High-power AlGaAs Research Articles

Dopant Occupancy and UV–Vis–NIR Spectroscopy of Sc:Yb:Tm:LiNbO3 in the 300–3000 nm Wavelength Range

AbstractA series of Sc:Yb:Tm:LiNbO3 crystals with variable Sc3+ (0, 1, 2, and 3 mol%) concentration are grown by the Czochralski method. The effective distribution coefficients of Sc3+, Yb3+, and Tm3+ ions in the Sc:Yb:Tm:LiNbO3 crystals are determined by inductively coupled plasma atomic emission spectrometer. Sc3+ ions distribute uniformly in crystals when Sc3+ concentration reaches up to 3 mol%. The influence of Sc3+ concentration on the dopant occupancy and defect structure of Sc:Yb:Tm:LiNbO3 crystals is investigated by IR transmission spectra. Threshold concentration of Sc3+ ions in Sc:Yb:Tm:LiNbO3 crystals is nearly 3 mol%. By analyzing UV–vis–NIR absorption spectra, absorption property of Sc:Yb:Tm:LiNbO3 crystals is improved by doping Sc3+ ions. Additionally, the Sc:Yb:Tm:LiNbO3 crystals can be pumped by commercially available high power AlGaAs LDs.

The effect of current crowding on the heat and light pattern in high-power AlGaAs light emitting diodes

The results of the light and temperature micromapping in AlGaAs light emitting diodes grown by liquid phase epitaxy as double heterostructures and emitting at λ∼0.87 μm are presented. At a driving current well above the safe operating limit (>300 mA), the nonuniform light pattern and local self-heating (with temperature gradient of about 950 °C/cm) followed by catastrophic degradation of a device were detected with the charge coupled device and infrared microscopes operating in a pulsed mode. These were shown to result from the current crowding effect in the active and contact areas of a device. Good agreement between the theory and experiment was found.

A Cathodoluminescence Study of the Defects Created by the Degradation of High Power AlGaAs/GaAs Multiemitter Laser Bars

AbstractIn this work we study the defects responsible for the degradation of high power AlGaAs based laser bars. The mirror and cavity degradations are studied by spectral cathodoluminescence (CL) imaging. Following the analysis of the CL images the main defects generated during the laser operation are revealed, both facet and intracavity defects are observed. A thermomechanical model is used to describe the very beginning of the defect formation. The defects are formed by a local plastic deformation induced by local heating at defects.

Study of the degradation of AlGaAs-based high-power laser bars: V defects

In this work we report the results of damage induced by aging tests of high power AlGaAs based laser bars. Post-laser aging the mirror and cavity degradations are studied by cathodoluminescence (CL). Following the analysis of the CL images the origin of the defects arising in the mirror surface and causing ulterior laser cavity degradation is discussed in terms of stress packaging and thermal stress induced processes. The latter is estimated by a finite element modelling of the thermomechanical properties of the laser heterostructure at the facet.

Mounting-induced strain threshold for the degradation of high-power AlGaAs laser bars

A new detailed approach has been developed, whereby the individual performances of the emitters comprising a laser bar are assessed separately as part of a larger coupled system. The results reveal the existence of a strain threshold, wherefore degradation of the emitter performances is only observed when the local packaging-induced strain is above a certain critical value. This degradation which occurs after aging, is manifested in an increase in the apparent threshold current and a decrease in the apparent slope efficiency of the individual emitters. This degradation is also revealed by the presence of facet defects as previously reported. These results suggest that measurement and control of packaging-induced strain will allow significant improvement in the degradation behavior of high-power AlGaAs laser bars.

Packaging-induced stress distribution in high power AlGaAs laser diodes by photoluminescence mapping

The microphotoluminescence (μ-PL) technique is proposed for mapping local stress distribution in GaAs/AlGaAs high power laser diode arrays (LDAs). This technique will be used to monitor the stresses that can be induced on the bars during the packaging process. We show herein that also a detailed study of the stress profiles that could exist in the bars before mounting and after aging can be achieved with this technique.

Side-mode injection locking characteristics of 150 mW AlGaAs semiconductor lasers

A high-power AlGaAs semiconductor laser was side-mode injection locked for laser cooling with frequency 1300 GHz away from free-running states. The injection locking properties of the slave laser were measured with saturated absorption spectrum and optical heterodyne beat technique. The results show that the mode properties of master laser were completely transferred to the slave laser. The dynamics of injection locking with respect to the driven current of the slave laser and injection light power was studied. The relationship of the locking bandwidth versus injection light power is consistent with the theoretical calculation based on the multi-mode rate equation with an injection term.

Optical and photoelectric study of mirror facets in degraded high power AlGaAs 808 nm laser diodes

Mirror facets of broad area AlGaAs SQW 808 nm lasers with fast degradation of the output power have been investigated by photoluminescence microscopy (PLM), electroluminescence microscopy, and micro-photocurrent spectroscopy techniques. Over 2000 images of the photoluminescent light emitted from the facets of approximately 20 degraded laser bars have been made. Repeating patterns associated with the degradation have been noted and classified. Degraded lasers have dark lines on the mirror facet surface which are inclined from the epitaxial plane by 55°. Pairs of such lines often form V-shaped patterns. The orientation of the observed features suggest they are planar or line defects lying the the {111} crystallographic planes. The defects demonstrate a reduction in the lifetime of nonequilibrium electron–hole pairs and increased density of states in the forbidden gap of the active region of the laser structure, and are directly related to laser failure. Observations of the evolution in size and contrast of PLM patterns with ageing suggest the defects were initially created in the active region side of the laser structures during crystal growth or during the mounting procedure, and later propagate in the {111} planes, stimulated by the lasing action. We interpret the V formation to be a way to relax a compressive strain in the epitaxial plane. A dislocation on the {111} planes could actually translate the portion of the crystal bounded by the V upwards (away from the mounting of the crystal), in response to compressive strain.

Microphotoluminescence mapping of packaging-induced stress distribution in high-power AlGaAs laser diodes

Spatially resolved photoluminescence line scans were performed to determine the local stresses in AlGaAs laser diodes designed for high-power operation at 808 nm. In this approach, the sign and magnitude of the local stress are deduced from the spectral shift of the peak associated with band-to-band transitions in the n-type GaAs substrate. The sensitivity of the technique (minimal equivalent hydrostatic stress that can be detected) can reach 10 MPa or better. Correlations between solder-induced stress distribution in the devices and estimated lifetimes are demonstrated.

A new structure of 780 nm AlGaAs/GaAs high power laser diode with non-absorbing mirrors

A novel high-power AlGaAs laser structure, which is named MBG (melt-back-grown)-NAM (non-absorbing mirror), has been proposed. The NAM regions are formed on both sides of the resonant facets to prevent the catastrophic optical damage due to the optical absorption, which causes local temperature rise of the facets. Instead of conventional chemical wet etching, the melt-back process technique during the liquid phase epitaxy was used to form window regions to prevent the interface degradations. It is observed that the maximum output power of the laser diodes with the new structure was three times higher than that of the conventional-structure laser. Therefore, the new method of forming the non-absorbing mirror region can be considered quite effective to reduce the interface defects between the NAM and internal active region.

Low-noise, high-power AlGaAs laser diodes

Low-noise, high-power AlGaAs laser diodes

Tunable high-power AlGaAs distributed Bragg reflector laser diodes

Power exceeding 200 mW from high-power tunable distributed Bragg reflector (TDBR) lasers have been achieved. The low power consumption tuning mechanism is described, with a wavelength tuning of > 10 nm. A 20 000 h lifetest on DBR lasers is presented.

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.

High‐power ALGaAs single‐stripe laser diode with window‐grown‐on‐facets

AbstractA high‐power single‐stripe AlGaAs laser diode capable of reliable operation at an output power greater than 50 mW is useful for improvement in optical data storage systems and second harmonic generation elements. A novel window structure laser diode is developed and referred to as a window‐grown‐on‐facets (WGF) laser. Highly reliable operation is attained under 10 mW at 50°C beyond 10, 000 hours in the wavelength of 830 nm and under 70 mW at 60°C beyond 4000 hours in the wavelength of 780 nm, respectively. In the WGF laser, the window effects are found only in the case of the Al content of the window layer greater than that of the cladding layer. To explain the experimental results, calculation of carrier leakage from the active layer to the window layer is performed. The reduction of the window effects is caused by the carrier leakage.

Use of molecular beam epitaxy for high-power AlGaAs laser production

The results of statistical analysis of the characteristics of high-power semiconductor lasers grown by molecular beam epitaxy are presented. Three types of heterostructures are compared. It is shown that widening of a graded refractive index (GRIN) waveguide layer thickness from the standard value of 0.4 to 0.6 μm results in increased average differential quantum efficiency of the lasers. In addition, use of a 100 Å single quantum well decreases the scatter of the laser diode threshold current density as compared with the structures having a quantum well thickness of 200 Å.

Tunable, narrow-linewidth output from an injection-locked high-power AlGaAs laser diode array

An injection-locking technique has been employed to produce single-frequency tunable output from a high-power AlGaAs laser diode array. A narrow-linewidth external cavity laser is used as a master oscillator. With an injected power of 15 mW, a total output power of 1.0 W was obtained from the laser diode array with a spectral linewidth of less than 38 kHz, a wavelength tuning range of 13 nm, and a 0.67 degrees -wide single-lobed far-field beam.

A degradation rate study of MBE-grown high-power AlGaAs laser diodes

The influence of the growth temperature of ternary compounds on the degradation rate of AlGaAs/GaAs laser diodes was studied. The optimal temperature was found to be 700 degrees C. A further reduction in the degradation rate may be achieved by using a ridge-type stripe-array contact instead of a broad-area contact. The percentage of diodes with a lifetime exceeding 2500 hours (at Pout approximately=2 mW mu m-1 per facet) was four times larger for the former laser than for the latter.

High-power singlemode AlGaAs distributed Bragg reflector laser diodes operating at 856 nm

Data are presented describing AlGaAs distributed Bragg reflector (DBR) laser diodes operating at 856 nm with single transverse and longitudinal mode behaviour beyond 270 mW CW. The threshold current of these lasers is 35 mA, with a differential quantum efficiency of 58%. Preliminary lifetest data are presented.

High power AlGaAs quantum well laser diodes prepared by molecular beam epitaxy

Stable and reliable AlGaAs high power single quantum well lasers prepared by molecular beam epitaxy have been realized. We have prepared both 50-μm devices operating in multiple modes and ridge-waveguide single transverse-mode devices. Good reliability has been confirmed under the operating condition of 500 mW at 50 °C for the former type of devices and under the condition of 50 mW at 50 °C for the latter type of devices over 1000 h. These results indicate that molecular beam epitaxy is capable of making reliable high power laser diodes.

Coherent addition of injection-locked high-power AlGaAs diode lasers

Coherent addition with the use of injection-locked AlGaAs high-power diode lasers has been performed. The linewidths of the master and slave lasers were narrowed to less than 30 kHz by using the optical feedback from an off-axis confocal Fabry-Perot resonator. The coherently added output power of two diode lasers was increased up to 110 mW, which corresponds to an addition efficiency of 0.85. The residual phase fluctuation of the system was controlled within 0.25 rad. Addition of three high-power diode lasers has been also demonstrated for the first time to our knowledge, and a total output power of 150 mW with an addition efficiency of 0.68 was obtained.