Selective-area MOCVD growth for distributed feedback lasers integrated with vertically tapered self-aligned waveguide

The growth pressure and mask width dependent thickness enhancement factors of selective-area MOCVD growth were investigated in this article. A high enhancement of 5.8 was obtained at 130 mbar with the mask width of 70 μm. Mismatched InGaAsP (−0.5%) at the maskless region which could ensure the material at butt-joint region to be matched to InP was successively grown by controlling the composition and mismatch modulation in the selective-area growth. The upper optical confinement layer and the butt-coupled tapered thickness waveguide were regrown simultaneously in separated confined heterostructure 1.55 μm distributed feedback laser, which not only offered the separated optimization of the active region and the integrated spotsize converter, but also reduced the difficulty of the butt-joint selective regrowth. A narrow beam of 9° and 12° in the vertical and horizontal directions, a low threshold current of 6.5 mA was fabricated by using this technique.     

通用智能数据采集系统的开发

通用智能数据采集系统以单片机为核心,控制模/数转换芯片AD 7715实现对数据的采集,使用串行接口大容量FLA SH存储芯片AT 45D 041对数据进行存储,通过RS232口实现与上微机的通讯,并用LCD实时显示运行状态、测量结果等,重点阐述了单片机对AD 7715以及AT 45D 041的控制.该系统可广泛应用于需要对大量的实时数据进行采集的场合.     

基于积分束流变压器的加速器束团电荷量测量系统

 为满足清华大学加速器实验室光阴极微波电子枪实验平台的发展需求，设计了束团电荷量测量系统，可以实现实时测量加速器束团电荷量的目标。这套测量系统基于积分束流变压器，包括前置放大器、门控积分器、模数转换和数据传输模块。利用信号发生器模拟束流，对整套系统进行了离线测量实验。当前置放大器放大倍数取200和20时，AD转换值和束流电荷的比值分别为2.181 PC-1和0.195 PC-1，与理论值2.070 PC-1和0.207 PC-1基本吻合；其对应的电荷量测量误差分别小于2 PC和15 PC。测量结果和模拟束流电荷量值的拟合曲线线性度好，相关系数的平方均大于0.999 0。该结果验证了系统的可行性。     

多通道实时远距离人工计时信号采集

采用光电偶合器、A/D转换器和并行接口芯片等设计数字信号采集系统实现人工计时信号采集,提高人工计时的效率和准确性。计时裁判员独立操作计时器开关产生的开关量信号用屏蔽电缆通过自带电源式插转箱连接到光电偶合器进行光电隔离,再由A/D转换器进行开关量信号的模数转换,最后由并行接口芯片接收,并通过数据总线发送到计算机。用软件控制人工计时信号的采集、计算、处理、存储和输出,从而实现人工记时信号的采集。     

A Mode Converter with Multi-waveguide Output from the TE01 Circular Waveguide Mode to the TE10 Rectangular Mode for Millimeter Wave Gyro-device Applications

A mode converter with multi-waveguide output for millimeter wave gyro-device applications is proposed in this article, which is used to convert the TE₀₁ circular waveguide mode into the TE₁₀ rectangular waveguide mode. Computer simulations with Ansoft HFSS code show that the energy transmission coefficient of larger than 95.96% may be reached in the frequency range from 34.094 GHz to 35.8 GHz (a bandwidth of 1.706 GHz) at a VSWR of lower than 1.5 for the input operating mode.     

Use of porous silicon for double- and triple-layer antireflection coatings in silicon photovoltaic converters

Reflectance spectrum calculations of double- and triple-layer antireflection coatings made of porous silicon layer are performed, using the optical matrix approach method. Obtained results are compared with the reflectance spectrum of other type antireflection coatings. Lower reflectance value of both double- and triple-layer antireflection coatings made of porous silicon is obtained in comparison to that of SiO₂/TiO₂ antireflection coating. These results can be used in photovoltaic converters.     

Theoretical and Experimental Study on all-optical Wavelength Converters Based on the Single-port-coupled SOA

We analyze the all-optical wavelength converter (AOWC)-based on cross-gain modulation (XGM) in a single-port-coupled (SPC) semiconductor optical amplifier (SOA). A comprehensive dynamic model is developed by considering longitudinal variations of the carrier density, the residual rear-facet reflectivity of the SOA and the wide-band spontaneous noise emission. The numerical simulations for the novel wavelength conversion at 10 Gbit/s are presented based on the model. The extinction ratio (ER), conversion efficiency and pattern effect of the SPC-SOA-based wavelength converters are investigated, respectively. Compared with the traditional scheme of the double-portcoupled (DPC) SOA, the SPC-SOA scheme has better performance. We have obtained that the ER is higher than 10 dB with the pump wavelength turned over 15nm from experiments. The experimental results are in agreement with the simulation results.     

基于多值逻辑的 D/A转换器 分流电阻网络研究

本文通过对 D /A转换器表示的分析 ,用电流分流方法解释了二值 D /A转换器使用电阻网络的 物理实现 ,并在此基础上提出了四值 D /A转换器分流电阻网络 .该分流电阻网络在使用四值信号译码 的情况下将回到二值 D /A转换器.然而 ,这种基于多值逻辑的设计将导致一种新颖的 Π型电阻转换网 络 ,该网络比传统的 T 型电阻网络节省四分之一电阻数量 ,并可保证较高的转换精度.     

相对论返波管模式变换器的研究

 根据相对论返波管的需求设计计算了一种模式变换器兼反射器。它将工作模式TM₁₁模转换成TE₁₁模的同时将TE₁₁模反射回去,用普通的喇叭形成高斯波束发射输出。在我们的设计方案中,它是旁壁对称正弦波纹的圆波导,变换器的中心频率为10GHZ。数值模拟结果显示,变换器的长度为7个周期时,中心频率点转换的效率已经超过了90％,工作频带能够达到± 0.3GHz。     

Synthesis of novel copolymers obtained from acceptor/donor radical copolymerization of phosphonated allyl monomers and maleic anhydride

A series of four phosphonated‐bearing allyl monomers, that is, diethyl‐1‐allylphosphonate ( AP ), dimethyl‐1‐allyloxymethylphosphonate ( AOP ), 5‐ethyl‐5‐(allyloxymethyl)‐2‐oxo‐1,3,2‐dioxaphosphorinane ( AEDPH ), and 2‐benzyl‐5‐ethyl‐5‐(allyloxymethyl)‐2‐oxo‐1,3,2‐dioxaphosphorinane ( AEDPBn ) were synthesized. These monomers were then copolymerized by free radical polymerization in the presence of maleic anhydride, thus leading to alternated copolymers with phosphonate moieties. It was shown that both monomer conversion and reaction rate were dependent on the phosphonate moieties carried out by the allyl monomer: the bulkier the phosphonate group, the higher the polymerization rate. Thermogravimetric analysis of the copolymers revealed a high content of residue, also varying with the nature of the phosphonate moieties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011