Antiguide laser arrays have demonstrated near-diffraction-limited emission at CW power levels approaching 1 Watt under CW conditions, and up to approximately 10 Watts under short-pulse conditions. In this paper, the fundamental mode of operation is reviewed, and current high-power results are reported, including up to 32 Watts of peak power under short- pulse operations.

Near-diffraction-limited CW operation at 1 W power level is demonstrated, for the first time, from all-monolithic phase-locked diode-laser arrays. In pulsed operation purely diffraction- limited beams (0.4 degree(s) lobewidth) are obtained from relatively large-aperture (120 micrometers ) devices to power levels of 1 W, with 70% of the energy in the central lobe at 0.1 W. These record-high coherent powers are obtained from 20-element resonant-optical-waveguide (ROW) arrays of antiguided diode lasers by significantly increasing the aperture width while maintaining strong discrimination against high-order array modes via Talbot-type spatial filters.

The effect of gain spatial hole burning on antiguided arrays is analyzed for the first time. Nonresonant devices, due to the nonuniformity of the in-phase-mode intensity profile, experience self-focusing and multimode operation with increasing drive level similar to the behavior of evanescent-wave-coupled devices. Resonant and near-resonant devices (i.e. resonant-optical-waveguide (ROW) arrays), due to the uniformity of the in-phase mode, display some mild defocusing with increasing drive level, while the nearest high-order mode cannot reach threshold up to drive levels in excess of 10X threshold. These results explain the fundamental single-mode stability of ROW arrays, in excellent agreement with experimental data.

Design, fabrication, and characteristics of Antiresonant Reflecting Optical Waveguide (ARROW)-type diode lasers are presented. A complete two-dimensional optical waveguide analysis of the self-aligned-stripe (sas) ARROW-type laser indicates strong single-mode selectivity in these structures. Large core-width devices (10 micron) are expected to operate in a stable, single lateral mode, permitting the potential for reliable single-mode operation in the several hundred milliwatt range.

The recent development of semiconductor diode optical amplifiers and lasers having a laterally tapered gain region has changed the outlook for high-power semiconductor optical sources. For the first time, highbrightness, single-element, all-semiconductor sources which emit several watts of cw power in a nearly ideal, single-lobed, diffraction-limited beam have been demonstrated. As semiconductor sources these devices have the inherent advantages of high efficiency, small size, light weight, and reliability. The amplifier12 and all-semiconductor master-oscillator power-amplifier (MOPA) devices34 have gain regions linearly tapered from a few micrometers at the amplifier input to several hundred micrometers at the output. Device lengths are typically 2 mm or more. The angle of the taper is chosen to match the diffraction angle of the input beam which has its waist near the narrow end of the taper. Such a structure is shown schematically in Fig. 1 . The etched grooves have angled side walls and act as cavity spoilers, designed to prevent oscillation of the device as a broad-area laser. The devices are fabricated in single-quantum-well strained-layer InGaAs/AlGaAs graded-index separate-confinement heterostructure laser wafers grown by organometallic vapor phase epitaxy.5 The tapered devices also operate as laser oscillators6 by increasing the input facet reflectivity. For amplifiers, both the input and output facets are coated for low reflectivity (in Fig. 1 , Ri = R2 = 1%), but for oscillators, the input facet is left uncoated (R1 —30%). The oscillators also emit several watts of cw power into a nearly single-lobed, nearly diffraction-limited beam, though their beam quality is usually somewhat inferior to that obtained for amplifiers, particularly at the highest output powers. The lateral mode of the oscillator is similar to the modes described by Fox and Li7 for unstable resonators, except that the semiconductor medium has a significant effect on the self-consistent mode which oscillates. A beam propagation calculation has been carried out to model these effects, as described below. This paper includes a review of the properties of both tapered amplifiers and oscillators.

The design and operating characteristics of strained-layer InGaAsP/InGaAs active-grating surface-emitting amplified diode lasers are presented. For the first time, we report cw operation of an active-grating amplifier at a single wavelength of 1.7 micrometers with a cw power output in excess of 100 mW. In addition, we discuss, theoretically, the possibility of laterally scaling these devices using antiguided laser-array structures.

Rectangular broad area optical traveling-wave amplifiers have been demonstrated to emit 3.3 W CW of diffraction-limited output power when injected with 400 mW of Ti:Sapphire radiation. Improvement in the amplifier characteristics is realized by replacing the rectangular current-pumped contact with a flared or tapered contact, and amplifying a diverging beam. In this fashion, up to 5.25 W CW of diffraction-limited output is obtained from a 200 mW Ti:Sapphire master oscillator.

Based on a combination of high quality materials, advanced design considerations, and focused-ion-beam micromachining, unstable resonator semiconductor lasers (URSLs) have been fabricated in several material systems. GaAs/AlGaAs, InGaAs/GaAs, and GaInP/AlGaInP URSLs fabricated by FIBM have achieved brightness values of 100 to 400 MW/cm²/Sr which is one to two orders of magnitude greater than the brightness of commercial semiconductor lasers produced from the same material systems and with comparable dimensions.

Long wavelength surface emitting lasers (LWSEL) have important applications in optical fiber communications due to their inherent single-longitudinal mode operation and the ease of coupling into fibers. The high packing density and wafer scale testing capability make them potential low cost sources for optical fiber systems. However, high Auger recombination rates inherent to long wavelength materials and technological problems in fabricating long wavelength DBR mirrors have slowed the development of LWSELs compared to that of (In)GaAs vertical cavity lasers. In this paper, we present results on two devices which have achieved the highest reported operation temperatures of LWSELs to date. In the first section we discuss an optically pumped InGaAsP laser utilizing a GaAs/AlAs mirror fused to the InGaAsP structure. These devices operate at temperatures as high as 144 degree(s)C. The fusing process, room temperature lasing characteristics, and high temperature operation are discussed. In the next section, we present results of an electrically contacted, two-dielectric mirror structure which operates at temperatures as high as 66 degree(s)C, the highest operation temperature of an electrically pumped laser to date. The room temperature and high temperature lasing characteristics are described, as are the effects of non-uniform injection in the active region. In the final section of the paper, we discuss design considerations for room temperature, CW operation.

A reconfigurable architecture for parallel, board-to-board optical interconnections is described using a multi-stage optical switching network consisting of monolithically integrable binary optical switch nodes based on surface-emitting lasers and heterojunction phototransistors.

We discuss the potential of using coherently-coupled vertical cavity surface emitting laser arrays as high-intensity light sources. In particular, the design and performance of a novel two-dimensional phase-coupled grid Contact vertical cavity Surface Emitting Laser Array (C- SELA) is reported. We discuss the optical properties of the C-SELA; in addition to the usual out-of-phase array mode, we demonstrate in-phase SELA coupling. We introduce a simple physical model to describe our experimental results. Over 1.2 Watt optical power emission is obtained at room temperature from an electrically-excited 10 X 10 C-SELA. This laser array exhibited a low threshold current density of only 600 Amps/cm² and over 60% single-ended differential quantum efficiency.

We compare vertical-cavity surface emitting lasers grown by molecular beam epitaxial methods to those grown by metal organic chemical vapor deposition methods as sources for wavelength-division multiplexing systems.

One of the key technologies required for manufacturing vertical-cavity laser arrays at a production scale is rapid and nondestructive evaluation of the laser material. A brief review of methods for materials characterization of vertical-cavity semiconductor lasers is presented. Techniques based on reflectance spectroscopy, photoluminescence, photoreflectance, double crystal x-ray diffractometry, scanning electron microscopy, and transmission electron microscopy are used to determine alloy composition, cavity spacer thickness, and Bragg mirror layer thicknesses. Critical aspects of data gathering, analysis, interpretation, and simulation are highlighted. The optical simulation software used for computer aided device design and simulation of reflectance spectra is also briefly discussed.

We investigate experimentally the threshold and slope efficiency of a vertical cavity surface- emitting semiconductor laser with half-wave spaced quantum wells as functions of the pump wavelength in the 700 - 900 nm. While most of these devices demonstrated to date have employed pump wavelengths in the range 700 - 760 nm for optimum absorption in the spacers between the quantum wells (and minimal absorption in the epitaxial mirror structure), we show that equally good performance be obtained using longer wavelengths appropriate for diode laser pumping, provided that the pump wavelength is chosen to match a resonant cavity mode. For maximum pumping efficiency using the latter technique a stabilized single-mode pump laser should be used.

We describe the design, growth by atmospheric pressure metalorganic chemical vapor deposition (MOCVD), processing and characterization of single quantum well separate confinement strained layer InGaAs-GaAs quantum well lasers designed for high power operation at emission wavelengths near 1064 nm. Threshold current density is reduced by 39% for long cavity devices through design optimization. Broad area lasers operate at high cw (> 5 W) and pulsed (> 20 W) powers, with low threshold current density and high power conversion efficiency. Index guided ridge waveguide lasers show stable single spatial mode operation over a wide range of output power and temperature.

This paper demonstrates TE/TM mode switching in GaAsP/AlGaAs tensilely strained quantum-well laser diodes (LDs) with multiple electrodes. The quantum-well layers are grown by low-pressure metal organic vapor phase epitaxy. For a 250-micrometers -long cavity, the threshold current density of this LD wafer at room temperature is about 1.6 kA/cm². With a long cavity these LDs operate in the TM mode, but the TE mode dominates when the cavity is shorter than 200 micrometers . TE/TM mode switching is obtained in a two-electrode laser with electrodes 150 micrometers and 80 micrometers long. When current is injected into both electrodes this LD oscillates at 790 nm in the TM mode and with a threshold current of 40 mA. When current is injected only into the longer electrode, however, it oscillates at 800 nm in the TE mode and absorption at the region under the shorter electrode increases the threshold current to 80 mA. For both kinds of oscillation the suppression ratio is greater than 10 dB. This LD operates in the fundamental mode over an injection-current range of several milliwatts.

Physical parameters contributing to the threshold current and its temperature characteristics of 1.5 micrometers semiconductor lasers have been separately measured in lattice matched and compressively strained lasers. It is found that the reduction of threshold current density in strained devices is attributed to the reduction of Auger recombination, intervalence band absorption and transparency carrier density brought about by the introduction of strain. It is also found that the temperature sensitivity of both lattice matched and strained devices is dominated by the strong differential gain change with temperature, instead of Auger recombination.

We have studied wavelength tuning in three-section distributed feedback (DFB) laser diodes under pulsed and continuous biasing. In these devices the side sections are connected to each other enabling a tuning operation with two injection electrodes. The technological processes for the device fabrication are presented, emphasizing the preparation of the separation grooves. Under pulsed bias conditions we found a maximum modejump-free tuning range of 2.5 nm. The duty cycle was chosen appropriately in this case in order to isolate the nonthermal tuning effects. Under continuous biasing a maximum of total tuning range of 3.7 nm was measured in modejump-free operations. This value represents the interplay of all the wavelength tuning effects involved in these asymmetric three-section DFB lasers. Under both experimental conditions, pulsed and continuous biasing, comparably large modejump-free tuning ranges are obtained. Possible explanations of the enhanced wavelength tunability in these devices are discussed such as threshold gain modulation, plasma effect enhancement controlled by strong spatial hole burning, residual end facet phase effects, and asymmetric geometrical conditions for all section lengths and the position of the phase shift of the grating.

In this paper, we discuss issues related to maximizing the performance of gain in both compressive and tensile strained quantum wells. Effects of well width, barrier height, modulation doping, and heavy-to-light hole separation are theoretically examined.

Key components in the rapidly growing optical fiber communication networks are the distributed feedback (DFB) laser and the pump source for fiber amplifiers. There is a need for high reliability sources which are stable throughout operating life, not only in terms of electro- optic parameters but equally important in terms of performance factors specific to the application. Sources are assessed in terms of degradation hazards with the view to building in reliability at the design stage. The paper then reviews the progress towards achieving these objectives for 1.55 micrometers wavelength DFB lasers for direct detection systems and for 1.48 micrometers and 0.98 micrometers wavelength lasers to pump fiber amplifiers.

In 1991, strained InAlGaAs quantum well lasers were first proposed as alternatives to AlGaAs lasers for various applications, including solid-state pumping. Enhanced reliability was the rationale for their development, having been inspired by earlier observations of lattice hardening in strained InGaAs lasers. The hoped-for dark-line defect (DLD) suppression as well as a threshold current advantage for this system have already been documented. In this update, we will present further aspects of this work, including long-term reliability, maximum (catastrophic) power limits, epitaxial structure design bounds and parametric crystal growth investigations. Our work has enabled the demonstration of 15 W cw linear arrays and pulsed V-Groove Phased Arrays. Their performance and potential applications will also be discussed.

Laser diodes and superluminescent diodes have been fabricated using epitaxial structures employing a strained quantum well of InAlGaAs. These devices emit at wavelengths in the 800 - 900 nm range commonly addressed using unstrained GaAs quantum well structures. Results are presented which indicate that the strained layer devices exhibit a marked immunity from sudden unexpected ('freak') failure modes.

The longitudinal mode hopping and the related terminal electrical noise in InGaAs/GaAs ridge single quantum well (SQW) lasers are investigated. It is found that electrical mode hopping has a Lorentzian dependence. The correlation with the optical noise is experimentally shown for low and medium frequencies.

The lifetime potential of many electro-optic components is often given in literature and product data sheets based on unstated or, at best, very restricted operating conditions. Often, because of the high cost of test devices, life test equipment and the cost of conducting life tests, lifetime data is available over only limited operating ranges. Extending the operating ranges is attempted only if applications for the component demand it. This paper presents a test methodology that first establishes the maximum operating stress levels for laser devices. And then, an Experimental Design Methodology is used to model laser device lifetime as a function of those operating stresses. Adopting the intent of Test Method 5006 (Limit Testing) of MIL-STD-883, Step-Stress Operational Life Tests were conducted to 'establish the operational stress levels that will accelerate predominant failure mechanisms' for multi-emitter bar lasers. An eight cell step-stress test matrix was completed. The matrix consisted of stepping individual operating stresses while driving bar lasers in either a constant peak current or a constant peak power mode. This paper presents the results of the step-stress test matrix and provides the maximum operating stress levels for these components.

A precise localization of dark line defects in failed AlGaAs/GaAs laser diodes has been achieved by means of scanning optical microscope (SOM) techniques. The analytical scheme has been based on optical beam induced current (OBIC) and photoluminescence (PL) at three photon probes and different device bias voltages. The imaging analysis has been associated to a progressive chemical etching of the semiconductor material. Numerical simulation of the experiment has been performed for results interpretation. Results are in good agreement with previously published theories and with TEM analysis. The proposed analytical procedure can be applied to a wide variety of devices.

CW output power in excess of 60 mW at 110 degree(s)C with a fundamental-transverse mode and stable CW operation over 3000 hrs under 30 mW at 60 degree(s)C have been realized by employing a multiquantum well (MQW) active layer with optimized compressive strain. A window-structure laser fabricated by solid phase diffusion of Zn has exhibited high-power CW operation over 150 mW keeping the fundamental-transverse-mode. Systematical approach to the high power operation has also been discussed.

This paper describes phasing of semiconductor laser arrays placed in an external Talbot cavity for high coherent output power. The external Talbot cavity couples the light between many adjacent lasers such that all lasers operate at the same frequency and phase, resulting in a high power diffraction limited output beam. We first verified the concepts of the Talbot cavity exploiting a simple 1-D Talbot cavity with 20 elements and demonstrated over 600 mW cw total output power in a diffraction limited output beam. In order to fabricate a highly scalable 2-D phased array of lasers, a new type of monolithic 2-D surface emitter was developed for the 2-D Talbot cavity. We have demonstrated 50 W cw output power from a nonphased 2-D monolithic surface emitting laser array with 1500 laser elements. Finally, using a similar 2-D 12 by 12 element surface emitting laser array, we demonstrated 2-D coherence from a compact 2-D Talbot cavity which includes a GaP mass transport lens array, a liquid crystal array and a phase sensing and control system.

Strained InGaAs/GaAs quantum well three terminal lasers with monolithically integrated intracavity modulators were fabricated using low threshold current structures formed by the temperature engineered growth (TEG) technique. An on-off efficiency ratio of 556 with optical power contrast ratio of 7.5 was measured with a total DC power consumption of 25.3 mW. Preliminary digital modulation shows bit error rate (BER) lower than 10^-16 at 500 Mb/s. A theoretical analysis of the dynamic behavior of this device shows potential operation of 6.6 Gb/s with low inter-symbol interference.

A preliminary design for a broadband, multiple quantum well (MQW), distributed Bragg reflector (DBR), electronically tunable laser diode array has been developed for implementation into optical memory configurations. The proposed MQW DBR diode array and a waveguide hologram with a blazed grating and/or holographic diffraction grating will be integrated into a photonic random optical memory access (PROMAC) device. PROMAC is a low inertia, low power, sub-nanosecond, parallel (e.g. 64 bit wide), wavelength addressing device which exploits free space optical interconnects. The MQW DBR laser diode array will enhance the performance of PROMAC by offering advantages in speed, spectral resolution, holographic separation and scan efficiency. An increase in speed as well as a decrease in power consumption can also be realized. Thus, increased storage densities and faster access rates can be achieved.

In this paper a beam propagation model used to compute model reflectivities of HC SELs, amplifiers, and SLEDs will be presented. These devices all employ an intracavity 45 degree(s) micromirror which causes the light to propagate in a direction perpendicular to the epilayers. The lack of a waveguide structure for propagation perpendicular to the epilayers and the broad angular spectrum produced by highly confined transverse modes of GRINSCH-SQW devices must be considered when analyzing folded-cavity devices. The model includes Fresnel reflections from multilayer thin-films, angular errors in the 45 degree(s) micromirror, the dependence on the horizontal reflector separation, Fresnel beam propagation, and waveguide coupling losses of the reflected field. The model predicts good conversion efficiencies, despite low effective reflectivities from the folded-end-mirror. There is good agreement with experimental data.

We review in-plane surface-emitting laser diode arrays and their applications. Efficient operation of monolithic, large area (0.54 cm², 108 emitters) two-dimensional surface- emitting GaAlAs laser diode arrays mounted junction-down on microchannel heat exchangers has been demonstrated. Devices with 1.5 micrometers thick cladding layers were operated quasi- continuous-wave to high peak output power densities (> 100 W/cm²), exhibited high power conversion efficiencies (22%), and full width emission spectra of < 4 nm at 2% - 5% duty cycles. Arrays with a 2.5 micrometers thick cladding region were operated under continuous wave conditions to 46 W/cm² power density levels. This corresponded to a 550 W/cm² heat flux extracted by microchannel heat exchanges.

We report on the first demonstration of high power, short-wavelength, in-plane, horizontal cavity ion-beam-etched surface-emitting lasers with emission wavelengths of 740 nm and 635 nm, and surface-emitting output powers of 850 mW and 170 mW from GaAlAs/GaAs and GaInP/GaAlInP laser diodes, respectively.

For the first time, quasi-continuous wave (QCW) output power level of 1000 W from monolithic surface emitting laser diodes (M-SELDs) is reported. To realize the basic structure of the laser diodes, we have developed an original 2-D structure where the epitaxial structure is made on engraved GaAs substrate and the laser facets are made by micro-cleavage technique. With a compact planar association of 10 M-SELDs of 0.1 cm² which emits 100 W QCW each (optical power density equals 1 KW/cm²) on the same submount, a power source of 1000 W QCW has been obtained. The operating current is 150 A, the slope efficiency is 7.5 W/A and the optical divergence of the beam is lower than 20 degree(s) FWHM in the perpendicular direction.

Monolithic fanned-out amplifier lasers (acronym: FOAL), are capable of producing high optical power, greater than 1 watt. They operate single wavelength and can be collimated to generate a nearly Gaussian beam useful for applications requiring an inexpensive compact source of coherent radiation. Examples are space communication, frequency doubling, thermal writing, optical sensing, optical interconnection, and optical computing.

A new mechanism is described that is based on the modulation of the confinement factor with carrier density in quantum-well lasers. This new mechanism may limit modulation bandwidth for quantum-well laser with high threshold carrier density and narrow confining layer.

We investigate the characteristics of directly modulated semiconductor lasers with external cavity using 35 GHz sub carrier. We have achieved bit error rates 10^-9 for data transmission over short optical fiber links with a binary phase shift keying modulation of 35 GHz sub carrier.

A method of reducing the level of harmonic distortion introduced into an analogue amplitude modulated optical signal by a semiconductor optical amplifier is demonstrated experimentally. During preliminary experiments using a bias current feedback loop, an improvement of 3.5 dB is obtained in second harmonic distortion for a multimode optical input. The output noise power is lowered by 3 - 4 dB. A reduction in distortion of 17.75 dB, achieved using direct modulation of the bias current, indicates that better distortion results could be obtained from the feedback method if a higher level of electrical amplification were used. No gain enhancement is measured using the feedback method, but direct modulation of the bias current results in an increase of up to 2.8 dB in device gain.

We report in this paper the measurement results of the relative intensity noise (RIN) in GaAs- AlGaAs laser arrays, comparing with that of single stripe lasers. The results are in agreement with the noise theory based on the rate equation. The experimental measurements include dependence of relative intensity noise on drive current, modulation frequency and temperature. The results confirm in these circumstances the theoretical prediction that the maximum of the relative intensity noise occurs when the lasers run exactly at their threshold current level.

Nearly-degenerate four-wave mixing in a laser diode induces phase and amplitude modulations which can be described with a model emphasizing the effect of the laser resonator on the optical interactions. The characteristics of the optical and power spectra have direct dependence on many intrinsic laser parameters. With a simple experimental setup, the spectra can be taken for parasitic-free characterization of the intrinsic laser parameters to a high degree of accuracy.

High-power InGaAlP lasers operating at high temperature have been realized by using a strained active layer, a highly doped p-cladding layer, and a long cavity structure. The maximum operating temperature has been increased to 80 degree(s)C for a 50 mW operation of transverse-mode stabilized laser diodes, and also for a 100 mW operation of broad-stripe laser diodes. This improvement in the temperature characteristics has led to a highly reliable operation at a high output power. Transverse-mode stabilized InGaAlP lasers oscillating at 698 nm have exhibited a stable operation for 2,000 hours at a high output power of 40 mW with an ambient temperature of 40 degree(s)C. A highly reliable operation of broad-stripe structure lasers has also been achieved. A stable 100 mW operation for 1,500 hours at a temperature of 50 degree(s)C was obtained for InGaAlP lasers with a stripe width of 25 micrometers .

AlGaInP-based, high power laser diodes operating at wavelengths of 630 to 645 nm have been designed, fabricated, and characterized. Cw output powers approaching 1 Watt and thresholds below 400 A/cm² have been achieved. Measurement of internal laser parameters indicates low internal loss and transparency current, high gain, and moderate internal quantum efficiency. Characteristic temperature data suggest that the lowest practical operating wavelength of similar diodes is close to 620 nm. Examination of performance as a function of cavity length indicates an optimum length in the range of 1200 micrometers .

We report the Ga_0.86In_0.14As_0.13Sb_0.87 room temperature refractive index value obtained from direct reflectivity measurements and also estimated from laser transverse far field pattern measurements. The value n equals 3.78 obtained is higher than previous theoretical calculations and is high enough to support a good optical confinement in DH lasers with 27% Al in the confining layers. We also show that the active layer low resistivity gives the main contribution to the high threshold current (I_th) for narrow stripe lasers. This is partly solved by making the active region n-type. The minimum I_th obtained for n-type active layer lasers was 290 mA compared to 800 mA for p-type active layer lasers, the broad area threshold current being the same (3 kA/cm²) in both cases.