Showing papers on "Semiconductor optical gain published in 1989"

Self-phase modulation and spectral broadening of optical pulses in semiconductor laser amplifiers

Abstract: Amplification of ultrashort optical pulses in semiconductor laser amplifiers is shown to result in considerable spectral broadening and distortion as a result of the nonlinear phenomenon of self-phase modulation (SPM). The physical mechanism behind SPM is gain saturation, which leads to intensity-dependent changes in the refractive index in response to variations in the carrier density. The effect of the shape and the initial frequency chirp of input pulses on the shape and the spectrum of amplified pulses is discussed in detail. Particular attention is paid to the case in which the input pulsewidth is comparable to the carrier lifetime so that the saturated gain has time to recover partially before the trailing edge of the pulse arrives. The experimental results, performed by using picosecond input pulses from a 1.52- mu m mode-locked semiconductor laser, are in agreement with the theory. When the amplified pulse is passed through a fiber, it is initially compressed because of the frequency chirp imposed on it by the amplifier. This feature can be used to compensate for fiber dispersion in optical communication systems. >

Resonant periodic gain surface-emitting semiconductor lasers

Abstract: A surface-emitting semiconductor laser structure with a vertical cavity, extremely short gain medium length, and enhanced gain at a specific design wavelength is described. The active region consists of a series of quantum wells spaced at one half the wavelength of a particular optical transition in the quantum wells. This special periodicity allows the antinodes of the standing-wave optical field to coincide with the gain elements, enhancing the frequency selectivity, increasing the gain in the vertical direction by a factor of two compared to a uniform medium or a nonresonant multiple quantum well, and substantially reducing amplified spontaneous emission. Optically pumped lasing was achieved in a GaAs/AlGaAs structure grown by molecular-beam epitaxy, with what is believed to be the shortest gain medium (310 nm) ever reported. >

Wavelength-tunable optical filters: applications and technologies

Abstract: The authors review noncoherent, frequency-tunable filter (receiver) technologies. They describe three basic mechanisms of wavelength filtering: filters that are based on the wavelength dependence of interferometric phenomena, with emphasis on Fabry-Perot interferometer filters; filters that are based on the wavelength dependence of coupling between optical fields (modes) induced by external perturbations (both acoustooptic and electrooptic filters are described); and filters that are based on resonant amplification of optical signals in semiconductor laser diode devices (these devices provide gain in addition to wavelength selectivity). For each technology the authors explain briefly the principles of operation and quantify the relevant system parameters: tuning range, channel separation, number of channels, crosstalk isolation, gain and distortion, speed of wavelength tuning, and complexity. They present a unified picture of filtering mechanisms in an appendix. >

Picosecond Electronics and Optoelectronics

Abstract: This book presents papers on semiconductor lasers. Topics considered include a mode-locked laser with a single-mode fiber output, a fast multiple quantum well absorber for mode locking, the suppression of timing and energy fluctuations in a mode-locked semiconductor laser by cw injection, and parametric oscillations in semiconductor lasers.

The optical gain lever: A novel gain mechanism in the direct modulation of quantum well semiconductor lasers

Abstract: A new gain mechanism active in certain quantum well laser diode structures is demonstrated and explained theoretically. It enhances the modulation amplitude produced by either optical or electrical modulation of quantum well structures. In the devices tested, power gains of 6 dB were measured from low frequency to frequencies of several gigahertz. Higher gains may be possible in optimized structures.

Analysis of the noise spectra of a laser diode with optical feedback from a high-finesse resonator

Abstract: Noise spectra of a semiconductor laser with and without optical feedback from an external high-finesse resonator are calculated. Even very small amounts of optical feedback significantly reduce the low-frequency noise power, but the reduction depends on the source of the noise. The effect of various parameters on the noise reduction and on the stability of single-mode operation of the laser are determined, and the results are compared to recent experimental measurements. The results provide guidelines for the design of practical systems for achieving narrow emission linewidths and avoiding instability. The theoretical results show that a semiconductor laser with optical feedback functions as a laser with an optical servoloop and can be considered a self-injection-locked laser. >

Optical integrated circuit and optical apparatus

Abstract: An optical integrated circuit and an optical apparatus used in optical communication or an opto-electronics apparatus such as an optical disk recording apparatus, in which various kinds of aberration caused by wavelength variation of a light source when a semiconductor laser is used as the light source. An aberration correcting grating having such grating pitches as to nearly satisfy the Bragg condition preferably with respect to a certain wavelength of the semiconductor laser beam is used. As a result, lowering of incidence (entrance) and radiation (exit) coupling efficiencies of the grating coupler and aberration such as chromatic aberration can be prevented. Even if a multi-mode semiconductor laser is used as a light source, the characteristics of the optical integrated circuit and optical apparatus do not vary largely.

Spectral properties of the coherence collapsed state of a semiconductor laser with delayed optical feedback

Abstract: A theoretical analysis of the coherence collapsed state for a single-mode semiconductor laser with a moderate amount of delayed optical feedback that is operating well above threshold is presented. Both phase fluctuations and the amplitude fluctuations satisfy a bivariate Gaussian distribution. The autocorrelation properties are determined self-consistently from the rate equations. The asymmetry of the optical power spectrum is discussed. >

Improved rate equations for external cavity semiconductor lasers

Abstract: A set of improved Langevin rate equations for external-cavity semiconductor lasers which can be used to solve transient as well as steady-state problems is derived. A simple relationship among chirp reduction, line narrowing and dynamic stability is given. An experiment on an external-coupled-cavity semiconductor laser consisting of a 1.3- mu m buried-heterostructure laser diode with an antireflection (AR)-coated facet and a 4-mm GRIN rod is reported. Because of its strong optical feedback, it provides a stable single mode, which is not sensitive to the environmental perturbations. This agrees with the theoretical results. No mode jumping occurred during 12 h continuous observation. >

High power diode-pumped solid state laser with unstable resonator

Abstract: A large number of semiconductor laser sources coupled with tapered fibers provide a high energy density output for the purpose of longitudinal pumping of a solid state gain medium in an unstable resonator. Each semiconductor laser source generates a beam of radiation at the pump wavelength having characteristic lateral and transverse widths. A plurality of light transmitting fibers, each fiber having an input end and an output end, is coupled with the semiconductor laser sources for delivering the light from a remote location to pump the gain medium. The input end of each fiber has a cross-section substantially matching the transverse and lateral widths of the beams generated by the corresponding semiconductor laser source, and is coupled to receive the beam of radiation generated by a corresponding semiconductor laser source. The output ends of the light transmitting fibers are bundled to deliver the beams coupled into the fibers as a composite light source having a high energy density. Hundreds of watts of pump energy can be delivered to an unstable resonator design with a solid state gain medium from a remotely mounted and cooled array of semiconductor lasers.

Semmiconductor laser array including lasers with reflecting means having different wavelength selection properties

Abstract: Disclosed is a semiconductor laser array including a plurality of semiconductor lasers each having an active layer having a quantum well structure with at least two quantum levels. The semiconductor lasers have reflecting means having different wavelength selection properties.

Noise in nearly-single-mode semiconductor lasers.

Abstract: We report the results of a numerical study of nearly-single-mode semiconductor lasers. The stochastic nonlinear dynamical equations of the field and population inversion are integrated and the intensity fluctuations and line shapes of the laser are investigated. The second mode affects the coherence of the light output appreciably, particularly near the laser threshold regime. The accuracy of the linearized theory for a single-mode laser is tested from far below to far above threshold. It is found to be very accurate both far below and far above threshold, but significant discrepancies are seen in the threshold region. We automatically include the coupling of the intensity and phase fluctuations in the line-shape calculations, resulting in the experimentally observed asymmetry of the relaxation oscillation sidebands. The numerical technique developed here is easily applicable to multimode lasers and is shown to be a convenient and powerful probe of the coherence properties of semiconductor lasers.

Semiconductor laser array having high power and high beam quality

Abstract: A semiconductor laser array with features providing good beam quality at high powers, first by employing a laterally unguided diffraction region in which light from a set of waveguides is re-imaged in accordance with the Talbot effect and two arrays of waveguides may be used to provide a spatial filtering effect to select a desired array mode. This provides a laser array with increased power per unit solid angle, and with additional advantages of ability to scale the device up to larger arrays, ability to control the electrical excitation of the device for better optimization, and improved modal discrimination. A second aspect of the invention is the use of a resonance condition in an antiguide array, to produce a uniform near-field intensity pattern and improved coupling and device coherence. This resonance structure may be combined with the Talbot-effect structure to suppress the out-of-phase mode, or the out-of-phase mode may be suppressed by other means, such as by introducing interelement radiation losses or absorption losses in the antiguide array.

Many-body effects in gain and refractive-index spectra of bulk and quantum-well semiconductor lasers

Abstract: Gain and refractive-index spectra for bulk and quantum-well semiconductor lasers are computed using quantum-mechanical many-body theory The results clearly show the influence of band-gap renormalization, broadening, and Coulomb enhancement on the gain, the absorption, and the refractive-index spectra

Broadband tunability of gain‐flattened quantum well semiconductor lasers with an external grating

Abstract: Quantum well lasers are shown to exhibit flattened broadband gain spectra at a particular pumping condition. The gain requirement for a grating-tuned external cavity configuration is examined and applied to a semiconductor quantum well laser with an optimized length of gain region. The predicted very broadband tunability of quantum well lasers is confirmed experimentally by grating-tuning of uncoated lasers over 85 nm, with single longitudinal mode output power exceeding 200 mW.

Phase-locked array of semiconductor lasers using closely spaced antiguides

Abstract: A semiconductor laser diode array in which the lasing elements are formed as parallel negative-index waveguides, to provide operation at higher powers and in one of two stable array modes. Lasing in interelement regions, between the lasing elements, is suppressed by the inherently low transverse optical confinement factor provided by high-index semiconductor material in the interelement regions, and may be further suppressed by the use of an active layer that extends only through the lasing elements and not through the interelement regions. A desired array mode may be selected by the use of a structure favoring 0°-phase-shift array modes, such as a wide-waveguide interferometric structure. Both liquid-phase epitaxy (LPE) and metalorganic chemical vapor deposition (MOCVD) processes may be used in fabrication of the device.

Quantum well semiconductor lasers are taking over

Abstract: The author describes the principles and performance of semiconductor quantum-well lasers, which are characterized by confinement of the electrons and holes to extremely thin ( approximately 70 AA) regions. This leads to major improvement in all the operating characteristics of these lasers compared to conventional semiconductor lasers, specifically, to a reduction of more than an order of magnitude in threshold current and a much narrower spectral width. >

Semiconductor laser amplifier optimization: an analytical and experimental study

Abstract: Long-wavelength semiconductor laser amplifiers are investigated with respect to spectral gain properties such as peak gain wavelength shift and width of gain curve, employing different structural parameters such as thickness of the active layer and amplifier length. The model takes into account Auger recombination, thermal effects, and spontaneous emission. It is shown that there exists an optimum thickness of the active layer with respect to current density for a given gain and that increased length of the amplifier allows higher gains and reduced variation of peak gain wavelength with respect to variation of peak gain at the expense of increased saturation by amplified spontaneous emission and increased excess noise. An experimental verification of the theoretical model is reported. >

Observation of positive and negative nonlinear gain in an optical injection experiment: Proof of the cavity standing‐wave‐induced nonlinear gain theory in 1.3 μm wavelength semiconductor diode lasers

Abstract: The origin of nonlinear gain in 1.3 μm InGaAsP semiconductor diode lasers is studied by measuring the magnitude and phase of a probe laser’s frequency response to optical injection with orthogonally polarized light from a pump laser. The sign and magnitude of the gain nonlinearity induced by optical injection depend on wavelength separation between pump and probe laser. The maximum magnitude of the nonlinear gain parameter is about 1.5×10−15 cm2. These results are consistent with the recently proposed theory that nonlinear gain is caused by the feedback from the dielectric grating induced by the standing wave in the laser cavity.

Modulation method for use in a semiconductor laser and an apparatus therefor

Abstract: A method of modulating a semiconductor laser, a method of stabilizing a self-homodyne optical interferometer and a light modulation apparatus using a semiconductor laser is provided for use, for example, in various optical communication systems. To avoid the adverse affect on a semiconductor laser of wavelength chirping and to facilitate high-speed direct modulation, a predetermined short pulse current is superimposed on a bias current to drive a semiconductor laser, thereby phase-modulating the output light at a high speed, eliminating the phase deviation at the output of the light interferometer of the self-homodyne-type and achieving a stable output from the semiconductor laser. The average intensity of the output light is obtained, thereby applying a feedback to a wavelength of the input light or to a difference in an optical path length of the optical interferometer itself in accordance with the average intensity of the output light in order to correct the phase bias when modulating the intensity. To perform a high-speed stable phase intensity modulation, transmission data is subject to sign conversion in accordance with a predetermined rule and thereafter is subject to differentiation. The differentiated signal is superimposed on a constant bias current as a modulating current pulse to drive a semiconductor laser, and the output thereof is intensity-modulated through the self-homodyne optical interferometer.

Compound cavity modes in semiconductor lasers with asymmetric optical feedback

Abstract: We describe a static model for determining the oscillating modes of an external cavity semiconductor laser with asymmetric feedback induced by external mirror misalignment. The most significant prediction of this model, the existence of double loss minima leading to compound cavity mode splitting, has been confirmed directly by spectral measurements. This result is important for analyzing complex dynamical phenomena in semiconductor lasers with optical feedback.

Amplitude noise reduction in atomic and semiconductor lasers.

Abstract: The quantum noise properties of atomic and semiconductor lasers are compared. The intensity fluctuation spectrum of the output field is calculated for the case of regularly, i.e., sub-Poissonian, pumped lasers. The effects of spontaneous emission on the output amplitude fluctuations may be suppressed in regularly pumped atomic lasers by requiring the lifetime of the lower lasing level to be short in comparison with that of the upper laser level. The output amplitude fluctuations then tend to zero at the laser frequency. In regularly pumped semiconductor lasers, net stimulated emission of photons dominates over spontaneous emission because of the combination of pumping and rapid intraband thermalization due to Coulomb scattering.

Semiconductor laser optical amplifiers for multichannel coherent optical transmission

Abstract: The application of semiconductor laser optical amplifiers in multichannel coherent optical transmission systems is investigated. The amplifiers considered ( lambda =1.3 mu m) exhibit a gain of 24 dB at a grain ripple >

Gain and noise characteristics of a 1.5 μm near-travelling-wave semiconductor laser amplifier

Abstract: The spectral dependence of the gain and noise characteristics of a gas source molecular beam epitaxy (GSMBE)-grown BH-GaInAsP near-travelling-wave semiconductor laser amplifier are presented, from which an indication of nonresonant internal losses is given. An intrinsic noise figure of 6 dB at an internal gain of 28 dB is obtained.

Semiconductor laser optical amplifiers in switching and distribution networks

Abstract: Applications of semiconductor laser optical amplifiers in coherent multichannel systems are investigated with respect to the switching and distribution of many channels to a large number of customers. All-optical switching of data signals is achieved with the optical amplifier operating as a frequency converter. Measurements of the conversion efficiency and a transmission experiment with a 1500 GHz conversion range are described. Possible applications are all-optical ‘multipoint to point’ and ‘point to multipoint’ switching. Optical amplifiers may also be useful in multichannel distribution networks to compensate for combining and splitting losses. We discuss an example demonstrating how optical amplifiers increase the number of customers in a coherent multichannel distribution system.

Tunable active chirped‐corrugation waveguide filters

Abstract: A novel tunable semiconductor waveguide reflection filter is proposed and analyzed. The filter is based on spatially selective gain pumping of a chirped‐corrugation waveguide. This active chirped‐corrugation waveguide filter (ACF) is considered for monolithic broadband tuning of semiconductor lasers.

Nonlinear optical diagnostics of laser-excited semiconductor surfaces

Abstract: The effect of pulsed laser annealing of ion-implanted semiconductors was discovered in the late 1970's. As a result researchers concentrated on the fundamental problems related to the absorption of laser radiation localized in time and space and at the possible application of lasers to microelectronics. Experiments on laser annealing have raised a series of fundamental questions, including the role of dense electron-hole plasmas in fast melting semiconductors, the stages of the melting process and the mechanism of laser-induced amorphization. To answer these questions, which are only a small part of the full range of problems, it is vitally important to develop experimental techniques for the diagnostics of semiconductor surfaces and phase transitions. This book analyzes the current concepts of laser beam interaction with semiconductors and the potential of using optical methods in diagnostics. Also discussed is the new information which may come from optical techniques on the structure of semiconductor crystal surfaces and phase transitions.

Use of tilted-superlattices for quantum-well-wire lasers

Abstract: Summary form only given. Lasers with quantum-well-wire (QWW) active regions have been demonstrated using tilted-superlattice (TSL) structures with lateral dimensions in the low nanometer range. They are formed directly by molecular-beam epitaxy (MBE) without sophisticated lithography technologies. Separate-confinement-heterostructure lasers having TSL-QWWs as active regions were fabricated. The TSL-QWWs consist of a 5-nm GaAs layer and a 5-nm (AlGaAs(x=0.25)-GaAs) TSL layer which are sandwiched by AlGaAs(x=0.25) waveguide and AlGaAs (x=0.5) cladding layers. Threshold current densities as low as 460 A/cm/sup 2/ and differential quantum efficiencies of 29% per facet were obtained in a laser thus fabricated with a long cavity (1120 mu m) at room temperature. The lasing wavelength was 827 nm, which corresponds to the QWW state energy. >

Novel measurement method of linewidth enhancement factor in semiconductor lasers by optical self-locking

Abstract: We propose a simple, accurate and novel method to measure the value of the linewidth enhancement factor in semiconductor lasers. It utilises the asymmetry of the frequency locking range of a semiconductor laser with the optical feedback from the external CFP cavity. The measured value for a 0.8μm CSP-type AlGaAs laser was 3.07±0.26, which showed good agreement with those measured by other conventional methods.