Dramatic progress in the development of high-quality vertical-cavity surface-emitting lasers (VC-SELs) has been achieved during the last couple of years, with very strong contributions made by U.S. researchers. In particular, new concepts of microlasers and resonant-periodic- gain devices have been proposed and implemented, and devices with strained-quantum-well active regions have been demonstrated. This paper reviews the present status and future prospects for (VC-SELs), with emphasis on recent developments in the U.S.

A novel distributed feedback structure for wavelength-resonant surface-emitting semiconductor lasers is proposed and demonstrated. Compared to earlier resonant-periodic-gain devices, the total thickness of the new structure can be considerably smaller while retaining the characteristic features of the resonant-periodic-gain active medium. Room-temperature cw and pulsed operation of first distributed-feedback resonant-periodic-gain AlGaAs/GaAs/AlAs laser is reported.

Development and performance of large area (0.5 cm2) junction-down monolithic two- dimensional surface-emitting arrays is reported. This involves fabrication of 45 degree(s) and vertical micromirrors with +/- 2 degree(s) tolerances and < 0.2 RMS smoothness, lapping and polishing of 2 in. diameter wafers with < 10 micrometers thickness tolerances, integration of 100 micrometers thick current spreading electrodes which minimize ohmic losses, large area packaging, and mounting to heat exchangers for long pulse operation and minimum chirp. Single monolithic surface emitter diodes exhibit superior performance (slope efficiencies of (eta) d > 50%, threshold currents of Ith equals 220 mA, and output powers in excess of 720 mW). This projects to power densities > 860 W/cm2 and > 50% differential slope efficiencies for arrays of devices. Large area array operation (scaling) was demonstrated. Uniform lasing was achieved from 0.2 cm X 0.5 cm and 0.5 cm X 1.0 cm active area junction-down monolithic arrays (120 and 600 emitters respectively) using 100 microsecond(s) ec long pulses at a 1% duty cycle. Differential slope efficiencies of > 40% were achieved for rows of 12 emitters, and 8% for the large area arrays. The drop in efficiency was due to current leakage, which limited the output power densities to 150 W/cm2. Chirp in these devices was measured to be < 4 nm at twice the threshold current.

Dramatic progress in surface-emitting lasers in the past year has generated a lot of excitement in this area. Recent results with strained-layer quantum-well lasers detailing low threshold current (0.6 mA) and narrow linewidth operation (85 MHz with a linewidth power product of 5 MHz(DOT)mW) are discussed. Theoretical analysis indicates the potential for increased power output without significant threshold increase.

Two-dimensional monolithically integrated master oscillator power amplifiers have been fabricated that emit in a single longitudinal mode to an output power of 4.5 W.

The design procedures for the construction of corrugated waveguides of Al2O3 and the far field radiation patterns observed from such waveguides are presented. The design procedure is based on the physics of four layer waveguide structures. The corrugated waveguide is similar to a Bragg type diffraction grating. This corrugated structure provides 90 degree(s) reflections at certain specific wavelengths depending on the grating spacing. A particular advantage of such structures that behave like grating antennas is that their radiation pattern can be scanned electronically by changing the wavelength (frequency). This corresponds to changing the propagation constant of the propagating wave. The far field radiation pattern obtained from the experimental set up is compared against simulations carried out using the Huygen-Fresnel theory and a close agreement is seen between theoretical prediction and experimental observation. Specifically, the design and the measurements are made in the frequency range from 90 GHz to 100 GHz for a number of different kinds of structures including those with one as well as multiple sections of corrugations.

InGaAs/InP multiquantum well distributed feedback (DFB) lasers with the active layer based on either lattice matched or strained quantum wells are described. The active layer wells are placed in a carefully optimized graded index waveguide structure with very low internal loss. Buried heterostructure Fabry-Perot lasers based on these structures show low threshold current, high quantum efficiency and power output. These characteristics are to a large extent retained in distributed feedback lasers, with the DFB lasers showing mode rejection ratios as high as 50 dB and linewidths as low as 440 kHz. Transmission experiments at 1.7 Gb/s demonstrated dynamic chirp penalty a factor of 8-10 smaller than in conventional lasers.

Carrier recombination rates are measured in both strained and unstrained quantum well lasers, and as far as possible the various physical mechanisms behind these recombination rates are separated out. The effect of Auger recombination on the higher than expected temperature sensitivity of threshold of 1.5 micrometers quantum well lasers is also examined.

InGaAs/GaAs strained-layer quantum well (SQW) laser structures have been investigated for avionic applications requiring high-temperature performance. These lasers offer availability of wavelengths in the range of 0.9-1.1 micrometers for important applications in Er-doped fiber amplifiers and optoelectronic integrated circuits. For the first time, InGaAs/GaAs SQW lasers capable of cw operation up to 200 degree(s)C have been successfully demonstrated. The lasers show threshold current density of 200 A/cm2, differential quantum efficiency of 60%, output power of approximately equals 1 W for 50-micrometers oxide-stripe and 120 mW for 3-micrometers ridge- waveguide lasers, and characteristic temperature (TO) of 130-140K. In this paper, the optimization of the stripe width, orientation and cavity length for the laser performance have been studied. The characteristics of these devices are described. Measured I-V, L-I, spectrum, farfield pattern and reliability data are presented.

A new type of diode laser array (denoted 'leaky-mode' or 'antiguided') has recently been reported. Despite their success, these devices are difficult to fabricate since they require a deep wet-chemical etch which must be accurately controlled. The authors report a new strained GaInAs quantum well device structure which is produced by etching a thin (0.12 micrometers ), transparent GaAs waveguide layer. These devices have demonstrated fundamental mode operation up to 2A (172 mW/facet at 1A) at 1% duty cycle pulsed condition and 700 mA (62.5 mW/facet) for cw operation.

Predictions of the threshold current density of GaAs/AlGaAs graded refractive index (GRIN), separate confinement heterostructure (SCH), single potential well (SW) diode lasers at 25 degree(s)C and 125 degree(s)C using strict k-selection theory are made. A reasonable fit to the experimental data at both temperatures can be obtained without including carrier scattering. It is concluded that good predictions of threshold current density and differential quantum efficiency can be made provided one knows how to predict the temperature dependence of internal quantum efficiency.

McDonnell Douglas has been developing fiber optic communication links and data bases for aerospace applications since 1975. These efforts have been complemented by a strong program in fiber optic sensor development that began in 1977. This paper provides an overview of some of the highlights of these efforts and a partial listing of McDonnell Douglas publications and patents in the area.

This short article reviews the key technologies required for implementation of future Photonic and in particular FBL systems. These technologies include fiber— optic position sensors, multiplexers, fiber—optic data O-8194-0508-6/91/$4.OO SPIE Vol. 1418 Laser Diode TechnologyandApplications /11(1991) / 153 buses, and transceivers. Some of Boeing's work in these technologies is described briefly in this article, and is covered more completely in Reference 1.

A standardized interface for fiber-optic sensor systems based on wavelength-division- multiplexing (WDM) has been successfully demonstrated using a novel broad-spectrum quantum-well LED and a high-resolution waveguide spectrograph. This efficient interface allows a 40-decibel system loss in 20 sensor channels. The new broadband LED and slab- waveguide spectrograph represent key enabling components for the WDM interface system. The LED produces a spectral width a factor of 3 times larger than that from conventional edge emitting LEDs in the 750-900 nm range. The compact slab-waveguide spectrograph's channel resolution (4-5 nm) and grating efficiency (>50%) compare favorably with other multimode WDM elements.

This paper reviews applications of dry etching to the fabrication of InP-based laser diodes. The plasma and ion beam processing techniques and chemistries used to etch InP, InGaAs and InGaAsP are briefly described. The application of these techniques to the fabrication of gratings (for distributed feedback lasers), active stripe mesas and channels, facets, and angled mirrors is then reviewed. The authors concentrate on dry etched/wet etched device performance and reliability comparisons for buried heterostructure devices, and process improvements afforded by dry etching.

Rapid isothermal processing (RIP) based on incoherent sources of light is emerging as a reduced thermal budget (product of processing time and temperature) processing technique. As compared to a stand-alone annealing unit, the integration of RIP with other processing units leading to integrated RIP systems is very attractive for the next generation of devices and circuits. From cost and performance point of view, the integrated rapid isothermal processing of these devices offers several advantages compared to their ex-situ rapid isothermal annealed and furnace annealed counterparts. The authors have used an integrated RIP system for the in- situ rapid isothermal surface cleaning of InP and GaAs substrates and in-situ metallization of InP and GaAs Schottky diodes. As compared to ex-situ annealing, in-situ rapid isothermal cleaning of InP and GaAs surfaces prior to metallization followed by in-situ annealing results in improved electrical characteristics. In addition to the well established short time processing feature of RIP, the dominance of radiation spectrum from vacuum ultraviolet (VUV) region to visible region can provide lower temperature processing compared to furnace processing.

InGaAsP laser diodes and InGaAs photodiodes grown on GaAs substrates have been reviewed. The laser diodes exhibit low threshold current of 31 mA and high slope efficiency of 0.2 W/A which are comparable with the diodes grown on InP substrates. The InGaAs photodiodes also show the comparable characteristics with the photodiodes grown on InP substrates. A GaAs MESFET and an InGaAs photodiode have been monolithically integrated. This receiver OEIC has sensitivity of -28.1 dBm at transmission rate of 622 Mb/s with a bit error rate of 10-9.

A fabrication technique for semiconductor lasers in the indium phosphide materials system which offers excellent reproducibility and uniformity in active layer and lateral cladding widths using a novel photolithographic technique and self-aligned etching processes has been developed. Lasers fabricated by this technique demonstrated a record modulation bandwidth of 24 GHz and intrinsic resonance frequencies greater than 20 GHz. Mesa and active layer widths are controllable to +/- 0.10 micrometers , and regrown lateral cladding in InP widths are 0.1 to 0.2 micrometers across the entire wafer. Specific contact resistances were less than 10-5 ohm-cm2.

The fabrication of etched mirrors for AlGaAs semiconductor lasers is described. The coating techniques for the passivation and reflectivity modification of the etched mirror surfaces are presented. Measurements on coated lasers show excellent beam quality, and satisfactory uniformity of laser characteristics across a wafer. Lasers which operate in a single transverse mode at output powers up to about 50 mW and have catastrophic optical damage (COD) thresholds greater than 120 mW have also been demonstrated.

A technique has been developed to generate an image of the stress-induced birefringence which occurs in AlGaAs/GaAs ridge waveguides. Cross-sections of this image can be taken to yield quantitative results. A preliminary cross-sectional plot from a ridge waveguide shows that the birefringence is higher at the ridge edges due to stress caused by the waveguide structure, and agrees with the shape predicted by theory.

Strained-layer (In)GaAs laser technology is being pursued at a number of laboratories with a view to extending the emission spectrum to longer wavelengths and exploiting strain-induced band-structure effects. Recently, remarkable longevity has been demonstrated for such devices and the implications for existing applications should insure continued research activity. Moreover, all of the key laser performance parameters -- efficiency, threshold current density and characteristic temperature -- have matched or exceeded their values for high-quality GaAs quantum wells. Evidence is mounting that the degradation phenomenology in pseudomorphic InGaAs lasers is radically different than in GaAs -- and for the better. Dark-line growth is inhibited, the derivative 'freak' failures cease to limit the lifetime and gradual degradation rates are tolerably low. This leads to the prospect of unity yield and 100% survival without benefit of costly burn-in procedures. Documented (extrapolated) lifetimes of 14,000 (50,000) hours are reported.

A number of recent observations promise to have a significant impact on semiconductor laser reliability. Device life has been seen to depend on device architecture and processing, epitaxial structure and growth parameters, and alloy chemistry. Comparative studies have shown that dry-etched devices are at least as reliable as oxide-defined lasers, and that median life is a function of the quantum well count in the structure. Improved reliability has also been obtained by using longer cavity devices to improve thermal performance at the lasing junction. Elimination or reduction in the occurrence of sudden or freak failures which limit median life of diodes has been achieved by studying the factors influencing the growth and propagation of dark line defects (DLDs). Operating temperature, chip geometry, alloy effects, and epitaxial growth parameters have all been shown to affect device reliability.

Optical fiber amplifiers are rapidly emerging as one of the key components for future optical communication systems. Exciting optical system demonstrations have already been achieved utilizing optical fiber amplifiers. For practical systems a high-power, reliable and wavelength- controlled semiconductor laser source will be required. This paper reviews the progress towards achieving these source requirements at both 980 nm and 1480 nm.

A 980 nm ridge waveguide pseudomorphic InGaAs/GaAs/AlGaAs single quantum well laser with a maximum single-ended output power of 240 mW from a facet coated device has been fabricated from a graded index separate confinement heterostructure grown by molecular beam epitaxy. The laser oscillates in the fundamental spatial mode, allowing 22% coupling efficiency into a 1.55 micrometers single-mode optical fiber. Life testing at an output power of 30 mW per facet from uncoated devices reveals a superior reliability to GaAs/AlGaAs quantum well lasers but also the need for protective facet coatings for long term reliability at power levels required for pumping Er-doped fiber amplifiers.

The performance of AlGaAs/GaAs GRIN-SCH-SQW ridge waveguide amplifiers has been characterized as a function of the rib-width, the amplifier bias and the master oscillator injection power. The results of this study revealed that the mode width is weakly dependent on the rib-width, the bias voltage increases with the injection signal level, and the 3 dB gain bandwidth is approximately 45 nm.

1.1 W cw has been achieved from a 10-amplifier coherent array with an electrical to optical conversion efficiency of 28%. The amplifiers were injected with 20 mW from a master oscillator via a single-mode polarization-preserving optical fiber. Approximately 90% of the output power from the amplifier array was locked to the master oscillator's frequency.

A new class of distributed feedback (DFB) semiconductor lasers is reviewed, which incorporates a periodic variation in gain coefficient. Intrinsic single mode nature and reflection immunity are great advantages of the gain-coupled (GC) DFB laser. Moreover, its carrier- density-dependent dynamic resonator provides a capability of generating short optical pulses with very low chirping. Recent experimental results of research on the GC DFB laser are presented.

The novel concept of K-stabilizing layer is reported for the first time. The coupling coefficient (K) which determines the characteristics of distributed feedback laser diodes (DFB LDs) has been controlled by optimizing the grating depth and layer thicknesses. The coupling coefficient is less dependent on the variations of grating depth and layer thicknesses if an optimized K- stabilizing layer (lower index material like InP) is inserted between the active layer and the guide layer. The controllability of the coupling coefficient has been demonstrated by the standard deviation of the lasing wavelength and the threshold current across a wafer, 0.74 nm and 2.67 mA, respectively.

The effects of fabrication tolerances on the resonant frequency of Bragg gratings etched in glass waveguides are reported. The glass materials are chosen for low thermal drift of refractive index and consequent low thermal drift of Bragg resonant frequency. Fabrication and measurement of Bragg gratings with grating period held constant to 100 ppm are demonstrated. A monolithic array of notch filters with resonant frequencies shifted over a 5 nm range by choice of waveguide width, thickness, etc., is demonstrated.

The fabrication and performance of high-speed and low relative intensity noise (RIN) 1.3 micrometers InGaAsP semi-insulating buried crescent (SIBC) Fabry-Perot (FP) lasers with Zn- doped active layers are reported. These SIBC lasers have a 3-dB modulation bandwidth of 19 GHz for pulsed operation and 16 GHz for cw operation, and a RIN below -150 dB/Hz for biased current at 120 mA. This is the highest modulation bandwidth yet reported for InGaAsP lasers with semi-insulating current blocking layers.

This paper reviews the recent progress of the 0.6 micrometers wavelength range high power InGaAlP visible light lasers. A fundamental transverse mode cw oscillation was achieved over 40 mW for the transverse mode stabilized structure fabricated by metalorganic chemical vapor deposition. Stable operations over 5000 hours were attained under the condition of 10 mW output power and 40 degree(s)C ambient temperature. High power operation over 80 mW was achieved for a window structure InGaAlP laser which was made in a very unique and simple fabrication process using a bandgap energy change phenomena by the atomic ordering change of this material.

Diffraction-limited beam operation at high output power levels (0.36 W cw and 1.5 W pulsed) have been demonstrated from resonant-optical-waveguide array structures. Uniphase mode operation is achieved without the need for active phase control. As a result, a reliable monolithic device capable of watt-range coherent output power is obtained.

Ten optical fibers were aligned to a single diode laser bar. The fibers were fed through a single optical connector with an aperture diameter of 381 micrometers . Coupling efficiencies as high as 65% were achieved with antireflection-coated fibers approximately 3 cm in length. Over 6.5 W cw at a power density of 5.7 kW/cm2 was delivered from the connector output.

Four-beam individually addressable monolithic AlGaAs laser-diode arrays have been developed in which each laser element can emit over 100 mW of output power in single-mode operation. The structural features of this laser include current-blocking regions near the facets and a long cavity length to obtain higher power, as well as a cBN heatsink and a 70 micrometers - thick laser chip to improve thermal crosstalk between laser elements. The maximum output power of each laser element is about 200 mW and the lasing wavelength is about 834 nm. Thermal crosstalk between 100 micrometers -spaced neighboring elements is only 1.0% at 100 mW.

Detailed broad-area coupled-mode analysis of in-phase mode selection in carrier-guided arrays coupled to external cavities with spatial filters is presented and compared with experimental results. A high-power (68 mW with output facet reflectivity of 90% which corresponds to estimated 266 mW with output facet reflectivity of 30%), on-axis, single-lobe far field with nearly diffraction-limited (0.64 degree(s)) full width at half maximum is achieved from a ten- stripe carrier-guided anti-reflection-coated laser array by coupling to an external cavity with a spatial filter. The in-phase operation is verified by wavefront measurements using shearing interferometry.

High power diffraction-limited GaAs/GaAlAs phase-locked laser diode arrays are developed and fabricated by LPE technique, standard photolithographic technique, wet etching and proton bombardment. The tailored gain-guided arrays are carried out by varying width of channel of laser, while the spacing between lasers remains constant. This array consists of six lasers. Its optical output power per facet is 300 mW at 2.7Ith, single mode cw operation, single lobe far-field pattern with FWHM 1.9 degree(s).

The present states of the vertical cavity surface emitting lasers (SELDs) in Japan conducted by the Tokyo Institute of Technology, Sanyo Electric Co. Ltd., Furukawa Electric Co. Ltd., Seiko-Epson Corp. and Electrotechnical Lab. are outlined. Most of the lasers use the semiconductive distributed Bragg reflector and buried heterostructure (BH) either for the active region or whole optical cavity. Combination of the SELD and thyristor by NEC Corp. for the optical functional device was also introduced. Lateral injection SELDs will be another choice for the multiple quantum well structure and reduction of the series resistance. Regrowth and processing techniques developed in Japan which may be applicable for the more optimized design of SELDs are also discussed.

Performance trends in the development of monolithic two-dimensional, coherent grating surface emitting (GSE) laser arrays are presented. Such GSE arrays now operate continuously to more than 3 W/surface and pulsed to more than 30 W/surface. They have obtained cw threshold current densities of under 140 A/cm2 with cw differential quantum efficiencies of 20 to 30% per surface. Linewidths in the 50 MHz range have been obtained with output powers of up to 270 mW per surface. The arrays typically consist of 10 to 30 mutually injection coupled gain sections with 10 laterally coupled ridge-guided lasers in each gain section. A single GaInAs strained-layer quantum well with a graded index separate confinement heterostructure geometry allows junction down mounting with light emission through the transparent GaAs substrate. A surface relief grating is used for feedback and outcoupling.

A surface emitting DBR laser with cylindrical symmetry operating in a single lateral mode is investigated. The effective reflectivity resulting from the grating and the threshold gain of the different lateral modes are analyzed using the coupled-mode theory. The authors' results indicate that when a cavity is designed for operation in the odd lateral modes, all the even modes are effectively eliminated. A small perturbation is introduced into the complex dielectric constant of the active region to further suppress the unwanted lateral modes and produce single mode operation.

Surface emitting laser diodes (SELD) are characterized by the fact that light is emitted vertically from the surface of the chip. The hemispherical resonator consists of one spherical mirror and one flat mirror placed approximately at the center of curvature of the sphere. In the past, the InGaAsP/InP SELD with hemispherical etched mirror was demonstrated at 77K. The authors have made theoretical calculations, considering material losses, resonator losses and angle deviation from the axis of cavity. The theoretical calculations indicate that in the case of the cavity length L more than 10 micrometers , the InGaAsP/InP SELD with hemispherical resonator is featured by having lower threshold current density Jth than with plane parallel resonator and will be possible in room temperature cw operation by using R equals (root)R1 (DOT) R2 equals 0.75 (Jth is congruent to 80 KA/cm2) or R equals 0.9(Jth is congruent to 25 KA/cm2), L equals 50 micrometers , d equals 1 micrometers and B 1, R2 are reflectivities of planar and hemispherical mirrors separately, d is the active layer thickness and B is the angle deviation from axis of cavity.

A new fiber optic sensor for use in flexible structures is reported. The sensor is based on an extension of Rogowski's design, in which the laser-driven optical beam in the fiber is modulated at radio frequency and strain is detected by a shift in the phase delay as the fiber dimension is strained with the structure. This sensor -- FORISS -- differs in that it consists of an embedded closed loop of fiber coupled to a laser/detector/fiber optic delay line circuit through a 2 X 2 coupler. The closed loop has the characteristics of a Fabry-Perot cavity operating at radio frequency wavelengths within the fiber. A parametric model of the sensor that enables both physical characterization of prototype sensors and insights which guide design optimization of the sensor is described. Experiments were performed on fiber- embedded composite specimens tension-stressed to failure at 26 kpsi and 7400 microstrains. The sensor survived to the point of coupon failure. The data indicates that the sensor possesses the properties predicted by the theory.

Laser Doppler Anemometry (LDA) is well established in fluid dynamic research. Most wind tunnel and water tunnel experiments are supported by LDA measurements due to their ability to measure instantaneous velocities with high precision. However, the classical LDA equipment is very voluminous, has large power consumption and needs skilled staff for operation. Because LDA is a nonintrusive measuring procedure with no calibration needs, its use outside the laboratory would be very interesting. Process control and calibration of classical fluid sensors can be considered to be the main applications. Along with semiconductor lasers and detectors instead of gas lasers and photomultipliers, a dramatic reduction in spatial volume and power consumption results. Therefore, essential requirements for a sensor concept are fulfilled. The paper presents a miniaturized LDA as a sensor head. It has the dimensions of 4.7 cm by 4.5 cm by 5.7 cm. It consumes less than 3 W electrical power on a 12 V power supply. The measuring distance is 9.5 cm. The velocity range which can be covered reaches from 5 m/s up to 500 m/s.

A monolithically integrated optoelectronic transmitter is being developed for wideband microwave-modulated links. The transmitter is designed to operate at signal frequencies of several gigahertz. It combines a GaAs/GaAlAs ridge-waveguide laser with a GaAs MESFET driver circuit. The laser has one of its cavity mirrors formed by dry etching so that the die size of the transmitter is not limited to the laser cavity length. The single-stage driver circuit is matched to both the low impedance of the laser and the 50 (Omega) microwave input by the inclusion of reactive components. A single-growth, vertically integrated material structure is used. Potential step-coverage problems that might result from this vertical integration are avoided by the use of air-bridge connections. The submicrometer FET gates are formed by direct-write electron-beam lithography.

The combination of a scanning monochromator, a digitizing oscilloscope and a computer, allows time-resolved spectral measurements on laser diodes. The flexible system described covers a wide range of timescale, well below 1 microsecond(s) ec at a spectral resolution of down to 0.05 nm. With this system the authors have investigated quasi-cw laser diode bars that are designed for solid-state laser pumping, at various operating conditions. The time evolution of the center wavelength is quite well fitted by a square root function according to non-stationary thermodynamics. The measuring system enables judgement of the quality of mounting technique and helps in choosing the right heatsink to minimize the wavelength chirp during a light pulse.

Diode laser spectrometer for trace molecules' analysis in high-pure volatile substances has been developed. Spectrometer is equipped with heated evacuated system for gas input and gas mixtures' preparation. Analytical parameters were estimated for water traces determination in oxygen, argon, and monogermane. Detection limit was equal to 8 ppb, 4 ppb, and 4 ppb respectively for these gas-matrixes with 1.5 m optical path length.

The facet temperature and output power of uncoated AlGaAs single quantum well lasers operated at constant current were measured as a function of time until catastrophical breakdown. During operation, the laser facet temperature increases with time and the temperature rise consists of two regimes; an initial linear temperature rise accompanied by a gradual power degradation followed by a rapid nonlinear temperature rise at what appears to be a critical temperature leading to catastrophical optical damage (COD). The pre-COD facet temperature rise rate as well as the time to COD are found to have a strong dependence on the diode's bias current. This facet temperature behavior plus the data obtained from an argon laser probe beam induced heating experiment provide valuable information regarding the mechanisms leading to COD.

A GaAs single quantum well mushroom structure surface emitting laser with a threshold current as low as 1.6 mA and a large output power of 2.0 mW operating at continuous wave (CW) room temperature condition is reported. The sample was grown by molecular beam epitaxy (MBE) and mainly consisted of a 300 $ANS GaAs single quantum well as an active layer cladded by two AlAs/Al0.1Ga0.9As multilayers as the top and bottom mirrors. The devices were fabricated by chemical mesa etching and undercutting to form a mushroom structure. A low series resistance of 250 ohms was obtained on devices with a 10 X 10 micrometers 2 constricted active region using a selective zinc diffusion. The laser operated at 860 nm with a spectral linewidth of approximately 0.5 angstroms.

The development of SCH InGaAsP/InP structures with low internal optical losses made it possible to achieve 1.2 W cw output for (lambda) equals 1.3 micrometers diodes with 100 micrometers aperture. The diode-to-fiber coupling arrangement enables one to reach a 700 mW power level in a 200 micrometers fiber.

Recent work has demonstrated high power, spatially coherent operation of on-the-chip unstable resonator diode lasers. The unstable resonators were fabricated in SQW-GRINSCH material using photolithography and a dry chemical etch technique. The unstable resonator design provides mode selectivity in broad area devices by suppressing higher order lateral modes. These devices demonstrated twice diffraction limited far fields with high average power and strong lateral coherence.

Efficiency and mode control in coupled grating-surface-emitting diodes are important issues in the proper design of these devices. In these devices, radiation emission properties depend on the injection current of the different sections, and phase effects due to length variations, grating phase effects, and the boundary conditions of the particular design. A realistic model incorporating power saturation, saturable losses, and saturable dispersion effects is established. Optimization of operation by injection current control and phase modulation are studied.