Showing papers on "Semiconductor optical gain published in 1983"

High‐speed direct single‐frequency modulation with large tuning rate and frequency excursion in cleaved‐coupled‐cavity semiconductor lasers

Abstract: We report a new mechanism of direct frequency modulation, the cavity‐mode enhanced frequency modulation (CME‐FM), using the newly developed cleaved‐coupled‐cavity (C3) semiconductor laser. In this operation, one of the diode of the C3 laser was operated as a laser, while the other diode was operated as a frequency modulator. It was shown that a very large frequency excursion of 150 A and frequency tuning rate of 10 A/mA have been obtained with a C3 GaInAsP crescent laser operating at 1.3 μm. Time‐resolved spectral and spectral‐resolved pulse response measurements also showed that such C3 lasers operated in highly stable single‐longitudinal mode at all times even under high‐speed direct frequency modulation. In addition to the important application as the optical source in FM optical communication systems, the present CME‐FM C3 laser can also be used as the optical source in wavelength‐division multiplexing systems. Further, it opens the possibility of ultrahigh capacity multilevel optical FM information t...

Measurement of the linewidth enhancement factor α of semiconductor lasers

Abstract: A theory of the amplitude and phase modulation characteristic of a single mode semiconductor laser is presented. In this model the amplitude modulation couples through the complex susceptibility of the gain medium to the phase. We show that this coupling constant can be obtained by a high‐frequency modulation experiment. This measured coupling constant is used to infer the linewidth enhancement factor α as discussed by Henry, and Vahala and Yariv. Experiments confirmed the model and we measured a linewidth enhancement factor ‖α‖=4.6±1.0 for a GaAlAs buried optical guide laser.

Circuit modeling of the effect of diffusion on damping in a narrow-stripe semiconductor laser

Abstract: This paper describes a circuit modeling technique for directly modulated narrow-stripe semiconductor lasers with strong carrier confinement and index guiding It is shown that diffusion damping of the modulation response, due to a nonuniform electron density distribution in the active layer, can be accounted for in terms of an equivalent optical gain saturation Based on this equivalence, a small-signal ac circuit model of a narrow-stripe laser is derived The model can be used to determine the intensity modulation and frequency modulation response characteristics of a packaged device

On the linewidth enhancement factor α in semiconductor injection lasers

Abstract: A simple model for the linewidth enhancement factor α and its frequency dependence in semiconductor lasers is presented. Calculations based on this model are in reasonable agreement with experimental results.

Semiconductor laser linewidth in optical feedback configurations

Abstract: We present a theoretical analysis for semiconductor laser linewidth, employing optical feedback. This analysis is valid not only for weak feedback, but also for strong feedback including multiple reflections. The experimental result reported so far under a strong feedback condition is well explained.

Optical bistability and nonlinear resonance in a resonant-type semiconductor laser amplifier

Abstract: We report here on the first observation of hysteresis in the asymmetrical tuning curve of a semiconductor laser operating as a resonant-type amplifier. This bistable amplification resulting from a nonlinear resonance phenomenon is caused by the dependence of the refractive index on the injected carrier density.

Optical Bistability in a Semiconductor Laser Amplifier

Abstract: Optical bistability has been observed in a semiconductor laser operating as an amplifier. The bistability arises from the refractive index change due to a decrease in the active-region carrier density accompanied by optical amplification. Output pulsations due to the competition between the free-carrier and thermal effects have also been observed.

Frequency stabilization of lasers

Abstract: Apparatus including a semiconductor laser source and means for stabilizing the frequency of the laser. A feedback signal is provided by means such as a Fabry-Perot interferometer, which signal is coupled simultaneously to two feedback loops. One loop provides high frequency control of the drive current while the other loop provides low frequency control of the laser temperature.

Quantum Mechanical Size Effect Modulation Light Sources– A New Field Effect Semiconductor Laser or Light Emitting Device

Abstract: A new field effect semiconductor laser or light emitting device is proposed and analysed, in which the photon emission rate is modulated by the gate voltage mainly through changes in spatial distributions of the carriers. The switching speed in the device is expected to be free from recombination lifetime limitation in specific operation modes.

Picosecond optical pulse generation by impulse train current modulation of a semiconductor laser

Abstract: Optical pulses of less than 10‐ps duration have been generated by driving a GaAlAs laser with a train of 80‐ps full width at half‐maximum current impulses and a 20‐ns pulsed square wave bias.

Progress of coherent optical fibre communication systems

Abstract: The recent progress of coherent optical fibre communication systems is reviewed. System constituent technologies, such as coherent optical modulation-demodulation, optical direct amplification for repeaters and single polarization fibre transmission are outlined. Several important optical device technologies, such as frequency stabilization of semiconductor lasers, AM and FM quantum noise and their reduction, and integrated opto-electronic devices, are also described. Finally, on the basis of the current state of the art in these technological areas, the expected system performance and future problems are discussed.

Direct gain modulation of a semiconductor laser by a GaAs picosecond optoelectronic switch

Abstract: We report a novel application of high‐speed optoelectronic switches for direct gain modulation of semiconductor lasers. A GaAs/GaAlAs buried heterostructure laser is driven by a Cr‐doped GaAs photoconducting switch activated by a synchronously mode‐locked cw dye laser. Infrared light pulses of 55‐ps width are emitted from the semiconductor laser.

Modulation detuning characteristics of actively mode-locked diode lasers

Abstract: Existing frequency domain models for the active mode locking of diode lasers are appropriate for antireflection- (AR-) coated devices This paper presents the first frequency domain model for non-AR-coated devices The use of uncoated devices permits the independent measurement of all of the important laser parameters required for the model, so that no adjustable parameters are needed An additional novel feature of this model is that the effect of gain saturation on the exact shape of the gain waveform is allowed for in a completely self-consistent fashion Experimental studies were carried out on uncoated undegraded commerical laser diodes Threshold reductions of 25-30 percent were achieved for external cavity operation The mode-locking studies reported in this paper were carried out above the external threshold current, with a sinusoidal modulation near 1 GHz at a modulation index of 4 percent The results of these studies showed good agreement with the predictions of the model presented here, in contrast with the predictions of the existing models Specifically, the modulation frequency corresponding to the shortest most intense mode-locked pulses was found to occur at a fraction of 1 percent below the frequency matched to the external cavity roundtrip time As well, the predicted effects of gain saturation were observed in the detailed structure of the mode-locked pulses, and in their detuning characteristics

Stabilized biasing of semiconductor lasers

Abstract: In this paper we analyze the design of biasing and control circuits for semiconductor lasers in a generalized context based on an idealized laser characteristic. In particular, we address three major design considerations: whether to bias the laser above or below threshold, how to stabilize the optical output levels independent of variation in the average output power, and to what degree the output levels can be stabilized relative to various circuit and device parameters. Results of our study indicate that to eliminate from the optical output any dependence on either variation in laser device characteristics or the dc average of the input signal, feedback control of both the prebias and modulation current is necessary.

Gain spectra of quantum-well lasers

Abstract: The gain spectrum and its sensitivity to carrier density is calculated for a model quantum-well heterostructure semiconductor laser for a range of quantum-well widths. The gain spectra, especially for narrow wells, show better mode-to-mode gain discrimination than for the equivalent bulk laser. Good carrier confinement helps obtain this desirable feature.

Optoelectronic logic operations by cleaved-coupled-cavity semiconductor lasers

Abstract: We propose and demonstrate the operation of a new opto-electronic scheme of performing the set of logic operations including AND, OR, EXCLUSIVE OR, and INVERTER. The present scheme is not based on optical bistability, but rather utilizes the unique characteristics of the newly developed cleaved-coupled-cavity (C3) semiconductor laser. The C3laser always operates in a single longitudinal mode and the lasing wavelength can be tuned by varying the current levels (pulsed or dc) injected into the two optically coupled stripe-geometry laser diodes. Unlike the case of optical bistable devices (based on FP semiconductor diodes), which operate on optical inputs and produce optical outputs, the present device operates on electrical inputs and produces optical outputs. In addition to performing the logic operations, this can also serve as an electrical-optical interface. Further, the present scheme is also capable of producing multiple different logic outputs simultaneously for the same two inputs. Results from time-resolved spectral measurements using InGaAsP buried crescent lasers ( \lambda = 1.3 \mu m) showed that the switching time was in the subnanosecond region. This indicates that extremely high bit rate information processing in the Gbit/s range can be achieved by using the present C3semiconductor lasers as the logic gates. The present C3lasers are very compact ( \sim300 \times \sim200 \mu m) and rigid, and the scheme can be applied to semiconductor lasers with other types of stripe geometries and wavelengths.

Emission frequency stability in single-mode-fibre optical feedback controlled semiconductor lasers

Abstract: A newly designed semiconductor laser emitter with adjustable linewidth by controlling the coupling to a single-mode fibre is described with emphasis on thermal requirements to obtain a high-frequency stability. A stable operation has been achieved during more than 1 h using an AlGaAs laser diode with optical feedback from a 50 cm-long single-mode fibre resulting in a 50-fold reduction of the spectral linewidth.

Magneto-optic information storage system utilizing a self-coupled laser

Abstract: An optical information storage system wherein information is read from a magneto-optical storage medium by indicating the storage medium with a first laser beam generated by a semiconductor laser and exploiting the self-coupling effect of the semiconductor laser in response to light reflected from the storage medium to generate a second laser beam. A Faraday rotator is disposed in an optical path along which the reflected light from the magneto-optical storage medium returns to the semiconductor laser and a polarization rotating angle of the Faraday rotator is selected so that the oscillating polarization plane of the semiconductor laser is changeable in dependence upon the perpendicular magnetization direction of the magneto-optical storage medium. A linear polarizer is interposed between the semiconductor laser and a photodetector to extract from the second laser beam at least one polarization component parallel or perpendicular to a junction plane of the semiconductor laser with the extracted component being detected by the photodetector.

Influence of an external cavity on semiconductor laser phase noise

Abstract: Investigation of phase noise in semiconductor lasers allows one to understand the physical processes that influence both the width and the shape of the emission line. Furthermore, the limitations associated with phase noise have to be taken into account when semiconductor lasers are employed in coherent optical communication systems. In this letter we report phase‐noise measurements on single‐mode semiconductor lasers in the presence of optical feedback. We are able to observe, besides the expected linewidth reduction, a peculiar behavior in the high‐frequency region not yet reported in the literature, strongly dependent on the external cavity length.

Feedback-induced noise in index-guided semiconductor lasers and its reduction by modulation

Abstract: We report a reduction in feedback noise of 15-20 dB by direct modulation of the laser with a 2-5 mA modulation current. The reduction is almost independent of modulation frequency in the frequency range from 50 MHz to 200 MHz, but depends on the external cavity length. The external cavity lengths considered are 5-15 cm.

Optical coupling between single-mode semiconductor lasers and strip waveguides

Abstract: This analysis describes the optimum conditions for coupling a single-mode semiconductor laser to a single-mode strip waveguide, when both the laser and the waveguide have asymmetric optical beam profiles. The outputs are approximated by two Gaussian fields. Two waveguide cases are treated: 1) the case where the two orthogonal waveguide waists are independent and 2) where the ratio of these waists is fixed. The effect on the coupling efficiency of a spherical surface on the waveguide input face is discussed. The results demonstrate the importance of coupling in the laser far-field and indicate the advantage of having relatively large waveguide modes. An intrinsic minimum in the optimum coupling efficiency was found to exist in the near-field for asymmetric laser/waveguide systems. Expressions describing the optimum waveguide waists and the focal length of the lensed waveguide are given for the waveguide parameters that yield the best coupling conditions.

A Novel Technique for Measuring the Frequency Deviation of Semiconductor Lasers Under Direct Modulation

Abstract: A novel technique is proposed for measuring the frequency deviation of semiconductor lasers under direct modulation using a Michelson interferometer. This technique is applicable to a wide range of modulation frequency and does not require high-speed photo-detectors. The accuracy of the measurement is not reduced by the spectral line-width of lasers, the misalignment of the optical axes, or the depth of intensity modulation.

On the linewidth enhancement factor alpha in semiconductor injection lasers

Abstract: A simple model for the linewidth enhancement factor alpha and its frequency dependence in semiconductor lasers is presented. Calculations based on this model are in reasonable agreement with experimental results.

Mode‐locked semiconductor lasers with gateable output and electrically controllable optical absorber

Abstract: We proposed and demonstrated for the first time an electronically gateable mode‐locked semiconductor laser capable of coding information on the picosecond optical pulses emitted. We further introduced an electronically controllable optical absorber which made it possible to electrically control the optical performance of the mode‐locked semiconductor laser.

Tuning characteristics of optical amplification in 1.5 μm InGaAsP/InP lasers

Abstract: The bias current dependence of tuning wavelength in an optical amplifier is investigated in detail. Tuning wavelength decreases below threshold at the rate of -0.36 A/mA, mainly due to the change of carrier density, and increases at the rate of 0.11 A/mA above threshold due to the thermal effect.

Transient effects in external cavity semiconductor lasers

Abstract: In several important applications of external cavity operated semiconductor lasers, including studies for FM optical communication and frequency stabilized lasers for coherent communication systems, the transient response of the laser is of crucial importance. In this letter, we present a first study of the transient optical response following a step current excitation applied to an AlGaAs laser operating in a dispersive external cavity. The study shows for the first time that, for optical feedback near the gain peak of the laser, a steady state is reached after only three roundtrips in the external cavity. However, for optical feedback far (∼100 A) from the gain peak, 20 or more roundtrips are required before a steady state can be reached. It is also shown that under certain operation conditions the optical feedback can induce damped relaxation oscillations at each subsequent roundtrip in the external cavity.

Einstein relations for gain-guided semiconductor lasers

Abstract: The Einstein equations which relate the transition rates for stimulated emission, spontaneous emission and stimulated absorption in a laser active medium are re-examined for the special case of a semiconductor laser with complex wave-guiding. It is shown that, owing to the nonorthogonality of the gain-guided laser modes, the Einstein relations have to be modified. In particular, the spontaneous emission rate per laser mode no longer equals the stimulated emission rate per laser photon.

Gain scaling of short-wavelength plasma-recombination lasers.

Abstract: The theoretical Z7.5 dependence of the small-signal gain of plasma-recombination lasers on the ionization stage Z of the laser species implies a straightforward development of short-wavelength lasers but appears to be significantly experimentally achieved gain scaling. A new analysis, which incorporates a simple experimental parameter representing the efficiency of populating the upper level at a given plasma electron density, results in a gain scaling with ionization state (Z4.5) that is more consistent with experiments and also reveals a need for better experimental control of the ion-production and electron–ion-recombination process when one attempts to make such lasers.

Self-Coupled Optical Pickup

Abstract: A review is made on the current status of the study of the self-coupling effects in the semiconductor laser diode and on the application of the effects in optical memory readout. It is proposed and demonstrated that the operational instsabilities caused excess coherency of the laser output light is suppressed by placing either a polarzation rotator or a phase plate in the path of the light.

Role of impurities in the appearance of multifrequency emission from injection semiconductor lasers

Abstract: It is demonstrated that not only shallow acceptors but other impurities have considerable influence on the multifrequency lasing threshold even if the lasing is due to radiative transitions between the conduction and valence bands. (AIP)