Hydrogen sensors based on Pt-AlGN/AIN/GaN Schottky diode - art. no. 68291R

Pt/AlGaN/AlN/GaN Schottky diodes have been fabricated and characterized for H-2 sensing. Platinum (Pt) with a thickness of 20nm was evaporated on the sample to form the Schottky contact. The ohmic contact, formed by evaporated Ti/Al/Ni/Au metals, was subsequently annealed by a rapid thermal treatment at 860 degrees C for 30 s in N-2 ambience. Both the forward and reverse current of the device increased greatly when exposed to H-2 gas. The sensor's responses under different hydrogen concentrations from 500ppm to 10% H-2 in N-2 at 300K were investigated. A shift of 0.45V at 297K is obtained at a fixed forward current for switching from N-2 to 10% H-2 in N-2. Time response of the sensor at a fixed bias of 0.5 V was also measured. The turn-on response of the device was rapid, while the recovery of the sensor at N-2 atmosphere was rather slow. But it recovered quickly when the device was exposed to the air. The decrease in the barrier height of the diode was calculated to be about 160meV upon introduction of 10% H-2 into the ambient. The sensitivity of the sensor is also calculated. Some thermodynamics analyses have been done according to the Langmuir isotherm equation.

Ground target detection, classification and sensor fusion in distributed fiber seismic sensor network - art. no. 683015

This paper describes the ground target detection, classification and sensor fusion problems in distributed fiber seismic sensor network. Compared with conventional piezoelectric seismic sensor used in UGS, fiber optic sensor has advantages of high sensitivity and resistance to electromagnetic disturbance. We have developed a fiber seismic sensor network for target detection and classification. However, ground target recognition based on seismic sensor is a very challenging problem because of the non-stationary characteristic of seismic signal and complicated real life application environment. To solve these difficulties, we study robust feature extraction and classification algorithms adapted to fiber sensor network. An united multi-feature (UMF) method is used. An adaptive threshold detection algorithm is proposed to minimize the false alarm rate. Three kinds of targets comprise personnel, wheeled vehicle and tracked vehicle are concerned in the system. The classification simulation result shows that the SVM classifier outperforms the GMM and BPNN. The sensor fusion method based on D-S evidence theory is discussed to fully utilize information of fiber sensor array and improve overall performance of the system. A field experiment is organized to test the performance of fiber sensor network and gather real signal of targets for classification testing.

High-performance multiplexed vibration sensor system based on fiber lasers - art. no. 683019

This paper describes a high-performance multiplexed vibration sensor system using fiber lasers. A serial vibration sensor array consists of four short cavity fiber lasers. The system employs a single, polarization-insensitive, unbalanced Michelson interferometer to translate individual laser wavelength shifts induced by vibration signals into interferometer phase shifts. A dense wavelength division demultiplexor (DWDM) with high channel isolation is inserted to demultiplex each laser signal as a wavelength filter. Finally, a digital phase demodulator based on the phase generated carrier technique is used to achieve high-resolution interrogation. Experimental results show that no observable crosstalk is measured on the output channels, and the minimal detectable acceleration of this system is similar to 200ng/root Hz at 250Hz, which is fundamentally limited by the frequency noise of the lasers.

Advances in high power semiconductor diode lasers - art. no. 682402

High power semiconductor lasers have broad applications in the fields of military and industry. Recent advances in high power semiconductor lasers are reviewed mainly in two aspects: improvements of diode lasers performance and optimization of packaging architectures of diode laser bars. Factors which determine the performance of diode lasers, such as power conversion efficiency, temperature of operation, reliability, wavelength stabilization etc., result from a combination of new semiconductor materials, new diode structures, careful material processing of bars. the latest progress of today's high-power diode lasers at home and abroad is briefly discussed and typical data are presented. The packaging process is of decisive importance for the applicability of high-power diode laser bars, not only technically but also economically. The packaging techniques include the material choosing and the structure optimizing of heat-sinks, the bonding between the array and the heat-sink, the cooling and the fiber coupling, etc. The status of packaging techniques is stressed. There are basically three different diode package architectural options according to the integration grade. Since the package design is dominated by the cooling aspect,. different effective cooling techniques are promoted by different package architectures and specific demands. The benefit and utility of each package are strongly dependent upon the fundamental optoelectronic properties of the individual diode laser bars. Factors which influence these properties are outlined and comparisons of packaging approaches for these materials are made. Modularity of package for special application requirements is an important developing tendency for high power diode lasers.

Measurement and analysis of microwave frequency response of semiconductor optical amplifiers - art. no. 682406

The measurement and analysis of the microwave frequency response of semiconductor optical amplifiers (SOAs) are proposed in this paper. The response is measured using a vector network analyzer. Then with the direct-subtracting method, which is based on the definition of scattering parameters of optoelectronic devices, the responses of both the optical signal source and the photodetector are eliminated, and the response of only the SOA is extracted. Some characteristics of the responses can be observed: the responses are quasi-highpass; the gain increases with the bias current; and the response becomes more gradient while the bias current is increasing. The multisectional model of an SOA is then used to analyze the response theoretically. By deducing from the carrier rate equation of one section under the steady state and the small-signal state, the expression of the frequency response is obtained. Then by iterating the expression, the response of the whole SOA is simulated. The simulated results are in good agreement with the measured on the three main characteristics, which are also explained by the deduced results. This proves the validity of the theoretical analysis.

Fabrication and characterization of TO packaged high-speed laser modules - art. no. 682407

Various high-speed laser modules are fabricated by TO-Packaged processes, such as FP laser modules, DFB laser modules, and VCSEL modules. Furthermore,, the resonance among the circuit elements provides an approach to compensating the TO packaging parasitics, and improving the frequency response of the devices. The detailed equivalent circuit model is established to investigate both the laser diode and packaging comprehensively. The small-signal modulation bandwidths of the TO packaged FP laser, DFB laser and the VCSEL modules are more than 10, 9.7 and 8 GHz, respectively.

Wavelength tunable distributed Bragg reflector laser integrated with electro-absorption modulator by a combined method of selective area growth and quantum well intermixing - art. no. 68240N

Wavelength tunable electro-absorption modulated distributed Bragg reflector lasers (TEMLs) are promising light source in dense wavelength division multiplexing (DWDM) optical fiber communication system due to high modulation speed, small chirp, low drive voltage, compactness and fast wavelength tuning ability. Thus, increased the transmission capacity, the functionality and the flexibility are provided. Materials with bandgap difference as large as 250nm have been integrated on the same wafer by a combined technique of selective area growth (SAG) and quantum well intermixing (QWI), which supplies a flexible and controllable platform for the need of photonic integrated circuits (PIC). A TEML has been fabricated by this technique for the first time. The component has superior characteristics as following: threshold current of 37mA, output power of 3.5mW at 100mA injection and 0V modulator bias voltage, extinction ratio of more than 20 dB with modulator reverse voltage from 0V to 2V when coupled into a single mode fiber, and wavelength tuning range of 4.4nm covering 6 100-GHz WDM channels. A clearly open eye diagram is observed when the integrated EAM is driven with a 10-Gb/s electrical NRZ signal. A good transmission characteristic is exhibited with power penalties less than 2.2 dB at a bit error ratio (BER) of 10(-10) after 44.4 km standard fiber transmission.

On the performance analysis and design of a novel shared-layer integrated devices using RCE-p-i-n-PD/SHBT - art. no. 67820J

We have explored the shared-layer integration fabrication of an resonant-cavity-enhanced p-i-n photodector (RCE- p-i-n-PD) and a single heterojunction bipolar transistor (SHBT) with the same epitaxy grown layer structure. MOCVD growth of the different layer structure for the GaAs based RCE- p-i-n-PD/SHBT require compromises to obtain the best performance of the integrated devices. The SHBT is proposed with super-lattice in the collector, and the structure of the base and the collector of the SHBT is used for the RCE. Up to now, the DC characteristics of the integrated device have been obtained.

Design and performance of monolithic integrated electro-absorption modulated distributed feedback laser - art. no. 67820Y

High performance InGaAsP/InGaAsP strained compensated multiple-quantum-well (MQW) electroabsorption modulators (EAM) monolithically integrated with a DFB laser diode have been designed and realized by ultra low metal-organic vapor phase epitaxy (MOVPE) based on a novel butt joint scheme. The optimization thickness of upper SCH layer for DFB and EAM was obtained of the proposed MQW structure of the EAM through numerical simulation and experiment. The device containing 250(mu m) DFB and 170(mu m) EAM shows good material quality and exhibits a threshold current of 17mA, an extinction ratio of higher than 30 dB and a very high modulation efficiency (12dB/V) from 0V to 1V. By adopting a high-mesa ridge waveguide and buried polyimide, the capacitance of the modulator is reduced to about 0.30 pF corresponding to a 3dB bandwidth more than 20GHz.

Parallel optical communication subsystem based on VCSEL - art. no. 67833I

A parallel optical communication subsystem based on a 12 channels parallel optical transmitter module and a 12 channels parallel optical receiver module can be used as a 10Gbps STM-64 or an OC-192 optical transponder. The bit error rate of this parallel optical communication subsystem is about 0 under the test by SDH optical transport tester during three hours and eighteen minutes.

The effect of interposing nanocrystalline Si(B) P plus layer on the photovoltaic properties of a-Si: H tandem solar cells

Tandem amorphous silicon solar cells have attracted extensive interest because of better performance than single junction counterpart. As n/p junctions play an important role in the current transportation of tandem solar cells, it is important to design and fabricate good n/p junctions.The properties of the n/p junction of amorphous silicon (a-Si) were studied. We investigate the effect of interposing a nanocrystalline p(+) layer between n (top cell) and p (bottom cell) layers of a tandem solar cell. The crystalline volume fraction, the band gap, the conductivity and the grain size of the nanocrystalline silicon (nc-Si) p(+) layer could be modulated by changing the deposition parameters.Current transport in a-Si based n/p ("tunnel") junctions was investigated by current-voltage measurements. The voltage dependence on the resistance (V/J) of the tandem cells was examined to see if n/p junction was ohmic contact. To study the affection of different doping concentration to the properties of the nc-Si p(+) layers which varied the properties of the tunnel junctions, three nc-Si p(+) film samples were grown, measured and analyzed.

Zinc phthalocyanine (ZnPc) incorporated into silicon matrix grown by plasma enhanced chemical vapor deposition (PECVD)

Hybrid composites composed of zinc phthalocyanine embedded in silicon matrixes have attracted attention because of the potential for solar energy conversion. We produce hybrid composites by thermal evaporation for the plithalocyanine and PECVD (Plasma Enhanced Chemical Vapor Deposition) for the silicon matrix. Deposition of ZnPc/a-Si(amorphous silicon) composites was achieved in a sequential manner. The compound films were characterized by optical transmittance spectra and photoconductivity measurement. The optical transmittance measurements were carried out in the visible region (500 - 800 nm). Compared to pure silicon film, the photosensitivity of compound functional films was enhanced by one order of magnitude. This demonstrates the Si sensitized by adding ZnPc.

Reliable concentrated photovoltaic system with compound concentrator

Concentrated photovoltaic systems (CPVSs) draw more and more attention because of high photovoltaic conversion efficiency, low consumption of solar cell, and low cost of power generation. However, the fallibility of the tracker in such systems has hindered their practical application for more than twenty years. The tracker is indispensable for a CPVS since only normal-incident sunlight can be focused on the solar cell chips, even a slight deviation of incident light will result in a significant loss of solar radiation, and hence a distinct decrease in electricity output. Generally, the more accurate the tracker is, the more reliable the system is. However, it is not exactly the case for a CPVS reliability, because the more accurate the tracker is, the better environment it demands. A CPVS is usually has to subjected to harsh environmental conditions, such as strong wind, heavy rain or snow, and huge changes of temperature, which leads to the invalidation of the system's high-accuracy tracker. Hence, the reliability of a CPVS cannot be improved only by enhancing the tracker's accuracy. In this paper, a novel compound concentrator, combination of Fresnel lens and photo-funnel, has been adopted in a prototype CPVS. Test results show that the compound concentrator can relax the angle tolerance from one tenth to five degrees of arc at 400 suns, which can help a CPVS endure serious environment and remain its reliability over long period. The CPVS with compound concentrator is attractive for commercial application.

High speed silicon optical switches based on carrier depletion - art. no. 67812D

The novel design of a silicon optical switch on the mechanism of a reverse p-n junction is proposed. The figuration of contact regions at slab waveguides and the ion implantation technology for creation of junctions are employed in the new design. The two-layer rib structure is helpful for reduction of optical absorption losses induced by metal and heavily-doped contact. And more, simulation results show that the index modulation efficiency of Mach-Zehnder interferometer enhances as the concentrations of dopants in junctions increase, while the trade-off of absorption loss is less than 3 dB/mu m. The phase shift reaches about 5 x 10(-4) pi/mu m at a reverse bias of 10V with the response time of about 0.2ns. The preliminary experimental results are presented. The frequency bandwidth of modulation operation can arrive in the range of GHz. However, heavily-doped contacts have an important effect on pulse response of these switches. While the contact region is not heavily-doped, that means metal electrodes have schottky contacts with p-n junctions, the operation bandwidth of the switch is limited to about 1GHz. For faster response, the heavily-doped contacts must be considered in the design.

Research of Face Detection System Applied for Detecting Faces with Complex Background and Illumination

An effective face detection system used for detecting multi pose frontal face in gray images is presented. Image preprocessing approaches are applied to reduce the influence of the complex illumination. Eye-analog pairing and improved multiple related template matching are used to glancing and accurate face detecting, respectively. To shorten the time cost of detecting process, we employ prejudge rules in checking candidate image segments before template matching. Test by our own face database with complicated illumination and background, the system has high calculation speed and illumination independency, and obtains good experimental results.