the optical feedback strength. We identify the regimes of low-frequency fluctuations (LFFs), fully developed coherence collapse, and a large regime of the coexistence of LFFs and stable emission on single high-gain external-cavity mode extending over more than one order of magnitude of optical feedback strengths. Thus, we provide experimental evidence for one major prediction of the theoretical model based on the Lang-Kobayashi equations, which proposes a deterministic mechanism underlying the LFFs.

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

Abstract: 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. @S1050-2947~98!07501-5# PACS number~s!: 42.55.Px, 78.66.2w The analysis of the static and dynamical properties of semiconductor lasers requires a knowledge of the coupling between the active semiconductor material and the optical field within the active region. In a semiclassical approach @1#, which constitutes the foundation for simpler descriptions as the rate equation ~RE! approximation @2#, the optical field is described by means of Maxwell’s equations, and its coupling to the material is described by the electrical susceptibility of the active medium. The imaginary part of the electrical susceptibility describes the energy exchange ~absortion or stimulated emission! between the field and the medium, while its real part describes the dispersive effect ~refractive

Microscopic theory for the influence of Coulomb correlations in the light-emission properties of semiconductor quantum wells

Abstract: A nonequilibrium Green's-function $T$-matrix approach is presented for the consistent computation of semiconductor quantum-well optical spectra including strong Coulomb correlations in the coupled photon and carrier system. Numerical solutions of the Bethe-Salpeter-type equations yield good agreement with recent absorption and/or gain and emission experiments.

Effects of Si-doping in the barriers of InGaN multiquantum well purplish-blue laser diodes

Abstract: Optical gain spectra of InGaN multiquantum well laser diode wafers having Si-doped or undoped InGaN barriers were compared. Although evidence for effective band-gap inhomogeneity was found in both structures, the wells with the Si-doped barriers exhibited a smaller Stokes-like shift. Si doping suppressed emergence of a secondary amplified spontaneous emission peak at 3.05 eV, which was uncoupled with the primary one at 2.93 eV. Furthermore Si doping reduced the threshold power density required to obtain the stimulated emission.

High-power mode-locked external cavity semiconductor laser using inverse bow-tie semiconductor optical amplifiers

Abstract: This paper presents experimental results of using an inverse bow-tie gain guided semiconductor optical amplifier (SOA) as the optical gain element in a high-power external cavity semiconductor laser. An average output power of 700 mW is demonstrated in continuous-wave (CW) operation while 400 mW of average power is obtained in both passive and hybrid mode-locked operation, with subsequent optical amplification in an identical SOA. The mode-locked laser operates at a repetition rate of 1.062 GHz, owing to the interplay between the gain and saturable absorber dynamics. Optical pulses are generated with a temporal duration of 5 ps, which implies a pulse energy of 376 pJ, and a peak power of 60 W. Further reduction of the optical pulsewidth to 1.3 ps is also achieved by using dispersion compensation techniques. These results show the promise of novel SOA devices for use as gain elements in external cavity semiconductor lasers. The generated output pulse characteristics from mode-locked operation is sufficient for use in novel three-dimensional data storage applications, and in large-scale commercial printing and marking applications.

Mechanism for reducing recovery time of optical nonlinearity in semiconductor laser amplifier

Abstract: We propose and demonstrate a novel scheme to reduce the recovery time of optical nonlinearity in a semiconductor laser optical amplifier driven under a loss condition for the signal light pulse. Additional light, which is set at a transparency wavelength in the active layer, promotes stimulated recombination of excess carriers induced by the absorption of the signal light. This scheme excludes any additional carrier transport mechanism and nonradiative recombination and hence generation of heat. The principle of operation is experimentally verified by measuring time-domain transmission variance using a pump–probe method. A drastic reduction of the excess-carrier lifetime to less than 70 ps was confirmed.

Measurement of optical cavity properties in semiconductor lasers by Fourier analysis of the emission spectrum

Abstract: We present several observations on a novel method for the evaluation of the internal loss properties in semiconductor lasers. The method we use involves Fourier analysis of the Fabry-Perot mode spectrum when operating the device below lasing threshold. The observation of various structural features in the Fourier transform domain allows us to extract important information on the laser cavity. As one example, the amount of cavity propagation loss/gain, or net gain, can be derived from the decay rate of harmonics of the Fourier spectrum. A comparison between experimental and calculated gain versus wavelength data for lasers fabricated in the AlGaAs, AlGaInP, and AlGaInN material systems is given. As a second example, this method also allows the identification of the density and strength of intracavity scattering centers. This is an important capability for the fabrication of blue diode lasers in the gallium-nitride material system.

Semiconductor laser, semiconductor light emitting device, and methods of manufacturing the same

Abstract: There are provided a semiconductor laser, a semiconductor light emitting device, and methods of manufacturing the same wherein a threshold current density in a short wavelength semiconductor laser using a nitride compound semiconductor can be reduced. An active layer is composed of a single gain layer having a thickness of more than 3 nm, and optical guiding layers are provided between the active layer and cladding layers respectively.

Technique to compensate waveform distortion in a gain-saturated semiconductor optical amplifier using a semiconductor saturable absorber

Abstract: A technique to compensate waveform distortion induced in a gain-saturated semiconductor optical amplifier (SOA) is proposed and demonstrated. A saturable absorber, which is actually an SOA biased below the transparency current, is placed after an SOA. The loss dynamics of the absorber compensate the SOA gain dynamics and a less distorted signal can be output.

Vertical-cavity-surface-emitting semiconductor devices with fiber-coupled optical cavity

Abstract: A semiconductor light-emitting device having an optical cavity with a fiber grating. A vertical-cavity-surface-emitting laser can be constructed to produce single-mode tunable laser oscillation and signal wavelength conversion.

Mechanisms of optical gain in cubic gallium nitrite

Abstract: We report on the mechanisms of optical gain in cubic GaN. Intensity-dependent gain spectra allow a distinction of the processes involved in providing optical amplification. For moderate excitation levels, the biexciton decay is responsible for a gain structure at 3.265 eV. With increasing excitation densities, gain is observed on the high energy side of the cubic band gap due to band filling processes. For the highest pump intensities, the electron-hole plasma is the dominant gain process. Gain values up to 210 cm−1 were obtained, indicating the high potential of cubic GaN for device applications. The observed gain mechanisms are similar to those of hexagonal GaN.

Semiconductor optical device and method of manufacturing the same

Abstract: A semiconductor optical device has a gain region for oscillating a laser light beam and a spot-size conversion region for converting a spot-size of the laser light beam emitted from the gain region. Further, an optical waveguide is formed by the use of a selective growth mask along the gain region and the spot-size conversion region. With such a structure, the optical waveguide includes a waveguide taper portion and has a width and a facet. In this event, the width gradually becomes narrower towards the facet. As a result, the waveguide taper portion is tapered along a direction from the gain region towards the facet.

Low-frequency fluctuation induced by injection-current modulation in semiconductor lasers with optical feedback.

Abstract: Low-frequency fluctuations in semiconductor lasers with optical feedback are investigated when high-frequency modulation is applied to an injection current. Synchronization of the laser output power with the modulation within +/-3 MHz centered at the frequency corresponding to the external cavity mode was observed. However, for modulation of the detuned frequency from the external cavity mode, low-frequency fluctuations were induced in the laser output power, and these fluctuations were observed within a range of modulation of approximately +/-100 MHz at the center frequency of the external cavity mode.

Optical coupler optically coupling a light beam of a semiconductor laser source with a single mode optical waveguide or fiber

Abstract: A semiconductor laser and an optical waveguide of an optical coupler, formed on a substrate are optically coupled with each other by aligning their positions horizontally by using a plurality of laser elements and cores for the laser and the waveguide respectively and arranging them in an array respectively so that a difference between their pitches is less than double of tolerance tolerated for optically coupling with each other, the waveguide having partially a composite core composed of: a main core; a sub core surrounding the main core and having a refractive index lower than that of the main core; and a cladding layer surrounding the sub core and having a refractive index lower than that of the sub core.

Frequency stabilized laser and method for preparing thereof

Abstract: A frequency stabilized laser using an integrated external cavity, comprising a semiconductor laser diode and an optical waveguide installed on the same substrate, and having an optically induced grating formed in the optical waveguide suppresses mode hopping due to a temperature change to stabilize the oscillation frequencies of the laser. A material having a refractive index temperature coefficient opposite in sign to the refractive index temperature coefficient of the semiconductor laser diode is installed on that portion of the optical waveguide between the semiconductor laser diode and the optically induced grating which has been formed by removing an upper cladding and a core, or removing the upper cladding, the core, and a lower cladding.

1.1-W continuous-wave 1480-nm semiconductor lasers with distributed electrodes for mode shaping

Abstract: Diffraction-limited high-power devices may suffer from self-focusing effects due to nonuniform gain saturation. In this letter, we propose the concept of the distributed electrode, which allows one to improve the modal behavior of these lasers and to reduce spatial-hole burning effects by preferentially localizing current injection in the center of the structure, therefore shaping the optical mode. Utilizing this concept, we have realized unstable cavity lasers exhibiting single-lobe far-field patterns. We report the first realization of flared unstable cavity lasers emitting at 1480 mm with maximum output powers up to 1.1-W continuous-wave and external efficiencies as high as 0.45 W/A.

Microscopic theory of laser gain in semiconductor quantum wells

Abstract: This article reviews a microscopic theory to com- pute gain and absorption spectra of semiconductor quantum- well structures. The single-particle energies (band structure) are calculated by using Luttinger-Kohn theory in the en- velope function approximation. The Coulomb-interacting electron-hole plasma in the laser gain region is treated at the level of quantum-kinetic equations in the Markov limit. Ex- amples for results are presented for narrow- and wide-gap III-V and II-VI quantum-well systems.

Investigation of mid-infrared intersubband stimulated gain under optical pumping in GaAs/AlGaAs quantum wells

Abstract: We have investigated the mid-infrared intersubband stimulated emission under optical pumping in GaAs/AlGaAs coupled quantum wells. The quantum wells exhibit four levels bound in the conduction band. The energy between the ground and first excited subband is close to the optical phonon energy enabling population inversion. Intersubband stimulated gain between subbands E3 and E2 is observed around 14 μm wavelength by optically pumping the E1−E3 intersubband transition at 10 μm. The gain measurement is performed by time-resolved pump-probe experiments using a two-color picosecond free-electron laser. The dependence of the intersubband stimulated emission is analyzed as a function of the pump intensity, and the pump and probe wavelengths. We show that very large intersubband stimulated gain can be achieved at liquid nitrogen temperature in a 2 mm thick waveguide. The stimulated gain is resonant with the pump wavelength with a broadening ≈25 meV. The experimental results are explained with a nonperturbative ma...

Performance of a reconfigurable wavelength converter based on dual-pump-wave mixing in a semiconductor optical amplifier

Abstract: We report on a wavelength converter based on dual pump wave mixing in an 1-mm-long bulk semiconductor optical amplifier. Very high conversion efficiency (more than 0 dB) and signal-to-background-noise ratio (SBR) (16 dB), for large down- or up-wavelength shifts (30 mn) has been achieved using parallel polarized pumps with low optical power (-13 dBm). Orthogonal polarized pumps result in worse performance, having the advantage of polarization insensitivity for small wavelength spacing between them. The converter operates in a fixed input-tunable output or a tunable input-fixed output mode of operation. In each mode, the measured SBR is almost independent of the wavelength shift for either up- or down-conversion.

Optical feedback effects on the spectral linewidth of semiconductor laser sensors using self-mixing interference

Abstract: The spectral characteristics of a semiconductor laser are significantly affected by optical feedback in the active cavity of the diode. In this paper, the influence of weak optical feedback on the linewidth is examined and a new relationship proposed. Feedback-induced changes in the power spectral density are also determined by a theoretical analytical model, in good agreements with experiments. These results are then discussed for sensing applications using self-mixing interference, as the maximum range of distance and displacement sensors can be limited by half the coherence length of the laser diode modified by the optical feedback.

Fast optical amplifier gate array for WDM routing and switching applications

Abstract: Summary form only given. Recently, arrays of four clamped gain semiconductor optical amplifiers (CG-SOAs) which were fully packaged have been reported with excellent performances using bulk tensile strained active material. Here we believe we present for the first time subnanosecond switching of such a four CG-SOA array driven by integrated InP HBT drivers.

Numerical simulation of vertical cavity surface emitting lasers.

Abstract: The semiconductor laser simulator MINILASE is being extended to simulate vertical cavity surface emitting lasers (VCSELs). The electronic system analysis for VCSELs is identical to that for edge emitting lasers. A brief discussion of the capabilities of MINILASE in this domain will be presented. In order to simulate VCSELs, the optical mode solver in MINILASE must be extended to handle the reduced index guiding and significant gain guiding typical of many VCSEL structures. A new approach to solving the optical problem which employs active cavity modes rather than the standard passive cavity modes is developed. This new approach results in an integral eigenvalue equation in required gain amplitudes and corresponding modal fields. Sample results from an early implementation of a gain eigenvalue solver are shown to clarify the possibilities of this approach.

An infinite order perturbation approach to gain calculation in injection semiconductor lasers

Abstract: Nonlinear gain in injection semiconductor lasers is analyzed by applying an infinite order perturbation treatment to the density matrix analysis and taking in account the electron relaxation processes in single-mode operation. The infinitely expanded gain can be applied to future laser developments having much lower threshold current. Formulas for linear and higher orders of the expanded density matrix element and for their corresponding orders of the gain coefficient are investigated. The infinitely expanded gain is obtained in closed form which, in general, cannot be handled analytically. This closed form is simplified in the simple case of plane-wave fields and is approximated to the previously reported gain formulas within limits of perfectly homogeneous and inhomogeneous gain broadening. Numerical examples are given for the case of GaAs lasers having a specified intraband relaxation time. Based on these numerical results, simplified expressions are presented for linear and higher orders of the gain coefficient in terms of the injected carrier number. Furthermore, numerical criteria to truncate the infinite gain expansion for different higher orders are investigated based on the values of the lasing power. In the case of conventional semiconductor lasers, where the injection current is up to three times its threshold value, the third-order gain expansion corresponds to the infinitely expanded gain. However, the fifth-order expansion gives a more accurate description at higher current up to ten times the threshold. More exact gain analysis at higher ranges of the injection current requires higher orders in the gain expansion.