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The Christiansen Effect occurs when the refractive index (η) of a given material matches that of its surrounding medium at a particular wavelength, leading to a transmission window. When air is chosen as the medium, the Christiansen Effect is observed when the refractive index of a given material passes through η=1 at a specific wavelength (λ), thereby matching that of air, and subsequently producing a transmission at wavelength (λ). In general, materials that exhibit a refractive index of η=1 in the near infrared are of particular interest for a variety of glass optics and imaging applications. In this paper, spectroscopic ellipsometry (SE) is used to determine the complex refractive index of bulk Indium Tin Oxide (ITO) in the near Infrared (IR) and shortwave IR region. This work utilizes the SE results and optical reflectance measurements to demonstrate the utility of using bulk indium tin oxide (ITO), in combination with air, as a means of generating and tuning the Christianson Effect within the near infrared region. Colloidal suspensions of ITO particles produced from the bulk wafers were also studied to explore the Christiansen effect for obscurant applications.

The demand for high-speed and/or high-temperature infrared (IR) scene projectors has led to the development of systems based on IR light-emitting-diode (LED) arrays. Using mid-wave (3--5 ${\mu {\text{m}}}$ ) superlattice LED arrays, a 512 $\times$ 512 pixel scene projection system operating at 100 Hz has been fully developed. These LEDs, flip-chip bonded to a read-in integrated circuit, display temperatures of up to 1350 K when cooled to liquid nitrogen temperature (77 K). Using custom drive electronics and packaging, the array has been nonuniformity corrected (NUCed) and has survived hundreds of hours of operation at multiple facilities. This system is fully configurable by the user and has a digital visual interface to display content.

This paper explores a new nonlinear control algorithm for variable speed centrifugal pumps at water/wastewater pump stations that leads to specific energy savings over the conventional linear one. The algorithm is useful for facilities where pump speed is a linear function of liquid level in order to transport fluid and smooth inflow peaks. A nonlinearity in the form of a quadratic term is added to the conventional linear one in order to produce efficiency gains, with a single parameter, curvature, varied to optimize energy savings. Results obtained by implementing the new algorithm on a pilot-scale pump station show significant energy savings for fixed pump flow, with a parabolic correlation of specific energy savings versus curvature of the nonlinear quadratic determined. In addition, the cost of implementing this algorithm is minimal to none, so the work presented has major industrial potential.

Smart glass or switchable transparency panels are being commercialized for applications ranging from privacy panels to controlling solar load for buildings and vehicles. However, the technologies that have been developed such as electrochromic, polymer dispersed liquid crystal, and suspended particle devices are complex and expensive, and additionally switch from partial transparency to a tinted or scattering state, not having a highly reflective state, which limits applications. Our group has developed an optofluidic smart glass which should have 10x lower cost than current technologies. It is based upon a reflective structure that switches to transmissive by introducing an index-matching fluid. Previously, we have shown such a panel that consists of a solid plastic corner-cube array with a thin cavity behind it. With air in the cavity the panel is highly reflective based upon total internal reflection. We have shown inexpensive index matching fluids that when pumped into the cavity result in near-perfect transparency. However, our corner-cube array panels suffer from transmission at angles larger than 20 degrees in the reflective state. This transmission is refractive passing oblique rays at a different angle than line-of-sight, but nonetheless compromises performance. Here, we show a two-layer structure consisting of two one-dimensional solid corner reflector arrays with the layers having rotated axes. Rays beyond the TIR angle for one layer are refracted below the TIR angle for the second layer. Each layer has a cavity layer for introducing index matching fluid, and we show high transmission switching up to 60 degrees.

Smart glass or smart windows are an innovative technology used for thermal management, energy efficiency, and privacy applications. Notable commercially available smart glass relies on an electric stimuli to modulate the glass from a transparent to a translucent mode of operation. However, the current market technologies, such as electrochromic, polymer dispersed liquid crystal, and suspended particle devices are expensive and suffer from solar absorption, poor transmittance modulation, and in some cases, continuous power consumption. The authors of this paper present a novel optofluidic smart glass prototype capable of modulating visible light transmittance from 8% to 85%.

The following article presents the results obtained in experiences that use the Impulse Frequency Response Analysis (IFRA) method with a transformer in service. The IFRA method has been implemented in order to transform the transient signals to the frequency domain using Discrete Fourier Transform (DFT). However, it can be considered that the DFT is not the most suitable tool for this type of analysis, since, by definition, this tool is useful for processing stationary signals. Taking that into consideration, the analysis of transient signals could be hypothetically improved by using continuous wavelet transform (CWT), given their variable time/frequency resolution. The analysis of transient signals in Wavelet domain has improved the repeatability of the frequency response curves, as it has been observed in experimental results. The proposed on-line IFRA method, based on Wavelet transform, was validated under load and noload conditions on a 150 kVA three-phase transformer 13200/225 Volts, in the Campus of the Universidad del Valle, Cali, Colombia.

The addition of nitrogen to III–V alloys has been widely studied as a method of modifying the band gap for mid-infrared (IR) applications. Lattice matching these alloys to convenient substrates such as GaSb, however, is challenging due to the significantly different lattice constants. One approach is to use InGaSbN/InAs grown on GaSb where the InGaSbN layer has a larger lattice constant than the substrate, and the InAs layer has a lower lattice constant, and thus the compressive and tensile stress of the superlattice layers can be balanced in a so called strained-layer superlattice. In this paper, we report InxGa1−xSb1−yNy/InAs strained-layer superlattices with type-II (staggered) energy offsets on GaSb substrates, where the design of the layer thickness is based on the lattice constants and the elastic moduli. Three different strain balance conditions are reported: fixed superlattice period thickness, fixed InAs well thickness, and fixed InxGa1−xSb1−yNy barrier thickness. Eight-band k · p simulations of these structures were used to analyze the superlattice miniband energies. For fully strain balanced InxGa1−xSb1−yNy/InAs superlattices lattice matched to the GaSb substrate, careful consideration of strain balance conditions was needed to achieve a lower effective miniband gap needed for longer cutoff wavelength detectors. For non-strained balanced InxGa1−xSb1−yNy/InAs superlattices, long-wavelength cutoff up to 8 μm can be achieved as part of a trade-off between the deleterious effects of strain and the reduction of the barrier band gap through N incorporation.

Nowadays, smart composite materials embed miniaturized sensors for structural health monitoring (SHM) in order to mitigate the risk of failure due to an overload or to unwanted inhomogeneity resulting from the fabrication process. Optical fiber sensors, and more particularly fiber Bragg grating (FBG) sensors, outperform traditional sensor technologies, as they are lightweight, small in size and offer convenient multiplexing capabilities with remote operation. They have thus been extensively associated to composite materials to study their behavior for further SHM purposes. This paper reviews the main challenges arising from the use of FBGs in composite materials. The focus will be made on issues related to temperature-strain discrimination, demodulation of the amplitude spectrum during and after the curing process as well as connection between the embedded optical fibers and the surroundings. The main strategies developed in each of these three topics will be summarized and compared, demonstrating the large progress that has been made in this field in the past few years.

Single element 33×33 μm2 InAs/GaSb superlattice light-emitting diodes (SLEDs) operating at 77 K with peak emission at approximately 4.6 μm are demonstrated. A peak radiance of 2.2 W/cm2/sr was measured corresponding to an apparent temperature greater than 1350 K within the 3-5 μm band. A 48 μm pitch, 512 × 512 individually addressable LED array was fabricated from a nominally identical SLED wafer, hybridized with a read-in integrated circuit, and tested. The array exhibited a pixel yield greater than 95%.

The authors of this paper present new experimental data on optofluidic smart glass for energy efficiency, thermal management, and privacy applications. Performance data from experimental cycling and variable angle transmittance tests are discussed.

To achieve high energy conversion efficiency, a solar module architecture called lateral spectrum splitting concentrator photovoltaics (LSSCPV) is being developed. LSSCPV can concentrate available sunlight and laterally split a single beam into bands with different spectra for absorption by different solar cells with band gaps matched to the split spectrum. Test assemblies of a sample LSSCPV architecture were constructed, each of which contains four p-n junctions and two optical pieces. Independent experiments or simulations had been implemented on the components but by using optimal assumptions. In order to examine the actual performances of all the components, which are dependent on each other and the light source, direct outdoor measurements were made. A set of self-consistent efficiency definitions was articulated and a test bed was developed to measure the parameters required by the efficiency calculation. By comparing the component efficiency items derived from the outdoor measurement and the expected values based on independent simulations, the potential opportunities for efficiency improvement are determined. In the outdoor measurement at the University of Delaware, the optical component demonstrated 89.1% efficiency. Additional assemblies were tested at the National Renewable Energy Laboratory. One assembly demonstrated 36.7% submodule efficiency, which compares favorably with the 32.6% previously reportedmore » verified submodule efficiency.« less

Optical links have successfully displaced electrical links when their aggregated bandwidth-distance product exceeds ~100 Gb/s-m because their link energy per bit per unit distance is lower. Optical links will continue to be adopted at distances of 1 m and below if link power falls below 1 pJ/bit/m. Providing optical links directly to a switching/routing chip can significantly improve the switched energy/bit. We present an early experimental switched CMOS-vertical-cavity surface-emitting laser (VCSEL) system operating at Gigabit Ethernet line rates that achieves a switched interconnect energy of less than 19 pJ/bit for a fully nonblocking network with 16 ports and an aggregate capacity of 20 Gb/s/port. The CMOS-VCSEL switch achieves an optical bandwidth density of 37 Gb/s/mm2 even when operating at a modest line rate of 1.25 Gb/s and is capable of scaling to much higher peak bandwidth densities (~350 Gb/s/mm2) with 5-10 pJ/switched bit. We also review a silicon photonic system design that will lower link energies to 300 fJ/bit, while providing multiterabits per second per square millimeter bandwidth densities. This system will ultimately provide switched optical interconnect at less than a picojoule per switched bit and computer/router system energies of tens of picojoule per bit. We review progress made to date on the silicon photonic components and analyze an energy and bandwidth-density roadmap for future advances toward these goals.

This paper will describe the first-of-a-kind development and demonstration of dilute nitride strained layer superlattice detectors with detectivity as high as 4 × 10 10 cm Hz 1/2 /W and cut-off wavelength of 11-μm for an LWIR design and a cut-off wavelength of 22-μm for a VLWIR design. The developed dilute nitride SLS detectors are based on ultra-low leakage dilute nitride epitaxial layers and/or strained layer superlattices (SLS) of InAs/InAsSbN and InAs/GaInSbN that could enable high VLWIR detectivities at elevated temperatures and at low cost.

The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system–PV modules for portable applications that operate at greater than 50% efficiency. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space. Our approach is driven by proven quantitative models for the solar cell design, the optical design, and the integration of these designs. Optical systems efficiency with an optical efficiency of 93% and solar cell device results under ideal dichroic splitting optics summing to 42·7 ± 2·5% are described. Copyright © 2008 John Wiley & Sons, Ltd.

In this paper, various techniques for normal incidence, free-space optical data porting to embedded data busses are presented. In the first approach, externally powered optical transmitter and receiver devices are coupled to an embedded electrical bus. This embedded link proves to be reliable through environmental and mechanical testing, and demonstrates data transmission up to 10 kHz. A self-powered transceiver is then fabricated and coupled to an optical fiber, showing data transmission up to 1 MHz. Finally, a self-powered bus using a dye-impregnated optical fiber is demonstrated to operate at speeds greater than 15 MHz. All methods explored overcome many of the problems associated with traditional physical connectorization, and are suitable for normal incidence remote querying of embedded passive elements, active devices, sensors, or networks.

This paper demonstrates a low cost, optofluidic smart glass capable of modulating visible transmittance from 0% - 86%.

Space heating and cooling account for a significant percentage of a building's overall energy usage profile. The construction of a building's envelope is an essential component that impacts the overall heating and cooling load. For many years, flat roofs were covered with low albedo materials such as asphalt or modified bitumen, which can reach temperatures of 60 °C–80 °C during summer months. More recently, alternative technologies, such as “white roofs,” have been put forth to mitigate the problem of unwanted thermal gain. However, these traditional roofing materials and recent innovations are passive structures and only promote seasonal benefits. This paper proposes and demonstrates the concept of a controllable reflectance roofing system that can tailor solar loads to desired heating or cooling, significantly reducing overall space heating and cooling energy requirements and costs.

As crystalline silicon solar cells may be approaching efficiency limits, a promising approach to further efficiency gains is a stacked, tandem system consisting of silicon and below silicon band gap cells capable of utilizing a larger range of the solar spectrum. In this work, we analyze a textured silicon cell with coatings optimized to transmit below band gap photons. For the first time, our model takes into account multiple reflections in such a transparent but light trapping cell. We find an efficiency of 26.5% is attainable, for an absolute efficiency gain of 1.3% over a standalone, light trapped silicon cell.

One of the approaches proposed for Non-Intrusive Load Monitoring (NILM) of residential appliances is based on the analysis of switching transient voltages. The transients induced when and appliance is operated can be learned or classified and thus it can be determined when appliances are turned on and off via analysis of the transients. Acquisition of the transient requires two steps: first, the detection of a transient in the ongoing power line signal, and second, the filtering of the electric power signal itself (e.g., in the US, the 60 Hz signal and its harmonics) to provide a clean transient signal to analyze. Here, a detection method using a masked (envelope trigger) oscilloscopetype instrument is adopted. That allows no computation to take place until a transient is actually detected, thus saving greatly on computational requirements. Then, the filtering is performed mathematically. A novel recursive filtering algorithm is presented here, allowing removal of the natural response of the mathematical filter. By using the methods presented in this article, very clean transient signals from household appliances, with full removal of the power signal and its harmonics, can be obtained, thus greatly facilitating the posterior analysis and classification of these transients.

Dynamic gain equalization filters (DGEFs) are important for high-performance wavelength division multiplexed (WDM) communications. One of the first demonstrated DGEF used a micromechanical etalon filter array illuminated with free-space spectral demultiplexing optics. Here, we present subsequent research on etalon-based dynamic spectral filters, including vertical device structures which linearize and reduce the drive voltage from 70 to 40 V, and spatially-segmented etalons which allow channelized spectral equalization and further reduce drive voltage. We describe a prototype using a simplified cylindrical optomechanical package with a 104-nm broadband spectral response, 7.5-dB insertion loss and less than 16-V operation voltage. Finally, we show the use of a 42-nm bandwidth DGEF prototype with feedback stabilization to more than double the number of channels and operating bandwidth of a conventional Erbium-doped fiber amplifier while maintaining < 1-dB power uniformity.

We describe the packaging and testing of a two-dimensional array parallel-optics module with 36 channels with each channel operating up to 3.3 Gb/s. This represents the first commercial module based on direct integration of vertical-cavity surface-emitting lasers (VCSELs) onto silicon very large scale integration (VLSI) circuits using a hybrid optoelectronic-VLSI technology. The module eliminates wire bonds between the driver/receiver chips and the corresponding VCSELs thereby reducing crosstalk and power dissipation, simplifying packaging and alignment, and simultaneously improving bandwidth and total link jitter performance.

Space heating and cooling contributes a significant percentage of a building’s overall energy usage profile. The construction of a building’s envelope is an essential component that impacts the overall heating and cooling load. For many years, flat roofs were covered with low albedo materials such as asphalt or modified bitumen, which can reach temperatures of 150°F to 180°F during summer months. More recently, alternative technologies, such as “white roofs”, have been put forth to mitigate the problem of unwanted thermal gain. However, these traditional roofing materials and recent innovations are passive structures and only promote seasonal benefits. This paper proposes and demonstrates the concept of an active variable reflectance roofing system that can tailor solar loads to desired heating or cooling, significantly reducing overall space heating and cooling energy requirements and costs.

It is shown, via detailed comparison between measured electroabsorption spectra and electroabsorption spectra calculated by a full excitonic Green’s function method, a decoupled excitonic Green’s function method and a variational method, that accurate description of the Coulombic coupling between different subband pairs, including unbound quantum well states above the quantum well edge, is crucial for a correct prediction of electroabsorption in extremely shallow quantum well structures.

We present a single-chip asynchronous multiprocessor optoelectronic bit-sliced arrayed (AMOEBA) crossbar switch. The AMOEBA switch addresses the challenge to produce a large-scale, nonblocking packet switch through dense integration of photonic devices directly onto silicon VLSI circuits. Optoelectronic-VLSI technology is used to integrate the switch fabric, routing controller, packet buffers, line interface circuits, and optoelectronic conversion devices on a single chip. We show how free-space optical interconnects and wavelength-and-space-division-multiplex networking on single-mode fibers can provide switched interconnection between multiple nodes in a distributed computing environment. An optomechanical transceiver package accomplishes the free-space-to-fiber interfacing. We report the implementation and testing of the key components of a 16-channel AMOEBA prototype switch with a potential capacity of 12.8 Gb/s (or 800 Mb/s/channel), and capable of switching 16 million packets per second.

Large-area InP-based multiple quantum-well modulators were grown by molecular beam epitaxy and fabricated for free-space optical communication. The 6times6 mm devices were fabricated as pixilated 6times6 element arrays of 1times1 mm each. Transmission contrast of 3 dB was obtained with 15-V bias. Reverse bias leakage was measured across the arrays to obtain yield information. Yield was determined to be 92% of pixels with less than 300 A leakage at 15 V. Thus, we conclude these devices may be manufactured to operate at a single wavelength, that is, temperature stabilized. However, yield decreased greatly at larger biases which are required to achieve greater shifts of the exciton and wider wavelength range, which translates into wider temperature range. Thus, with the semiconductor material used here, finer pixilation would be required, or defect count must be reduced, to operate without temperature stabilization.

We present very large arrays of InGaAs-InP p-i-n photodetectors flip-chip bonded to Si. The photodiodes are designed for operation at zero bias, e.g., for spectroscopic applications. Our design maintains depletion at zero bias resulting in /spl sim/99% photocurrent collection efficiency. The series resistance of our photodiodes is

Optomechanical fiber-optic attenuators are bulky and slow. The mechanical antireflection switch (MARS) modulator offers a high-speed alternative for applications including dynamic gain control in fiber amplifiers. This paper describes a compact electrically controlled variable attenuator using a micromechanical device where electrostatic deflection of a silicon nitride quarter-wave dielectric layer suspended over a silicon substrate creates a variable reflectivity mirror. This device is packaged with two fibers in one ceramic ferrule placed in contact with a gradient index (GRIN) collimation lens, so that the input light reflects from the modulator in the collimated beam plane and couples into the output fiber. Using a 300 /spl mu/m diameter MARS attenuator and a 500 /spl mu/m diameter collimation lens, the total insertion loss at 1550 nm was 3.0 dB with no applied voltage, increasing to 31 dB at 35.2 V. The polarization dependent loss was less than 0.06 dB. Full attenuation with more than 100 mW input power produced no damage. The response time was 2.8 /spl mu/s to move from maximum to minimum transmission and 1.1 /spl mu/s to return to maximum transmission.

A vertical-cavity surface-emitting laser (VCSEL) 1 times 12 array flip-chip bonded to a 1 times 12 GaAs monitor photodiode array is demonstrated, and faithful monitoring of the VCSEL threshold current, optical power, and subthreshold emission is recorded. Extremely small monitor crosstalk is measured. This is the first published report of an optically monitored VCSEL array

Optical retrocommunication links have been demonstrated using microelectromechanical system (MEMS) etalon modulators. Here, designs for high data rate membrane MEMS modulators are shown with angular coverage up to 170/spl deg/.

We demonstrate the integration of a large (64 x 68)p-i(MQW)-n GaAs diode array to a silicon CMOS chip, using flip-chip solder bump bonding techniques together with concomitant GaAs substrate removal. The capability of removing a relatively large area of GaAs substrate cleanly and uniformly is attributed to the introduction of a new selective etch stop with a smooth isotropic etchant for the GaAs substrate removal. The presence of the lattice matched In 0.49 Ga 0.51 P selective etch stop layer has no detrimental effect on the performance of the GaAs/AlGaAs optical detector/modulator diodes, which gives the chip the large I/O count of 4352.

We present results on carrier transport in shallow multiple-quantum-well GaAs-Al/sub x/Ga/sub 1-x/As p-i-n diodes (x=0.02, 0.04, 0.08) at various bias voltages. We show that only carrier drift and enhanced diffusion dominate response times of these devices. We also emphasize that the drift of holes plays different roles in determining the response times: at low bias, the slow drift of holes adds to enhanced diffusion, slowing down the decay-times; at high bias, the drift time of holes can be comparable to the time of electrons and contribute to the rise-times. From picosecond time-resolved pump/probe electroabsorption measurements, we obtain the drift times, effective drift velocities, and effective mobilities of electrons and holes. The effective drift velocities (especially for holes) appear rather insensitive to the Al concentration in the barriers.

An electrode metallization is demonstrated that absorbs nearly all light incident upon it at specified wavelengths. This electrode may see application in reflective displays and spatial light modulators where stray light reflected off circuit metallization is deleterious. Reflection suppression of −35 dB is shown in a highly conductive metallization.

We show here a laboratory demonstration of a free-space optical retrocommunication link using a laser at a wavelength of 1.064 /spl mu/m. The link consists of a transmissive mechanically active antireflection switch array and a corner cube reflector. This link is 3 m long and the beam diameter at the chip is 1.5 mm. A 40% modulation has been achieved at 30-V peak-to-peak bias for a data rate of 2.5 kb/s in atmosphere. We have previously shown that the small etchant hole in the membrane causes a slower data rate, which can be fixed by operating the device in a rough vacuum.

We propose an optical interconnect system for chip-to-chip communication using gold bond wires as a two wire waveguide. Here the loss of such a waveguide is determined for near-IR wavelengths, for different wire sizes and configurations, and show that we can achieve transmission loss coefficients less than 0.4 mm(-1) (1.7 dB/mm) making chip-to-chip optical communication possible using two-wire transmission lines made of standard gold bond wires. Such an optical waveguide scheme would greatly simplify inter-chip optical communication compared with existing waveguide concepts.

We study exciton ionization induced by an axial electric field in a strongly coupled GaAs/${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As superlattice at low temperatures. The field-induced ionization times of the heavy-hole 1s exciton in the miniband field regime are determined from transient four-wave-mixing experiments and theoretical model calculations. They are found to decrease with increasing field, and lie in the picosecond and subpicosecond ranges for fields on the order of a few kV/cm. They are considerably longer than those calculated for a 1s exciton in bulk GaAs. We explain this difference as a result of the nonparabolicities in the superlattice miniband dispersion. In addition to studying the field-induced ionization of the 1s resonance, we also investigate the field dependence of excitonic wave packets composed of both bound and continuum states of the exciton. It is found that the continuum components of the wave packet are more sensitive to low electric fields than the 1s component. \textcopyright{} 1996 The American Physical Society.

We present the first high-speed optoelectronic very large scale integrated circuit (VLSI) switching chip using III-V optical modulators and detectors flip-chip bonded to silicon CMOS. The circuit, which consists of an array of 16/spl times/1 switching nodes, has 4096 optical detectors and 256 optical modulators and over 140K transistors. All but two of the 4352 multiple-quantum-well diodes generate photocurrent in response to light. Switching nodes have been tested at data rates above 400 Mb/s per channel, the delay variation across the chip is less than /spl plusmn/400 ps, and crosstalk from neighboring nodes is more than 45 dB below the desired signal. This circuit demonstrates the ability of this hybrid device technology to provide large numbers of high-speed optical I/O with complex electrical circuitry.

We present the methods used to fabricate a micromechanical silicon optical modulator for use in a fiber-to-the-home applications. We emphasize the efforts made to realize a practical, robust, manufacturable, and easily packaged device. In addition, recent speed, temperature stability, and reliability results are presented. Rise and fall times of 132 and 125 ns, respectively, have been observed in response to a square wave drive signal. The device has been temperature cycled from -50/spl deg/C to 90/spl deg/C and shown greater than 10-dB optical contrast ratio over this temperature range. Finally, the device has been cycled at 500 kHz for a period of nearly two months (two-trillion cycles) without a noticeable loss in performance.

We present the fabrication and performance of a Si MARS (mechanical antireflection switch) micromechanical optical modulator for fiber-in-the-loop applications. Device performance is reported showing rise and fall times of less than 100 ns, greater than 10 dB optical contrast ratio at ambient temperatures from -50 to 90/spl deg/C, and evidence of reliability exhibited in operation at 500 kHz for over two months (two trillion cycles) without noticeable loss in performance. Bit error rate measurements show potential performance at 1.5 Mb/s with a 10/sup -9/ bit error rate. Emphasis is placed on our efforts to produce a device which is practical, robust, and inexpensive to manufacture and package.

Current pumped terahertz (THz) emitting devices have been fabricated from gallium doped silicon. The time resolved peak power was 12μW per facet at a peak pumping current of 400mA, and the emission was observed up to temperatures near 30K. The spectra occurred in two distinct series at 7.9–8.5THz, and at 13.2–13.8THz. The emission was attributed to the radiative transitions of holes from the split sublevels of the 1Γ8 excited state to the sublevels of the 1Γ8+ ground state and the 1Γ7+ ground state, yielding an energy separation of 22±0.07meV between the two ground states. These results indicated that emitters based on Ga impurity transitions open up a range of THz frequencies, and the properties of their spectra can improve the understanding of impurity level physics.

We demonstrate here an optical link for free-space retrocommunication based on an optical microelectromechanical system array with a structure of mechanically active antireflection switch using a thin Si/sub 3/N/sub 4/ membrane. The array consists of 215 identical single devices with a total active area of 36 mm/sup 2/ and was fabricated with the normal surface sacrificial micromachining. An overfilled reflectance contrast of 3 dB was observed at 6328 /spl Aring/ and a data rate of 100 kb/s shown in 50 mtorr vacuum. A design tradeoff between the high optical filling factor and the high working frequency is discussed.

We study exciton ionization induced by an axial electric field in a strongly coupled GaAs/Al0.3 Ga0.7 As superlattice at low temperatures. The field-induced ionization times of the heavy-hole 1s exciton in the miniband field regime are determined from transient four-wave-mixing experiments and theoretical model calculations. They are found to lie between the field ionization times of excitons in bulk semiconductors, and in strongly confined quantum well systems.

We investigate the optical bandwidth of p-i(multiple quantum well [MQW])-n modulators employing various MQW designs. The optical bandwidth translates directly into an operating temperature range due to the shift of the band gap with temperature. We find that although greater maximum modulation may be obtained with narrow (/spl sim/90 /spl Aring/) quantum wells operating below the band edge (absorption increases with field), uniform large performance may be obtained over a larger bandwidth using wider (/spl sim/110 /spl Aring/) quantum wells operating at the exciton (absorption decreases with field). We obtain a usable bandwidth of 7.7 nm, which translates into a operating temperature range of 27/spl deg/C. >

Continuous Wavelet Transform (CWT) analysis to find feature vectors for switching voltage transients for Non-Intrusive Load Monitoring (NILM) is presented and discussed, and compared with the previously used short time Fourier transform (STFT). The feature vectors computed from both CWT and STFT were used to train Support Vector Machines (SVMs) that identify the connection or disconnection of appliances for a NILM system. Experimental results show that the CWT analysis based on the complex Morlet wavelet improves classification accuracy as compared to the analysis based on STFT. More importantly, a 20× reduction of the vector size requirement is shown, thus greatly lowering computational requirements. It can be expected that commercial transient-based NILM will be based upon the CWT methods shown here.

We report anion incorporation into GaAsP during gas source molecular beam epitaxy that vary systematically with the alloy lattice constant as it changes from a relaxed layer to an elastically strained component in non-pseudomorphic and strain balanced superlattices. We measure significant differences in incorporation when incident arsenic is As 4 , As 2 , or cracked AsH 3 , because in the latter case, monomers are the principal output species of our hydride crackers.

This paper investigates non-contact, surface normal interrogation of reflection-based fiber Bragg grating sensors embedded in composite materials. The approach is based on a novel polishing technique integrating high quality mirrors onto the optical fiber.

Key elements of a multi-material hybrid integration concept for implementing high-density chip-scale optical interconnects are demonstrated. Polymer waveguides with curved facets are used to couple light in and out of the MQW devices flip-chip bonded to silicon.