In-fiber integrated accelerometer

A compact in-fiber integrated fiber-optic Michelson interferometer based accelerometer is proposed and investigated. In the system, the sensing element consists of a twin-core fiber acting as a bending simple supported beam. By demodulating the optical phase shift, we obtain that the acceleration is proportional to the force applied on the central position of the twin-core fiber. A simple model has been established to calculate the sensitivity and resonant frequency. The experimental results show that such an accelerometer has a sensitivity of 0.09 rad/g at the resonant frequency of 680 Hz.     

Refractive index sensor based on tapered PCF in-line interferometer

A simple and compact refractive index sensor is demonstrated by tapering a photonic crystal fiber (PCF) in-line interferometer. The PCF is spliced between two single-mode fibers and tapered via hydrofluoric acid etching. Its sensitivity in liquid is more than an order of magnitude larger than the untapered one. By optimizing the etching process, we can fabricate more uniformly and thinly tapered PCF interferometers with higher sensitivity in the future.     

外腔式光纤Fabry-Perot干涉型高温应变传感器

介绍了一种外腔式光纤Fabry-Perot干涉型(EFPI)高温应变传感器,传感器是在两段切割平整的单模光纤之间熔接一段空心光纤构成。实验证明,传感器在1000℃以下时能够稳定工作,腔长变化灵敏度为0.17nm/με,应变测量灵敏度可达±1με,线性度高达0.99998。EFPI高温应变传感器结构紧凑,工艺简洁,成本低廉,是一种可靠、优秀的高温应变传感器。     

Terahertz beat frequency generation from two-mode lasing operation of coupled microdisk laser

We propose a coupled microdisk laser as a compact and tunable laser source for the generation of a coherent continuous-wave terahertz radiation by photomixing. Using the Schr?dinger-Bloch model including the nonlinear effect of active medium, we find single-mode and two-mode lasings depending on the pumping strength. We explain the transitions of lasing modes in terms of resonant modes that are the solutions of the Schr?dinger-Bloch model without active medium and nonlinear interaction. In particular, a two-mode lasing is shown to generate a terahertz oscillating frequency originating from the light beating of two nearly degenerated resonant modes with different symmetries.     

X-band continuously variable true-time delay lines using air-guiding photonic bandgap fibers and a broadband light source

We propose a novel implementation of true-time delay (TTD) using air-guiding photonic bandgap fibers (PBGFs) and a broadband light source. The air-guiding PBGFs are experimentally studied and used in the TTD module for the first time, to the best of our knowledge. The proposed approach shows the advantages of simple architecture, compact size, larger dispersion, low-temperature sensitivity, and high immunity to nonlinear effects in our experiments. The PBGFs were spliced with single-mode fibers with a 2 dB loss, and the characteristics of the PBGFs were measured. The PBGF-TTD with a continuously tunable time delays from 0 to 500 ps was demonstrated using the amplified spontaneous emission light of an erbium-doped filter amplifier as a broadband light source.     

Twist sensor based on Sagnac single-mode optic fiber interferometer

An optical fiber twist sensor based on Sagnac single-mode optic fiber interferometer is proposed. The stress-induced birefringence of single-mode optical fiber is obtained by applying a transverse force against a short length of singlemode fiber. A high sensitivity and resolution of the twist angle measurement of 0.19 nm/° and 0.002° is achieved experimentally, respectively. The proposed sensor is more convenient and simple than that of standard polarization-maintaining fibers.     

Frequency Characterization of the Nonlinear Refractive Index in Optical Fiber

The Kerr and the electrostrictive contributions to the intensity-dependent nonlinear refractive index in optical fibers are discussed on both theoretical and experimental bases. Particular attention is devoted to the electrostrictive contribution that under particular conditions is enhanced by resonances. The resonant behavior of the electrostrictive effect is calculated, measured, and discussed for standard single-mode fibers and dispersion shifted fibers. Experimental results are also reported. Measure ments have been carried out with a simple and effective technique based on the cross-phase modulation effect that also allows one to evaluate the nonlinear refractive index at any bit rate. Electrostriction contributes 20 % to the total nonlinear refractive index but in the resonant regime becomes comparable to the Kerr effect.     

光纤法布里-珀罗干涉温度压力传感技术研究进展

光纤法布里-珀罗干涉温度和压力传感器具有灵敏度高、制作简单、成本低、体积小和抗电磁干扰能力强等优点,已被广泛应用于军事和民用领域.在某些环境恶劣,如具有强电磁干扰和腐蚀性,或提供给传感器的安装空间非常有限的特殊工业领域,微型光纤温度和压力传感器发挥着重要的作用,国内外诸多高校、科研院所都在对其进行研究.本文综述了光纤法布里-珀罗干涉仪的基本原理、制备技术、及其压力和温度传感应用的研究进展.详细介绍了湿法化学腐蚀制备法、电弧放电制备法、飞秒激光制备法、聚合物辅助制备法等常见光纤法布里-珀罗腔传感器的制作工艺,分析了不同制作工艺的优缺点;详细介绍了光纤法布里-珀罗干涉仪在温度传感、压力传感和温压一体传感领域的应用;最后对光纤法布里-珀罗干涉温度压力传感器的发展进行了总结和展望.     

Generalized nonlinear coupled mode equations for ultrashort pulse propagation in optical fibers

A generalized model to describe the ultrashort pulse propagation in optical fibers with arbitrary modes present by taking advantage of the coupled mode approach is proposed. First the generalized nonlinear coupled mode equations in the frequency domain are derived exactly. Then the simplified forms for the weakly guiding optical fibers are obtained both in the frequency domain and in the time domain. Finally we discuss the particular forms in two special cases, i.e., ideal single-mode fibers and birefringent single-mode fibers.     

Temperature sensor based on an isopropanol-sealed photonic crystal fiber in-line interferometer with enhanced refractive index sensitivity

We fabricate a simple, compact, and stable temperature sensor based on a liquid-sealed photonic crystal fiber (PCF) in-line nonpolarimetric modal interferometer. Different from other reported PCF devices, it does not need expensive polarimetric devices, and the liquid is sealed in one fiber. The device consists of a stub of isopropanol-filled PCF spliced between standard single-mode fibers. The temperature sensitivity (-166 pm/°C) increases over an order of magnitude compared with those of the previous sensors based on air-sealed PCF interferometers built via fusion splicing with the same mechanism. In addition, the refractive index sensitivity also increases. Higher temperature sensitivity can be realized by infiltrating some liquid having a higher thermo-optic coefficient into the microholes of the PCF.     

Compact FBG diaphragm accelerometer based on L-shaped rigid cantilever beam

A compact fiber Bragg grating(FBG) diaphragm accelerometer based on L-shaped rigid cantilever beam is proposed and experimentally demonstrated.The sensing system is based on the integration of a flat diaphragm and an L-shaped rigid cantilever beam.The FBG is pre-tensioned and the two side points are fixed,efficiently avoiding the unwanted chirp effect of grating.Dynamic vibration measurement shows that the proposed FBG diaphragm accelerometer provides a wide frequency response range(0-110 Hz) and an extremely high sensitivity(106.5 pm/g),indentifying it as a good candidate for embedding structural health monitoring and seismic wave measurement.     

基于包层模谐振的三包层石英特种光纤温度传感特性研究

提出了一种基于包层模谐振的光纤温度传感器. 它是通过将三包层石英特种光纤(TCQSF)两端分别与普通单模光纤(SMF)电弧熔接构成的SMF-TCQSF-SMF结构. 根据耦合模理论, 首先将TCQSF等效为三个同轴波导, 按各波导模场的分布特点标量计算其传输模式的色散曲线, 并深入研究其耦合长度与传输谱线之间的关系; 其次根据光纤的热光效应及热膨胀效应, 分析计算该传感器的温度灵敏度; 最后选取耦合长度为一个拍长时的传感器进行温度传感实验. 实验结果表明, 在35-95 ℃的温度变化范围内, 其温度灵敏度为73.74 pm/℃, 与理论计算结果一致. 因此, 该传感器具有结构简单、制备容易、灵敏度高、包层模激发可控等优点, 可用于工业生产、生物医学等温度传感领域.     

纤芯失配熔接的高灵敏度光纤折射率传感器

提出并实验验证了一种基于马赫泽德干涉仪(MZI)的高灵敏度光纤折射率(RI)传感器。传感头由一段单模光纤(SMF)夹熔在两段较短的细芯光纤(TCF)中组成TCF SMF-TCF结构,其总长度为9 mm。由于光纤纤芯失配导致的纤芯模和包层模发生干涉,干涉谱对传感头外部折射率的响应极其敏感。使用该传感器检测具有不同折射率的甘油水溶液,实验结果显示:传感器干涉谱的共振波长随环境折射率的增大向长波方向漂移,其折射率灵敏度在1.33 RIU～1.38 RIU范围内约为159 nm/RIU。该传感器具有结构简单、易于制造、成本较低、灵敏度高、抗电磁干扰能力强等优点,在生物化学与环境监测等领域具有较大的应用潜力。     

Experimental research of temperature sensor based on twin-core fiber

A low-cost, compact, and lossless temperature sensor based on a twin-core fiber (TCF) is demonstrated and manufactured by splicing two single-mode fibers to the ends of a TCF. The extinction ratio of the comb transmission spectrum is bigger than 15 dB, and the temperature sensitivity of the coupling angle is –0.02 rad/(°C· m) at–30–90°C and –0.032 rad/(°C· m) at 90–175°C. Finite element method is used to calculate the supermodes of the TCF, and the result agrees well with the experiment.     

Measurement of the frequency response induced by electrostriction in optical fibers

Accurate measurements of the frequency response of the nonlinear refractive index induced by the combined effects of Kerr nonlinearity with electrostrictional excitation of acoustic waves in optical fibers are presented. A detailed experimental investigation of both standard (zero-dispersion wavelength,lambda(0) approximately 1.31microm) and dispersion-shifted (lambda(0)=1.55microm) single-mode fibers showed the presence of several resonant peaks induced by the electrostrictive nonlinearity in the fiber structure. This investigation has provided better insight into the frequency behavior of the electrostriction-induced acoustic waves in optical fibers.     

高功率O型慢波器件的纵向模式选择研究

利用传输线理论说明了由于慢波结构与其输入、输出端阻抗不匹配导致同一横模对应的不同纵模的形成;根据S参数方法，研究了过模慢波结构TM01模对应各纵模的频率、场分布和Q值，并分析了慢波结构周期数对纵模的数目、纵模间的频率间隔以及各纵模Q值的影响等.在此基础上提出在O型慢波器件中使用谐振腔，可减少慢波结构周期数，不但使器件结构更为紧凑，还可避免纵模竞争，从而提高器件效率、稳定产生微波频率. 关键词： 纵模选择 传输线理论 慢波结构 谐振腔 O型高功率慢波器件     

共光声池腔芯轴型空气衬底光纤麦克风

声传感器和光声池是激光光声光谱技术的核心组件。结合光纤迈克耳孙干涉仪、相位载波解调技术和纵向共振光声池,提出一种共光声池腔的芯轴型空气衬底光纤麦克风。光纤麦克风中的铜毛细管被用作光声池的共振腔,传感臂由10 m长的超细光纤缠绕在铜毛细管上构成,参考臂为5 cm长的短臂且已进行隔声隔振处理。基于结构共振频率稳定的特点,优化光纤麦克风的共振频率,使其略低于光声池的一阶纵向共振频率,以实现准双共振。实验结果表明,麦克风在共振频率为1443 Hz处的最小可检测声压为0.69μPa√Hz。在1 kHz处,声压电压响应线性度为99.98%(5 mPa~3 Pa),动态范围为112.52 dB。该光纤麦克风适用于高温、易爆和高电磁干扰等特殊环境下痕量气体的高精度检测。     

A new multi frequency compact microstrip antenna

A single layer, single feed, multi frequency, compact rectangular microstrip antenna is proposed. Resonant frequency has been reduced drastically by cutting unequal rectangular slots at the edge of the patch along with two tiny circular slots created inside the patch to improve return loss. Antenna size has been reduced by 64% with an increased frequency ratio (the ratio of second or higher resonant frequency to the first resonant frequency).     

基于光子晶体光纤和拉锥式单模光纤的超连续光谱产生的实验研究

本文使用重复频率为250 MHz、脉冲宽度为135 fs、最大功率为2.2 W的锁模掺镱光纤激光作为种子源,利用光子晶体光纤和自制的拉锥式单模光纤两种高非线性光纤研究了超连续光谱的产生特性,通过对比两种光纤的结构、色散等特性,分析了拉曼孤子、色散波及其他非线性效应对产生的超连续谱形状的影响,并均得到了大于一个倍频程的超连续光谱,特别是拉锥式单模光纤产生的超连续光谱,耦合效率达到60%,这为众多研究领域,尤其是光学频率梳的建立提供了实用的超连续光源.     

Experimental study on vibration frequency response of micro-bend optic-fiber sensor

We make an experimental study on vibration frequency response of micro-bend optic-fiber sensor, and single-mode fibers and multi-mode fibers are used as the sensitive optic-fibers. Contrast between the two sensitive fibers is presented. Result shows that the micro-bend optic-fiber sensor has good frequency response characteristics and strong ability to restore the waveform. With the frequency varying in the range of 500 - 4762 Hz, the vibration sensors using multi-mode optic-fiber as the sensitive fiber is more sensitive than that using single-mode optic-fiber. And the former has better frequency response characteristics and stronger capacity of waveform revivification. But with the frequency in the range of 287 - 500 Hz, the latter is better.