GaAs-based Lasers Research Articles

Optically Pumped Edge-Emitting GaAs-Based Laser With Direct Orange Emission

Room temperature lasing operation at 599 nm for a AlGaInP/AlInP/GaAs edge-emitting laser structure is reported. The structure was grown on GaAs substrate and pumped optically with a 532 nm Q-switched laser. The lasing threshold for a 2 mm long and 25 μm wide ridge waveguide structure was 30 mW of average pump power. The orange output beam had an optical spectral width of 1.7 nm.

The Influence of Imperfections and Absorption on the Performance of a GaAs/AlO $_{\rm x}$ High-Contrast Grating for Monolithic Integration With 980 nm GaAs-Based VCSELs

This paper discusses the influence of fabrication imperfections and absorption on high contrast grating (HCG) reflectivity and reveals that HCGs show considerable tolerance to both factors. A fully vectorial optical numerical model was used to design an HCG for use as the top mirror of a 980 nm GaAs-based vertical-cavity surface-emitting laser. Parameters providing a high degree of reflectivity were determined with special attention to optimizing the low refractive index layer.

Dynamic Analysis of GaAs-based Quantum Cascade Laser

The quantum cascade lasers are such unipolarity lasers that have the emissivity from mid infrared to far infrared range. In this paper the dynamic effects of quantum cascade lasers (QCL) GaAs/AlGaAs characteristics in the mid-infrared range of λ=9μm is investigated by solving the numerical equations. Calculating of the spontaneous emission rate changes, its effects on the number of carriers, the number of photons, and the output power are the objectives of the presented study. Finally, the output power changes, by increasing the number of stages in the quantum cascade laser, have been studied. The obtained results showed that, the increase of spontaneous emission rate parameter causes delay in the laser output. In addition, there is a direct relationship between the number of stages and the output power.

Basic Aspects of High-Power Semiconductor Laser Simulation

The aim of this paper is to review some of the models and solution techniques used in the simulation of high-power semiconductor lasers and to address open questions. We discuss some of the peculiarities in the description of the optical field of wide-aperture lasers. As an example, the role of the substrate as a competing waveguide in GaAs-based lasers is studied. The governing equations for the investigation of modal instabilities and filamentation effects are presented and the impact of the thermal-lensing effect on the spatiotemporal behavior of the optical field is demonstrated. We reveal the factors that limit the output power at very high injection currents based on a numerical solution of the thermodynamic based drift-diffusion equations and elucidate the role of longitudinal spatial hole burning.

High optical strength GaAs-based laser structures

The optical-strength properties of 3S PHOTONICS GaAs-based semiconductor laser structures are presented. After some general considerations about this robustness issue, typical of high-power diode lasers, the performances in both CW and pulsed current injection of our best vertical structures are presented and it is shown that our current generation of 980nm laser diodes can withstand very high facet temperatures (180–200°C) in stable CW operation. Thus, we demonstrate a large margin between the facet temperature in operation conditions and the observed maximum critical value. Maximum CW saturation powers exceeding 3W from a single-lateral mode device have been obtained with the longest laser cavities (7.5mm) at around 5A. Also, very high peak powers are demonstrated in pulsed current experiments opening the way to new specific applications, using available production devices. Specific degradation patterns after high peak current single-pulse induced damage have been observed by cathodo-luminescence imaging and are also discussed. Finally, comparisons between devices emitting at 980nm and 1060nm are considered.

On the importance of non-thermal far-field blooming in broad-area high-power laser diodes

High-power broad-area laser diodes often suffer from a widening of the slow-axis far-field with increasing current (lateral far-field blooming). This effect is commonly attributed to self-heating. Utilizing self-consistent electro-thermal-optical simulations, we analyze previous experimental investigations of 970 nm broad-area GaAs-based Fabry-Perot lasers and reproduce the blooming mechanism in good agreement with the measurements. The simulations reveal that a substantial part of the far field blooming is not caused by self-heating but by increasing carrier and gain non-uniformity in the quantum wells.

InAs/In0.83Al0.17As quantum wells on GaAs substrate with type-I emission at 2.9 μm

This work reports on InAs quantum wells (QWs) grown on GaAs-based metamorphic In0.83Al0.17As buffers for type-I mid-infrared (MIR) emission. X-ray diffraction and Raman measurements show that the GaAs-based quantum wells have similar lattice and strain conditions with the InP-based structure. Atomic force microscope shows the smoother surface of the structure on GaAs substrate. For the GaAs-based quantum wells, favorable photoluminescence emission at 2.9 μm at 300 K has been achieved, and the optical quality is comparable to the structure on InP substrate. It is promising to employ this metamorphic quantum well structure for the demonstration of GaAs-based antimony-free mid-infrared lasers.

Enhanced photoluminescence efficiency in Er-Yb codoped InAlP native oxides

Demonstrated is the effectiveness of Yb as a sensitiser to enhance the optical emission of Er in an InAlP native oxide host, which can potentially be integrated with a GaAs-based semiconductor laser. Photoluminescence (PL) and PL excitation spectroscopy are used to evaluate the efficacy of Yb codoping. Compared to samples without Yb, an increase of ∼13 times is observed in both the PL and PLE signals for Er-Yb codoped samples with an Er:Yb ratio of 1:3, indicating that the Yb effectively absorbs the pump power and transfers the absorbed energy to the Er ions. The Er PL decay lifetime remains unchanged after codoping with Yb, with the PL emission linewidth decreasing only negligibly from 39 to 35 nm.

High-power low-divergence 1060 nm photonic crystal laser diodes based on quantum dots

GaAs-based photonic band crystal diode lasers with low vertical divergence and high output power have been designed and realised with a quantum dot active area at a wavelength of 1060 nm. Broad area lasers with 100 µm stripe width show low transparency current densities of 129 Acm−2 and high differential efficiency of 70 %. Devices of 1 mm length deliver up to 17.7 W pulsed output power and 2.6 W continuous-wave output power is demonstrated for 2 mm-long devices. The maximum output power is presently limited by catastrophic degradation in the pulsed case and by thermal rollover in the continuous-wave case. The full width half maximum vertical divergence of the fundamental mode of the devices is reduced to 13°, being nearly independent of driving current.

Efficiency-limiting processes in Ga(NAsP)/GaP quantum well lasers

We report on the carrier recombination mechanisms in dilute nitride Ga(NAsP)/GaP quantum well lasers. Spontaneous emission measurements show that defect-related recombination in the devices is less significant compared with other GaAs-based dilute nitride lasers. From temperature dependent measurements, we find that the threshold current density, Jth is dominated by non-radiative recombination process(es), which account for at least 91% of Jth at room temperature. The characteristic temperature, T0 (T1) is measured to be ∼104 K (∼99 K) around 200 K, which drops to ∼58 K ( ∼37 K) around room temperature. Hydrostatic pressure measurements reveal a strong increase of threshold current with increasing pressure. This implies that current leakage dominates carrier recombination which is also responsible for their low T0 and T1 values at room temperature.

High power density vertical-cavity surface-emitting lasers with ion implanted isolated current aperture.

We report on GaAs-based high power density vertical-cavity surface-emitting laser diodes (VCSELs) with ion implanted isolated current apertures. A continuous-wave output power of over 380 mW and the power density of 4.9 kW/cm2 have been achieved at 15 °C from the 100-μm-diameter aperture, which is the highest output characteristic ever reported for an ion implanted VCSEL. A high background suppression ratio of over 40 dB has also been obtained at the emission wavelength of 970 nm. The ion implantation technique provides an excellent current isolation in the apertures and would be a key to realize high power output from a VCSEL array.

Design of Low Threshold Photonic Crystal Surface Emitting Lasers

We have investigated the influence of various thicknesses on different layers in GaAs-based photonic crystal surface-emitting lasers (PCSELs), by using the transfer matrix and coupled wave methods to increase the vertically optical confinement factor and to reduce the threshold gain. In addition, the relationship between the threshold gain and the filling factor has been considered. This letter provides an efficient calculation method for designing square-lattice-type PCSEL structures, which shall be useful for the fabrication of low-threshold PCSELs in the near future.

Combination of Low-Index Quantum Barrier and Super Large Optical Cavity Designs for Ultranarrow Vertical Far-Fields From High-Power Broad-Area Lasers

When active regions that use low refractive index quantum barriers (LIQB) are combined with super large optical cavity (SLOC) designs in GaAs-based diode lasers, high-power operation with extremely narrow vertical far-fields is observed. However, LIQB designs are found to have lower slope efficiency and increased operation voltage. Comparison of experiment and finite element device simulation shows that this is due to hole accumulation at the edge of the active region. Example devices using an 8.6-μm thick SLOC deliver 30 W at 1065 nm with vertical divergence of 15.6° (95% power).

Thermal modeling of GaAs-based semiconductor disk lasers

Thermal characteristics including the temperature, the heat flux, and the temperature gradient of GaAs-based semiconductor disk lasers (SDLs) under various conditions are modeled using the finite element method. The effects of the substrate thickness, the pump spot radius, the heatspreader, and the pump power on the thermal properties of laser are simulated, and the maximum temperature rise in active region is highlighted. Numerical analysis predicts that SiC is an ideal substitute for diamond as a heatspreader. Instead of the sophisticated completely-etched substrate, the use of a high-thermal-conductivity heatspreader along with partly-etched substrate can provide sufficient thermal management to the laser.

Mechanisms and fast kinetics of the catastrophic optical damage (COD) in GaAs‐based diode lasers

AbstractCOD diagram determined for a batch of broad‐area AlGaAs diode lasers. The time to COD within a single current pulse is plotted versus the actual average optical power in the moment when the COD takes place. Full circles stand for clearly identified COD events (right ordinate), whereas open circles (left ordinate) represent the pulse duration in experiments, where no COD has been detected. A borderline (gray) exists between two regions, i. e., parameter sets, of presence (orange) and absence of COD (blue). This borderline is somewhat blurred because of the randomness in filamentation of the laser nearfield and scatter in properties of the involved individual devices.

Strained Active Regions in GaAs-based Quantum Cascade Lasers

This paper explores the effects of low indium concentration in deep-well AlGaAs/GaAs quantum cascade laser structures. Photon emission from these strained active regions involves nonlinear optical processes, which reduce the emission wavelength. Designs that incorporate strain in one and two wells of the active region, respectively, on (111) GaAs are compared. Results demonstrate wavelength extendibility in compressively strained deep-well GaAs-based devices.

Spotted Custom Lenses to Tailor the Divergence of Vertical-Cavity Surface-Emitting Lasers

We demonstrate the output beam collimation of GaAs-based vertical-cavity surface-emitting lasers by means of self-aligned polymer microlenses deposited on SU-8 pedestals using a cantilever-based spotter. We show that this fabrication technique ensures a reproducible lens shape because the contact angle and the deposited volume are constant for a given surface. Device properties are presented and compared to optical beam propagation modeling results. We demonstrate that the final beam divergence is only controlled by pedestal design parameters and can be reduced with this method by a factor 10 (to 1.2° for single-mode devices) with no significant lasing performance modification.

Characterization and optimization of 2-step MOVPE growth for single-mode DFB or DBR laser diodes

We have studied the MOVPE regrowth of AlGaAs over a grating for GaAs-based laser diodes with an internal wavelength stabilisation. Growth temperature and aluminium concentration in the regrown layers considerably affect the oxygen incorporation. Structural characterisation by transmission electron microscopy of the grating after regrowth shows the formation of quaternary InGaAsP regions due to the diffusion of indium atoms from the top InGaP layer and As–P exchange processes during the heating-up procedure. Additionally, the growth over such gratings with different facets leads to self-organisation of the aluminium content in the regrown AlGaAs layer, resulting in an additional AlGaAs grating, which has to be taken into account for the estimation of the coupling coefficient. With optimized growth conditions complete distributed feedback laser structures have been grown for different emission wavelengths. At 1062 nm a very high single-frequency output power of nearly 400 mW with a slope efficiency of 0.95 W/A for a 4 μm ridge-waveguide was obtained.

Dual-wavelength mode-locked quantum-dot laser, via ground and excited state transitions: experimental and theoretical investigation

We report a dual-wavelength passive mode locking regime where picosecond pulses are generated from both ground (lambda = 1263 nm) and excited state transitions (lambda = 1180 nm), in a GaAs-based monolithic two-section quantum-dot laser. Moreover, these results are reproduced by numerical simulations which provide a better insight on the dual-wavelength mode-locked operation.

Switching operation of lasing wavelength in mid-infrared ridge-waveguide quantum cascade lasers coupled with microcylindrical cavity

We demonstrated switching operation of lasing wavelength in GaAs-based mid-infrared coupled-cavity quantum cascade lasers. Our cavity structures consist of a ridge-waveguide Fabry–Perot cavity coupled with a microcylindrical cavity. Individual control of currents injected into both cavities enabled single-mode operation and facilitated intentional mode switching between coupled-cavity modes with spacing over 120 nm. The integrated microcylindrical cavity expanded the separation of coupled-cavity modes due to the small size of the cavity and enabled switching the lasing wavelength over a wide spectral range.