基于相位解调的双光束薄膜干涉型光纤传声器

针对基于相位解调的双光束薄膜干涉型光纤传声器的特性展开了研究,仿真分析了三路信号的直流分项、交流分项以及相位差对双光束薄膜干涉型光纤传声器输出性能的影响。采用对比法,并通过实验研究了基于相位解调的双光束薄膜干涉型光纤传声器的输出特性,实现了灵敏度为193 mV/Pa@1 kHz、频率响应为200 Hz～4 kHz@±3 dB的声信号测量。本研究能够很好地应用于声探测、语音识别等领域。     

高灵敏度光纤应变传感器

提出一种基于锥形光纤和光纤F-P腔组合结构的光纤应变传感器。该传感器包含单模光纤拉锥形成的锥区和石英毛细管构建的F-P腔2个应变敏感区域。理论分析了光波在该传感器中的传播过程,获得了该传感器的光强传输函数。由于锥形光纤中激发出的包层高阶模参与干涉,导致传感器干涉光谱具有调制特性。实验获得了该传感器的干涉光谱,通过分析谐振波长偏移或消光比变化对应变实现独立测量,在0~500 με的测量范围内,该传感器的应变灵敏度为14.6 pm/με。利用锥形光纤引发的模式干涉和F-P腔的双光束干涉效应共同作用形成受调制的干涉谱型进行应变传感,应变灵敏度高,同时具备2种独立的应变检测手段(谐振波长和消光比检测)。     

一种基于反馈环的全光纤干涉型传声器

设计了一种基于光纤反馈环的全光纤干涉型传声器，它直接利用声压作用于光纤时产生的光弹效应对光相位进行调制，并通过3×3耦合器构建的反馈环结构形成干涉效应，从而使得输出光信号经光电转换和放大后可以直接驱动扬声器还原出原输入语音信号。我们从理论和实验上对这种全光纤传声器进行了研究，在该传声器的重要参数测量方面均取得了较好的效果。     

基于Vernier效应的法布里-珀罗传感器增敏方法

设计了一种分离型光纤传感增敏结构,并联连接两个腔长相近的法布里-珀罗(F-P)腔。理论分析了此结构的增敏原理并制备了两组增敏结构。实验结果表明,增敏结构的压强灵敏度值由单F-P结构的4.85 nm/MPa提高到43.95 nm/MPa,温度灵敏度由单F-P腔的0.0675 nm/℃提高至0.40364 nm/℃,在相同温度下采用双腔结构可消除温度交叉敏感对测量结果的影响。此结构克服了集成式增敏结构的缺陷,在不影响原传感器结构的情况下提高了灵敏度,且可通过更换辅助腔来调节灵敏度,具有移植性好和交叉敏感小等优势。     

基于激光微加工的新型光纤法布里-珀罗折射率传感器

提出了一种新型的光纤法布里-珀罗(F-P)折射率传感器,该传感器由单模光纤头端面和靠近该端面的由157 nm激光加工而成的短空气腔构成.短空气腔两个端面的反射光和光纤头端面的反射光发生干涉形成了传感器的反射谱干涉条纹.干涉条纹的对比度受光纤头端面外部的折射率影响,在干涉条纹包络的波谷处具有最大的对比度,外部待测折射率可通过计算该处的对比度得到.传感器对温度不敏感同,测量范围广.在1.33至1.441范围内,折射率灵敏度约为27 dB,分辨率约为1.12X10-4;在1.45～1.62范围内.折射率灵敏度约为24 dB,分辨率约为1.26×10-4.     

微型非本征光纤法布里-珀罗压力传感器

设计并研制了一种新的微型非本征光纤法布里-珀罗(F-P)压力传感器。传感器采用普通的商用单模光纤和多模光纤制作。全石英结构,能长期使用,且稳定性好。传感器制作过程仅通过切割光纤、腐蚀光纤和光纤熔接实现,基于F-P多光束干涉原理测量压力。分析了F-P腔的直径、膜厚与灵敏度的关系,确定了传感器的膜厚和腔深等参量,设计了传感器的加工步骤,讨论了氢氟酸腐蚀多模光纤与熔接光纤的关键技术。用单峰谱峰波长法解调出传感器的腔长。建立了实验解调系统,实验结果表明,在0~0.1 MPa范围内,传感器线性好。     

用于光纤法布里-珀罗传感器腔长互相关解调的光楔的数学模型研究

光楔是实现光纤法布里-珀罗(F-P)传感器互相关解调的重要光学元件.根据互相关解调的原理分析了造成光楔和光纤F-P传感器F-P腔的反射光相位不同的因素,进而建立了光楔的干涉光强的数学模型,在此基础上对具有不同反射率的光楔的干涉光强进行了数值仿真,和相同反射率的光纤F-P传感器F-P腔的干涉光强对比之后建立了光楔的简化数...     

带微通道的新型光纤法布里-珀罗折射率传感器

报道了一种新型结构的光纤法布里-珀罗(F-P)折射率传感器。使用腐蚀工艺在切割好的掺铒光纤端面制作一个封闭的微槽,然后与一段单模光纤熔接形成封闭的F-P腔。腐蚀产生的微槽底部是一个凹谷,靠近凹谷切割并研磨产生一个微通道,同时光束也能够返回并不损坏F-P干涉仪,利用毛细作用液体可进入F-P腔。根据F-P干涉原理,传感头反射光谱的波谷波长与腔内折射率成线性关系。实验表明当折射率在1.3333～1.3899内变化时,线性度为0.9996,灵敏度为1068 nm/RIU(refractive index unit)。该传感器为全光纤结构,具有体积小、结构稳定、精度高、耐腐蚀等特点,适用于液体和气体折射率的微型化测量。     

基于光纤光栅的应变与温度分离技术的研究

理论分析了光纤光栅交叉敏感的物理机制,重点研究了基于双波长矩阵法和双参量矩阵法的应变与温度分离技术。提出了一种基于双参量矩阵法的应变与温度测量系统,该系统传感头由FBG和非本征型F-P干涉腔(EF-PI)构成,其中FBG对应变敏感,EFPI测温精度高。     

基于空芯光纤的集成式全光纤法-珀干涉式湿度传感器

利用空芯光纤制作的法布里-珀罗(Fabry-Pérot,F-P)干涉传感器具有较低的温度敏感性,由于传感器干涉光光程差与空芯光纤制作的F-P干涉腔腔内介质折射率有直接依赖关系,提出在空芯F-P干涉传感器的腔内填充一种具有较强吸水性的新型纳米复合水凝胶从而构成一种温度低敏感的微型湿度计。当水凝胶通过吸收空气中的水蒸汽而使自身的折射率发生变化时,就会导致F-P腔干涉光的光程差发生变化,通过检测这一光程差的变化就可实现对环境相对湿度的测量。实验结果表明,填充自制的水凝胶,在38%～98%的相对湿度变化范围内,传感器的光程差从608.7180μm变化到了604.0488μm,在水凝胶折射率变化范围内,其光程差与相对湿度的灵敏度为77.82nm/(1%)。     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

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.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.