GaAs Injection Lasers Research Articles

Room-temperature continuous wave vertical surface-emitting GaAs injection lasers grown by molecular-beam epitaxy

Summary form only given, as follows. Room-temperature continuous-wave oscillation with emission power in excess of 1 mW was achieved in vertical-cavity surface-emitting lasers containing a 0.5- mu m-thick GaAs active layer sandwiched between a distributed Bragg reflector (DBR) and a metal-DBR hybrid reflector grown by MBE. The threshold current is 50 mA for a 15- mu m-diameter device. Th temperature dependence of the threshold current gives T/sub 0/=115 K.

Collision broadening of optical gain in semiconductor lasers

The energy-dependent intraband relaxation with polar-optical-phonon scattering is incorporated in the calculation of the linear gain and the refractive index change of the GaAs injection laser with an undoped active region. Comparison with the conventional model, which assumes a constant intraband relaxation, shows that it is difficult to fit the overall gain spectra exactly by single, energy-independent intraband-relaxation time. Moreover, the calculated gain spectra wth phonon broadening show strong temperature dependence due to the change of the relaxation time and the Fermi functions.

Addendum: Noncontact electro-optic sampling with a GaAs injection laser

Addendum: Noncontact electro-optic sampling with a GaAs injection laser

Noncontact electro-optic sampling with a GaAs injection laser

30 ps pulses from a diode laser have been used to perform noncontact electric field measurements using a versatile ‘finger probe’ electro-optic sampling technique.

Relaxation time broadening on emission spectrum of a Zn-doped p-type GaAs injection laser

Spontaneous emission and lasing gain profiles of semiconductor injection lasers which have Zn-doped GaAs active regions were experimentally determined, and the tailing phenomenon into the band gap of these profiles was theoretically explained as a result of relaxation time broadening due to scattering of electrons and holes. Especially, the tail of the gain profile was found to show a concave shape, which was better explained by the relaxation time broadening model than by the band tail state model.

Longitudinal mode spectrum of GaAs injection lasers under high-frequency microwave modulation

Experimental observations of the lasing spectrum of a single mode semiconductor laser under continuous microwave modulation reveal that the lasing spectrum is apparently locked to a single longitudinal mode for optical modulation depths up to ∼80%, beyond which the lasing spectrum becomes multimoded, whose envelope width increases very rapidly with further increase in modulation depth. These results are satisfactorily explained by a theoretical treatment which enables one to predict the dynamic lasing spectrum of a laser from its cw lasing spectra at various output powers.

Ultrahigh speed modulation-doped heterostructure field-effect photodetectors

We have developed a sensitive, ultrahigh speed photodetector which has a structure of a modulation-doped AlxGa1−xAs/GaAs field-effect transistor. In spite of a large gate-drain spacing of >8 μm and a gate length of >20 μm, this detector exhibited a rise time of 12 ps and a full width at half-maximum of 27 ps. When tested by a 8200-Å GaAs injection laser, the detector showed an ac (>20 MHz) external quantum efficiency of >630%, i.e., 9 times more sensitive than a pin photodiode. In view of its high sensitivity, ultrahigh speed, and compatibility with modulation-doped field-effect transistors, this detector has promise for a variety of high-speed optical applications.

High-Frequency Impedance of Proton-Bombarded Injection Lasers

Experimental and theoretical results are given of an investigation of the capacitance behavior with frequency of GaAs injection lasers. It is shown that, for shallow-bombarded stripe geometry lasers, the zero-bias capacitance decreases rapidly beyond a certain frequency. This is interpreted in terms of confinement of the low-level radio frequency current under the stripe at high frequencies. Comparison of the experimental results with the analytically derived expressions provides a measure of the material resistivity adjoining the active region. This inferred material resistivity is shown to be in good agreement with results obtained by more direct measurements. Finally, the general conclusions are also applicable to other optoelectronic devices operating at high frequency, such as light-emitting diodes.

Gain Calculation of Undoped GaAs Injection Laser Taking Account of Electronic Intra-Band Relaxation

The intra-band relaxation of electrons is a basic factor to be considered for the characterization of injection lasers, especially in the investigation of modal behavior under lasing operation. This paper discusses the gain and refractive index in quantitative terms and considers the intra-band relaxation phenomenon in undoped GaAs lasers. The linear and third order gain coefficients are summarized in arithmetic equations by numerical calculation. Some characteristic parameters in the equations are also confirmed experimentally through measurements of the output spectral profile and laser threshold. The results give a more consistent interpretation of non-oscillating and oscillating states than previously-established theories, which do not take into account the intra-band relaxation.

Ultimate frequency response of GaAs injection lasers

The maximum frequency response attainable in GaAs injection lasers under constraints of limited current density and optical power density is examined in this communication. It is found that under a prescribed current and optical limit, an optimum cavity length exists at which the frequency response attains its maximum. Fundamental frequency limitations under various operating conditions are depicted graphically.

Electrooptically tuned external-cavity CW semiconductor laser and FM optical communications

We report the operation of an external-cavity CW double-heterojunction GaAs injection laser that can be electrooptically tuned rapidly over a large spectral range (∼ 50 Å) and experiments demonstrating the feasibility of FM optical communications using electronically tunable semiconductor lasers and CW and mode-locked dye lasers. An experiment on binary pulse-code FM optical communication is also reported and discussed.

Investigation of the polarization of radiation from single-channel injection lasers

Results are presented of an experimental investigation of the polarization characteristics of the radiation from single-channel GaAs injection lasers. It is shown that single-channel cw lasers operated at T=77°K emit linearly polarized radiation over a broad range of injection currents. On application of a uniaxial pressure perpendicular to the p-n junction plane, the plane of oscillations of the vector E is rotated through 90° and the pressure range in which this rotation occurs depends on the width of the emitting area.

Coherence of the radiation emitted from single-frequency injection lasers

An experimental investigation was made of the dependence of the coherence length of the radiation emitted from single-frequency GaAs injection lasers on the radiation power and intensity. For intensities of ~0.5×105 W/cm2 the emission line became considerably broader. The dependence of the coherence length on the radiation power in the weak-field regime, i.e., for intensities I105 W/cm2, was used to estimate the upper value of the saturation parameter. The results were in good agreement with the corresponding theoretical predictions.

Dual-beam laser: A GaAs double-cavity laser with branching output waveguides

A new GaAs injection laser is reported with dual output beams at one mirror. The device is fabricated by incorporating a branching taper in the optical cavity. Minor changes in the layer parameters allow device operation either as a power divider or a mode splitter. One dominant longitudinal mode with suppression of unwanted structure is observed due to coupling of dual optical cavities.

Radiative characteristics of a single-channel GaAs injection laser

An investigation was made of the radiative characteristics of gallium arsenide laser diodes with a luminous region several microns in size. A special feature of these lasers was that they emitted a single longitudinal mode in a wide range of injection currents at 77/sup 0/K. The maximum output power in this mode was approx.50 mW in the cw regime. The output was highly coherent: the coherence length exceeded 10 m. A comparison was made of the energy characteristics of the lasers with active regions 6 and 200 ..mu.. wide, operating in the single-frequency regime. Single-channel lasers were found to be 10 times as effective in conversion of electrical energy into coherent radiation than wide diodes.

Single-frequency GaAs injection laser

An experimental investigation was made of single-frequency GaAs injection lasers which were operated continuously at 77/sup 0/K. The emission of a single longitudinal mode from a plane-parallel resonator was observed in a wide range of injection currents (up to a sevenfold excess over the threshold value) and the total output energy exceeded 50 mW.

Fiber waveguides: a novel technique for investigating attenuation characteristics

Light from a pulsed GaAs injection laser is coupled into a glass fiber via a taper coupler. The time dependence of the light backscattered within the fiber as the pulse travels down the waveguide is recorded. From these data the total loss may be determined, as well as an estimate of the scattering and mode mixing characteristics of the fiber.

Suppression of the relaxation oscillation in the modulated output of semiconductor lasers

Practical rates of direct pulse modulation of semiconductor lasers have so far been limited to below several hundred megahertz, owing to serious distortion in the output signal caused by the relaxation oscillation of the light intensity. Based on theoretical analysis of the dynamic properties of lasing under constant injection of external radiation into the cavity modes, light injection is proposed as a method for suppressing the relaxation oscillation. The effectiveness of this method has been confirmed in a series of preliminary experiments which employed GaAs injection lasers both as the modulated laser and as the external source of the injected radiation.

Epitaxial growth on optical gratings for distributed feedback GaAs injection lasers

Good quality epitaxial overgrowth of Al 0.3Ga 0.7As on corrugated GaAs and Al 0.12Ga 0.88As surfaces has been achieved by molecular-beam epitaxy. The electrical properties of the interface appear to be equivalent to those prepared by LPE without growth interruption. The corrugations were third order Bragg gratings of ∼0.37 μm period and ∼0.20 μm depth and were formed by ion milling. Separate confinement heterostructure injection lasers with these periodic corrugations in the optical cavity have demonstrated lasing behavior characteristic of distributed feedback. They have operated with room-temperature threshold current densities as low as 2.2 kA/cm 2. These results suggest that the MBE overgrowth is a useful technique for the fabrication of integrated optoelectronic structures which include active devices.

Operating injection lasers by fast square current pulses of variable amplitude

A simple solid state circuit was used to drive GaAs injection lasers by fast (∼100 nsec) square pulses of variable amplitude (0–25 A). The amplitudes of the current pulses and the corresponding emitted light pulses were measured by a dual peak detector circuit. Using these circuits we were able to plot automatically the current vs light curve and determine the threshold current of the laser diodes.