InGaAs-GaAs strained layer quantum well heterostructure lasers offer availability of emission wavelengths in the range of 0.9-1.1 micron, otherwise largely inaccessible with semiconductor diode lasers. Here, InGaAs-GaAs strained layer lasers and laser arrays grown by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) are described. The growth conditions for preparing these strained layer structures by MOCVD are presented, and time zero characterization of oxide defined stripe broad area lasers is outlined as a function of InGaAs layer composition and thickness, relative to the critical thickness. Various structures, grown throughout the 0.9-1.1-micron wavelength range and having In mole fractions from x = 0 - 0.50, are shown to have low broad area threshold current densities (Jth less than 200 A/sq cm) and other characteristics of unstrained quantum well heterostructure lasers. Recent results indicating highly reliable CW operation of oxide stripe strained quantum well heterostructure lasers are reviewed.

Both gain-guided and index-guided InGaAs/AlGaAs pseudomorphic laser diodes have been fabricated and tested. The characteristics are similar to lattice-matched GaAs/AlGaAs lase diodes in that the threshold current, differential efficiency, and maximum output powers are comparable. Output powers of 3 W CW have been achieved at 960 nm from a 100 micron aperture laser. An increase in the gain coefficient by 30 percent has been measured in the lasers with strained active regions. Single-mode lasers have also been fabricated which operate to 350 mW, 180 mW in a single transverse and longitudinal mode.

High-performance strained InGaAs/AlGaAs lasers fabricated from material grown by atmospheric pressure organometallic vapor phase epitaxy are demonstrated in a variety of structures. The results suggest that the poorer performance observed in the longer wavelength, more highly strained structures is due to an increasing density of interfacial defects even in quantum wells (QWs) of subcritical thickness. Despite this, a graded QW structure improved the performance of highly strained QW lasers, presumably because it reduces lattice mismatch at the active region interfaces. Long-lived InGaAs QW lasers are demonstrated, and strained layer materials are applied to two kinds of two-dimensional laser arrays with performance comparable to GaAs QW lasers

Strained layer GaInAs graded-index separate-confinement heterostructure quantum well lasers grown by molecular beam epitaxy (MBE) are now demonstrating performance comparable to, or superior to, those grown by organometallic vapor phase epitaxy. The improvement in performance of the MBE grown lasers is largely due to optimized growth conditions which result from previous studies of the growth of strained layer channels for strained modulation doped field effect transistors. In this presentation, discussion covers the range of growth conditions for strained layer GaInAs/GaAs structures, the properties of these strained layer materials, and the dc and microwave performance of lasers fabricated from layers grown under these conditions.

Monolithic stacking of up to three quantum well lasers has been demonstrated. CW threshold current densities per well and differential quantum efficiencies are comparable to those for individual devices, and transverse far-field patterns indicate phase-locking. Catastrophic optical damage levels increase with increasing quantum-well count and are substantially higher than those achieved with a single quantum-well laser when GaAs wells are involved.

A low threshold coplanar vertical injection laser diode (CPVI-LD) has been newly developed utilizing impurityinduced disordering of a single quantum well. The threshold current as low as 13 mA has been realized in CW operation. The behavior of Si and Zn solid phase diffusion is precisely investigated for the realization of the CPVJ-LD.

The application of high-power single-emitter lasers to coherent optical communication in studied. Measurements of laser properties essential to heterodyne detection systems are presented for high-power lasers and compared to standard single-mode 30-mW laser diodes. The advantages of the new high-power laser structures are demonstrated in a heterodyne frequency-shift-keyed communication system.

The application of high power single emitter lasers to coherent optical communication is studied. Measurements of laser properties essential to heterodyne detection systems are presented for high power lasers and compared to standard single mode 30 mW laser diodes. The advantages of the new high power laser structures are demonstrated in a heterodyne frequency-shift-keyed communication system.

The degradation mechanisms of laser diodes are studied. It is shown that the reliability of the SDL-5410 and the SDL-2441 result in projected lifetimes of greater than 60,000 at 25 C and 200,000 at 15 C, respectively. The high maximum output power protects the laser from optically induced degradation; residual degradation is due to thermally- or field-induced recombination centers.

Two types of high-power GaAlAs single-element lasers with nonabsorbing mirrors are described. One is a high-power laser which oscillates at wavelengths as short as 780 nm. The difficulty of growth on high AlAs-content surface has been overcome by optimizing the flow rate of arsine in the covering MOCVD growth. The fabricated 780-nm nonabsorbing mirror-buried twin-ridge substrate (NAM-BTRS) laser has achieved maximum output power of 200 mW due to complete suppression of catastrophic optical damage together with remarkable improvement in reliability by suppressing mirror degradation. The other type or NAM structure laser is a built-in composite-cavity laser which has achieved stable longitudinal mode operation in a temperature range as wide as 50 C for output powers from 3 mW to 100 mW without mode hopping as a result of mode selectivity in the composite-cavity NAM-BTRS laser.

A 100 mW high-power AlGaAs laser with the current-blocking regions near the facets and a long cavity length has been developed. The length and the channel width of the current-blocking region, and cavity length were examined in order to obtain a high-output power. As a result, a stable fundamental transverse mode operation is obtained up to 180 mW, and maximum output power is 230 mW under CW operation. Stable operation under 100 mW of output power was confirmed for more than 2000 hours at 60 C.

A 100 mW high-power AlGaAs laser with the current-blocking regions near the facets and a long cavity length has been developed. The length and the channel width of the current-blocking region, and cavity length were examined in order to obtain a high-output power. As a result, a stable fundamental transverse mode operation is obtained up to 180 mW, and maximum output power is 230 mW under CW operation. Stable operation under 100 mW of output power was confirmed for more than 2000 hours at 60 C.

The 780nm 35mW I2SPB lasers(Inverted Inner Stripe Laser with a p- GaAs Buffer Layer) with a thin active layer have been successflly developed by employing MOCVD. Accelerated aging tests on the ISPB lasers with the cavity length of 400iim at 60 °C, 30mW project lifetimes (MTTF) greater than l0000hrs. The narrow standard deviations of beam divergences parallel and perpendicullar to the junction plane, respectively 0.18 and O.2Odeg, are achieved. The small astigmatic distance less than 6iim and the high optical S/N ratio more than 65dB (at f=2OkHz, BW=300Hz and P=3OmW) are obtained. These exellent results indicate that the I2SPB lasers are available for the Magneto-Optical Disk (MOD) applications.

A total of 64 high power laser diodes with wide stripe and multistripe structures have been selected for long term pulsed reliability testing at 120 Mbits/s with peak output power of 150 mW. This data rate and peak power were selected for a potential intersatellite communication link between geosynchronous satellites. The laser diodes were selected through two stringent burn-in tests. First they were burned-in at 100 C for 100 hours, biased below threshold. The second burn-in was performed at 70 C with lasers operating at a peak power of 150 mW, 120 Mbits/s, 50 percent duty cycle for 100 hours. Only those lasers that did not change threshold current more than 5 percent were selected for the life test. The laser diodes were fully characterized before the life test. The electrooptical, spectra, spatial and modulation characteristics of the laser diodes are presented as well as the details of the burn-in processes, the life test results, and failure mechanisms of the lasers.

High power superluminescent diodes (SLD) with buried crescent heterostructure have been successfully developed. The output power as high as 10 mW at 180 mA and the spectral width as wide as 30 nm are achieved. The fabrication and performance characteristics of these diodes are described. Good far field patterns are obtained in both directions. Measured I-V, L-I and emission spectrum are presented.

Stabilized in-phase mode oscillation is demonstrated from large-aperture 20-element antiguided diode laser arrays. 20-element resonant optical waveguide arrays emit 160 mW total power at 2.8 x I(th) in a diffraction-limited beam and have high spatial coherence across the entire array. CW operation of nonresonant 20-element array structures is demonstrated to high output power levels.

A compact external cavity configuration consisting of a gain guided array, a graded index lens, and a mode selective mirror was investigated. Results obtained from this external cavity configuration show 410 mW total power (CW) with a diffraction limited far field pattern.

A modal reflector having a high reflective (about 40 percent) region with 24 microns, 48 microns or 96 microns width on the output facet, and applied to gain-guided wide (150 microns) stripe lasers, is described. The partially high reflective region composing the modal reflector consists of an Al2O3/a-Si multilayer whose thickness is determined so as to match in phase between a part of the output from the highly reflective region and remaining outupt from the low reflective ( about 1 percent) region in order to reduce side peaks (fringes) in far-field patterns. Single-lobed far-field patterns for lateral direction as narrow as from 0.88 deg to about 3.5 deg are observed at up to 0.4 W under CW condition.

Monolithic AlGaAs laser structures one cm in width and capable of 200 W peak power output with a 200 microsec pulse width have been fabricated and tested. The laser structure is similar to the single quantum well structures reported for CW bars. The devices are suitable for pumping neodymium-doped laser media.

Good continuous-wave lifetimes have been demonstrated for single and multiple emitter A1GaAS laser diode arrays at the highest power levels ever reported (2 watts/200 um single emitter and 10 wattst2000 multiple emitter).

Recent advances in the development of a 10-amplifier active integrated-optic device are reviewed. High coherence is demonstrated for the array, which integrated power splitters, turning mirrors, phase modulators, and optical amplifiers on a single chip. Techniques for controlling the most significant parameters, the rib dimensions and the turning mirror roughness, are described. The performance of the various component and integrated devices is discussed.

Failed or degraded monolithic linear laser diode arrays and integrated optoelectronic devices were analyzed to identify failure mechanisms that limit reliability and lifetime. The primary failure mechanism identified in the laser diode arrays was 110-line-oriented dark line defects behind the facet. The cause was due to operation at too long of a pulse width at high peak optical power levels. In addition, facet anomalies contributed to the failure in some cases. Failure mechanisms identified in integrated optoelectronic devices were bulk degradation due to surface damage, facet-related mechanisms, and heat sink bond degradation.

Progress in the development of surface emitting distributed feedback lasers and arrays is reported. Single devices have been demonstrated with as much as 8 percent net power efficiency, 250 mW CW output power, and 5000 hours of reliable CW operation. Continuous wave operation of arrays has been demonstrated with as much as 3 W of output power. Silicon microchannel heat sinks can achieve a much lower thermal resistance than predicted by an idealized analysis due to finite size effects and lateral heat flow in the sink package. Techniques for feeding in large electrical currents are discussed.

Coherent cw operation has been obtained with a 10x4 array of Grating Surface Emitting (GSE) lasers consisting of 40 lasers and 50 emitting sections. The array is a GaAs quantum well device, grown on an A1GaAs substrate, operating at 861 nm to which the substrate is transparent. It is mounted p-down to metallized traces on a BeO slab to provide isolated electrical contacts and thermal contact to a simple chilled-water cooler. A single spectral line 0.5 A wide indicates coupling of the 40 laser sections. More detailed measurements on a section of an array containing ten laterally coupled lasers, 20 outputs, show that it is operating at a junction temperature of 30°C, has a line width of 0.1 5A, and a measured coherence of <75%. The expected wavelength stabilization with temperature due to the DBR grating is found, with a value of =0.6A/°C. An array of 4 longitudinally coupled lasers produced a line width of 130MHz and evidence of high coherence.

The coherent operation of one-dimensional linear arrays of grating-coupled surface-emitting lasers is experimentally investigated, for different laser designs (gain lengths, grating parameters. For laser arrays with shallow grating teeth and strong interelement coupling, a diffraction-limited far field of 0.012 deg FWHM was obtained from up to six coupled lasers extending over a length of 3.5 mm.

The steady-state properties of a two-gain section/three-grating surface-emitting laser are studied theoretically as a function of length-induced phase variations. In particular, the optical length of one gain section is varied with respect to the other by up to one grating period. It is found that several mode hops occur. Although the number of these can be reduced by optimizing the design, stable single-mode laser operation requires control of the optical length of each gain and grating section to better than one wavelength.

Two-dimensional surface-emitting AlGaAs diode laser array modules, each containing two 1 sq cm hybrid arrays, have been fabricated and tested. For quasi-CW operation, peak output powers greater than 300 W/sq cm appear to be easily achievable at repetition rates up to 500 Hz. The measurements also indicate that CW output powers of 100-150 W/sq cm can be achieved from these arrays.

Use of resonant periodic gain media provides enhanced gain for a specific design wavelength and propagation direction. The modal properties and emission spectra of CW optically pumped GaAs/AlGaAs resonant periodic gain surface-emitting lasers are described as functions of pump power, and for small temperature variations in the vicinity of 300 K. The achievement of fundamental transverse mode operation and hence narrow spectral widths is considered in detail.

Large-numerical-aperture microlenses have been fabricated in compound semiconductors by chemical etching and mass transport (surface-energy minimization) and have been monolithically integrated with GaInAsP/InP surface-emitting lasers. The microlenses showed smooth surface, accurate profiles, and near diffraction-limited beam collimation. Techniques have been developed for accurate alignment between microlenses and buried-heterostructure waveguide gain regions fabricated on opposite sides of a substrate. The integrated devices showed room-temperature pulsed threshold currents of 70 mA, narrow beam divergence of 1.25 deg, and are potentially advantageous for fiber coupling, optical interconnects, laser-array applications, etc.

Progress in the development of surface emitting distributed feedback lasers and arrays is reported. Single devices have been demonstrated with as much as eight percent net power efficiency, 250 mW cw output power, and 5,000 hours of reliable cw operation. Continuous wave operation of arrays has been demonstrated with as much as 3 waits of output power. We find that silicon microchannel heat sinks can achieve a much lower thermal resistance than predicted by an idealized analysis due to finite size effects and lateral heat flow in the heat sink package. Techniques for feeding in large electrical currents are discussed.

Coherent cw operation has been obtained with a 10x4 array of Grating Surface Emitting (GSE) lasers consisting of 40 lasers and 50 emitting sections. The array is a GaAs quantum well device, grown on an A1GaAs substrate, operating at 861 nm to which the substrate is transparent. It is mounted p-down to metallized traces on a BeO slab to provide isolated electrical contacts and thermal contact to a simple chilled-water cooler. A single spectral line 0.5 A wide indicates coupling of the 40 laser sections. More detailed measurements on a section of an array containing ten laterally coupled lasers, 20 outputs, show that it is operating at a junction temperature of 30°C, has a line width of 0.1 5A, and a measured coherence of >75%. The expected wavelength stabilization with temperature due to the DBR grating is found, with a value of =0.6A/°C. An array of 4 longitudinally coupled lasers produced a line width of 130MHz and evidence of high coherence.

We have investigated, experimentally, the coherent operation of 1-dimensional linear arrays of grating coupled surface emitting lasers for different laser designs (gain lengths, grating parameters). For laser arrays with shailow grating teeth and strong inter-element coupling a diffraction limited far field of 0.012 degrees full width half maximum was obtained from up to 6 coupled lasers extending over a length of 3.5mm.

A novel U-groove distributed feedback (U-DFB) laser structure is reported for the first time. This new U-DFB laser shows threshold current of 34 mA, external total quantum efficiency of 0.4 mW/mA from both facets and side mode suppression ratio of 30 dB.

An advanced cooling technique has been developed to remove very high heat flux levels from two-dimensional arrays of GaAs laser diode bars using stackable wafer thin coolers. The thermal performance of these coolers is expected to surpass previous versions, and a unique sealing technique has been designed to allow these coolers to be packaged in a very compact arrangement. The cooler design and fabrication, coolant manifold and sealing, and test procedure are described.

How nonlinear optics can be used to obtain high brightness from diode lasers is described. The use of two-wave mixing to combined and clean up the output of any frequency-locked high-power device is addressed. The application of phase conjugation for coupling to lock lasers is considered.

The spectral tunability of properly designed quantum well lasers is demonstrated to equal the range of dye lasers. Theoretical and measured gain spectra are presented to support this statement, and stepwise wavelength tuning over a 125 nm span in GaAs/AlGaAs lasers and 175 nm in InGaAs/AlGaAs lasers are shown.

Coherent operation of a monolithic linear array of InGaAsP buried—heterostructure lasers operating at X = 1.3 .un has been achieved by means of a spatial filter in an external cavity. An array of mass—transported InP microlenses was used to collimate the beams of the individual laser elements and couple the laser array output to the external cavity. The coherent array output exhibited a narrow (3.2 mrad), three—lobe far-field pattern with —65% of the energy concentrated in the central peak.

A seven-element gain-guided AlGaAs diode laser array is used to establish an external cavity which relies on weak diffractive coupling for its operation. Collimation of the lasers is achieved using a binary-optics microlens array. A nematic liquid crystal phase modulator is placed in the image plane of the lenslet array to provide individual phase control of each laser stripe. It is shown that the liquid crystal phase modulator is capable of establishing partial coherence by independent adjustment of the laser optical path lengths.

A supercompact microcollimated laser diode (MCLD) was developed without attaching any other external collimating lens. The MCLD consists of 780-nm quantum well laser diode dice and a microcollimating lens in the smallest commercially available laser package. In addition, the MCLD has high reliability against humidity and temperature variations, as all of the elements are assembled in the package filled with dry nitrogen gas. A short focal length micro Fresnel lens is used as the collimating lens to obtain the compact MCLD and narrow collimated laser beam. Additional details are provided on the micro Fresnel lens, the quantum well laser diode dice, and the microcollimated laser diode.

The design of high frequency lasers involves three issues. These are: a) Design and choice of structures with low parasitics. b) Low parasitics packaging techniques. c) Maximized intrinsic frequency response. The first two issues have been discussed at length in the literatures. We will concentrate on the third issue regarding the technique for maximizing the intrinsic frequency response and the possible bandwith limitation due to excessive damping cause by nonlinear gain.

Measurements of the simultaneous pulse response of the individual modes of high power laser diode arrays and broad-stripe laser diodes are presented in this paper. The modes of AlGaAs laser diodes were dispersed with an echelle grating and individually imaged onto a scanning avalanche photodiode (APD) and alternately a streak camera. Considerable power sharing over a period of 60 ns was observed among the modes of these lasers. Experimental conditions were varied and it was found that both the modulation depth and bias current had a considerable effect on the severity of the modal transients. The experimental modal transients were compared to theoretical values obtained using a finite element code to simulate temperature transients in the active area of the lasers.

Various power-versus-current characteristics of TE and TM emission from 1.3-pm InGaAsP/InP semiconductor lasers are observed. They are categorized into the single-plarization lasers, the two-polarization coexisting lasers, and the two-polarization switching lasers. A polarization-related rate-equation model with self-saturation and crosssaturation terms are proposed to simulate these measurements. Emission of only one polarization is explained by large difference of gain and loss between the two polarization modes. Coexisting or switching of both polarizations is determined by the self-saturation and cross-saturation of the gain of the two polarization. The rate equation model is justified by the strain-dependent susceptibility. Several possible sources of strain are the slight lattice-mismatch, the superficial silicon-dioxide, and the die bonding and handling.

Several on-the-chip designs of diffraction-limited, broad-area semiconductor lasers are described. In all cases, the devices achieve single lateral-mode operation as unstable resonators with magnifications greater than, or approximately equal to, two. In the first class of devices, the unstable resonator is realized by creating a diverging mirror at the outcoupling facet. In the second class, a diverging quadratic index profile is created under the active region so that the divergence is distributed uniformly between the front and back facets. The modeling shows that optimum device designs exist for both types of devices. For these optimum designs, stable diffraction-limited operation is predicted for up to six times threshold.

A first-principle method for calculating reflection, transmission, and scattering of light at a boundary between a diode laser and an adjoining waveguide is presented. The electric field on each side of the boundary is expanded in terms of the trapped modes and radiation modes of the laser and waveguide. A matrix equation for the coefficients of each mode is then obtained by matching the fields and their longitudinal derivatives at the boundary. This equation is solved numerically to obtain a reflection and scattering matrix for the fraction of the incident light reflected into each trapped mode of the diode laser, scattered into radiation modes, and transmitted into an adjoining waveguide. Results obtained from this method are compared with calculations using the effective index of refraction technique and an overlap integral analysis to determine when these simpler approaches are valid.

Several alternative modulation waveforms and associated device technologies available for diode laser radar are described. These, included pulsed intensity modulation, discrete frequency intensity modulation, linear chirped optical frequency modulation, and intensity modulation with linear chirp of the modulation frequency. Ladar performance relations that determine range-measurement resolution, absolute range capability, and measurement time or data rate in terms of the critical design parameters are discussed. The design parameters include laser chirp bandwidth, modulation frequency, optical coherence length, laser and receiver noise sources, optical power, and receiver/processor data rate.

The influence of small amounts of scattered light on the behavior of laser diodes is studied. Particular attention is given to the application of these effects, including laser radar and precision metrology of optical systems. The influence of optical feedback on the mode structure of the oscillation is studied.

The analysis, design, and testing of a high-precision linear position sensor using diode laser radar techniques and fiber-optic signal distribution is described. A frequency-chirped, intensity-modulated semiconductor diode laser is used as the transmitter. Each sensor head consists of two reflectors -one moving and one fixed -in a differential ranging mode to cancel apparent range changes caused by temperature induced fiber length variations. The returned (round trip delayed) chirps are direct detected by a photodiode and then are mixed with the original (undelayed) chirp to produce a sum of beat frequencies, each proportional to the range of a reflector. Several sensors heads, located at different fiber distances, can be optically multiplexed by a single laser transmitter using a reflective or transmissive network. The performance of the laser radar position sensor is anal,rzed by first calculating the return signal-to-noise ratio (SNR). A Cramér-Rao lower bound is derived to relate the SNR, chirp bandwidth, and chirp duration to the root-mean-square (RMS) range error. The theoretical optimum performance of the experimental sensor system is determined. An experimental system was built that achieved 58 pm RMS range error using a 1 ms chirp duration with a processing time of 50 ps.

A new method of distance measurement using frequency chirped optical radiation is discussed, and contrasted with other techniques. This measurement is by a phase-based method, rather than as an amplitude-based technique. The conventional frequency chirped coherent scheme uses an amplitude measurement of Fourier harmonics to determine the distance information. The proposed new method takes advantage of the ease with which optical phase can be measured. The proposed system relies upon the use of line-narrowed laser diodes with external cavities. The ease of obtaining such optical line narrowing offers the possibility of achieving an extended range and/or a high resolution (in the micrometer range, if necessary).

A breadboard diode-laser-based distance-measuring interferometer which measures relative thsp1ement has been developed. A temperature-controlled Fabry-Perot etalon is used in a closed-loop system to lock the wavelength emitted by the diode laser source to one of its passbands. Experiments performed using a wavemeter and a commercial laser position transducer indicate that the locked wavelength is returned to the same absolute value to within 1 ppm (part per million) from turn-on to turn-on of the control system, and that the wavelength fluctuation is reduced to less than 0.1 ppm.

Semiconductor laser diodes have demonstrated remarkable performance in recent years. They are also beginning to make inroads into applications traditionally reserved for other laser technologies. Examination of the array of possible applications reveals the need for two main categories of laser diode components. One is the diffraction limited, single frequency laser with outputs from a few hundreds of milliwatts to 1 watt for communications, scanners, data storage, etc. The other requires high power (tens to hundreds of watts) and high efficiency for solid state laser optical pumps, illuminàtors, radar, etc. This paper will examine the past and 'project future advances in semiconductor laser diode performance and costs. In particular it will address the steps necessary to reduce high power laser costs and expand the acceptance of these devices into the high volume applications.

This paper describes the use of a generic switch from dc to GHz frequencies comprising a two-dimensional semiconductor laser diode array and a Si device. A single two-sided PIN device, activated by two 1 kW laser arrays yielded a holding voltage of 1.3 kV and conducted 192 A. The 'on' time of this 1/4 MW switch was 290 ns. In addition, this paper describes the use of optically controlled devices at HF (2-30 MHz) using high voltage PIN diodes as switching devices, and a unique optically controlled attenuator/switch at 60 GHz using a Si slab inside a waveguide. PIN devices tested in an RF circuit between 2.5 and 30 MHz yielded isolation between 28 and 49 dB in the off-state and insertion losses as low as 0.1 dB when illuminated with 280 W of optical power. Measurements at 60 GHz have shown a 0.9 dB insertion loss in the on-state, and an isolation value of better than 21 dB in the off-state.

Work on a diode laser-based collision-avoidance approach which utilizes differential absorption at the oxygen A band to make the atmosphere encode propagation distance on a one-way beam is discussed. This system's principal features are covertness and low power requirements, though its range resolution is comparable to conventional two-way systems. A laser thermally tuned to an oxygen resonance at 760.45 nm was modulated through the line at 1 KHz, and the dropouts associated with passage through the oxygen line were seen at different distances by employing a small photodiode with a transimpedance amplifier. Within the 1/e length of 33 m associated with this particular line, the dropout width was observed to be largely invariant, whereas the depth of dropouts varied with distance as expected.

This paper presents the results of analytical and numerical studies into synchronization of a large number of optically coupled resonators with random detuning of eigenfrequencies. The 'nearest-neighbor' coupling model with allowance made for gain saturation is considered. Assuming that the coupling coefficient has zero imaginary part, the problem of steady-state phase distribution over the aperture of the two-dimensional array reduces to the problem of temperature distribution in a two-dimensional medium in the presence of heat sources and coolers with random powers. It is shown that the steady-state phase distribution over the aperture has domainlike form. Phases in adjacent domains differ by values of the order of pi. Combining the scheme with nearest-neighbor coupling and external signal injection, it is easy to attain synchronous lasing from large arrays.

The planar niicrolens (PML) is a 2-D integrated niicrolens array fabricated by the ion-exchange technique. This paper demonstrates light coupling between LD and optcal fiber using the planar inicrolens. In oder to accept the light power from LD effctively, two classes of High NA planar inicrolens are prepared. A coupled planar inicrolens and new planar inicrolens with swelled structure are evaluated. The minimum coulping loss between LD and single mode fiber was - 5.3 dB using planar muicrolens with the swelled stuctre. (Including 0. 71 dB of Fresnel loss)

Continuous-wave GaAs/GaAlAs edge-emitting diode lasers were used to pump GaAs/AlGaAs and InGaAs/AlGaAs vertical cavity surface-emitting lasers (VCSELs) with resonant periodic gain (RPG) at room temperature. Pump threshold as low as 11 mW, output powers as high as 27 mW at 850 nm, and external differential quantum efficiencies of about 70 percent were observed in GaAs/AlGaAs surface -emitters; spectral brightness 22 times that of the pump laser was also observed. Output powers as high as 85 mW at 950 nm and differential quantum efficiencies of up to 58 percent were recorded for the InGaAs surface-emitting laser. This is the highest quasi-CW output power ever reported for any RPG VCSEL, and the first time such a device has been pumped using an injection laser diode.

This paper reviews the recent resulis for our transverse-mode stabilized InGaAltP visibite semiconductor lasers. From the material viewpoint, InGaA1P/InGaP heterostructure has disadvantages with respect to the laser operation compared with the GaAlAs/GaAs one. By optimizing the laser structure, we have developed practical usable InGaAlP visible semiconductor lasers of relatively low power levels (<5mw). To extena the application field, though in the development stage, we realized the 670nm high power operation at more than 20mW and the short wavelength cw operation at 638nm.

Minimum threshold current density (Jth) less than 2.OkA/cm2 is obtained at optimum hole concentration in the Zn-doped cladding layer (NH) of 3"4x 1O'7ca3 in the AlGaInP laser diodes. At NM lower than optimum one, Jth increases gradually due to poor electron confinement in the active layer. At NH higher than optimum one, Jth also increases due to Zn diffusion from the Zn-doped cladding layer to the active layer during epitaxial growth. One of the reasons is that Zn atoms act as nonradiative recombination centers in the active layer. By optimizing NH in the index guide AlGaInP laser diodes with 6u a width stripe, threshold current of 4OmA and astigmatism smaller than 8 m are achieved.

Operating principles of Self-Locking, Externally-Doubled Diode (SLEDD) lasers are described. Recent experimental work in which 0.45mWof432-nm output was generated at an input power of 1 5mWwith an external mirror ring laser is described.

Nonlinear characteristics of laser diodes have very significant impact on applicability of high-speed fiberoptical communication systems. Large-signal modulation dynamics of laser diodes with (asymmetric) and without (symmetric) back facet reflective coating are theoretically and experimentally presented. Comparison of asymmetric and symmetric lasers in terms of harmonics and two-tone intermodulation distortion indicates that the former is best for data transmission whereas the latter is best suited for distribution of frequency reference, which is used for optical injection locking of oscillators.

A number of different techniques have been used for nonlinear frequency upconversion of near-infrared semiconductor diode lasers. Intracavity frequency doubling of a diode-laser-pumped 946-nm Nd:YAG laser led to the generation of 9.5 mW of blue 473-nm power. A special electronic servo technique was devised to lock the output frequency of a single-mode GaAlAs diode laser to a monolithic KNbO3 resonator. Using the approach, 41 mW of 428-nm output were obtained with an electrical-to-optical conversion efficiency of about 10 percent. Strained-layer InGaAs/GaAs diode laser operating at about 1 micron have been fabricated for noncritically phase-matched frequency doubling in KTiOPO4. A 802-nm GaAlAs diode laser was used for upconversion pumping of a YLiF4:Er(3+) laser which operates at 551 nm with a threshold power of 50 mW at 77 K.