Analysis of grating-coupled radiation in GaAs:GaAlAs lasers and waveguides--II: Blazing effects

Grating-coupled radiation in lasers and waveguides is analyzed for trapezoidal-shaped grating teeth which includes all triangular shapes. A perturbation technique is used which involves calculating the modes in a geometry with an inhomogeneous refractive index profile in the grating region. Curves are presented for radiated power from traveling waves as a function of blazing angle, grating tooth height, refractive index, and grating period. It is shown that the ratio of power radiated into the outer media depends greatly on tooth shape and size. By judiciously selecting parameters this ratio can exceed 50:1.     

On grating-coupled radiation from waveguides

We show that grating coupled radiation from a waveguide is a very sensitive oscillatory function of waveguide thickness when substrate and guide indices differ greatly. Because of this phenomenon, computed results are strongly dependent on the choice of waveguide geometry used to calculate the unperturbed modes.     

GaAs/GaAlAs curved rib waveguides

Curved dielectric optical waveguides suffer from radiation loss due to bending. To minimize the bending loss and reduce the radius of curvature, it is necessary to fabricate guides which provide strong optical confinement. This paper gives a brief review of curved waveguide analysis and presents some experimentally measured loss values for GaAs/GaAlAs curved rib waveguides. The rib waveguides, fabricated using ion beam milling, have a large rib height and are tightly guided structures. When corrected for reflection losses and input coupling efficiency, a minimum loss of approximately 3 dB has been achieved for a multimode 90° curved guide with a radius of curvature of 300 μm, and 8.5 dB for a single-mode curved guide with a radius of curvature of 400 μm. It is believed that most of this residual loss is not radiation loss due to bending, but rather scattering loss due to rib wall imperfections.     

Fabrication of tapered couplers in GaAs/GaAlAs rib waveguides

Tapered couplers have been fabricated in GaAs/GaAlAs single-mode rib waveguides. A new etching technique has been used to fabricate transitions of 1 μm over lengths of approximately 160 to 300 μm. Losses for the TE and TM fundamental modes have been measured at a wavelength of 1.3 μm     

Attenuation measurements on MOCVD-grown GaAs/GaAlAs optical waveguides

We report loss measurements on MOCVD-grown GaAs/GaAlAs optical waveguides, by sequential cleaving with allowance for Fabry-Perot resonator effects. Upper bound values are 1.4 dB/cm for strip-loaded and 2.5 dB/cm for fully etched ridge waveguides.     

Kink-free narrow-stripe proton-isolated GaAlAs/GaAs injection lasers

Totally kink-free and very-narrow-stripe proton-isolated injection lasers are presented. The standard gold-indium metal-contact bonding system has been investigated, and as a result an improved bonding technique is presented. Kink-free lasers with output power up to 20 mW have been accelerated at 80°C ambient for 1000 h without any change in thermal resistance and with an expected lifetime of above 106 h at room temperature.     

GaAs/GaAlAs diode lasers with angled pumping stripes

Operation of DH GaAs/GaAlAs stripe contact lasers with stripes oriented nonorthogonally to the cleaved end facets of the laser is described. Such lasers, with misalignment angles ofsim2deg, do not exhibit "kinking" behavior to power levels greater than 90 mW/facet, and do not exhibit relaxation oscillations under pulsed operation. Data showing the dependence of laser wavelength, spectral half-width, transverse mode structure, facet reflectivity, and output beam angle on both stripe angle and pump current level are also presented.     

夜视系统用GaAs/GaAlAs半导体激光器

利用改进的液相外延技术生长出了ＧａＡｓ／ＧａＡｌＡｓ 夜视系统用光源。样品质量达到了设计要求。测量结果表明,样品在１０ Ｋ 下的光荧光谱的峰值波长为９２６ ．２６ ｎｍ 。利用该材料制作的激光二极管,其峰值输出功率达到１５ Ｗ。     

Structure dependent axial mode stability in GaAlAs/GaAs injection lasers

The influence of structure on the saturation behaviour of mode gain and the axial mode stability is investigated for different types of AlGaAs injection lasers. Both experimental and theoretical results confirm that carrier confinement along the lateral direction is effective for axial mode stabilisation.     

Low threshold GaAs/GaAlAs BH lasers with ion-beam-etched mirrors

We report the use of the ion-beam etching (IBE) technique to produce GaAs/GaAlAs BH lasers with one etched and one cleaved mirror facet. Low threshold currents of 12 mA have been measured in devices with 100 ?m-long cavities.     

Low-threshold oxide stripe GaAs/GaAlAs lasers grown by MOCVD

MOCVD-grown insulator defined stripe GaAs/GaAlAs lasers with stripe widths of 6, 10, 20 and 150 ?m have been characterised. Uniform CW threshold currents as low as 45 mA, differential quantum efficiencies as high as 74%, and kink-free power levels as high as 20 mW/facet have been obtained in 160 ?m long, 6 ?m stripe lasers. The internal differential quantum efficiency measured from our 6 ?m stripe lasers approaches one. Single longitudinal mode operation of these lasers has also been observed.     

Temporal and spectral characteristics of rapidly gain-switched GaAs/GaAlAs buried-heterostructure lasers

The temporal and spectral output of GaAs/GaAlAs buried-heterostructure lasers under excitation with 60 ps electrical pulses is investigated for different DC bias conditions. Optical pulses comparable in width to the electrical pulses can be obtained only if the DC bias is below or close to threshold, where multimode emission is observed. For DC bias well above threshold the laser remains single-mode; however, the optical pulses are considerably broadened.     

Characteristics of grating-coupled GaAs-GaAlAs lasers

Two types of grating-coupled (GC) GaAs-GaAlAs lasers with an unpumped corrugated region have been fabricated in order to clarify the characteristics of GC lasers. From the theoretical consideration, the efficiency of the GC output power was found to depend on the unpumped region loss and the edge-emission loss. To reduce the unpumped region loss, we adopted the separate confinement heterostructure (SCH) in place of the double heterostructure (DH). By taking the SCH structure, about 10 times larger efficiency was obtained than that of DH structure. More improved efficiency would be obtained by the reduction of the edge-emission loss. For this purpose, we propose a new structure with roof-top reflectors, which is able to be made by chemical etching technique and to be made into the monolithically two-dimensional GC laser array.     

Analysis of directional grating-coupled radiation in waveguide structures

Radiation scattered from diffraction gratings on the surface of waveguides is analyzed using the volume current method. This technique allows the interpretation of the grating elements as scattering centers of the underlying waveguide mode, and radiating sources for the diffracted fields. The framework allows separation of the effects of the grating array global periodicity and the effects of the specific shape of the individual grating elements. A straightforward analogy between the effects of the grating element shape and the behavior of phased-antenna array systems allows a clear and intuitive understanding of the effects of blazed gratings on the directionality of grating-coupled radiation. The analysis is applied to some specific geometries.     

Substrate radiation losses in GaAs heterostructure lasers

Double-heterostructure (DH) diode lasers with a thin Ga1-xAlxAs layer between the active GaAs region and the GaAs substrate or superstrate are analyzed. In these devices power flows through the thin Ga1-xAlxAs layer and is radiated into the substrate or superstrate. Three methods for computing the laser thresholds are developed and compared. The first is an analytic perturbation technique, which yields accurate results in many cases of practical interest. The second and third are rapidly convergent numerical iteration techniques. The former utilizes overlap integrals to compute absorption losses and thresholds; the latter includes all losses and gains directly in the formulation. We show that conventional DH diode lasers can be designed with thick active GaAs layers and still achieve lowest order TE-mode operation. These devices will produce better collimated, higher power output beams than do similar devices with thinner active regions. Transverse-mode control is achieved because all higher order modes have increased penetration through the thin Ga1-xAlxAs , and therefore exhibit inereased radiation losses into the substrate or superstrate. A design example is included in which it is shown that with proper choice of the Ga1-xAlxAs-layer thickness the TE0-mode threshold increases by 5 percent compared with a 110-percent increase in the TE1threshold. These results are virtually independent of the substrate power-absorption coefficient. Threshold current densities are computed for a set of diodes studied experimentally by Casey and Panish and the results are shown to be in excellent agreement.     

High bit rate modulation of narrow-stripe proton-implanted GaAs/GaAlAs injection lasers

High bit rate modulation up to 2 Gbit/s of a narrow -stripe (3 ?m) proton-implanted injection laser using resonance oscillation has been achieved. These results indicate that the narrow-stripe laser has possibilities of high bit rate modulation comparable to the broad-stripe laser. To obtain optimum modulation conditions, pulse height distortion was studied for various bias and pulse currents. Optimum was found for a bias current 5% above threshold and a pulse current of 42 mA in a laser with a threshold current of 111 mA.     

GaAs:GaAlAs ridge waveguide lasers and their monolithic integrationusing the ion beam etching process

The fabrication and performance characteristics of GaAs/GaAlAs ridge waveguide lasers are discussed. Threshold currents as low as 8 mA and differential quantum efficiencies as high as 90% were obtained for 250-μm-long graded-index separate-confinement heterostructure with single quantum well (GRINSCH SQW) lasers. High-speed short-cavity ridge waveguide lasers for which both the ridge stripe and one-mirror facet were formed by Ar-ion beam etching were achieved. The dependence of threshold current and lasing spectra on the cavity length were theoretically and experimentally investigated. This process was successfully used to integrate a laser diode monolithically with a photodiode or a field-effect transistor     

Low threshold current GaAs/GaAlAs GRIN-SCH stripe lasers grown by OMVPE

The letter describes the characteristics of stripe lasers formed in GaAs/GaAlAs single-quantum-well graded-composition separate-confinement heterostructures (GRIN-SCH) grown by low-pressure organometallic vapour phase epitaxy (LP-OMVPE). We show that the low threshold current density that has been achieved with the GRIN-SCH structure allows low threshold currents (38 mA) to be achieved in a simple gain-guided stripe-geometry laser. These low thresholds have been obtained without resorting to a complex nonplanar (lower yield) technology, and it is shown that the good uniformity offered by OMVPE is maintained through to the mounted device stage.     

Low-loss GaAs/GaAlAs strip-loaded waveguides with high coupling efficiency to single-mode fibres

We report measurements of low-loss MOVPE-grown GaAlAs/GaAs strip-loaded waveguides with high coupling efficiency to single-mode fibres. A propagation loss of 2 dB/cm and a coupling efficiency of 70% has been achieved for a p+-i-n+-structure waveguide. A propagation loss of 0.7 dB/cm and a coupling efficiency of 61% has also been achieved for an n?-i-n?-structure waveguide.