中红外大气甲烷乙烷双组分气体的同步移动监测

为了实现大范围、长距离的大气烷烃气体检测,将研制的中红外双组分甲烷、乙烷传感器以车载方式,对某一地区的大气甲、乙烷含量进行了移动探测。该传感器系统采用中红外室温连续的带间级联激光器(ICL)作为光源,采用高速数据采集卡采集信号,利用上位机LabVIEW平台编写程序产生激光器扫描及调制信号、获取探测器信号并提取二次谐波,通过计算,确定大气烷烃气体浓度。根据气体采样时间、实时风速及车速,计算得到系统的响应时间为82.5s,实验测量为85~95s,与理论一致。对系统噪声水平进行测试,实验室中甲烷浓度波动为±40nL/L,乙烷波动为±2nL/L,车载过程甲烷浓度波动为+40至-80nL/L,乙烷波动为±4nL/L。为验证传感器性能,与美国Aeries公司的商用传感器结果做了对比,二者呈现较好的一致性。最后,给出了车载传感器系统在某条线路上的甲烷、乙烷浓度移动探测结果,以及某小区甲烷、乙烷浓度的二维分布测绘结果,分析了二种烷烃气体的变化关系。本文所开展的工作为探测烷烃气体泄漏并监测大气质量提供了技术保障。     

1550nm低推挽电压聚合物定向耦合电光开关的设计

应用保角变换法、镜像法、耦合模理论和电光调制理论设计了一种推挽电极聚合物脊形波导定向耦合电光开关,阐述了基本结构和工作原理,给出了器件的设计和优化过程,主要分析了耦合长度、开关电压、输出光功率、插入损耗、串扰等特性.为了实现正常的开关功能,讨论了制作公差、波谱漂移以及单模光纤耦合损耗对器件性能的影响.模拟结果表明,所设计的开关的耦合长度为3082μm,开关电压为2.14V;插入损耗小于1.14dB,串扰小于-30dB.与BPM仿真结果以及实验结果的对比表明,文中提出的波导和电极的理论分析与计算方法具有较高的精度和可行性.     

离散多音调制可见光信道非线性失真及参数优化

为了改善离散多音调制(DMT)点对点可见光通信(VLC)性能,首先给出了DMT技术原理并建立了实验装置,进而研究了16-相位键控(16-PSK)DMT信号直流偏压和探测器偏置电阻对VLC信道非线性失真的影响。为了使VLC信道工作于良好的线性区,优化得到了不同通信距离下系统的最佳直流偏压和探测器偏置电阻。在VLC信道响应存在非线性失真和调节系统参数使其工作于线性区两种情况下,在0.2Mbit/s数据传输速率下分别开展了通信实验,并测试了系统在不同通信距离处的误码率(BER)。结果显示,BER可由未做参数优化时的10-1量级降至10-3量级;且在20~90cm通信距离范围内BER几乎恒定,表明系统稳定性也得到了明显改善。本文的实验测试和分析结果为进一步优化系统参数及改进通信性能提供了数据依据。     

基于ARM7的校园一指通系统设计

研究了一种可替代校园饭卡付费系统的指纹识别系统,该系统由服务器管理模块和操作终端模块构成,二者经由网线通信。设计了基于ARM7的操作终端硬件电路,编写了驱动USB接口芯片和网卡芯片的C语言程序。主机服务器安装指纹比对程序通过对终端传输来的指纹图像信息进行比对确认学生身份,进而进行计费操作。同时由于该系统在现有的网络条件下通过拓展终端可以方便的扩充系统,因此具有较好的发展空间和应用前景。     

硫系玻璃狭缝波导微环的模拟分析

硫系玻璃材料在中红外波段具有高的透过率,成为制备中红外光波导光学传感器的首选材料。为了提高光与待测物的作用,减小器件体积,优化设计并分析了硫系玻璃狭缝光波导微环器件。通过COMSOL软件对狭缝波导进行了建模,为了减小高折射率衬底的影响、减小电极材料对红外光的吸收并避免共振吸收,优化了下缓冲层厚度、上缓冲层厚度、电极厚度。采用优化的狭缝波导结构,设计了圆形和跑道型硫系玻璃狭缝波导微环谐振器,优化了微环谐振器半径,分析了品质因数、自由光谱区、以及谐振光场分布等性能参数。分析结果显示,圆形微环谐振器具有更高的品质因数(28452),谐振峰更加尖锐,对光的选择性更好;而跑道型微环谐振器的自由光谱区更小(6.2nm),用电极调节谐振峰的波长时,谐振峰更容易和气体的吸收峰对齐,更适合于红外气体检测。     

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.     

便携式点对点可见光通信终端的实验研究

利用开关键控-非归零码(OOK-NRZ)调制编码技术,设计并实现了一对基于ARM7处理器(LPC2148)的便携式点对点可见光通信(VLC)收/发终端。发送端由编码器、光源驱动器及单个白色发光二极管(WLED)构成,接收端由可见光探测器、信号处理电路及解码器构成。实验研究了WLED的发射谱和可见光探测器的响应谱,测试分析了VLC信道的时域和频域的电-光-电(EOE)响应。阐述了系统结构和原理,编写了通信软件并制定了相关协议,实现了系统的软、硬件集成。利用研制出的通信装置,建立了点对点通信链路,并开展了数据通信实验。结果表明,在发送端,为了最大化地降低误码率(BER),WLED的调制系数应设置为0.68~1.00,即在一定的交流调制信号幅度下,需要向WLED提供合适的直流偏置电压;在接收端,在一定的阈值判决门限电压下,VLC传输呈带通特性。在所优化选择的系统参数下,系统的通信距离为0.5m,可达到的最快信息传输速率约为4 Mbps,BER小于10-6。利用多个WLED构成阵列光源,系统可进一步满足更长距离的通信需求,从而在室内、外短途通信方面具有潜在的应用价值。     

Optimal design of a high-speed polymer Mach-Zehnder interferometer electro-optic switch over 260 GHz

By using the proposed 3-D mode propagation analysis method and point-matching method, a polymer multimode interference (MMI) Mach-Zehnder interferometer (MZI) electro-optic (EO) switch is designed and optimized for enhancing the EO modulating efficiency and matching the impedance and the velocity. The designed switch possesses low driving voltages of ±1.375 V with a short EO active region length of 5 mm under 1550 nm wavelength, and the estimated cutoff switching frequency is up to 263 GHz due to the less mismatch between the lightwave velocity and microwave velocity. The 3-dB lightwave bandwidth is 60 nm, and within the wavelength range of 1520–1580 nm, the insertion loss and crosstalk are less than 6.71 and −30 dB, respectively.     

A near-infrared methane detection system using a 1.654 µm wavelength-modulated diode laser

By adopting a distributed feedback laser (DFBL) centered at 1.654 µm, a near-infrared (NIR) methane (CH4) detection system based on tunable diode laser absorption spectroscopy (TDLAS) is experimentally demonstrated. A laser temperature control as well as wavelength modulation module is developed to control the laser’s operation temperature. The laser’s temperature fluctuation can be limited within the range of ?0.02—0.02 °C, and the laser’s emitting wavelength varies linearly with the temperature and injection current. An open reflective gas sensing probe is realized to double the absorption optical path length from 0.2 m to 0.4 m. Within the detection range of 0—0.01, gas detection experiments were conducted to derive the relation between harmonic amplitude and gas concentration. Based on the Allan deviation at an integral time of 1 s, the limit of detection (LoD) is decided to be 2.952×10-5 with a path length of 0.4 m, indicating a minimum detectable column density of ~1.2×10-5 m. Compared with our previously reported NIR CH4 detection system, this system exhibits some improvement in both optical and electrical structures, including the analogue temperature controller with less software consumption, simple and reliable open reflective sensing probe.     

Non-blocking four-port optical router based on thermo- optic silicon microrings

By using silicon-on-insulator(SOI) platform, 12 channel waveguides, and four parallel-coupling one-microring resonator routing elements, a non-blocking four-port optical router is proposed. Structure design and optimization are performed on the routing elements at 1 550 nm. At drop state with a power consumption of 0 m W, the insertion loss of the drop port is less than 1.12 d B, and the crosstalk between the two output ports is less than-28 d B; at through state with a power consumption of 22 m W, the insertion loss of the through port is less than 0.45 d B, and the crosstalk between the two output ports is below-21 d B. Routing topology and function are demonstrated for the four-port optical router. The router can work at nine non-blocking routing states using the thermo-optic(TO) effect of silicon for tuning the resonance of each switching element. Detailed characterizations are presented, including output spectrum, insertion loss, and crosstalk. According to the analysis on all the data links of the router, the insertion loss is within the range of 0.13—3.36 d B, and the crosstalk is less than-19.46 d B. The router can meet the need of large-scale optical network-on-chip(ONo C).