AlGaAs Double-heterostructure Lasers Research Articles

Carrier heating and the power independent linewidth in semiconductor lasers

We present linewidth measurements on AlGaAs double heterostructure lasers as a function of temperature and power. The data, which plot observed linewidth as a function of reciprocal power, reveal decreasing slopes and increasing vertical axis intercepts, or power independent linewidths, with falling temperature, consistent with previous experimental observation [D. Welford and A. Mooradian, Appl. Phys. Lett. 40, 560 (1982)]. To explain the power independent linewidth broadening observed in these continuous wave single frequency lasers, we propose that carrier heating processes create a thermal nonequilibrium between electrons and the semiconductor lattice, and that this leads to a power dependent linewidth enhancement factor. From a carrier thermal model we find that the power independent linewidth is mediated by the longitudinal optical (LO)-phonon lifetime (τLO); as τLO is increased (for example, by decreasing the lattice temperature), the noneqilibrium condition is enhanced, and, consequently, the power independent linewidth increases.

Laser-excited fluorescence of perylene by using self-induced second-harmonic and sum-frequency radiation emanating from high-power AlGaAs double hetero-type diodes

High-power (12 W) pulse-operated AlGaAs double-heterostructure lasers with a large thickness of the active layer (1.5 µm) are able to produce internal second-harmonic and sum-frequency generation with a peak power of 10 mW. The corresponding portion of the electroluminescence spectra has a maximum at 405 nm. Clearly resolved mode structures of the fundamental and harmonic radiation are analysed in detail. Particular transverse modes exhibit different conversion efficiencies. Violet resonances without modal precursors in the infrared spectrum make a marked contribution to the light intensity. The harmonic signal serves as an excitation source in photoluminescence studies. A technique of single-photon counting is applied in order to perform spectral measurements under weak-intensity levels. Bright fluorescence spectra of saturated solution of perylene ino-xylene are presented. The spectrum obtained when the solution is illuminated with a gas discharge lamp shows no differences with respect to the positions of the intensity peaks. This allows us to suggest that AlGaAs high-power lasers can be used as convenient excitation sources in photophysics, in particular in time-resolved experiments.

Metalorganic chemical vapor deposition grown AlGaAs lasers with grown optical facets

AlGaAs double heterostructure laser diodes with grown optical window structure facets have been fabricated by single-step metalorganic chemical vapor deposition (MOCVD) growth on grooved substrates for the first time. We report a new technique which permits the simultaneous formation of optical feedback mirrors and a submicron-thick window region. [01 1 ]-oriented dovetail grooves on a GaAs(100) substrate were prepared by wet etching. The growth was carried out by atmospheric-pressure MOCVD. The resulting broad area laser diode with a 0.3 μm thick window region has a threshold current and slope efficiency similar to that of a laser diode with conventional cleaved facets. The light output power versus current characteristics were improved.

Detection of Persisting Photoelectrons in AlGaAs Double Heterostructure Laser Diodes by DLTS

LPE-made AlGaAs double heterostructure laser diodes were investigated by deep level transient spectroscopy. In the Sn-doped n-type confinement layers two electron traps named DX1 and DX2 here were always found. Under non-saturation conditions a significant change of the low-temperature part of DLTS spectra curves was observed after applying forward voltage for a short time. Relaxation of DLTS signal and sample capacitance at 80 K took several hours. Only the DX2 trap contributed to this persistent photoconductivity effect.

Ion beam sputtered (SiO_2)x(Si_3N_4)_1−x antireflection coatings on laser facets produced using O_2–N_2 discharges

The chemical composition of a (SiO(2))(x)(Si(3)N(4))(1-x) film produced by ion beam sputtering was precisely controlled by the ratio of O(2) and N(2) flow rates under a discharge current kept constant to within an accuracy of +/-0.05 A. The reproducibility of the refractive index was improved to +/-0.01. This film was applied to form antireflection coatings with extremely low reflectivity on facets of 830-nm AlGaAs double heterostructure lasers. The minimum reflectivity was 6.8 x 10(-5), and a reflectivity of 1 x 10(-4) was achieved reproducibly. Experimental studies show that antireflection coatings are effective for suppressing the interferometric light output variation of composite cavity lasers.

Improvement in Signal-to-Noise Ratio of a Longitudinally Coupled Cavity Laser by Internal Facet Reflectivity Reduction

Improvement in signal-to-noise ratio (SNR) is described for 830 nm AlGaAs double heterostructure lasers longitudinally coupled to a short complex cavity formed by a laser facet and an external mirror separated from the facet by a few micrometers. The SNR degraded by external cavity length (spacing) variation is improved by reducing internal laser facet reflectivity using an anti-reflection coating. A variation ratio, newly defined to evaluate light output variation due to spacing, reaches 1.6 at a reflectivity of 6.8×10-5. The SNR degraded by laser intensity noise is improved to 56 dB by biasing the drive current at an optimum corresponding to the noise valley which appears for lower laser facet reflectivity. The SNR degraded by temperature variation is improved by linear current control, maintaining a maximum value of it from 10 to 45°C.

Behavior of gain-guided lasers generating high-power nanosecond pulses

Computer-controlled apparatus was used in an investigation of gain-guided narrow-stripe AlGaAs double heterostructure lasers. These lasers were excited with current pulses of 10 ns duration and amplitudes up to 3 A. The watt-ampere characteristics together with near- and far-field radiation patterns were considered using an analytic model of the lasers. The results showed that the values of the gain under a stripe contact or of the absorption outside this region varied with the output power.

Investigation of single-frequency semiconductor lasers with a fiber Michelson interferometer

A fiber Michelson interferometer, which is an analog of a scanning Michelson interferometer, was constructed from single-mode fiber waveguides and several highly directional Y-type couplers operating at the wavelength of 0.85 μ. It was found that this interferometer could be used to investigate the coherence of radiation from single-frequency lasers with a spectral line width in the range from 10 kHz to 1 GHz. The experimental dependences of the degree of coherence on the optical path difference were determined for cw single-frequency AlGaAs double heterostructure lasers with an external dispersive resonator, operating in the regime of self-stabilization of single-frequency emission. It was found that the width of the spectral lines was between 10 kHz and 1 MHz, and that the line profiles were Lorentzian.

High-power (710 mW cw) single-lobe operation of broad area AlGaAs double heterostructure lasers grown by metalorganic chemical vapor deposition

Broad area, conventional double heterostructure lasers were fabricated by metalorganic chemical vapor deposition. Continuous wave output power level of 710 mW and stable, single-lobed far-field patterns with a beam divergence as narrow as 2.1° (2.2 times diffraction limit) at 50 mW and 2.9° at 200 mW for a 50-μm-wide laser were obtained.

Ｉｎフリー基板マウント法ＭＢＥによる半導体レーザの開発

GaAs and AlGaAs films were grown by Molecular Beam Epitaxy (MBE) using direct substrate heating instead of conventional In-bonding method. The substrate with IR-absorbing layer was mounted on a hole in a molybdenum-block and heated dilectly by flat heater.Using this method, self-aligned AlGaAs double-heterostructure lasers were fabricated.The threshold current of this laser was 40 mA in CW operation at room temperature. The emission wavelength was 780 nm and a fundamental transverse mode oscillation was obtained.

Schottky barrier restricted AlGaAs laser with an etched mesa ohmic contact

A gain-guided AlGaAs double heterostructure laser which employs a Schottky barrier in conjunction with a p-GaAs etched mesa contact for current isolation has been fabricated. This Schottky barrier restricted structure provides a device whose electrical and optical characteristics are comparable to that of other gain-guided lasers and which is simple to fabricate. Preliminary aging data indicate high reliability of the Schottky barrier restriction.

Heterostructure semiconductor lasers prepared by molecular beam epitaxy

<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.72-0.88 \mu</tex> m (AlGa)As, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.3-1.65 \mu</tex> m GaInAsP and AlGa-InAs, and 1.78 μm AlGaSb double-heterostructure (DH) lasers were prepared by molecular beam epitaxy. For AlGaAs DH lasers very low 300 K threshold current densities and long operating life (mean time to failure >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> h at 300 K) were achieved and optical transmitters containing MBE-grown lasers have been field-tested. For lasers with lasing wavelength <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;1\mu</tex> m, MBE is in the development stage. The unique capabilities of MBE as an epitaxial growth technique and its important contributions to the field of optoelectronics are illustrated by a discussion of a new class of laser structures including quantum well heterostructure of GaAs/ Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> AS and Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</inf> In <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</inf> As/InP, double-barrier double-heterostructure, and graded-index waveguide separate-confinement-heretostructure lasers. These new lasers, made possible by MBE, have characteristics unmatched by conventional liquid phase epitaxial growth techniques.

Optical stability of narrow stripe, proton-isolated AlGaAs double heterostructure lasers with gain guiding

Optically stable, proton-isolated, gain-guided (AlGa)As double heterostructure injection lasers are described. A narrow stripe width (3.5 μm) and a very shallow implantation are employed (1.3 μm from the active layer); this results in a cosh−2-like optical mode of ∼9.0-μm full width at half-maximum. The far-field profiles possess strong sidelobes at high optical output power. The optical material loss coefficient and the antiguiding parameter are derived from the measured far-field profiles, using the theory of gain guiding. Key parameters in the description of the optical mode distribution are calculated for several values of output power.

Resonance phenomena on bias current dependence of AlGaAs double heterostructure laser amplifier

We report the first observation of the resonance phenomena on the bias current dependence of the amplified light output for AlGaAs double heterostructure laser. We also show that this resonance phenomenon is mainly caused by the change in the refractive index of the active layer due to the bias current change in terms of the simple theoretical calculations taking into account the effect of the refractive index change in the active layer.

Semiconductor laser FSK modulation and optical direct discrimination detection

FSK signals are generated in an AlGaAs double heterostructure laser by employing an electrical equalising circuit to compensate for its nonuniform FM modulation characteristics. A 10?9 bit error rate is achieved at a 100 Mbit/s data rate in the optical direct discrimination detection with a Michelson interferometer. The optical FSK discrimination detection performance is studied in terms of receiving signal power level and laser spectral linewidth.

Optical FSK signal detection in a heterodyne system using semiconductor lasers

A 10−8 bit error rate is achieved for 100 Mbit/s signals in an FSK heterodyne frequency-discrimination detection system, in which AlGaAs double-heterostructure lasers are used as both the FSK transmitter and the local oscillator. Receiving signal power level to achieve a low bit error rate is experimentally obtained, which confirms the principle of optical heterodyne detection. AM quantum noise in the laser local oscillator and FM quantum noise are important factors which determine the system performance.

Degradation behavior of AlGaAs double-heterostructure laser diodes aged under pulsed operating conditions

AlGaAs DH laser diodes pulsed operating test results, obtained at 70°C under 5 mW/facet conditions, are reported, and degradation behavior is discussed. No additional degradation modes peculiar to the pulsed operations were observed. Experimental results are analyzed qualitatively by taking into account three degradation accelerating factors: junction temperature, net lasing time length, and injected current. Pulse duty cycle and dc bias magnitude effects on degradation behavior are clarified. Threshold current increasing rates under pulsed operating tests were smaller than the values expected from net lasing time estimated from pulse duty. Experimental results led to the conclusion that pulsed operations are more favorable than CW operations.

The effect of cavity length on picosecond pulse generation with highly rf modulated AlGaAs double heterostructure lasers

We report the generation of picosecond pulses with oxide-isolated-stripe, double heterostructure GaAlAs laser diodes of varying lengths. A pulse width of 15 ps at a repetition frequency of 1 GHz is achieved with a 60-μm-long device. The experiments indicate a linear relation between pulse width and laser length.

Carrier-induced index change in AlGaAs double-heterostructure lasers

A large carrier-induced index change is reported for conventional 8 μm-stripe oxide-isolated AlGaAs double-heterostructure lasers. At threshold, the index change of the active layer is −0.05 to −0.07, which is a factor of 5 to 10 larger than previously reported. It is accompanied by an even greater change in dispersion. These effects cannot be explained by a free-carrier effect, and are most likely caused by a carrier-induced shift of the absorption edge.

Single-growth embedded epitaxy AlGaAs injection lasers with extremely low threshold currents

A new type of strip-geometry AlGaAs double-heterostructure laser with an embedded optical waveguide has been developed. The new structure is fabricated using a single step of epitaxial growth. Lasers with threshold currents as low as 9.5 mA (150 μm long) were obtained. These lasers exhibit operation in a single spatial and longitudinal mode, have differential quantum efficiencies exceeding 45%, and a characteristic temperature of 175° C. They emit more than 12 mW/facet of optical power without any kinks.