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.

Direct Wafer Bonding Technology employing vacuum-cavity pre-bonding

A novel low temperature direct wafer bonding technology employing vacuum-cavity pre-bonding is proposed and applied in bonding of InGaAs/Si couple wafers under 300 degrees C and InP/GaAs couple wafers under 350 degrees C. Aligning accuracy of 0.5 mu m is achieved. During wafer bonding process the pressure on the couple wafers is 10MPa. The interface energy is sufficiently high to allow thinning of the wafers down from 350um to about 100um. And the tensile strength test indicates the bonding energy of bonded samples is about equal to the bonded samples at 550 degrees C.

High-power operation of quantum cascade lasers endured prolonged air-oxidation

High-power strain-compensated In1-xGaxAs/ln(1-y)Al(y)As quantum cascade lasers (lambda similar to 5.5 mu m) are demonstrated. Peak power at least 1.2W per facet for a 32 mu mx2mm uncoated laser stored in ambient condition for 240 days, is obtained at 80 K. Considering the collection efficiency of 60%, the actual output power is 4W at this temperature.

Terahertz pulse generation with LT-GaAs photoconductive antenna

Low-temperature-grown GaAs (LT-GaAs) of 1-um thickness was grown at 250 degrees C on semi-insulating GaAs (001) substrate using EPI GEN-II solid-source MBE system. The sample was then in situ annealed for 10 min at 600 degrees C under As-rich condition. THz emitters were fabricated on this LTGaAs with three different photoconductive dipole antenna gaps of 1-mm, 3-mm, and 5-mm, respectively. The spectral bandwidth of 2.75 THz was obtaind with time domain spectroscopy. It is found that THz emission efficiency is increased with decreasing antenna gap. Two carrier lifetimes, 0.469 ps and 3.759 ps, were obtained with time-resolved transient reflection-type pump-probe spectroscopy.

High resolution interrogation technique based on linear photodiode array spectrometer for fiber Bragg grating Sensors - art. no. 65952C

A linear photodiode array spectrometer based, high resolution interrogation technique for fiber Bragg grating sensors is demonstrated. Spline interpolation and Polynomial Approximation Algorithm (PAA) are applied to the data points acquired by the spectrometer to improve the original PAA based interrogation method. Thereby fewer pixels are required to achieve the same resolution as original. Theoretical analysis indicates that if the FWHM of a FBG covers more than 3 pixels, the resolution of central wavelength shift will arrive at less than 1 pm. While the number of pixels increases to 6, the nominal resolution will decrease to 0.001 pm. Experimental result shows that Bragg wavelength resolution of similar to 1 pm is obtained for a FBG with FWHM of similar to 0.2 nm using a spectrometer with a pixel resolution of similar to 70 pm.