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The main goal of this paper is the study of the stimulated Brillouin scattering (SBS) in multimode fibers, at 1550 nm wavelength, cw operation, in order to build high power IR fiber lasers. Two theoretical models are considered, the usual plane wave model and a modal model, developed in this paper. The theoretical results for SBS threshold and SBS reflectivity are compared with the experimentally determined values. Good agreement was obtained when using mode structure analysis., Presented at the Conference on Optics (7th), ROMOPTO 2003, held in Constanta, Romania, on 8-11 Sep 2003. Pub. in Proceedings of SPIE, v5581 p654-661, 2004. ISSN 0277-786X. ISBN 0-8194-5534-2. This article is from ADA434629 ROMOPTO 2003: Conference on Optics (7th), Held in Constanta, Romania, on 8-11 September 2003

The growing need for antimonide-based, room temperature, 2-5 micrometers, semiconductor lasers for trace gas spectroscopy, ultra-low loss communication, infrared countermeasures, and ladar motivated this work. To extend the wavelength of semiconductor lasers beyond 2 micrometers, increased arsenic content has been needed to reduce the bandgap and maintain a lattice match to GaSb. This has resulted in degraded performance due in part to a smaller valence band offset. In this work, the need for lattice match between the active region and the GaSb substrate is avoided by the use of metamorphic AlInSb buffer layers. This provides a virtual substrate to extend the wavelength of GaInSb quantum wells. With the use of lattice constants larger than GaSb, the need for arsenic has been eliminated resulting in pure antimonide crystals, which provides for large valence band offsets. Samples are grown by solid source molecular beam epitaxy. The AlInSb metamorphic buffer layer is a superlattice consisting of alternating layers of AlxInl -xSb and AlyInl -ySb where the indium content and thickness ratios are chosen to provide the desired average indium content. Using these buffer layers, optically pumped GaInSb/AlGaInSb multiple quantum well lasers with as much as 76% indium content in the quantum well and emission wavelength as long as 3.3 micrometers at room temperature have been achieved. The best performing room temperature laser emits at 2.8 micrometers with a threshold power density of 169 W/cm2 and a differential quantum efficiency of 28%., The original document contains color images. All DTIC reproductions will be in black and white.

The AFOSR Optoelectronics Research Center has maintained a broadly based program at the forefront of optoelectronics with efforts in linear and nonlinear materials, device processing, device design, and in device integration. Examples of materials and structures are quantum dots, superlattices, digital alloys, and strained-layer semiconductors, and new nonlinear materials. Processing developments relate to smaller dimensions and improved techniques for the selective deposition, modification and removal of materials. Improved devices, based both on semiconductors and on fibers, have also resulted from increased understanding of the underlying device and material physics and from innovative approaches to device design and synthesis., The original document contains color images. All DTIC reproductions will be in black and white.

The UNM portion of this program focused on two areas, namely: (1) Efficient, wavelength-switchable fiber lasers for Air Force applications; (2) The development of mid-IR sources, namely 3 micrometers fiber lasers for pumping longer wavelength sources for IRCM applications. More specifically, we developed and/or demonstrated: (1) A precisely and rapidly wavelength-switchable 1.5 micrometers fiber laser source with switching times of ^18 microseconds; (2) A widely tunable wavelength-selectable fiber laser for 8 channels using an FBG string for channel pinning with output powers of each channel of ^l2 dBm(16 mW); (3) A broadly tunable wavelength-selectable source using a fiber Sagnac loop filter, with over 25 wavelength-switchable channel outputs with precise 50 GHz channel spacing, excellent output power uniformities of +/- 0.8 dB over the whole tuning range, and very large (65 dB)side mode suppression ratios; (4) A single-mode tunable wavelength selectable fiber laser operating at 8 uniquely selectable wavelength-channels with individual linewidths of < 300 kHz in each channel 5. That the optimal pump wavelength for 'the 800 nm pump band' pumping of high-power 3 micrometers mid-IR fiber laser is 799 +/- 1 nm (as opposed to earlier reports implying an optimal pump wavelength of 791 nm); (6) Optimal designs for custom double-clad Er:ZBLAN fibers for power scaling of such mid-IR lasers to average powers of > 10 Watts 7. Compact diode-pumped Q-switched (both actively and passively) mid-IR fiber lasers., Original contains color plates: All DTIC reproductions will be in black and white.

Working protonated gate MOSFET transistor memories with gate lengths down to 5 microns and gate oxide thicknesses down to 20 nm have been produced using standard Si-based technological steps. Hysteresis in the source-drain current-versus-gate voltage as large as - 11 V was measured in 40 nm gate oxide transistors. The sensitivity of the memory to X rays was measured using an ARACOR source up to total accumulated doses of 2 Mrad (SiO2) . No variation in the hysteresis voltage (which would correspond to a loss of protons) was ascertained, nor was there measurable data loss (by deviation of the current/voltage characteristic which would result if the protons redistributed themselves in the gate oxide). A buildup of fixed oxide charge in the gate oxide due to irradiation was measured and it was characteristic of that expected in an unhardened oxide.

This report describes research on the study of novel all-fiber devices based on the electro-optic effect in poled fused silica. The focus of the current work was on electro-optically tunable all-fiber waveplates, since they form the basis of the design of a large array of novel all-fiber devices, including all-fiber modulators and all-fiber tunable filters for WDM telecommunications systems. The all-fiber waveplates studied are applicable for the design of in-line phase retarders, in-line polarization controllers, and in-line tunable fiber Bragg gratings, as elucidated in this study. Unfortunately, the highest second-order nonlinearities obtained were < 0.04 pm/V, necessitating operating voltages of several kilovolts, and limiting their applicability to practical telecom devices. Further studies need to be conducted to reliably and reproducibly increase the observed electro-optic nonlinearities before practical implementation of the novel all-fiber devices that were the key targets of the present work., Original contains color plates: All DTIC reproductions will be in black and white.

The Staib Instruments EK-15-R RHEED System purchased on this DURIP grant has been mounted in the University of New Mexico's (UNM) Vacuum Generators VH80 MBE system and used extensively for RHEED studies during the growth of antimony-bearing semiconductors. The beam rocking feature in this unit has been critical in establishing the exact angle of incidence needed for clear observation of reconstruction patterns during the growth of bulk and digital alloy materials, and for the observation of RHEED oscillations to determine the precise growth rate. Observation of RHEED reconstruction patterns is particularly crucial in the growth of Digital Alloy (DA) materials. Arsenic-free GaInSb quantum well lasers for 2-5 nanometer applications were fabricated by growing a graded digital alloy AlInSb metamorphic buffer layer on GaSb to tailor the lattice constant The relaxation of the AlInSb DA buffer layer generates dislocations that are turned along the slip plane at strained heterojunctions. By increasing the number of heterojunctions, filtering of dislocations is possible. Below 200K the laser threshold was virtually constant, and a characteristic temperature T0 of 107K was found above 200K. This is the highest reported T0 for a semiconductor laser at this wavelength.

The Hewlett-Packard 8722D microwave network analyzer and cables that were obtained under the Grant have been used to perform the first electrical measurements of the carrier lifetime, Tau(sub d), and radiative recombination in quantum dot LEDs. Our analysis shows that the ground and excited quantum dot energy states exhibit significantly different radiative recombination rates. We have measured Tau(sub d) as a function of current density for quantum dot LED samples using the microwave equipment and used this data to calculate the functional relationship between the carrier lifetime, carrier density, and radiative efficiency. The results indicate that carrier filling on the different dot energy levels has a strong influence on the radiative behavior of the devices and that the radiative rate coefficient, B, for different QD levels can vary considerably.

The new mid-IR PL/optical pumping setup has been invaluable in the study of GaInAsSb and AlInAsSb materials that are MBE grown on a GaSb substrate. A PL intensity plot vs. wavelength for GaInAsSb grown at the University of New Mexico is displayed on the last page of the report. This PL trace was generated using the equipment purchased with the grant money. We believe that new alloys constructed from AlInAsSb and GaInAsSb will be the backbone of future antimonide-based semiconductor lasers. UNM grows the AlInAsSb using the digital alloy method. This technique employs the growth of several phase-stable alloys (binaries, ternaries, quarternaries, etc.), each a fraction of a monolayer to several monolayers thick. The net composition of these thin layers yields the desired alloy. For our work, InAs, AlSb, and InSb binaries were used to build the AlInAsSb quaternary. Whereas the research community has found that bulk growth of optical quality AlInAsSb with large Al is impossible due to a miscibility gap, UNM has recently shown that high-quality digital alloy growth of non-phase-separated AlInAsSb is possible up to 40% Al composition. One of the next steps is to determine the energy bandgaps of these materials, which as of now are unknown.

The Hewlett-Packard 8722D microwave network analyzer and cables that were obtained under the Grant have been used to perform the first electrical measurements of the carrier lifetime, Tau(sub d), and radiative recombination in quantum dot LEDs. Our analysis shows that the ground and excited quantum dot energy states exhibit significantly different radiative recombination rates. We have measured Tau(sub d) as a function of current density for quantum dot LED samples using the microwave equipment and used this data to calculate the functional relationship between the carrier lifetime, carrier density, and radiative efficiency. The results indicate that carrier filling on the different dot energy levels has a strong influence on the radiative behavior of the devices and that the radiative rate coefficient, B, for different QD levels can vary considerably.

The AFOSR Optoelectronics Research Center maintains a broadly based program at the forefront of optoelectronics with efforts in linear and nonlinear materials, device processing, device design, and in device integration. Examples of materials and structures are quantum dots, superlattices, digital alloys, and strained-layer semiconductors, and new nonlinear materials. Processing developments relate to smaller dimensions and improved techniques for the selective deposition, modification and removal of materials. Improved devices, based both on semiconductors and on fibers, also result from increased understanding of the underlying device and material physics and from innovative approaches to device design and synthesis.

The goal of this research program is to develop a novel technology for the epitaxial growth and fabrication of vertical-cavity surface-emitting laser structures with lasing wavelengths in the 110 nm to 1500 nm regime, with special emphasis on the 1300 nm VCSEL's and monolithic VCSEL arrays These are useful for the parallel optical data links that will interconnect future computer networks, whose nodes may be distributed across a wide range of distances and are interconnected by optical fibers. The use of 1300 nm VCSEL's will provide improved fiber transmission performance as well as a more unified technology platform for the different levels of the interconnect hierarchy. The GalnNAs!GaAs VCSEL technology represents a novel approach that is potentially manufacturable using conventional growth systems and device fabrication techniques.

Future computer networks will contain clusters of processors of various sizes that are interconnected over a wide range of distances, from dense local clusters to spatially distributed computer networks. To permit the simultaneous communication amongst many nodes, it will be necessary to develop practical networking technologies that provide multiple access, dynamic reconfigurability, and simultaneous communication through a shared channel. The objectives of this program are to investigate novel optical multiplexing architectures for interconnecting computer networks, and to develop their enabling technologies. To achieve these ends, we will investigate networks that combine wavelength, space, and time division multiplexing in new and different ways. For larger networks, new multiplexing techniques are needed that will use wavelength, space or time more efficiently, either by re-using the available channels or by combining several multiplexing platforms within a single network. These optical multiplexing techniques and their underlying technologies are the focus of the research program.

Light emission properties of InGaN quantum wells are reviewed and discussed including performance in wide range of temperatures (up to 450 K). The typical anomaly of "blue" temperature induced shift of the luminescence spectral peak is explained in terms of the band tail model. The model is applied to the InGaN active medium in LEDs and in lasers. The tail states are associated with composition variations in the alloy. They seem to be favorable for efficient radiative recombination., Pres: 7th Int Symp Nanostructures: Physics and Technology, St Petersburg, Russia. 14-18 Jun 1999. p329-335. This article is from ADA407055 Nanostructures: Physics and Technology. 7th International Symposium. St. Petersburg, Russia, June 14-18, 1999 Proceedings

Periodic structures were designed, fabricated and characterized to control the emission of electromagnetic radiation. These electromagnetic crystals were fabricated using interferometric lithography, a technique that lends itself to large area periodic structures. The characterization was done using a Fourier Transform Infra-red Spectrometer. Extensive rigorous modeling was developed based on rigorous coupled-wave analysis and was shown to provide a route to "design-to-performance" for these structures., Original contains color plates: All DTIC reproductions will be in black and white.

The two areas that we focused on in this period were (1) the integration of a microstrip patch antenna with a two-dimensional photonic crystal substrate, and (2) the time and frequency domain detection of superluminal group velocity in one-dimensional photonic crystals. For the two-dimensional photonic crystal substrate work, we studied the effects of a finite sized ground plane on the resonance frequency of a microstrip patch antenna. A finite difference time domain (FDTD) code was used for these studies, and the calculations were found to be in good agreement with the experimental characterizations. The effect of a defect state under the antenna location was also studied and found to improve the performance. For the one-dimensional photonic crystal characterization studies, a transfer matrix technique was used to obtain analytical closed form expressions for both the transmission and reflection coefficients of a plane wave incident onto it. We were able to experimentally measure superluminal group velocities for propagation through the stop bard of a one dimensional photonic crystal. This result is not inconsistent with special relativity or causality since the frontal (forerunner) velocity of the signal never exceeds the speed of light in vacuum. These results are important for a fundamental understanding of electromagnetic wave propagation through short interaction regions with anomalous dispersion.

With the approval of the program manager, the equipment purchased on this grant was changed to a Plasma Therm, Inc. SLR-770 inductively coupled plasma (ICP) processing system. The SLR-770 has been invaluable in the study of plasma etching of AlGaAsSb and GaSb-materials that form the backbone of antimonide-based semiconductor lasers. AlGaAsSb is especially difficult to pattern with wet chemicals because it is prone to oxidation. The combination of sputtering and chemical etching in plasmas represents the only reproducible means of etching this quaternary alloy. Specifically, we have studied etch rate and selectivity of GaSb and AlGaAsSb in plasmas containing BCl3, Cl2, and Ar as a function of process pressure, DC bias, ICP power, and reactant concentration. Smooth and anisotropic etching was obtained over a variety of process conditions. This research will benefit future efforts to fabricate ridge-waveguide, DFB, and etched mirror laser diodes designed with antimonide semiconductors.

The goal of this research program is to develop novel techniques for the epitaxial growth and fabrication of vertical-cavity surface-emitting laser structures with lasing wavelengths in the 1.1-1.5 micron regime. Special emphasis will be on the realization of 1300 nm VCSELs and monolithic VCSEL arrays that are useful for the parallel optical data links that will interconnect future computer networks, whose nodes may be distributed across a wide range of distances and are interconnected by optical fibers. The 1300 nm VCSELs will provide improved fiber transmission performance as well as a more unified technology platform for the different levels of the interconnection heirarchy. One goal is to design and demonstrate a practical 1300 nm VCSEL structure that can be grown by a single epitaxial growth on a convention, high quality GaAs substrate. These structures will use InGaAsN quantum wells, as well as GaAs/AlAs distributed Bragg reflector (DBR) mirrors with a large index difference, which reduces the total thickness to a tractable level that makes a single-growth approach possible. In this program, we will develop an optimum device design for the fabrication of these VCSEL structures, and we will integrate them into monolithic arrays. We will evaluate the performance of the VCSELs in parallel optical links as well as in VCSEL-based optical switching networks.

This Equipment Grant enabled upgrades in our scatterometer research instrumentation and computational capability. This provided a unique capability to develop the metrology technique through performing collaborative investigations with SEMATECH, Texas Instruments, and IBM. These efforts demonstrated the potential of scatterometry to provide the semiconductor industry with a metrology tool for characterizing sub-0.1 m (and larger) features.

This program began with the objective of developing a novel optical interconnect technology that would provide parallel optical interconnections between electronic processing in a dynamically reconfigurable manner. The goal was to develop a switching fabric consisting of integrated optoelectronic switch arrays that offer a very compact, very-high-information-throughout optical interconnect architecture. The technology we had chosen was based on the monolithic integration of VCSELs with other photonic and electronic technologies, including heterojunction HPTs and photothyristors, PIN and MSM photodiodes, and heterojunction bipolar HBTs. We have played a leading role in the development of monolithic OEIC technology based on VCSELs, as well as advancing the state-of-the-art in VCSEL technology itself. We have developed an optical interconnect architecture and a high-speed OEIC switching technology that can provide reconfigurable interconnections between electronic processors, allowing then to communicate through a network of integrated optoelectronic transceivers and compact, monolithic space-division-multiplexed switches that provide an optical link to other nodes and electrical access to each processor These reconfigurable binary HPT/VCSEL switches can detect, regenerate and spatially reroute optical data, and can be programmed by simple voltages to perform different optical routing, fanout and logic functions. Arrays of switches with high optical gain were optically cascaded to form a multistage optical switching network that provide multipoint interconnections between nodes, through which multiple data channels can be routed in parallel without intermediate OE signal conversion. The functional capabilities of the reconfigurable optical switching fabric have been demonstrated at a data rate of >500 Mb/s.

The Optoelectronic Materials Center is a collaborative program involving the University of New Mexico. Stanford University, and the California Institute of Technology. Sandia National Laboratories and MIT Lincoln Laboratory are also involved in this program under separate contract vehicles. This program emphasizes three main areas: (1) diode-based visible sources, (2) two- dimensional optical interconnects, and (3) high-speed optoelectronics. Progress on individual tasks is discussed briefly in this report. Several tasks affect more than one of the above areas. For simplicity, the tasks are arranged by institution in an order roughly determined by the above areas.