Recent advances in high power semiconductor lasers can be divided into two categories. These are partially coherent semiconductor lasers and coherent laser diodes. This paper will review advances in the operation of both such laser devices.

An extremely low threshold InGaAsP DFB laser diode has been developed by the MOCVD and LPE hybrid process. The threshold current of 3.1mA is the lowest value among InGaAsP laser diodes so far reported including those of the conventional Fabry Perot type. Using this low threshold DFB laser, 1 Gbit/s RZ zero bias modulation has been demonstrated.

A four-beam semiconductor laser was developed in which a monolithic array of four individually addressable GaAlAs high power lasers and four integrated Si photodiodes for monitoring the light output power of laser beams are housed in a single package. The main specifications are as follows; output power per beam, 40 mW; wavelength, 830 nm; and monitoring current at 30 mW, 100~200 Thermal analysis by numerical simulation was carried out and compared to experimental values observed during simultaneous operation of the multiple elemental lasers. The operating lifetime is estimated to be more than 10,000 hrs at room temperature.

Focused-ion-beam micromachining is a new technique for forming optical quality surfaces in semiconductor laser materials. It exploits the precise, computer controlled, maskless, sputter-etching afforded by a beam of 15 - 25 keV Ga+ ions focused to a 50 to 250 nm spot to fabricate features in semiconductor laser dice and wafers. Diode laser output mirrors of quality comparable to that of cleaved facets have been fabricated. Focused-ion-beam micromachined (FIBM) single stripe coupled cavity lasers have demonstrated widely and continuously tunable single mode operation. As much as 80 mW of pulsed tunable single longitudinal mode optical power has been achieved with FIBM coupled cavity phase-locked arrays of AlGaAs semiconductor lasers. Hundreds of milliwatts of pulsed optical power has been observed from surface-emitting phase-locked arrays with FIBM turning and oscillator mirrors. The use of vector scanning of the ion beam to produce arbitrary surface contours, such as linear and curved turning mirrors and micron pitch gratings with various profiles, has been demonstrated. Recent results from elevated temperature aging tests suggest that FIBM does not cause significant damage to transverse junction stripe laser diodes and that it can be a promising tool for fabrication of etched mirrors for optoelectronic integrated circuits. Continuing research includes work on the fabrication of (i) monolithic dual micromachined coupled cavity single frequency lasers with wavelength separations continuously variable from 0 to 600 GHz, (ii) linear and parabolic turning mirrors for two-dimensionally coherent surface emitting arrays of lasers, (iii) total-internal-reflection mirrors to route light in the plane of the wafer, (iv) single wavelength micromachined coupled cavity lasers tunable at high frequencies, (v) a methanometer with a continuously tunable micromachined coupled cavity InGaAs/InP optical source, (vi) curved laser mirrors, and (vii) submicron, arbitrarily profiled, diffraction gratings for distributed feedback and dis-tributed Bragg reflector lasers.

A new laser-assisted processing technique for thinning or removing GaAs and AlGaAs quantum well (QW) layers during epitaxial growth is demonstrated. In the particular application reported here, epitaxial growth of an optoelectronic device structure is interrupted while the QW active layer is locally heated with superimposed Ar+ and Nd:YAG laser beams. The evaporation rate of the GaAs or AlGaAs is greatly increased by the optically induced heating, resulting in a local thinning of the QW. After exposure, epitaxial growth is resumed, burying the patterned QW within the crystal. Transmission electron microscopy and photoluminescence are used to characterize the spatial variation of the energy bandgap. Broad area and high power laser diodes are fabricated from the modified region of the wafer. As expected, the wavelength of operation varies from laser to laser, consistent with the spatial variation in the energy bandgap.

We report on the design, fabrication, and testing of a 10x10 monolithic integrated two-dimensional array of AlGaAs optoelectronic threshold elements (optical neurons) for neural network applications. The array has dimensions of 5x5 mm2 and the neuron has dimensions of 250x250 μm2. Each neuron consists of a light emitting diode (LED) driven by a double-heterojunction bipolar transistor, which is driven by the output of a double-heterojunction phototransistor. We demonstrated the partial functional operation of 2-D array of optical neurons by independently characterizing each device on the integrated circuit. DC current gain of 30 was obtained at the collector current density of 1.0x103 A-cm-2 with the emitter area of 3.5x10-5 cm2 in a single transistor without spacer layers. The output power densities of the light emitting diodes were about 1.0x102 W-cm-2 at a current of 20 mA. However, the overall integrated structure showed the semiconductor controlled rectifier characteristics with the breakover voltage of 75 V, the holding current of 10 mA at the holding voltage of 25 V, and the reverse breakdown voltage of 60 V. This is attributed to the parasitic p-n-p transistor that exists due to the sharing of the same n-AlGaAs collector between the transistors and LED.

Many of the growing number of applications of laser diodes are demanding high power diffraction limited sources. For such applications real refractive index guided laser diodes have been used. For the past few years the highest power available commercially from an index guided single mode diode has been 30 mW cw. Recently several manufacturers have introduced single mode diode lasers which emit much higher powers rated reliably at 100 mW.

High power, single spatial mode (A1Ga)As/GaAs quantum well lasers have been fabricated which combine very high power operation with a low threshold current. Optimisation of the performance of these lasers has been aided by modelling the electron-photon interaction (hole-burning) at high drive levels. Single, element ridge waveguide lasers have been fabricated using a combination of wet and dry etching techniques. These structures combine a high continuous wave burn-off power density of 9.0 MW/cm (non facet-coated) with a high single spatial mode purity. Single spatial mode powers in excess of 128mW have been measured on non-coated devices. Performance improvements have been obtained by facet coating giving zero-order mode powers of 175mW, burn-off power levels in excess of 300 mW and slope efficiencies of 0.84mW/mA.

Two rows of surface-emitting (ten-element each), linear arrays were coherently locked to an external master oscillator. Tuneable operation was achieved over a greater than 40 A wavelength range, and coherence was confirmed by far-field interference.

We report long-life GaAlAs lasers showing fundamental-mode high-power operations, which have been developed by providing current blocked nonabsorbing mirror (NAM) regions in the conventional buried twin ridge substrate (BTRS) structure. Suppression of the mirror degradation due to local heating for the NAM and use of the loss-guide mechanism for the BTRS structure are the main cause of the excellent operations. For the fabrication, use of a substrate having a mesa on it and a hybrid epitaxial technique of LPE and MOCVD is an essential point. As a result we have obtained the stable fundamental spatial mode operations up to 120 mW and the maximum output power of 300 mW under a CW operation. Degradation has been insignificant for 6000 hours under the output power of 100 mW and the temperature of 50°C.

Two kinds of modal filter for high power diode lasers with a wide stripe have been examined. The first one is a partially narrow region formed in the active region. Flared-SBA(self-aligned bent active layer) laser in which the active layer flares the width from the narrow filter region to the wide output facet oscillates in a fundamental transverse mode under cw condition up to the output power of 64mW. The second one is a partial coating at the output facet of lasers. By applying it to an SBA laser whose stripe width is 150 μm, the laser oscillates in a single lobed far-field pattern up to 300mW, whose divergent angle is as narrow as 1.7° in FAHM(full angle at half maximum) under cw conditions.

High power fundamental lateral-mode operation up to 80 mW in CW condition is achieved in a broad-area laser diode. This diode has built-in lens-like effective refractive index distributions in the direction perpendicular to the laser beam. These distributions effectively suppress higher order lateral-mode generation.

Three approaches to fabricating two-dimensional surface-emitting GaAs/AlGaAs diode laser arrays are discussed: a hybrid approach in which linear arrays of edge-emitting lasers with cleaved end facets are mounted on microchanneled Si heatsinks with integral 45° deflecting mirrors, a monolithic approach in which edge-emitting lasers are fabricated with deflecting mirrors adjacent to both end facets of each laser, and a monolithic approach in which horizontal-cavity lasers are fabricated with intracavity 45° deflecting mirrors. In both monolithic approaches, all the laser facets and deflecting mirrors are fabricated by ion-beam-assisted etching.

Coherence between elements of a laser diode array can be established either by coupling the individual oscillators together on-chip or by coupling the array as a whole to an external cavity. Several techniques for on-chip coupling have been demonstrated 1,2,3, however these approaches typically produce an output having low Strehl ratio due to the difficulty of maintaining adequate control of the phase and amplitude of the emitters across the length of the chip. Several authors have reported phase locking of small laser diode arrays by placing the diode array in an external cavity and making use of a spatial filter in a Fourier transform plane of the array to force mutual coherence between the diodes 4,5,6. This technique works well for relatively small arrays, but becomes impractical for large scale arrays. Recently an external cavity technique has been demonstrated that takes advantage of the Talbot self-imaging effect 7 to phase lock an array of laser oscillators 8,9,10,11,12. A significant advantage of the Talbot cavity as opposed to previous external cavity approaches is that the Talbot cavity can be scaled to accommodate arrays containing a large number of lasers if attention is paid to control of the oscillating modes of the array. In this paper we demonstrate how mode control of an array of diode lasers in a Talbot cavity can be achieved through the use of intracavity spatial filters or phase masks. The Talbot (or "Self-Imaging") cavity makes use of the diffractive properties of the Fresnel (near-field) zone of a periodic array of coherent sources, which has a set of characteristic self-image planes associated with it. At distances 2nD2/A from the array an image of the array is formed (D is the separation between elements in the source array and n is an integer). In addition to these planes, there also exists a set of planes at distances D2/mA, (m=1,2,3,...) from the source array in which multiple images of the source are formed, we refer to these planes as "subrimage planes." In the "m-th" sub-image plane, "m" separate images of the source array are formed, the different images having relative phase shifts between them. Figure 1 shows the locations of the first few image planes and the relative phases of the images in the planes.

Application of a broad area laser for a light triggered thyristor valve system was investigated. The maximum light output powers of 1.8 W and 2.7 W were obtained in 80 um wide and 160 um wide laser, respectively. Lasers operated for more than 1000 hours in 100 times accerelated aging condition except for rapidly degraded ones. The rapidly degradation rate consistent with substrate defect dencity.

Recently, we have demonstrated a novel surface-emitting semiconductor laser with a wavelength-resonant periodic gain medium, which has performed significantly better than conventional double-heterostructure and multiple-quantum-well vertical-cavity devices. The gain medium consists of a series of half-wave-spaced quantum wells which provides enhanced longitudinal gain at a selected wavelength in the vertical direction, reducing transverse amplified spontaneous emission, lowering the threshold and raising the quantum efficiency. However, because the antinodes of the standing-wave optical field must coincide with the quantum wells, considerable attention must be devoted to designing the vertical cavity. Here we examine various cavity configurations in which the wavelength-resonant periodic gain medium has been incorporated. Multilayer epitaxial reflectors are particularly attractive for fabricating monolithic vertical-cavity surface-emitting lasers.

We report measurements of the near-field phase of a two-dimensional array of grating surface emitter diode lasers. The measurements were performed by scanning single and double slits. We use the individually measured phases over 300 μm x 50 μm emitting regions to predict the beam quality, and we compare the predictions with measured data.

The on-axis fields from separate elements of a coherent laser array can interfere either constructively or destructively, depending upon the relative phases. We describe thin film transistor (TFT) and direct-drive controlled arrays of liquid crystal phase shifters, which provide both phase matching and fine beamsteering. The transmissive liquid crystal devices contain homogeneously aligned layers of nematic liquid crystals sandwiched between two glass plates. The devices impart electrically controllable analog phase delays to laser beams passing through the cells. The devices are divided into arrays of individually controlled elements using separate transparent electrodes.

Experimental results are presented which indicate the existence of index-guided lateral modes between stripes in multistripe laser diode arrays fabricated from planar double heterostructure material. Through a comparison to measurements made on twin-stripe arrays, each adjacent pair of stripes in a three-stripe array is observed to support index-guided modes. A comparison of the measured far-field intensity pattern with the calculated far-field diffraction pattern from the three-stripe array suggests that out-of-phase coupling between the two index-guided modes has been observed just above threshold, while at higher currents the two modes run independently. The presence of higher-order index-guided modes has also been observed as the current is increased. Measurements made on a commercially available ten-stripe laser also suggest the presence of index-guided lateral modes.

A computer model for the optical gain of graded-index, separate-confinement-heterostructure, single-quantum-well (GRIN-SCH-SQW) Alx Ga1-xAs diode lasers is presented, and compared with experimental data. The model combines many individual features not heretofore included together, and gives good agreement with gain vs current density data for two different structure variations. In addition, the threshold temperature dependence agrees well with data for typical laser conditions, the observed high-gain discontinuity in T_° vs temperature is explained, and new predictions are made concerning T_° discontinuities at gain cross-overs.

We have developed a theory describing the effect of external optical feedback on the steady-state noise characteristics of a single-mode semiconductor laser. This theory is valid for arbitrarily strong feedback and arbitrary external cavity. The general formalism includes relaxation oscillations, and allow us to analyze the effect of feedback on both the laser linewidth,frequency noise, relative intensity noise and the relaxation oscillation sidebands in the field spectrum.

The linewidth enhancement factor a of a semiconductor injection laser is defined to be the ratio of the changes in the real and imaginary parts of the complex susceptibility of the laser medium due to carrier density variations. We have devised a novel method for measuring this parameter by observing the changes in the optical frequency and external quantum efficiency due to coherent optical feedback. The wavelength dependence of a close to the room-temperature gain peak was measured for GaAs/GaAlAs channeled-substrate-planar devices.

The effects of fabricational variations on the gain spectra of quantum wires are calculated within the limits of first order perturbation theory. Gain spectra and density of states for 50A radius and 150A radius cylindrical quantum wires are calculated and plotted for several different fabrication tolerances. The wave functions for a finite, cylindrical potential are calculated and a quasi-critical radius, below which the carriers are weakly confined by the potential, is established. This sets a lower limit on quantum wire size. Upper limits on the size of quantum wells, quantum wires, and quantum boxes are also discussed. The threshold current and differential gain of quantum wire lasers and quantum wire array lasers are calculated. These calculations indicate a possible reduction in threshold current of one to two orders of magnitude as compared to the best quantum well lasers to date.

A quantum well (QW) gain model was developed and was applied to optimization of surface emitting diode laser arrays. To increase output power density per unit surface area, short cavity lengths must be considered. We show how the maximum power density and power efficiency requirements lead to multiple wells; the performance is limited by gain saturation associated with QW subband filling at increased threshold gain requirements in short cavity lasers.

A new semiconductor laser design, the leaky-guided channeled substrate planar (LCSP) laser is presented. The analysis, by using the effective index method in the complex domain, shows that the LCSP structure provides better lateral mode stability than either gain guided or positive index step structures. The LCSP structure with reduced heating and strong lateral coupling effect may be more useful for high power linear array lasers.

The field of high speed semiconductor lasers has undergone substantial advances since the first demonstration of a laser with modulation bandwidth beyond 1OGHz[1]. Much of the present understanding on the high speed modulation of semiconductor lasers comes from a small signal analysis of the laser rate equations, which is basically a book-keeping of the rate of supply, annihilation and creation of carriers and photons inside the laser cavity and describes laser dynamics in a most basic manner. The resulting small signal bandwidth is given by the now standard formula [1]

Performance advantages and cost reductions are expected from the introduction of optoelectronic integrated circuit technology. A common technology base for different functions and applications will permit the fabrication of a wide range of different OEICs.

Self-aligned Buried Crescent Heterostructure (BCH) semiconductor lasers and LEDs have been successfully developed as superb light sources for fiber optic communications. The fabrication and performance characteristics of these InGaAsP/InP lasers and LEDs are described. For lasers, the threshold currents as low as 10 mA and differential quantum efficiencies as high as 50% are achieved. For LEDs, the output powers at 150 mA are higher than 1 mW. Good far field patterns are obtained in both the LEDs and lasers. Measured I-V, L-I, spectrum and far field patterns are presented.

Laser radar (ladar) performance parameters such as range accuracy, estimation time and target range are analyzed as a function of the component parameters that comprise the system. Design tradeoffs and performance comparisons are evaluated for two popular ladar system designs: intensity modulated(IM)/direct detection(DD) and frequency modulated(FM)/coherent detection(CD). The comparison includes practical discussions of modulation, signal processing and component performance. The analysis begins by presenting accurate signal to noise ratio (SNR) equations that include the often omitted phase noise and intensity noise terms. Next, the SNR is related to the range accuracy, estimation time and modulation frequency or bandwidth via the Cramer-Rao lower bound (CRLB) for optimal processing. The results of the analysis are used to identify critical component design and performance issues for precision IM/DD and FM/CD ladar systems.

Coupled-cavity tunable-single-frequency diode lasers are used in conjunction with an electronically tunable external cavity to increase the range of a coherent lidar system. Three-terminal DFB lasers and cleaved-coupled-cavity lasers are used which allow continuous wavelength tuning over a range greater than 2A by direct modulation of the injection current. This tuning range results in a distance resolution of less than a centimeter, without signal averaging or other enhancement techniques. By using an electrooptic waveguide phase modulator in the external cavity we have maintained a narrowed laser linewidth while simultaneously tuning the solitary laser. We have achieved a coherence length of 50 meters, a tuning range of 40 GHz, and a simultaneous tuning range-coherence length product of 750 GHz-m.

This paper describes the development of a Coherent Laser Radar utilizing a Frequency Modulated (FM) GaAlAs laser diode as an optical source. Both metrology (low speed, high accuracy) and vision (high speed, low accuracy) systems have been developed. Characteristics of presently available laser diodes important to this application are discussed, including coherence length, modal and tuning properties, and the effect of back reflected light on the laser diode's performance. Techniques to overcome current laser limitations are presented. These include an electronic linewidth narrowing scheme to enhance the coherence length of the source laser and thus the ultimate range of the radar, and the use of tuning linearization electronics. Finally, the impact of future laser diode technology, such as electronically tunable lasers, is discussed with respect to this application.

By splitting the electrical contact of a conventional distributed feedback (DFB) laser into two sections, the frequency tuning characteristics of the DFB laser are modified and the DFB two-mode degeneracy becomes electrically controllable. As a result, novel device functions can be achieved. Several applications of two-electrode DFB lasers are described: (1) active single-mode stablization, (2) control of spectral reliability and wavelength chirp under amplitude modulation, (3) logic gate operations utilizing the DFB two-mode degeneracy for switching, routing, and optical computing, and (4) frequency modulation of the DFB laser for FSK coherent communication systems and optical sensing.

Improved, yet cost-effective laser-based analog video transmitters are required for single mode fiber for video distribution to subscribers. Both Fabry-Perot and DFB lasers in the 1300 nm and 1550 nm regions are commercially available which facilitate transmission of both digital and analog video signals. Three representative system applications of such devices explored recently by Bellcore are described with emphasis on desirable laser characteristics and requirements which govern overall performance.

Modern frequency standards, such as hydrogen masers, generate very stable frequency references for various applications in communications and metric tracking systems. The frequency stability of some standards currently exceeds 1 X 10-15 for 1000 second averaging times.1 For various reasons of redundancy and cost efficiency there is a need to distribute stable reference signals to remote users without significantly degrading their frequency stability. However, distribution systems generally degrade the frequency stability of transmitted signals by degrading the Signal-to-Noise-Ratio (SNR) of the signal and causing group delay variations in the signal path with respect to time. Thus achieving the required frequency stability in frequency distribution systems has become a difficult technical challenge. The ability to distribute precise frequency references over distances of tens of kilometers will result in considerable cost savings, improved performance and better reliability in the NASA/JPL Deep Space Network (DSN). This ability, for instance, will enable the use of a centralized frequency and timing facility and therefore reduce the number of expensive frequency standards needed in a Deep Space Communications Complex (DSCC). To this end, fiber optic frequency reference distribution system development is an ongoing task at JPL. The present goal is to achieve a transmission stability of 1 X 10-18 for 1000 seconds averaging times over a distance of 29 kilometers. This paper will describe the mechanisms in a distribution system that cause degradation of frequency stability of a transmitted signal. In particular instabilities that result from the use of a semiconductor laser transmitter will be discussed. Finally, it will describe the fiber optic frequency reference distribution systems developed at the Jet Propulsion Laboratory, and now in use at the Goldstone DSCC.

Communications in space utilizing lasers has been considered since their realization in 1960. It was soon recognized that, though the laser had the potential for the transfer of data at extremely high rates, much work was required in system and component development, particularly for space-qualified hardware. Advances in system architecture, data formatting, and component technology over the past quarter century have now made laser communications in space a viable and attractive approach to space based communications. In particular, semiconductor laser diodes offer important advantages over other laser sources, in size, weight, volume, efficiency, and data rate. There are however, performance restrictions which impact the system design and the direct application of laser diodes for communications in space. This paper presents an overview of space-borne laser communication systems and key laser diode parameters which affect their application.

An all fibre interferometer device is presented which allows the measurement of speed to be made using an electronic processing system and is contrasted with the measurement of velocity through an optical processing technique which, however, is more complex and expensive to implement. The overall simplicity of the electronic technique, the low cost of components and the use of an all-fibre arrangement make this a convenient system to implement.

To write messages with diode lasers they are current driven. The words correspond to different impulse packets. The size of the pulses and the repetition rate are variables which are organized to suit the needs to convey a particular phrase. The radiation pattern of a diode laser is influenced by both current and pulse signal and repetition rate. The emitted light is structured in a way that the area where the message can be read varies strongly. This is used to make some messages reach into wider areas and some messages into more confined space. This paper shows the results pertaining a collimator for two types of pulse sizes and two different messages. One which is aimed very precisely and the other which is meant to cover a larger portion of space. The diagrams of spot size and its evolution through space are presented. As an example and for the best situation as regards our application the area of the narrow beam passes through a minimum along its propagation path. Also changes in the elliptical orientation of the pattern are reported.

A review of high frequency InGaAsP/InP laser structures is presented. The performance of these devices is analyzed based on a rate equations model. The effects of packaging and device parasitics on high speed modulation are also considered through a circuit configuration. The model is used to compare the relative advantages of the main high frequency laser structures in order to maximize the obtainable modulation bandwidth. The characteristics of buried crescent lasers with semi-insulating current-blocking layers are highlighted. A 3-dB direct modulation bandwidth of 11 GHz together with 42-mW output power has been achieved with this device.

Strained-layer InxGa1-x As quantum well lasers have attracted considerable attention of late due to the materials configurations made possible. Interest in the semiconductor laser community stems in part from the prospect of accessing the spectral window near 1 um for pumping new solid state hosts and in part for space communications if an advantage can be demonstrated. Technologists in these areas have fostered the hope that strain accommodation and perhaps lattice hardening 2-4 by In can enable viable long-lived devices. Steady progress in the development of high-performance Inx Ga 1-x As lasers 5-11 has been encouraging with the first cw life-test reports coming quite recently.'" Among other recent advances we cite achievement of high-power, low-threshold buried heterostructure devices operating near 1.1 We will be presenting recent progress in performance and reliability of (In)GaAs lasers of three very different types. First we will discuss devices emitting near 1 pm with demonstrated cw lifetimes exceeding 5000 hours. Next we turn our attention to two extreme cases. The first structure utilizes low levels (2.5%) of In in the quantum well of an otherwise conventional (A1)GaAs graded-index separate confinement heterostructure single quantum well (GRINSCH-SQW) laser and thus constitutes a small perturbation on a familiar device. Finally, a step-index structure with a In 0.51 Ga 0.49 As quantum well will be discussed.

For high-performance optical data storage applications, AIGaAs/GaAs diode lasers were stressed at various power levels, temperatures, and operating conditions. The devices tested were V-channeled structures mounted with the junction side down. These lasers came from a single production run to eliminate the statistical variances associated with multilot tests. Cumulative failure plots for cells at 30 mW stressed at 65°C and 40 mW stressed at 55 and 65°C show that two failure mechanisms are present, which we designated as intrinsic and wear-out failure regions. Using the data from the wear-out region and assuming an Arrhenius model for the temperature dependence of the reliability function, we found that the activation energy for this lot of lasers is 0.37 eV. From this evaluation, we project a median lifetime of 3.4 khrs for 40 mW operation at 35°C, and a median lifetime of 36.7 khrs at 30 mW and 35°C, which is an order of magnitude greater. Fot :4 power model where the median lifetime is proportional to power raised to the -n, we calculated that n is 4.3 for powers between 30 and 40 mW. Other data to be discussed was accumulated from low-power continuous-wave and pulsed stress cells. In addition, failure analysis results correlated with the various failure regions will be presented. All the devices were fully characterized prior to stressing, and throughout the stress period they were periodically characterized for changes in operating current at 7 mW and 30 mW, for parallel and perpendicular far-field distributions, and for astigmatic length. To our knowledge, this is the first experimental data that tracks these optical properties over the life of a laser diode. With the exception of the drive current to maintain a given optical power, all other electro-optic properties exhibit stability throughout the diode lasers' lifetime. The data also shows that there is no precursor to failure. Our results show that acceptable reliability targets can be met for high-performance optical storage applications as long as the operating temperature is maintained below 35°C and the optical power is limited to 30 mW.

The design considerations involved in the primary packaging of semiconductor laser diodes are major factors in the performance, reliability, cost and ultimate commercial success or failure of the finished device. The requirements of the package are as varied as the uses to which semiconductor laser diodes are put; they include such considerations as physical outline, ruggedness, mechanical stability, thermal efficiency, electrical characteristics, unit cost, and handlability. The experience gained by device designers and manufacturers through development and commercial production of semiconductor laser diodes provides the data base from which design proposals are made for new products. However, performance requirements are increasing significantly beyond previous experience and both chip and packaging design engineers are having to turn to new materials and novel design methods to meet these challenges.

The ability of a laser diode module package to maintain precise laser-to-fiber alignment with mechanical stress or temperature change is critical for stable performance. This paper examines an optical-mechanical package configuration in which both laser and fiber are mounted on the same surface with high-temperature solder, thereby minimizing degraded package performance caused by exteraneous thermal or mechanical changes.

An experimental approach to evaluate the heat load of a laser diode module has been performed. In this experiment, stable CW light output operation up to 125°C was achieved by adding an external high capacity thermoelectric cooler to the laser diode module. By monitoring the temperature of the laser diode package, the cold side of the thermoelectric cooler, the heat sink temperature, the ambient temperature and compare these temperature data with the performance curves of the thermoelectric cooler, we have identified that the major source of heat is from the laser diode package case. Heat is originated from both the ambient and the hot side of the thermoelectric cooler. Proper thermal design of the module package is important to the optimum performance of the laser diode in an actual operating environment. These results are of considerable significance for the development of temperature stable diode laser source for military and aerospace application.

Many applications for semiconductor lasers that require high average power are limited by the inability to remove the waste heat generated by the diode lasers. In order to reduce the cost and complexity of these applications a heat sink package has been developed which is based on water cooled silicon microstructures. Thermal resistivities of less than 0.025°C/01/cm2) have been measured which should be adequate for up to CW operation of diode laser arrays. This concept can easily be scaled to large areas and is ideal for high average power solid state laser pumping. Several packages which illustrate the essential features of this design have been fabricated and tested. The theory of operation will be briefly covered, and several conceptual designs will be described. Also the fabrication and assembly procedures and measured levels of performance will be discussed.

The attractive prospect of CW AlGaAs/GaAs monolithic linear diode laser arrays (aka bar arrays) arises from the continuing improvement of the attributes of pulsed diode lasers, such as external quantum efficiency, lifetime, and coherence capabilities. Unfortunately, for close packed arrays, CW operation of an array at ambient temperature is limited to a few watts of optical power. Wafer thin coolers (on the order of lmm thick) that have been designed to remove heat fluxes of over 100W/cm2 from laser array packages (a diode bar soldered directly to the coolers via a 'sandwich' package) which operate more effectively in a CW mode. Tests were conducted to compare the thermal and optical performance of five types of such wafer thin coolers; a double pass microchannel cooler, two types of single pass microchannel coolers, and two versions of a compact high intensity cooler (CHIC). Thermal tests were conducted on the coolers alone at heat fluxes from 5 to 125W/cm2. CW power vs. current (P-I), uniformity of emission, and wavelength vs. current measurements were made for each cooler/bar package. The optical experiments were conducted at 5 and 15kg/hr flow rates, and at 15° and 25°C inlet temperatures, using water as the cooling fluid. Results of the optical tests performed on 0.9cm linear arrays mounted on the wafer thin coolers showed impressive performance, such as 19.4W CW at 30 amps input current, and a very small wavelength spread across a bar. Such performance levels warrant these cooler/bar packages as a standard in CW bar operation.

An experiment was conducted to establish an effective burn-in and screening procedure for long life SINSCH-SQW laser diodes. The laser diodes were grown by MOCVD and processed with 20μ wide oxide defined stripes. The devices had a high reflective back facet coating with a small etalon bonded to a passivated front facet to ensure single mode operation. The laser diodes were bonded p-side up to copper heat sinks using indium solder. A total of 48 devices were selected prior to burn-in and were operated at 200mA constant current for 2000 hours at an average heat sink temperature of 55°C. The average initial output power was 45mW per device. At the end of the test, the output powers ranged from lmW to 85mW. Most of the devices with the low final power failed catastrophically within 24 hours from the start of the test. Many laser diodes showed very little change in output power while others degraded gradually by varying amounts. Failure analysis showed that failures were facet, bulk, or heat sink related. The temporal output power degradations (i.e., gradual degradation, etc.) can be explained by the identified failure mechanisms. From the test results and failure analysis, a screening strategy based on inspection and burn-in can be devised to reject devices that may fail early. Also, improvements in processing can provide potential yield improvements. After accounting for degradation related to processing, a very long material lifetime is predicted for these SINSCH-SQW laser diodes.