激光非接触曲面面形传感器

提出一种用于空间自由曲面测量的激光非接触曲面面形传感器。该传感器结构简单，在光学原理上传感器的输出量与被测量成线性关系，接收物镜绕系统光轴３６０°接收目标面的漫射光，目标面的倾斜产生的影响很小，解决了困扰空间自由曲面测量中阴影效应、倾斜等问题。该传感器的测量范围为４ｍｍ，分辨率为２μｍ，当目标面（漫反射面和金属等镜面反射面）倾斜角为±８５°时，仍能保证２０μｍ的测量精度。     

基于F-P腔干涉的膜片式光纤微机电系统压力传感器

基于法布里-帕罗腔的干涉原理,采用微机电系统技术加工制作了一种光纤微机电系统压力传感器,采用浓硼扩散自停止腐蚀和磁控溅射的方法,制备厚度为6μm、机械灵敏度为0.502μm MPa的传感器敏感膜.基于强度解调技术,利用干涉腔的反射功率与压力的关系对压力进行解调,分析了腔长变化对反射率的影响,确定传感器线性工作点的波长,建立稳定的压力传感测试系统,测试结果表明,该传感器压强最小分辨率为62 Pa,灵敏度达到0.51nW/WKPa,具有良好的线性度、灵敏度和重复性,适用于于人体内压力测量和口腔义齿压力测量.     

适用于硅微谐振器件测量的光纤位移传感器研究

对一种适用于硅微机械谐振器件测量的光纤位移传感器进行了研究,该光纤位移传感器探头采用了单根光纤探测形式和光纤“X”耦合器结构,在微弱光电传感信号处理上采用了“锁相放大器”提取方案,可以实现对静态位移和振动位移两种场合进行测量.对该传感器的实测结果表明:该传感器测量范围为0～100 μm,测量灵敏度3.95 mV/μm,精度等级优于1%,重复性优于0.5%.为作为应用实例,运用该传感系统对一种微悬臂梁硅微谐振器件进行了测量,成功提取了硅微谐振器件的微弱谐振信号,证实了该传感器可以实现对硅微谐振器件的非接触和无损测量,并具有非接触、易调试、高灵敏度等优点.     

基于荧光机理的光纤温度测量仪

基于普朗克定律的荧光光纤测温仪,采用蓝宝石光纤作为温度探头,蓝宝石光纤物理化学性能稳定,熔点高(超过2000℃),在0.3～0.4μm波段范围内透光性好,具有光波导的特点,在温度光纤传感和近红外传感等领域有很好的应用前景。利用快速傅里叶变换的拟合方法对荧光寿命进行测量,从第一个非零相的相位角的正切值得出被测的荧光寿命,具有速度快,误差小,不受本底干扰等优点,提高了测量的分辨率。测量范围为0℃～450℃,分辨率达到0.4℃。实验表明该测温仪能有效地消除光源不稳定及测量通道中光强变化对测量结果的影响,具有抗电磁干扰强,测温准确,分辨率高等特点。     

面向地壳形变观测的超高分辨率光纤应变传感系统

高分辨率光纤应变传感系统是地球物理学中地壳微弱形变观测的有力工具.相比于传统的地壳应变观测技术,光纤应变传感器具有测量分辨率高、抗干扰能力强、尺寸小、可复用、易于安装布设等特性,在建立新型地壳形变监测网络中具有很大的应用潜力.本文围绕面向地壳形变观测的纳应变级分辨率光纤应变传感器技术,阐述了应变传感原理与实现超高测量分辨率的机理,并详细介绍了扫频探测、Pound-Drever-Hall解调技术、边带探测、双回路锁定传感、传感器时分复用等技术及相应的传感器系统实现方案,最后,给出了超高分辨率光纤传感器在现场观测的实验结果与分析.     

光纤瓦斯传感系统的研制

利用光电检测理论和波分复用技术，研制出安全型光纤瓦斯传感器。系统传感头利用CH4气体在1.331μm处的谐波吸收谱工作。系统采用双波长差分吸收的工作方式，其参考波长为1.27μm，消除了非光吸收的其他散射和微扰等影响。由微机用软件控制12位A／D／A转换卡进行数据采集与处理，系统分辨率达0.001％，实现了实时显示。该系统不仅能对瓦斯气体进行准确检测，而且由于采用了光学测量的方式，所以既安全又可靠，不仅可以应用于煤矿矿井内的瓦斯气体含量的实时测量，还可以实现远程监控。     

基于光纤侧边抛磨技术的醋酸浓度光纤传感器

演示了两种利用光纤侧边抛磨技术制备的用于醋酸浓度检测的光纤传感器.其中一种光纤传感器采用轮式抛磨法对光纤光栅的光栅区包层进行侧边抛磨加工而成,将醋酸溶液覆盖于光纤光栅的抛磨区,利用侧边抛磨光纤光栅反射峰波长的变化对醋酸浓度进行测量;另一种光纤传感器采用轮式抛磨法对普通单模光纤包层进行侧边抛磨加工而成,将醋酸溶液覆盖于光纤抛磨区,利用抛磨光纤插入损耗的变化对醋酸浓度进行测量.两种光纤传感器的实验都表明:光纤包层抛磨表面与纤芯的距离越小,测量分辨率越高.剩余包层厚度为 0 μm 的侧边抛磨光纤光栅传感器测量醋酸溶液浓度分辨率为6.67%;剩余包层厚度为O.5μm 的侧边抛磨光纤传感器测量醋酸溶液浓度分辨率为0.55%.     

一种基于大角度倾斜光纤光栅包层模的低频声传感方案

利用倾斜光纤光栅在发生弯曲时其存在的多种纤芯-包层模式耦合方式容易发生改变,进而使其光谱特征发生明显变化的特点,提出并验证了一种基于大角度倾斜光纤光栅包层模的低频声传感方案.将倾斜光纤光栅与设计的聚对苯二甲酸乙二酯(PET)换能膜片及腔体结构相结合,得到了一种有效的低频声传感系统.该换能膜片在被测声波信号作用下产生振动,使固定在膜片表面的倾斜光纤光栅发生周期性动态弯曲,引起倾斜光纤光栅的包层模式光谱发生周期性漂移,最后采用边缘滤波法进行解调,实现低频被测声波的有效探测.实验结果显示,该传感方案可以在45—220 Hz范围内实现高灵敏度声波探测,在传感系统固有频率附近54 Hz处获得最大声灵敏度115.88 m V/Pa,且最小探测声压为539.2μPa/Hz^1/2.该传感方案具有灵敏度高、重复性好、结构简单、容易加工等优势,在低频声探测等相关应用领域具有较大的发展前景.     

多用途温度传感器

York传感器公司发展了一种用分布温度传感器提供温度和位置连续分布的技术。此系统用标准远距离通信多模50/125μm光纤检测由于温度变化引起局部光散射功率的改变。长20km的单根光纤起传感元件的作用,可从10000个位置测量温度和位置。在距离、空间分辨率、温度分辨率和测量时间方面要作权衡。在5s、±1℃分辨率、1km距离范围,可达到1m的空间分辨率。在60s内1m空间分辨率和10km距离,或10m空间分辨率及20km情况下,可达到±2.5℃温度分辨率。     

强度型激光光纤传感系统的神经网络补偿方法

提出一种考虑激光光纤传感系统中的激光器输出功率波动的神经网络跟踪补偿方法。在这种方法中，神经网络不仅用于削弱激光器输出功率波动对测量系统的影响，而且还同时用于传感非线性校正。提高了光强调制型光纤传感器的长期工作稳定性及测量精度，并有利于扩大激光光纤测量系统的测量范围。以光纤位移传感器为例，说明了该方法的有效性。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.