Electrical-efficiency analysis of GaN-based light-emitting diodes with interdigitated-mesa geometry

We propose a novel method to analyze the current-voltage (I-V) characteristics of GaN-based light-emitting diodes (LEDs) with different p-type electrodemesa geometries. The electrical efficiency is analyzed by calculating the electric field under the quasi-coplanar electrodes of GaN-based LEDs. The experimental results for GaN-based LEDs of chip sizes of 350×350 μm² and 1,000 × 1,000 μm² with interdigitated fingers are compared. A good agreement is obtained between the experimental and theoretical electrical efficiency of the GaN LEDs with a chip size of 1,000×1,000 μm². The current-crowding effect is analyzed by measuring the electroluminescence spectra of the devices. The result indicates that the current-crowding effect is largely reduced by increasing the number of interdigitated fingers. The electrical efficiency of a LED with a chip size of 1,000×1,000 μm² can be also enhanced by increasing the number of interdigitated fingers, showing the advantages of GaN LED with interdigitated-mesa geometries.     

Design and Analysis of 4×4 Arrayed Waveguide Grating Multiplexer

The operation principle of an arrayed waveguide grating(AWG) multiplexer is introduced and the 4×4 AWG with following design parameters is discussed in detail, such as the choice of wavelength, the neighboring arrayed waveguide distance ΔL, the channel frequency interval Δf, and the free spectral range. The structure of 4×4 AWG is designed and the result of stimulated test is also given. Analysis shows that the 4×4 AWG is characterized by a wide dynamic range, low crosstalk, better spectrum properties, and a compact structure.     

Development of a portable mid-infrared methane detection device

Based on direct absorption spectroscopy (DAS), a portable methane (CH4) detection device was implemented. The device mainly includes a dual-channel non-dispersive infrared sensor (integrated with an infrared light source, light path and pyroelectric detector), a driving circuit of the sensor, an ARM11 embedded WinCE system, and a LabVIEW-based data-processing platform. Experiments were carried out with prepared CH4 samples to investigate the sensing performance. The relative detection error is less than 9.14% within the measuring range of 0—7×10-2. For a CH4 sample with concentration of 0 (i.e., pure nitrogen), the measured concentration fluctuation range is ?1.2×10-5—+2×10-5. An Allan deviation analysis on the gas sample with concentration of 0 indicates that the 1σ limit of detection (LoD) of the device is 4.8×10-6 with an average time of 1 s. Experiments were performed on three CH4 samples with different concentrations to test the response time, which is validated to be less than 20 s. Due to the small size of the ARM11 embedded system and the powerful data processing capability of the LabVIEW platform, the proposed portable and miniaturized CH4 sensor shows a good application prospect in mining operations and some other industrial fields.     

掺杂硅微通道板的帕尔贴效应

The Seebeck coefficient is determined from silicon microchannel plates (Si MCPs) prepared by photo-assisted electrochemical etching at room temperature (25 ℃). The coefficient of the sample with a pore size of 5 × 5 μm², spacing of 1 μm and thickness of about 150 μm is -852 μV/K along the edge of the square pore. After doping with boron and phosphorus, the Seebeck coefficient diminishes to 256 μV/K and -117 μV/K along the edge of the square pore, whereas the electrical resistivity values are 7.5 × 10^-3 Ω·cm and 1.9 × 10^-3 Ω·cm, respectively. Our data imply that the Seebeck coefficient of the Si MCPs is related to the electrical resistivity and is consistent with that of bulk silicon. Based on the boron and phosphorus doped samples, a simple device is fabricated to connect the two type Si MCPs to evaluate the Peltier effect. When a proper current passes through the device, the Peltier effect is evidently observed. Based on the experimental data and the theoretical calculation, the estimated intrinsic figure of merit ZT of the unicouple device and thermal conductivity of the Si MCPs are 0.007 and 50 W/(m·K), respectively.     

Fabrication and characterization of transparent conducting titanium-zinc oxide nanostructured thin films

Nano transparent conducting titanium-zinc oxide (Ti-ZnO) thin films were prepared on glass substrates by radio frequency (RF) magnetron sputtering technique. The deposited films are characterized by X-ray diffraction (XRD), four-probe meter and UV-visible spectrophotometer. The effects of Ti-doping content on the structural, optical and electrical properties of the films are investigated. The XRD results show that the obtained films are polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The structural and optoelectronic characteristics of the deposited films are subjected to the Ti-doping content. The Ti-ZnO sample fabricated with the Ti-doping content of 3% (weight percentage) possesses the best crystallinity and optoelectronic performance, with the highest degree of preferred (002) orientation of 99.87%, the largest crystallite size of 83.2 nm, the minimum lattice strain of 6.263´10-4, the highest average visible transmittance of 88.8%, the lowest resistivity of 1.18×10-3 W?cm and the maximum figure of merit (FOM) of 7.08×103 W-1?cm-1. Furthermore, the optical bandgaps of the films are evaluated by extrapolation method and observed to be an increasing tendency with the increase of the Ti-doping content.     

Influence of Crosstalk on Signal Power Based on Arrayed-waveguide Grating as N × N Optical Router

The fact that the signal results in signal-crosstalk is confirmed for arrayed-waveguide grating as N × N optical router,and the relation between the crosstalk and power penalty is obtained.The method reveals the random distributions of optical path phase errors in two multiplexers with channel numbers of 10 and 160. It is shown that the crosstalk must be less than -28 dB for a power penalty below 1 dB at a bit error rate of 1×10 -9 .It is found that when N =100,crosstalk power value is -20 dB with compensation power of 2-3 dB,so the compensation power is not ignored.     

12GHz Low Noise Amplifier MMIC

<正> Shown in the front cover is a scanning electron micrograph of a 12GHz two-stagelow noise amplifier MMIC's chip with the size of 3.22×1.49×0.2mm~3, consisting of 2GaAs MESFETs, 6MIM capacitors, 8 airbridges and 9 microstrip lines fabricated byNEDI in 1988. Optimization of the circuits has been done employing our own NAMPprogram, resulting in a noise figure of 3.1dB and an associated gain of 14dB at11.7-12.2GHz.     

An Electroabsorption Modulator Monolithically Integrated with a Semiconductor Optical Amplifier and a Dual-Waveguide Spot-Size Converter

A semiconductor optical amplifier and electroabsorption modulator monolithically integrated with a spot-size converter input and output is fabricated by means of selective area growth,quantum well intermixing,and asymmetric twin waveguide technology.A 1550～1600nm lossless operation with a high DC extinction ratio of 25dB and more than 10GHz 3dB bandwidth are successfully achieved.The output beam divergence angles of the device in the horizontal and vertical directions are as small as 7.3°×18.0°,respectively,resulting in a 3.0dB coupling loss with a cleaved single-mode optical fiber.     

Optical performance of hybrid dielectric loaded plasmonic waveguide using PTFE for nano-scale light confinement

Different characteristics of fundamental mode of hybrid dielectric loaded plasmonic waveguide have been explored at 1 550 nm wavelength, to resolve the issue of large propagation loss and diffraction limit with minimal waveguide dimension.Propagation length of 432 µm has been achieved with the optimal dimension of 200 nm×40 nm. Through the numerical simulation results, the effective area of 0.021μm2 and normalized intensity of 40.71 μm-2in the spacer region of the waveguide have been realized. To accomplish the ultra-compact directional coupler, the smaller coupling length of about 1.42 µm has been achieved. PTFE-based waveguide can be highly beneficial for the realization of monolithic integration with active optical devices.     

Monolithically Integrated Laser Diode and Electroabsorption Modulator with Dual- Waveguide Spot-Size Converter Output

A 1.60μm laser diode and electroabsorption modulator monolithically integrated with a novel dual-waveguide spot-size converter output for low-loss coupling to a cleaved single-mode optical fiber are demonstrated.The devices emit in a single transverse and quasi single longitudinal mode with an SMSR of 25.6dB.These devices exhibit a 3dB modulation bandwidth of 15.0GHz,and modulator DC extinction ratios of 16.2dB.The output beam divergence angles of the spot-size converter in the horizontal and vertical directions are as small as 7.3°×18.0°,respectively,resulting in a 3.0dB coupling loss with a cleaved single-mode optical fiber.