Etched facet lasers are important components to realize laser arrays and optical integrated circuits (OEICs), in which reduction of the processing complexity is one of the key issues. We found that C₂H₅Cl gas-phase etching produces a vertical etched facet along the [0-1 1] direction in GaAs and AlGaAs. The vertical etching with the velocity of 2.5 to 1.6 micrometer/hour is obtained in GaAs and Al_0.5Ga_0.5As, respectively, with the C₂H₅Cl gas-phase etching at 680 degrees Celsius along a SiO₂ mask parallel to the [0-1 1] direction. The angle of the facets is 85 degrees, which is not affected with the aluminum concentration. (111)B facets reveal along the [0-1 -1] direction. This gas-phase etching technique is combined with MOCVD regrowth to realize a BH AlGaAs/GaAs laser with etched facets and optical coating. The entire etched side walls, i.e. vertically etched facets and (111)B side walls along the laser stripes are immediately embedded with regrown AlGaAs in the same process chamber by switching an etching gas to metal organic sources. Conventional processing steps to fabricate an etched facet BH laser are comprised of initial etching for waveguide definition, regrowth to form BH structure, dry etching or cleaving for facet formation and facet coating. This in-situ gas-phase etching and regrowth technique reduces such 4 processing steps into gas manipulation inside of the same growth furnace and greatly reduces the processing cost of OEICs.

Commercial viability of the semiconductor lasers imposes several stringent conditions on device fabrication and/or materials: First of all, high yield should be achieved with minimum cost. High long-term reliability is also an extremely important issue for most of applications as the replacement cost of failed devices is prohibitively high, and thus the lifetime of the laser diodes can be a major factor determining the total cost of application systems. In this article, we discus some of the critical issues related to the commercial viability of semiconductor lasers. As an example of the successful commercialization of the semiconductor lasers developed in research laboratories, we discuss the recent transfer of Al-free laser technology from Northwestern University to Semiconductor Lasers International, Inc. The highly suitable features of Al-free system for industrial scale of production are discussed. The recent results obtained in the industry with low cost and high yield are shown to have high-performance of these Al-free lasers comparable to those observed in the research laboratory.

Zn_0.48Cd_0.52Se layers were grown on InP substrates by molecular-beam epitaxy. The n-type carrier concentration was controlled from 3X10¹⁶ cm^-3 to 7X10¹⁸ cm^-3 through the ZnCl₂ source cell temperature. Nitrogen doping was performed using a radio-frequency plasma. Capacitance-voltage measurement showed that the ZnCdSe:N layer was p-type with a net acceptor concentration (Na-Nd) of 3.5X10¹⁶ cm^-3. ZnCdSe p-n homojunction light- emitting diodes (LEDs) was fabricated. Orange luminescence intensity peaking at a wavelength of 590 nm was observed at room temperature. Double-heterostructure LEDs with a ZnSeTe contact layer were also fabricated and a higher luminescence intensity than in the homojunction LEDs was observed. The operating voltage ranged from 15 to 20 volts.

Basis of the developments discussed in the presentation are 10 mm GaAs diode laser bars mounted on copper micro channel heat sinks. Optimizing the micro channel heat sinks leads to decreased thermal resistance and decreased pressure drop. In the presentation the steps to ten times reduced pressure drop and optical power output of the diode lasers of over 100 Watts will be described.

An active layer structure with 658 nm-emission at 25 degrees Celsius has been optimized in order to reduce the operating current of the laser diodes (LD) under high temperature condition. For improvement of the maximum output power and the reliability limited by mirror degradation, we have applied a zinc-diffused-type window-mirror structure which prevents the optical absorption at the mirror facet. As a result, the CW output power of 50 mW is obtained even at 80 degrees Celsius for a 650 micrometer-long window-mirror LD. In addition, the maximum light output power over 150 mW at 25 degrees Celsius has been realized without any optical mirror damage. In the aging tests, the LDs have been operating for over 2,500 - 5,000 hours under the CW condition of 30 - 50 mW at 60 degrees Celsius. The window-mirror structure also enables reliable 60 degree Celsius, 30 mW, CW operation of the LDs with 651 nm- emission at 25 degrees Celsius. Moreover, the maximum output power of around 100 mW even at 80 degrees Celsius and reliable 2,000-hour operation at 60 degrees Celsius, 70 mW have been realized for the first time by 659 nm LDs with a long cavity length of 900 micrometers.

The fabrication and performance characteristics of high speed semiconductor lasers are described in this paper. These include InGaAsP/InP lasers emitting near 1.55 micrometer, InGaAs/GaAs lasers emitting near 1 micrometer and integrated electroabsorption modulated lasers emitting near 1.55 micrometer.

The electronic structure at the interface of GaAs/AlAs multilayers grown by molecular beam epitaxy is investigated on the (110) surface using scanning tunneling microscopy. The valence band bending, which is produced by an interface dipole layer, is observed from cross-sectional profiles exhibiting spike structures. It is found that the transition region of the AlAs/GaAs interface (3.0 - 4.0 nm) is smaller than that of the GaAs/AlAs interface (4.0 - 5.0 nm). Similar spike structures showing a transition region of 3.5 - 4.5 nm are also observed at the GaAs/Al_0.6Ga_0.4As interface.

Both collection and excitation modes of scanning near-field optical microscopy (SNOM) were used to study a low power visible multiquantum-well laser diode (LD). Collection mode SNOM provides the near-field optical propagating intensity distribution at the facet of LD. Excitation mode SNOM gives local photoconductivity information of the structure of LD facet. Results show highly localized spatial correlation of LD structure and its optical performance at the facet. Different sizes of apertures were used in both modes, and results of near-field interactions can be quite different. Results show obvious difference of photocurrent distribution caused by the different sizes of apertures in excitation mode. Two wavelengths of 543.5 nm and 632.8 nm were used in excitation mode SNOM. It can be deduced from the two pump photon energies that there exists defect level in the energy range of 60 - 380 meV below the conduction band edge in the n-(Al_0.7Ga_0.3)_0.5In_0.5P cladding layer. In addition to the highly localized images of topography, optical output, and optical beam induced current at the facet of LD, local near- field optical spectroscopy was performed as well. Spatially resolved near-field optical spectra of both stimulated and spontaneous emissions were obtained at the facet of LD. Longitudinal modes of stimulated emission of LD were observed locally.

We present a study on a novel method for the determination of the quality factor and the cavity loss in semiconductor lasers. The method we use involves Fourier analysis of the Fabry-Perot mode spectrum when operating the device below lasing threshold. The observation of the decay rate of higher order harmonics in the Fourier analysis of the spectra allows us to determine the amount of cavity propagation loss/gain. As an illustrative example, a Fourier analysis on experimental data for lasers fabricated in the AlGaAs material system will be given. In addition to the measurements on propagation loss/gain, this method allowed also the identification of the density and strength of intra-cavity scattering centers in optically pumped AlGaInN lasers. This is an important capability for the fabrication of blue diode lasers in the gallium-nitride material system.

High Power GaAs/AlGaAs laser diodes with a decoupled confinement heterostructure (DCH) have been developed. This novel structure features broadened waveguide layers and thin carrier block layers sandwiching an active layer. Catastrophic optical damage (COD) level was twice as high as the corresponding separated confinement heterostructure (SCH) laser diode due to the improvement of mode profiles. Al- content of cladding layers is greatly reduced in DCH laser diode without degrading temperature characteristics. The decrease of electrical and thermal resistivities allows high- power and high-efficiency operation. CW output, 4.6 W was obtained with a 50 micrometer-aperture 809 nm DCH laser diode. The maximum efficiency was 49% at 2.8 W. Life test was carried out over 2,000 hours under the conditions of 1.0 W - 50 degrees Celsius. The median life was estimated to be more then ten thousand hours at this condition. Decoupled confinement heterostructure is advantageous for the fabrication of the index guided structure, since the reduction of chemically active Al-composition relieves the process difficulties related to the chemical etching and the selective re-growth. Index guided laser diode with a buried ridge structure presented 400 mW single mode operation at 860 nm. The life test was carried out under the conditions of 300 mW - 50 degrees Celsius. All the 25 devices showed no failure up to 7,000 hours.

The high-speed modulation characteristics and performance in optical fiber transmission links of oxide confined vertical cavity surface emitting lasers are reported. The lasers have bandwidths of 13 GHz. Error-free transmission is obtained for both subcarriers modulated multichannel transmission and directly modulated digital transmission at 8 Gb/s.

High power multi-mode semiconductor lasers operating between 1 Watt and 2 Watts are widely used for pumping solid-state lasers, active fibers and direct materials processing. In this paper, we present the high power and high temperature performance characteristics of 100 micrometer aperture broad area lasers. In addition, we will present lifetest data that supports mean lifetimes in excess of 500,000 hours for this class of lasers. 1

The Polyplanar Optical Display (POD) is a unique display screen which can be used with any projection source. This display screen is 2 inches thick and has a matte-black face which allows for high contrast images. The prototype being developed is a form, fit and functional replacement display for the B-52 aircraft which uses a monochrome ten-inch display. The new display uses a 200 milliwatt green solid- state laser (532 nm) as its optical source. In order to produce real-time video, the laser light is being modulated by a Digital Light Processing (DLP^TM) chip manufactured by Texas Instruments, Inc. A variable astigmatic focusing system is used to produce a stigmatic image on the viewing face of the POD. In addition to the optical design, we discuss the DLP^TM chip, the opto-mechanical design and viewing angle characteristics.

Laser displays have been investigated by engineers and scientists since shortly after the invention of the laser. The majority of these systems have been based on gas lasers or lamp-pumped solid-state lasers which are expensive, large in size, and require significant cooling systems. Due to these negative attributes, laser displays have been limited to applications which are not sensitive to size or cost. Recent advances in compact, air-cooled, diode-pumped, solid-state, visible microlasers have enabled the development of portable laser displays. Lasers are under development for both 'backlit' displays, where the lasers replace arc-lamps in an LCD/DMD projector, and 'direct-write' displays, where the image is formed by directly modulating and scanning the laser beam. Compact, multi-watt RGB laser modules have been demonstrated for use as 'light engines' in projection displays generating greater than 500 ANSI lumens. Advantages of microlaser-based displays include large color gamut, color accuracy, image uniformity, high resolution, large depth of focus, and low maintenance due to the long lifetime (greater than 10,000 hours) of the lasers. These advantages make them attractive for near term applications such as simulators, command and control centers, high end CAD workstation monitors, and longer term applications such as electronic cinema.

In arts, as well as in entertainment, visual effects are often used to gain the attention of people. A striking effect can be the main reason for the success of an artist's or an entertainment product. Modern optical technologies are very interesting for some artists to highlight their art objects by some nice optical effect. In our paper, we report about an unusual but attractive project between the Berlin Institut of Optics and the German artist Leonore Zimmermann. The idea of the project was to combine a laser-optical effect with an art print. In this context we have designed a diode laser effect illuminator which can be used to display an image of a lion associated with an art print of Leonore Zimmermann. The optical key component of this illuminator is a diffractive element the transmission function of which has been computed to obtain the desired object image by exploitation of the diffraction effect. The diode laser effect illuminator is a simple device which can be used to display almost arbitrary images or short image sequences. In combination with printing arts, we hope, it will surprise and fascinate people by its nice effects.

Laser diodes are an important optical pump source for achieving high luminous efficiencies (i.e., total projected lumens per watt of input power) for laser video projectors. The commercial viability of these projectors will rely on extremely stable, diode-pumped near infrared lasers and high- quality nonlinear crystals to generate the required powers of red, green and blue light. Since pulsed lasers achieve the high peak powers that lead to efficient nonlinear interactions, there is a compelling argument for projectors to use pulsed rather than cw infrared lasers to create the RGB primaries. A method of spatial light modulation compatible with pulsed light sources is acousto-optic line writing, by which the modulation for an entire row of pixels (i.e., line of video) is captured by a single pulse of light. This modulation scheme, however, requires that the laser(s) produce short pulses at high rep rate to display the full resolution of the input video signal. Diode-pumped Nd:YVO₄ lasers are well suited for variable resolution projectors for their ability to deliver short pulses (less than 20 ns) over a wide range of rep rates (up to 90 kHz). We describe in this paper how pulsed Nd:YVO₄ lasers and AO modulators, enable variable resolution laser projectors that can display 2xNTSC, 4xNTSC, VGA, SVGA, XGA, and SXGA video formats.

Continuously tunable single-mode emission of high performance quantum cascade (QC) lasers is achieved by application of the distributed feedback (DFB) principle. The devices are fabricated either as loss-coupled or index-coupled DFB lasers. Single-mode tuning ranges of approximately equals 100 nm have been measured in both of the atmospheric windows at emission wavelengths around (lambda) approximately equals 5 micrometer and 8 micrometer. Linear thermal tuning coefficients of 0.35 nm/K and 0.55 nm/K have been obtained above 200 K for (lambda) approximately equals 5 micrometer and 8 micrometer, respectively. The side-mode suppression ratio is better than 30 dB. Pulsed single-mode operation has been achieved up to room temperature with peak power levels of 60 mW. The lasers also operated single-mode in continuous wave at temperatures above liquid Nitrogen temperature; a single-mode tuning range of 70 nm has been measured in the temperature range from 20 K to 120 K. The gas sensing capabilities of the QC-laser have also been demonstrated using both direct absorption and wavelength modulation techniques. A pulsed, room temperature, QC-DFB laser operating at (lambda) approximately equals 7.8 micrometer was used to detect N₂O diluted in N₂. The detection limit was found to be approximately equals 500 ppb- m. In addition, the high resolution capability of the QC-DFB lasers (at 77 K) has been demonstrated via continuous, rapid- scan, direct absorption measurement of the Doppler limited R(16.5) lambda doublet of NO at (lambda) approximately equals 5.2 micrometer.

Highly sensitive and accurate measurements of numerous trace gases are required to further our understanding of atmospheric processes. Tunable diode laser systems, which offer many advantages in this regard, can be designed for reliable field measurements on both ground-based and aircraft platforms. The present paper describes the long term effort at the National Center for Atmospheric Research (NCAR) to develop, employ, and validate a highly sensitive tunable diode laser absorption spectrometer for the measurement of various trace gases, including formaldehyde and carbon monoxide. This system was successfully employed on three recent aircraft campaigns. The present paper describes the aircraft instrument along with hardware and software features incorporated for high sensitivity, with particular emphasis on major modifications to the NCAR aircraft system over the past year.

The development of high power, single mode and continuously tunable diode lasers in the visible to near-infrared region, and antimonide diode lasers operating in the 2 - 3 micrometer region near room temperature, is opening measurement opportunities in wavelength regions hitherto inaccessible by diode lasers. The spectroscopic properties of antimonide-based diode lasers operating in the 2.2 - 2.3 micrometer region have been examined for application to high sensitivity monitoring of carbon monoxide and formaldehyde. In a second application, nonlinear- up-conversion of diode laser output in order to access strong electronic transitions of atoms and molecules in the UV wavelength region is described. A tunable 308 nm beam was generated by sum frequency mixing high power diode laser output with single frequency Ar^PLU laser output, and high sensitivity absorption and laser induced fluorescence detection of the hydroxyl radical was demonstrated. Finally, direct doubling of the near-infrared output from an external cavity diode laser/power amplifier module was used to generate a tunable, near-UV laser beam to demonstrate the feasibility of optical flux monitoring of Group III atomic beams in an MBE chamber by spatially resolved optical absorption/LIF detection.

We have utilized the high brightness of state-of-the-art diode laser sources, and a variety of emerging optical technologies to develop a new class of thin, uniquely styled automotive brake and signal lamps. Using optics based on thin (5 mm) plastic sheets, these lamps provide appearance and functional advantages not attainable with traditional automotive lighting systems. The light is coupled into the sheets using a 1 mm diameter glass fiber, and manipulated using refraction and reflection from edges, surfaces, and shaped cut-outs. Light can be extracted with an efficiency of approximately 50% and formed into a luminance distribution that meets the Society of Automotive Engineers (SAE) photometric requirements. Prototype lamps using these optics have been constructed and are less than one inch in thickness. Thin lamps reduce sheet metal costs, complexity, material usage, weight, and allow for increased trunk volume. In addition, these optics enhance lamp design flexibility. When the lamps are not energized, they can appear body colored, and when lighted, the brightness distribution across the lamp can be uniform or structured. A diode laser based brake lamp consumes seven times less electrical power than one using an incandescent source and has instant on capability. Also, diode lasers have the potential to be 10-year/150,000 mile light sources.

We derive approximate expressions for transient output power and wavelength chirp of high-peak-power laser-diode bars assuming one-dimensional heat flow and linear temperature dependences for chirp and efficiency. The model is derived for pulse durations, 10 less than (tau) less than 1000 microseconds, typically used for diode-pumped solid-state lasers and is in good agreement with experimental data for Si heatsink mounted 940 nm laser-diode bars operating at 100 W/cm. The analytic expressions are more flexible and easily used than the results of operating point dependent numerical modeling. In addition, the analytic expressions used here can be integrated to describe the energy per unit wavelength for a given pulse duration, initial emission bandwidth and heatsink material. We find that the figure-of-merit for a heatsink material in this application is ((rho) C_pK)^1/2 where (rho) C_p is the volumetric heat capacity and K is the thermal conductivity. As an example of the utility of the derived expressions, we determine an effective absorption coefficient as a function of pump pulse duration for a diode-pumped solid-state laser utilizing Yb:Sr₅(PO₄)₃F (Yb:S-FAP) as the gain medium.

Based on a pair of step-mirrors for beam rearranging we coupled the emission of three high-power diode laser arrays into an optical fiber of 800 micrometer diameter. We compressed the fast axis collimated beams of three diode lasers in respect to their fast axes by means of a step prism and symmetrized the beam parameter product by reordering the radiation which is focused into a fiber then. By simple optimization a coupling efficiency of 70% can be obtained.

In Electron Heating Modulation, a microwave field is applied to the active region of a semiconductor laser to change the electron temperature, and thereby to indirectly change the optical transition and to achieve high speed modulation. A detailed theoretical model by including the electron temperature has been developed to investigate this modulation scheme, and to identify the principal difference and limitations in comparison with the traditional scheme, Current Injection Modulation. Optical gain peaks for various electron temperature are calculated. Small signal analysis reveals that a semiconductor laser can be modulated beyond 50 GHz by electron heating, a few times higher than that by Current Injection Modulation. However, this benefit is not retained in large signal operation. In fact, in large signal simulation the modulation bandwidth by both schemes are shown to be similar, at 16 GHz. In view of the fact that the modulation bandwidth of conventional method is limited by the spontaneous recombination time, a method combining the Electron Heating Modulation and the Current Injection Modulation, is an intriguing alternative. Large signal simulations shows that there are some merit to this combined method.

A new concept for optical signal transmission and amplification has been demonstrated. By connecting the lasers of an integrated array in series, rather than the usual parallel connection, significant quantum gain has been achieved. The forward voltage, dynamic resistance and external incremental slope efficiency of the array are simply the sum of the characteristics of the individual laser elements. However, the threshold current is the same as that of a single laser, thus avoiding the very high threshold currents found for parallel laser arrays. By choosing the appropriate number of laser elements the dynamic resistance of the array can be made to equal 50 Ohms giving an intrinsic broadband match for RF modulation without needing any additional resistors or impedance matching circuitry. Thus we demonstrate a ten element AlGaAs laser array with a forward voltage of 15 Volts, a broadband (DC to 500 MHz) impedance of 50 Ohms and a slope efficiency of 4.97 W/A per facet. In combination with a photodiode this forms an optically coupled transistor with a current gain of 3 dB. Such laser arrays can be used in low loss fiber optic links where the increased quantum efficiency compensates for losses within the system, and broadband insertion gain is potentially feasible.

In many modern military systems it is necessary to digitize wideband data of bandwidth up to 10 GHz or more at say 8-bit accuracy for subsequent processing by computer. This is currently beyond the capability of any single current electronic A/D converter, and a variety of alternative techniques have been investigated to alleviate this problem. In the laboratory a digital sampling oscilloscope can digitize signals of bandwidth up to at least 50 GHz, but only through the use of a repetitive input waveform. Our technique involves amplitude-modulating a single radar return on to the output of a laser diode, and using of an assembly of single-mode optical fiber delay lines and couplers to replicate this optical waveform in time, effectively converting it into a repetitive (optical) waveform. This repetitive waveform is converted back to the electrical domain through a photodiode, and sampled with a conventional (relatively) low-speed ADC. The latter operates in a Vernier mode, taking successive samples at different elapsed times in the replicated electrical waveforms, so as to build up a complete record of the waveform. The paper discusses the design of the system and various practical issues, and presents preliminary results on its operation.