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Optoelectronics, Proceedings of the Sixth Chinese Symposium

Date 12-14 Sept. 2003

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Displaying Results 1 - 25 of 80
  • Optics of LCOS projection system based on wire-grid polarizers

    Page(s): 189 - 192
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (275 KB) |  | HTML iconHTML  

    The efficiency and the contrast ratio of the projection system based on wire-grid polarizers (WGP) are investigated as a function of the incident angle. We shall show that of the four possible combinations of configurations, only one offers the best contrast and efficiency. We also shall show that WGP offers some distinct advantages over conventional polarizers, in terms of large extinction ratios and large numerical apertures. Also it is found that the optimal incident angle onto the WGP is dependent on the physical design of the polarizer, and is seldom 45°. At the optimal angle, both the transmission and reflection contrast can be quite good. However, WGP suffer from the drawback of large absorption due to free carrier absorption by the metal grid. View full abstract»

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  • Formation and characteristics of wide band gap II-VI semiconductor quantum dots

    Page(s): 23 - 26
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    CdSe and ZnCdSe quantum dots (QDs) were grown under Stranski-Krastanow (S-K) mode by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The formation process of CdSe QDs below critical thickness was observed by atomic force microscopy (AFM). The formation mechanism of CdSe QDs below the critical thickness was due to the effect of surface diffusion and strain release. ZnCdSe QDs were grown based on the calculated critical thickness. Two kinds of variations in the ZnCdSe QDs appeared over time, the Ostwald ripening process and dot formation process. ZnSeS dots were grown under Volmer-Weber (V-W) mode. With increasing the growth duration, the size of dots becomes larger and the density decreases, which is explained by virtue of the surface free energy. View full abstract»

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  • Indium aggregated quantum dot structures in InGaN compounds

    Page(s): 27 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB) |  | HTML iconHTML  

    We will summarize the optical characteristics and microstructures of the indium-aggregated quantum dots in InGaN compounds, including intended InGaN/GaN quantum well structures and InGaN epi-layers. In quantum well structures, the dependencies of optical properties and material structures on well width and nominal indium content are to be discussed. Also, the effects of silicon doping will be reported. Furthermore, the effects of post-growth thermal annealing on the formation of quantum dot-like structures and their variations of optical properties will be presented. In InGaN epi-layers, we have studied the optical and material properties of such films with high indium contents. From the images of cathodo-luminescence and high-resolution transmission electron microscopy, quantum dot structures could be observed. After thermal annealing, the original yellow emission became blue in color in one of the samples. In the other sample, the original red emission became the combination of red, yellow and blue photons, leading to white in color. View full abstract»

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  • Fabrication of semiconductor optical amplifiers and a novel gain measuring technique

    Page(s): 62 - 65
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (289 KB) |  | HTML iconHTML  

    The design and fabrication of 1550 nm semiconductor optical amplifiers (SOAs) and the characteristics of the fabricated SOA are reported. A novel gain measurement technique based on the integrations of the product of emission spectrum and a phase function over one mode interval is proposed for Fabry-Perot semiconductor lasers. View full abstract»

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  • Photonics research in the Hong Kong Polytechnic University

    Page(s): 32 - 35
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    The activities being carried out in the Photonics Research Center of The Hong Kong Polytechnic University was described. View full abstract»

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  • Top-emitting organic light-emitting diode using Al as anode

    Page(s): 193 - 195
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    Top-emitting organic light emitting diodes (Top-OLED) were made with Al capped with very thin platinum (Pt) and praseodymium oxide (Pr2O3) as the anode. Efficient Top-OLED were obtained with a microcavity design. It was found that this Top-OLED was highly non-Lambertian. It emitted more photons than conventional bottom-emitting-OLED after integration over all angles. View full abstract»

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  • Structural characterization and elastic strain of InGaN/GaN multiple quantum wells

    Page(s): 40 - 45
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (409 KB) |  | HTML iconHTML  

    X-ray diffraction, transmission electron microscopy and Rutherford backscattering/channeling are used to characterize the structure of an InGaN/GaN multiple quantum well (MQW) grown on an Al2O3(0001) substrate. Using the combination of these measurements, not only the layered structure of the MQW is revealed clearly but also the In content x (0.16) of the InxGa1-N component can be determined reliably, which is a prerequisite for further determination of the elastic strain of the MQW. X-ray θ-2θ scans of the (0002) and (101~4) diffractions are used to determine the average lattice parameters epi> and epi> of the MQW, consequently the average parallel elastic strain 11> = -0.25% and the average perpendicular elastic strain ⊥> = +0.13% of the MQW are deduced. The experimental result of ⊥>/11> = -0.52 is in good agreement with the value deduced from the elastic constants. View full abstract»

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  • Long-period waveguide gratings

    Page(s): 140 - 143
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (306 KB) |  | HTML iconHTML  

    Long period waveguide gratings (LPWG) based on a low-loss negative tone epoxy Novolak resin polymer have been fabricated on SiO2/Si substrate using standard cleanroom processes: UV photolithography and reactive ion etching. A maximum attenuation of -18 dB and a minimum 3 dB bandwidth of 6 nm were measured, and the grating length is as short as 1 cm. View full abstract»

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  • Synthesis of gallium nitride film and gallium oxide nano-ribbons by plasma immersion ion implantation of nitrogen into gallium arsenide

    Page(s): 132 - 136
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (365 KB) |  | HTML iconHTML  

    The preparation of gallium nitride (GaN) and gallium oxide (Ga2O3) nano-ribbons were accomplished by plasma immersion ion implantation (PIII) of nitrogen into GaAs. After PIII of nitrogen, rapid thermal annealing (RTA) was conducted on the sample. For samples annealed at 850°C for 2 minutes we observed the formation of GaN on the GaAs surface. Raman spectrum revealed a peak at 575 cm-1, which was attributed to be a blue-shifted peak (from 568 cm-1) associated with compressively strained GaN. X-ray diffraction and transmission electron microscopy (TEM) imaging were also conducted. They showed that the thickness of the region containing GaN was about 40 nm. When RTA was performed at 950°C for 2 minutes, Ga2O3 nano-ribbon was found on the GaAs sample surface. The ribbons were 0.1 to 2 μm in width, several tens of nanometers in thickness and several tens of micrometers in length. Raman spectroscopy confirmed that the ribbons are single crystalline Ga2O3. In addition, the Ga2O3 ribbons were found to possess strong visible photoluminescence. View full abstract»

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  • High-brightness AlGalnP tunnel-regenerated multi-active-region LEDs

    Page(s): 66 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (285 KB) |  | HTML iconHTML  

    Scalability of TRMAR LEDs is investigated in this paper. Both theoretical and experimental results show the optical output power and quantum efficiency scale with the number of cascaded active regions. Temperature distribution image measured by scanning thermal microscope is demonstrated that the two active regions emit light simultaneously. The maximum on-axis luminous intensity of 5 cd of TRMAR LEDs with two active regions was obtained with 15° angle cap. View full abstract»

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  • Liquid crystal devices for optical communication systems

    Page(s): 204 - 207
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (389 KB) |  | HTML iconHTML  

    Liquid crystals (LCs) prove to be the basic material for various applications in electronic imaging and displays as well as optoelectronics. We will review the following LC optoelectronic devices for optical communication systems. 1. Fast reliable low power optical switches. We shall demonstrate the new possible configurations of the fast LC shutters for fiber-optical system, based on (i) STN-LCD cell and (ii) fast deformed-helix ferroelectric liquid crystal (DHF-FLC) mode. 2. Passive elements of optical communication systems. The software for optimization of the LC light modulation characteristics has been developed. The new photo-aligning technology for efficient LC applications in optical communication systems has been made. 3. Passive fiber optical elements based on photonic crystals (PCs) and liquid crystals (LCs). A method for the formation of controllable PCf/C structures, based on multiple-redrawing technique, applied for different types of glass, filled with photo-aligned LC is discussed. View full abstract»

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  • Key technologies for novel wavelength-selective photodetectors

    Page(s): 54 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    One-Mirror-Inclined Three-Mirror-Cavity (OMITMiC) photodetector, which combines a Fabry-Perot filtering-cavity with a taper absorption-cavity, features high-speed, high quantum efficiency and ultra-narrow spectral linewidth simultaneously and allows wide range tuning when proper tuning mechanism is introduced. First fabrication and demonstration of this kind of device on GaAs substrate had been done in our laboratory. A quantum efficiency of 75% and a spectral linewidth of 0.8 nm (FWHM) were achieved with an absorption layer as thin as 0.119 μm. Relevant micromechanical tunable Fabry-Perot filter with a tuning range about 30 nm had been achieved. Research works on the key technologies to transfer our success to InP based long wavelength device are also presented. View full abstract»

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  • ZnO thin films grown by plasma-assisted metal-organic vapor phase epitaxy

    Page(s): 292 - 296
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    ZnO films were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire and Si substrate. Thermal annealing was performed on ZnO thin films deposited on Si substrate. X-ray diffraction spectra indicated that all ZnO films were strongly c-oriented. Strong ultraviolet (UV) emission was observed. X-ray photoelectron spectroscopy (XPS) measurements were performed to confirm the stoichiometry of ZnO film. Optical pumped UV lasing was obtained at room temperature. N-doped ZnO samples were realized by ionizing N2 and NH3. High resistive ZnO films were obtained by N-doping. View full abstract»

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  • Comparison of temperature dependent electroluminescence of InGaN/GaN and AlGaInP based LEDs

    Page(s): 196 - 199
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB) |  | HTML iconHTML  

    Light emitting spatial inhomogeneity in InGaN/GaN multiple quantum well (MQW) blue and green LEDs were observed directly with a microscope. Electroluminescence (EL) spectra of InGaN/GaN QW blue and green LEDs were studied in the temperature range of 10-300 K at an injection current of 5 mA. Some anomalous behavior was observed. Intensity of the EL main peak increased monotonically with temperature from 10 to 200 K and slightly decreased with further temperature increase in the 200 K range. This is in contrast with the monotonic decrease of EL with increasing temperature for conventional AlGaInP QW red LEDs. The anomalous behavior can only be observed on InGaN/GaN systems. The origin of such behaviors was discussed using a model of quantum dot clusters in the InGaN/GaN pseudo-quantum wells, with a small potential barrier at the boundary of the quantum dots. View full abstract»

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  • Study of free-standing GaN substrates prepared by hydride vapor phase epitaxy technology

    Page(s): 46 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    Free-standing GaN substrates has been prepared by hydride vapor phase epitaxy (HVPE) technology. Round substrates with diameters up to 1.5 inch and thickness up to 350 micron can be achieved. Various measurement tools, including X-ray diffraction, atomic force microscopy (AFM), and etch pit density (EPD) measurement, have been applied to characterize the optical and the structural properties of these substrates. The typical full width at half maximum of the PL spectra and the [002] X-ray diffraction peak was 10 nm and 120 arcsec respectively, compared to the typical values of 10 nm and 200 arcsec obtained on epitaxial GaN layers grown by metalorganic chemical vapor deposition (MOCVD) technique on Al2O3 substrates. Yellow bands usually detected in PL spectra can be eliminated, indicating reduction of related point defects. AFM measurements revealed a surface roughness of 5 nm or larger after growth and separation. With proper polish, the surface roughness can be reduced to less than 1 nm. EPDs on these substrates can be as low as in the 105 cm-2 range, compared to the typical values of 108-1010 cm-2observed in MOCVD GaN layers grown on Al2O3 substrates. Without doping, the free-standing GaN substrates showed electron concentrations less than 1016 cm-3. But with proper doping, electron concentration as high as 1019 cm-3, and hence resistivity lower than 0.1 Ω-cm, can be achieved. Maximum electron mobilities higher than 800 cm2/V-sec and 400 cm2/V-sec were detected in lightly doped and heavily doped substrates respectively. In this paper, the procedure of producing these free-standing GaN substrates will be briefly described, and the above measurement results, along with their indications, will be discussed. View full abstract»

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  • Real-time bit error monitoring system (BEMS) for optical communication by use of high speed optical logic gates

    Page(s): 172 - 174
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (278 KB) |  | HTML iconHTML  

    A novel bit error monitoring system is realized all-optically using cascaded optical NOT and optical NOR gate operating at different thresholds. This scheme generates real time optical monitoring signal which indicates the positions and duration of bit and burst errors in 10 Gbit/s signal. View full abstract»

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  • Structural monitoring of Tsing Ma Bridge using fiber Bragg grating sensors

    Page(s): 144 - 146
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB) |  | HTML iconHTML  

    In this paper, we present the results of the 'trial-test' of using fiber Bragg grating sensors to monitor the dynamic strain and temperature of Tsing Ma Bridge. Sensor packaging, installation technique as well as comparison of the measurement results of FBG sensors and electrical strain gauge sensors will be discussed. View full abstract»

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  • Analytical method for designing grating compensated dispersion-managed soliton systems

    Page(s): 158 - 161
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (314 KB) |  | HTML iconHTML  

    We show two useful methods to design grating compensated dispersion-managed systems. Our method is in good agreement with the numerical results even in the presence of group delay ripples in the gratings. View full abstract»

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  • The application of optical interconnection for computer system

    Page(s): 70 - 73
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (351 KB) |  | HTML iconHTML  

    In this paper, some recent achievements of optical interconnection network in Tianjin University are overviewed. These works are divided into two categories: One is demonstration of optical interconnection network for massively parallel processing systems. An opto-electronic hybrid parallel processing system with 64 processors, which are interconnected by optical fiber links, have been designed. Another is optical interconnection technique for computer clusters. A giga-bit/s optical links, hardware-routing has optical rings and wavelength-routing dual rings have been realized. Meanwhile, the communication latency has been reduced to 200 ns adopting hardware-routing technique. To further reduce the data packet routing-latency, wavelength routing technique has been implemented in a dual-wavelength ring. A star-ring combined network based on MEMS optical switch was realized, it demonstrated that, using MEMS optical switch in the network could be un-sensitive for data throughput of communication. View full abstract»

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  • Defects in III nitrides

    Page(s): 78 - 81
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (470 KB) |  | HTML iconHTML  

    Defects were investigated in undoped GaN and AlGaN epilayers grown on Al2O3 substrates by metal organic vapor phase epitaxy. Threading dislocations (TDs) and horizontal dislocations (HDs) in GaN were imaged and classified into different types. Precipitates and their punching out dislocations were recognized in undoped AlGaN. Defects at AlGaN/GaN interface are analyzed to result from compressive stress. View full abstract»

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  • Fabrication of ultrathin ZnO nanowires and their photoluminescence properties

    Page(s): 86 - 90
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (370 KB) |  | HTML iconHTML  

    Ultrathin ZnO nanowires have been fabricated by a vapor-phase transport process via the vapor-liquid-solid mechanism. The average diameter of the nanowires is about only 10 nm and the length is up to several micrometers. The experimental results show that the growth of the nanowires is very sensitive to the temperature, catalyzer materials, the content of oxygen in the carrier gas, and the gas pressure. The diameter of the nanowires is directly determined by the size of eutectic alloy droplets related to the thickness of Au catalyzer film and the gas pressure. Ultrathin ZnO nanowires can only be synthesized at a certain pressure of about 300 Torr and the temperature in the range from 450-500 °C when a layer of 20 nm Au catalyzer film is employed. Photoluminescence spectrum of the ultrathin ZnO nanowires is also measured, and an intensive ultraviolet light emission centered at 389 nm has been observed. View full abstract»

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  • Reduction of fiber alignment shifts in high-speed laser module packaging

    Page(s): 247 - 250
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (327 KB) |  | HTML iconHTML  

    The post-weld-shift (PWS) induced fiber alignment shifts of fiber ferrule-clip (FFC) joints in high-speed butterfly laser packaging by laser welding technique has been studied experimentally and numerically. There are two types of clip design in the FFC joint: the type I design is without a gap between clip and fiber ferrule and type II is a 5 μm gap. Using a novel 230× high magnification video probe camera with image acquisition system, the measured results showed that the fiber shifts of FFC joints with the type II exhibited shifts less than that with the type I. The experimental measurements of fiber shifts were in reasonable agreement with the numerical calculations of the finite-element method (FEM) analysis. This study has demonstrated that the FEM is an effective method for predicting PWS induced fiber alignment shifts in laser module packaging. View full abstract»

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  • Active medium inside photonic band structured microcavity

    Page(s): 116 - 119
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (322 KB) |  | HTML iconHTML  

    Microcavity that has inherent photonic band structure within exhibits unique optical characteristics. Based on electron-beam lithography, we have successfully created a two-dimensional wavelength-scale periodic texture on one of the cavity mirrors with nanometer precision. In the microcavity, Bragg scattering is expected to provide a full continuous optical bandgap and flat dispersion of optical waveguide modes in the visible regime. When the luminescing material such as Alq3 is placed inside the 2-D patterned microcavity, the coupling of the luminescing matter to the photonic eigenmodes of the metallic microcavity is observed. Careful tailoring of the photonic lattice parameters allows us to tune the emission characteristic of the microcavity. From the transmission result, we found that planar microcavity result is in good agreement with the theoretical calculation. For the laterally structured metallic microcavity samples, we found that the dispersion of optical modes inside the microcavity is significantly altered compare with the planar metallic microcavity. View full abstract»

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  • Dispersion compensation using multi-mode injection locking in Fabry-Perot semiconductor laser

    Page(s): 162 - 165
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (430 KB) |  | HTML iconHTML  

    Dispersion compensation of 10 Gbits/s NRZ signal using two-mode injection locking in FP-LD was demonstrated. Our preliminary results show that this technique is able to compensate 10 Gbits/s NRZ signal after propagation over 100 km of standard single-mode fiber (total dispersion of 1700 ps/nm). Experimental demonstration of dispersion compensation of two 10 Gbits/s NRZ signals simultaneously using one FP-LD will also be presented. View full abstract»

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  • UV, blue, green, yellow-green and white LEDs fabricated by III-N semiconductors

    Page(s): 3 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (219 KB) |  | HTML iconHTML  

    Recent achievements in GaN-based light-emitting diodes (LEDs), which is linked to the use of new designs, such as p+-AlGaN/GaN strained-layer superlattice (SLS) and n+-InGaN/GaN short-period superlattice (SPS) top contact layer is reported. GaN-based LEDs with low-operation voltages, which are as low as 3 V (at 20 mA ) even lower, can be achieved by the use of these heavy-doped layers. In addition, conventional transparent conductive oxide, such as indium tin oxide (ITO), can be served as a transparent top contact layer in GaN-based LEDs other than thin metal film such as Ni/Au. Luminescence intensity in visible GaN-based LEDs can be significantly improved by this new design due to the high-transparency top contact layer. In the recent achievements, white LEDs including a variety of designs, such as phosphor-containing and phosphor-less device structures, will also be reported. Specifically, the high-efficiency yellow-green (λ∼565 nm) LEDs based on InGaN/GaN MQW emitting layers, which the luminescence intensity is comparable with the conventional AlGaInP yellow-green (λ∼575 nm) LEDs is achieved. This high-efficiency InGaN/GaN yellow-green LED makes a single-chip complementary white LED possible. View full abstract»

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