Showing papers on "Semiconductor optical gain published in 1985"

High-speed modulation of semiconductor lasers

Abstract: An overview is given of the direct modulation performance of high-speed semiconductor lasers. The high-speed response characteristics are described using a cascaded two-port model of the laser. This model separates the electrical parasitics from the intrinsic laser and enables these subsections to be considered separately. The presentation concentrates on the small-signal intensity modulation and frequency modulation responses, and the large-signal switching transients and chirping. Device-dependent limitations on high-speed performance are explored and circuit modeling techniques are briefly reviewed.

Density-matrix theory of semiconductor lasers with relaxation broadening model-gain and gain-suppression in semiconductor lasers

Abstract: The density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments. The dipole moment is given theoretically by the k . p method and is calculated for various semiconductor materials. As a result, gain and gain-suppression for a variety of crystals covering wide wavelength region are calculated. It is found that the linear gain is larger for longer wavelength lasers and that the gain-suppression is much larger for longer wavelength lasers, which results in that single-mode operation is more stable in long-wavelength lasers than in shorter-wavelength lasers, in good agreement with the experiments.

Analysis and application of theoretical gain curves to the design of multi-quantum-well lasers

Abstract: Gain/current curves for a single quantum well are calculated. The optimum well number, cavity length, threshold current, and current density of multi-quantum-well (MQW) lasers are derived in terms of this gain curve. The limiting performance of MQW lasers is found to be better than that of graded refractive index (GRIN) lasers, assuming comparable efficiencies and spontaneous emission linewidths. The optimum threshold current for an MQW laser with a 7 μm cavity and 90 percent facet reflectivity is \sim50 \mu A/μm.

Theoretical Gain of Quantum-Well Wire Lasers

Abstract: Gain is given theoretically for quantum-well wire lasers where electrons are confined one-dimensionally. Maximum gain is obtained for a quantum-well wire perpendicular to light propagation, due to anisotropy of the dipole moment. Although the density-of-states is infinite at subband edges, gain remains finite due to the intraband relaxation. Therefore, high gain can be obtained by reducing intraband scatterings. Gain in 100 A×100 A Ga0.47In0.53As/InP quantum-well wires is about twice that in 100 A thick conventional quantum-wells, and reduction of the laser threshold is expected.

Contribution of spontaneous emission to the linewidth of an injection-locked semiconductor laser

Abstract: We show that the spontaneous emission inside an injection-locked semiconductor laser does not alter the lasing field. For injection at the free-running frequency, the linewidth is only governed by the injected-field phase noise and may no longer follow the Schawlow-Townes dependence on emitted optical power.

High-speed modulation of semiconductor lasers

Abstract: An overview is given of the direct modulation performance of high-speed semiconductor lasers, The high-speed response characteristics are described using a cascaded two-port model of the laser. This model separates the electrical parasitics from the intrinsic laser and enables these subsections to be considered separately. The presentation concentrates on the small-signal intensity modulation and frequency modulation responses, and the large-signal switching transients and chirping. Device-dependent limitations on high-speed performance are explored and circuit modeling techniques are briefly reviewed.

Ultra-high speed semiconductor lasers

Abstract: Recent progress on semiconductor lasers having avery high direct modulation bandwidth of beyond 10GHz will be desribed. Issues related to application of these lasers in actual systems will be addressed. Possibilities of further extending the bandwidth of semiconductor lasers will be examined.

Etched-mirror unstable-resonator semiconductor lasers

Abstract: The operation and performance of the first etched-mirror high-loss (ray unstable) semiconductor diode lasers are reported and discussed. This is an alternate approach to conventional plane-parallel stripe geometry diode lasers or monolithic laser arrays for obtaining improved mode control and higher power.

Mode-hopping noise in index-guided semiconductor lasers and its reduction by saturable absorbers

Abstract: Mode-hopping noise in index-guided semiconductor lasers is investigated. It is found that random switching between lasing modes and output power differences in those modes cause mode-hopping noise. An effective method to suppress such mode-hopping noise is proposed. High Te doping to an n-type GaAlAs cladding layer completely suppresses the noise. Te in GaAlAs forms a DX center that acts as a saturable absorber. This property stabilizes the laser mode and prevents mode competition. The minimum loss difference between lasing and nonlasing modes to suppress mode-hopping noise is also discussed.

Tailored-gain broad-area semiconductor laser with single-lobed diffraction-limited far-field pattern

Abstract: We demonstrate a 60 μm-wide asymmetric tailored-gain broad-area semiconductor laser with a single-lobed diffraction-limited far-field pattern 2.5° wide. The method used to achieve gain tailoring may be used to create nearly arbitrary two-dimensional spatial gain distributions within a broad-area laser.

Effect of nonlinear gain on the bandwidth of semiconductor lasers

Abstract: The effect of nonlinear gain on the frequency response of semiconductor lasers at high bias powers is analysed using the multimode rate equations. In spite of the strong damping of the relaxation oscillations due to nonlinear gain, bandwidths of over 40 GHz appear to be attainable in semiconductor lasers.

Optical coupling system with intermediate coupling medium

Abstract: An optical coupling system between a semiconductor laser and an optical fiber is disclosed. The system is characterized in that a medium having a refractive index greater than 1 but smaller than the refractive index of the semiconductor laser material is packed between the end surface of a distributed feedback type or distributed Bragg reflector type semiconductor laser and the end surface of an optical fiber.

Criteria for design of single-lobe phased-array diode lasers

Abstract: We present design criteria for real-refractive-index phased-array semiconductor diode lasers which radiate in a single narrow far-field lobe. An example of such an array is included.

Digital optical signal processing with polarization-bistable semiconductor lasers

Abstract: The operations of a complete set of optical AND, NAND, OR, and NOR gates and clocked optical S-R, D, J-K, and T flip-flops are demonstrated, based on direct polarization switching and polarization bistability, which we have recently observed in InGaAsP/InP semiconductor lasers. By operating the laser in the direct-polarization-switchable mode, the output of the laser can be directly switched between the TM 00 and TE 00 modes with high extinction ratios by changing the injection-current level, and optical logic gates are constructed with two optoelectronic switches or photodetectors. In the polarization-bistable mode, the laser exhibits controllable hysteresis loops in the polarization-resolved power versus current characteristics. When the laser is biased in the middle of hysteresis loop, the light output can be switched between the two polarization states by injection of short electrical or optical pulses, and clocked optical flip-flops are constructed with a few optoelectronic switches and/or photodetectors. The 1 and 0 states of these devices are defined through polarization changes of the laser and direct complement functions are obtainable from the TE and TM output signals from the same laser. Switching of the polarization-bistable lasers with fast-rising current pulses has an instrument-limited mode-switching time on the order of 1 ns. With fast optoelectronic switches and/or fast photodetectors, the overall switching speed of the logic gates and flip-flops is limited by the polarization-bistable laser to < 1 ns. We have demonstrated the operations of these devices using optical signals generated by semiconductor lasers. The proposed schemes of our devices are compatible with monolithic integration based on current fabrication technology and are applicable to other types of bistable semiconductor lasers.

Fundamental lateral mode oscillation via gain tailoring in broad area semiconductor lasers

Abstract: We show that by employing gain tailoring in a broad area semiconductor laser we achieve fundamental lateral mode operation with a diffraction‐limited single‐lobed far‐field pattern. We demonstrate a tailored gain broad area laser 60 μm wide which emits 450 mW per mirror into a stable, single‐lobed far‐field pattern 3 1/2° wide at 5.3 Ith.

Dynamic line broadening of semiconductor lasers modulated at high frequencies

Abstract: Directly modulated semiconductor lasers show a pronounced linewidth broadening. A general and simple expression for this broadening is derived and the consequences for optical communication systems are discussed.

Semiconductor laser and optical amplifier

Abstract: A semiconductor source of high power, spatially and temporally coherent light including means to prevent damage to the output face. A laser diode is disposed in optical contact with a power amplifier having a diverging active area which causes emitted light to be distributed over a large facet area.

Lasers and non-linear optics

Abstract: Einstein's Quantum Theory of Radiation Interaction of Radiation with Matter Masers Theory of Some Simple Optical Processes Basic Principles of Lasers Solid State Lasers Gas Lasers Semiconductor Lasers Liquid-, Dye- and Chemical Lasers Dynamics of the Laser Processes and Advances in Laser Physics Holography Non-Linear Optics Multiphoton Processes Laser Spectroscopy Some Laser Induced Phenomena Applications of Lasers Appendices References Index.

Analysis of the dynamic response of multielement semiconductor lasers

Abstract: We present a derivation of the dynamic response of a semiconductor laser consisting of more than one active element. We show that the amplitude and phase of the modulated cavity adiabatically follows the complex resonance of the composite cavity; and using this relation, plus linearized carrier equations, we calculate the parameters characterizing the modulation response of the composite system. In the process, "effective" differential gain constants and linewidth enhancement factors arise which take the place of the corresponding parameters in single-element lasers. In the case of a two-section laser, we show that frequency chirping under modulation is present except under special conditions; we identify those conditions and show how chirping can be avoided.

A Highly Stabilized Semiconductor Laser and Its Application to Optically Pumped Rb Atomic Clock

Abstract: Frequency stability of 1 x 1 0-1 at T = 100 S was obtained for 0.8 u m AlGaAs laser by using spectral lines of Rb vapor as frequency references. It was confirmed that this value of the stability was as high as the value limited by spontaneous emission noise. Through an analysis based on a semiclassical Langevints equation, it was estimated that the stability can be improved to as high as reduction was also tried to improve the coherence of the semiconductor laser. A novel technique, i.e., electrical feedback, was proposed for this reduction instead of using a conventional technique of optical feedback. The linewidth was stably reduced by this technique. The minimum value obtained was 330 kHz for an InGaAsP laser at 1.5 p m, which was fifteen times narrower than that of a free-running laser. It was estimated that the linewidth can be ultimatelyreducedtoa value less than 1 kHz by this technique. Experiments on optical pumping for Rb atomic clock were carried out by using the highly stabilized semiconductor laser mentioned above. As the first step, experiments on saturated absorption spectroscopy of 87Rb D2 lines were carried out. Eleven lines, including cross-resonance lines, were clearly observed. As the next step, double resonance signal was obtained by laser optical pumping. The microwave frequency shift by the laser frequency and power were measured. The microwave frequency stability was also evaluated. Furthermore, a comment on the spectral lifetime of semiconductor laser for Rb atomic clock was given. 1.7 x 10-14 -112. Spectral linewidth

Bit-error-rate saturation due to mode-partition noise induced by optical feedback in 1.5-&#181;m single longitudinal-mode C 3 and DFB semiconductor lasers

Abstract: We report first measurements of the effect of optical feedback on the bit error rate (BER) as a function of received power of single longitudinal mode cleaved-coupled cavity (C3) and distributed-feedback (DFB) semiconductor lasers. Mode-partition noise, induced by the optical feedback, can cause a bit error-rate floor for large optical feedbacks, but it is shown that high-performance C3lasers and especially DFB lasers can withstand very large optical feedbacks without system degradation.

Narrow-band laser transmitter

Abstract: A narrow band laser transmitter comprising a semiconductor laser and an external optical resonator coupled by a coupling arrangement to the semiconductor laser characterized by the external optical resonator being a wavelength-selective fiber directional coupler in the form of a double core fiber whose cores have different refractive index discontinuities to the respective environments and different cross-sections. The laser transmitter is suitable for practical use, has a space-saving structure and is stable in operation.

Role of Petermann's K-factor in semiconductor laser oscillators

Abstract: The theory presented indicates that when the active region of a semiconductor laser is very thin the linewidth enhancement factor differs significantly from Henry's 1 + ?2 factor and can be reduced by a factor of 4. Petermann's K-factor may also play a role in the plane perpendicular to the junction.

A Proposed Receiver Structure for Optical Communication Systems that Employ Heterodyne Detection and a Semiconductor Laser as a Local Oscillator

Abstract: Coherent heterodyne detection in optical communication is degraded by phase instabilities present when a semiconductor laser is used as a local oscillator. Postdetection processing that accounts for these instabilities is suggested, based on a diffusion-process model for oscillator instabilities and a maximum-likelihood sequence-estimator of information symbols modulating the received light.

Light emitting chip and optical communication apparatus using the same

Abstract: This invention relates to a semiconductor laser of a buried-hetero structure. In this semiconductor laser, the side surfaces of an active layer are in contact with a plane having a stable state of interface. As a result, the threshold current value of this semiconductor laser is low, and a stable operation can be obtained without causing any kink (projection ) in the current-optical output characteristics. An optical communication system using this semiconductor layer has a low operating current, and can maintain high coupling efficiency with an optical fiber without the occurrence of noise, so that optical communication having high reliability is possible.

Single-longitudinal-mode condition for DFB lasers

Abstract: We show theoretically that the loss difference of about 10% is required between the main mode and the side mode for a semiconductor laser to oscillate in single-longitudinal mode. The DFB laser has been found to meet this requirement, and a side-mode suppression of more than 30 dB was observed under high-speed direct modulation.

Improved high-power twin-channel laser with blocking layer

Abstract: We present an improved version of the twin-channel laser as a prototype for a new concept in semiconductor laser array structures with a well controlled far-field beam pattern. The laser device constitutes the first CW semiconductor laser array structure on a p-type GaAs substrate using current-blocking layers and yields improved current utilisation and efficiency over previous structures.

Measured spectral linewidth of variable-gap cleaved-coupled-cavity lasers

Abstract: A variable-airgap 1.3 μm C3 semiconductor laser with the gap width set for optimum mode-suppression ratio (5000:1) has been used to achieve a measured linewidth of only 1 MHz at 3 mW power output and 250 kHz at 10 mW.

Semiconductor laser for a high optical output power with reduced mirror heating

Abstract: The semiconductor laser, which can be either electrically or optically pumped, characterized by quantum well structure for the body and by having a distance of the respective mirror structures from the end of the laser active zone which is dimensioned within tight limits. The structure provides a semiconductor laser in which problems with destruction or aging of the reflective properties of the mirror structure due to heating are reduced.