一种基于马赫-曾德干涉仪的全光纤传感器双参数测量技术

提出一种干涉式全光纤传感器,能够同时实现对折射率和轴向拉力或温度进行双参数测量。传感器由一个微腔和一个纤芯失配衰减器组成。其中微腔结构是由飞秒激光加工光纤纤芯形成,直径和深度分别是6μm和2.5μm。该干涉式传感器可以获得20dB的高品质干涉对比度。传感器透射谱波长为1496.68nm和1533.18nm的两个衰减峰对应的折射率灵敏度分别为-29.91nm/RIU和-16.72nm/RIU,拉力灵敏度分别为-1.55pm/με和-0.31pm/με。实验结果表明,传感器通过灵敏度矩阵可以同时测量折射率和轴向拉力或温度两个参数。     

基于偏芯熔接光纤的应力与折射率传感器

基于偏芯熔接技术构建了一种新型马赫-曾德尔干涉(MZI)原理的应力与折射率光纤传感器。该传感器是由一段单模光纤的两端实施偏芯熔接而成。利用光纤包层模、纤芯模对应力和折射率的敏感特性,实现对外界折射率和应力的测量。研究结果表明,施加轴向应力范围为0~500με时,传感器的近红外透射光谱的波长出现蓝移,在1585nm附近干涉谷处的应力灵敏度约为-7.00pm/με;外界折射率在1.331~1.398RIU(RIU为单位折射率)范围时,传感器的近红外透射光谱的波长出现蓝移,在1570nm附近干涉谷处的折射率灵敏度约为-55.223nm/RIU;且均具有良好的线性拟合效果。该传感器也可应用于温度等其他参数测量,具有非常广阔的应用前景。     

基于纤芯失配型马赫曾德尔光纤折射率和温度同时测量传感器的研究

设计和制作了一种基于单模多模细芯单模光纤马赫曾德尔(Mach-Zehnder)干涉仪结构,可同时测量折射率和温度的传感器。该传感器中,多模光纤和细芯单模熔接点充当光耦合器。导入光纤中传输的光经多模光纤后在细芯光纤的纤芯和包层中激发出纤芯模和包层模,不同模式光在细芯光纤中传输时将产生光程差,再经细芯单模熔接点耦合成为导出光纤的纤芯模而干涉。传感器透射光谱随着环境折射率和温度的变化发生漂移,通过监测不同级次的干涉谷可实现折射率和温度的同时测量。通过对传感器的透射光谱进行傅里叶变换分析可知该透射光谱主要由LP01模和LP16模干涉形成。该传感器透射光谱中1535nm附近干涉谷的折射率和温度响应灵敏度的理论值分别为-55.90nm/RIU和0.0501nm/℃(其中RIU为折射率单位);1545nm附近干涉谷的折射率和温度响应灵敏度的理论值分别为-56.26nm/RIU和0.0505nm/℃。在折射率和温度的变化范围分别为1.3449~1.3972和20℃~90℃的环境中对传感器的响应特性进行实验研究,结果表明:透射光谱中1535nm附近干涉谷的折射率和温度响应灵敏度分别为-53.03nm/RIU和0.0465nm/℃;1545nm附近干涉谷的折射率和温度响应灵敏度分别为-54.24nm/RIU和0.0542nm/℃。理论分析与实验结果相一致。该传感器在生物医学领域有较好的应用前景。     

基于光纤微腔的温度及折射率同时测量型传感器

基于多光束干涉原理,设计了一种基于光纤微腔的温度及折射率同时测量的反射型光纤传感器.该传感器将渐变折射率多模光纤的一端用氢氟酸腐蚀形成一个空气腔,带空气腔的渐变折射率多模光纤一端和单模光纤熔接,另一端切平构成传感头.实验选取渐变折射率多模光纤的长度为538.1μm,空气腔长度为40.8μm.结果表明:光纤微腔结构所形成的多光束干涉光谱条纹对比度与光纤微腔外的溶液折射率相关,干涉波峰移动与环境温度相关,通过监测条纹对比度和干涉波峰的移动,可以实现对折射率和温度的同时测量.当折射率在1.341 5~1.432 0RIU变化时,反射强度对折射率的灵敏度为57.24dB/RIU;当温度在30℃~70℃之间变化时,谐振波长对温度的灵敏度为12.3pm/℃,可检测到的最小温度变化为1.2℃,测得最小折射率变化为3.4×10-4.该传感器也可应用于其他参量的测量,具有良好的应用前景.     

基于无芯光纤的多参数测量传感器

设计并制作了一种基于单模-无芯-单模-无芯-单模光纤结构的马赫-曾德尔传感器,可用来同时测量折射率和温度.该传感器中,两处无芯光纤充当输入、输出耦合器,中间单模光纤作为传感臂.利用有限元仿真和理论分析,确定耦合器和传感臂的最优长度为15 mm.在无芯光纤中激发出的高阶模进入单模光纤的包层传输,由于倏逝场的作用,受到环境折射率和温度的影响.选取透射谱不同干涉级次的波谷作为研究对象,实现了折射率和温度的同步测量.实验结果表明:1545 nm附近干涉谷的折射率和温度灵敏度分别为–153.89 nm/RIU(refractive index unit)和0.166 nm/℃;1570 nm附近干涉谷的折射率和温度灵敏度分别为–202.74 nm/RIU和0.183 nm/℃.该传感器在实现折射率和温度同步测量的同时,仍能保持较高灵敏度,在生物医疗等方面有着较好的应用前景.     

双S型光纤结构的传感特性

在剥除涂覆层的单模光纤上熔成两个间距为25mm的S型结构,构成双S型全光纤马赫-曾德干涉仪.入射光经过第一个S型结构时部分光被激发到包层,经过第二个S型结构时重新进入纤芯传播,S型结构中光纤的纤芯模和包层模耦合产生干涉.利用干涉光谱测量外界因素的响应并用于温度、折射率和微位移的测量.实验结果表明,温度、折射率和微位移的灵敏度分别为69pm/℃,132.64nm/RIU,-178pm/μm,且具有很好的线性度.该传感结构为全光纤结构,制作简单,易于实现且成本低.     

色散补偿光纤上刻写的光纤光栅对纵向拉力和温度的同时测量

在色散补偿光纤上刻写光栅,形成全光纤复合传感结构,将干涉结构和光栅结构集成在同一段光纤内.分析了干涉包层模式和布拉格谐振峰对纵向拉力以及温度的响应机理.通过监测包层模式和布拉格谐振峰的波长漂移量,建立矩阵方程,实现对纵向拉力和温度双参量的同时测量.实验结果表明,包层模式和布拉格谐振峰对温度的响应灵敏度分别为49.4pm/℃和11.0pm/℃,包层模式对纵向拉力的响应灵敏度为1.05pm/με,布拉格谐振模式对纵向拉力的响应灵敏度为0.651pm/με,且这四个参数均表现出良好的线性度.该传感器结构采用低阶包层模式和纤芯基模模式,对外界环境折射率不敏感,能较好地应用于纵向拉力和温度的同时测量中.     

芯内双微孔复合腔结构的光纤法布里-珀罗传感器研究

提出了一种基于芯内双微孔复合结构的全光纤干涉传感器结构,建立了传感器反射光谱的理论模型,给出了反射光谱强度与微孔长度、孔内介质折射率、微孔端面反射与损耗系数以及光纤的特性参数间的关系,并模拟了传感器光谱对温度和折射率变化的响应特性.利用193 nm准分子激光器,在普通单模光纤上加工制作了具有复合腔结构的全光纤多参量传感器,进行了传感实验研究.结果表明,该传感器具有优于99%的温度、折射率线性响应度,对应两套温度和折射率灵敏度分别为-0.172 nm/℃,1050.700 nm/RIU和0.004 nm/℃,48.775 nm/RIU,不仅能够实现温度、折射率以及它们的区分测量,还能够应用于气体压力的测量,测量精度可达0.3 kPa.     

基于空芯光纤和光纤布拉格光栅的温度应变同时测量传感器

提出一种新颖的温度和应变双参数同时测量的光纤传感器。该传感器由空芯光纤和光纤布拉格光栅级联而成。空芯光纤通过反谐振机理将光限制在空气纤芯内传输,满足谐振条件的光泄露出空气芯,在传输光谱上表现为周期性损耗峰。由于空芯光纤和光纤布拉格光栅的物理机理不同,对外界温度、应变的响应存在差异,利用耦合矩阵则可以精确地实现温度和应变双参数的同时测量。实验结果表明,在1550nm波长附近,空芯光纤和光纤布拉格光栅对应的温度灵敏度分别为24.55 pm/℃和12.76 pm/℃,应变灵敏度分别为-0.70pm/με和1.02pm/με,该级联结构的传感器制作简单且具有较高的测量精度。     

光纤锥在线型马赫-曾德干涉仪的折射率传感特性

提出了一种基于光纤锥的在线型光纤马赫-曾德干涉仪式折射率传感器.传感器是在一根单模光纤上使用光纤熔接机拉制出两个光纤锥,光纤锥的直径为43.7μm,长度为480μm.干涉仪中光纤锥充当光纤耦合器,激发出光纤高阶模,并将高阶模耦合进单模光纤使之与纤芯基模形成模间干涉.被环境溶液的折射率、温度的变化改变模式间相位差,将导致干涉仪的传输光谱发生漂移,从而实现传感测量.实验结果表明:当环境溶液的折射率变化范围为1.335~1.403RIU时,传感器的折射率灵敏度为-128.233nm/RIU;当水溶液的温度变化范围为30~75℃时,传感器的温度灵敏度为0.111nm/℃.该传感器具有制作方法简单、灵敏度高、成本低等特点,可应用于生物传感测量.     

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.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

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.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.