In this letter, a fiber Bragg grating (FBG) dynamic strain sensing system using a semiconductor optical amplifier (SOA)-fiber ring laser (FRL) and an arrayed waveguide grating (AWG) demodulator is proposed. Due to the characteristics of SOA, it can act as the gain medium as well as light source. The AWG module is used as the wavelength demodulator. It is shown that SOA-based FRL sensors can accurately respond to 1.5 με dynamic strain signal with high frequency up to 120 kHz and almost no distortion in the waveforms. Experimental results show that the system can be used for acoustic testing, such as underwater ultrasonic detection and external impact monitoring. In addition, the simultaneous dual-channel demodulated system is investigated in detail to verify the multiplexing. This dynamic strain sensing system can be widely utilized in structural health monitoring because of its high stability, low cost and good multiplexability.

A Sagnac fiber interferometer with the population grating formed in saturable erbium-doped fiber (EDF) for fiber Bragg grating (FBG) dynamic strain sensing is proposed. In this configuration, a semiconductor optical amplifier (SOA)-based fiber ring laser with an FBG reflector is employed in the sensing part and a Sagnac interferometer based on transient two-wave mixing (TWM) via dynamic population gratings in single-mode polarization maintaining erbium- doped fiber (PM-EDF) is used in this detecting part. Experimental results show that the Sagnac fiber interferometer detection system can stably respond to dynamic strains at high frequencies. As an example of application, the response of the sensor system to continuous sinusoidal ultrasonic signals is presented. The proposed simple and robust configuration has an all-fiber design based on commercially available elements, which makes it promising for applications in fiber optic ultrasonic sensors.

提出以单缺陷双边带非线性载流子输运方程描述InP∶Fe中光折变动态光栅的写入过程,通过微扰法将非线性方程线性化,从而求得小调制干涉图样下空间电荷场的稳态解,并用耦合波方程建立空间电荷场与增益系数的关系。研究温度、泵浦光强、外加直流电场和入射角对增益系数的影响。结果表明,增益系数存在温度-光强共振,最佳泵浦光强强烈依赖于晶体工作温度;施加直流电场对增益系数有明显提升作用,在10 kV·cm ^-1范围内增益随外加直流电场增加而线性增加;并且,在温度-光强共振条件下存在最佳入射角。在室温为298 K和外加电场为5 kV·cm ^-1时,最佳泵浦光强为218 mW·cm ^-2,最佳入射角为5°。通过InP∶Fe双波混频实验研究泵浦光强、外加直流电场和入射角对增益系数的影响,实验结果表明,增益系数变化规律与理论预测一致,验证了单缺陷双边带模型的合理性,该研究为Ⅲ-Ⅴ族半导体光折变晶体的双波混频研究提供重要的参考价值。

提出一种基于半导体光放大器的光纤环形激光器动态应变传感器系统。在此传感系统中,将基于半导体光放大器的光纤环形激光器结合光纤布拉格光栅作为光纤激光器的波长选择元件,用来探测外界的动态应变信号。激光腔的外部配置一个不可调谐的光纤法布里-珀罗滤波器作为强度解调器,同时配置光纤带通滤波器,可实现多个光纤光栅反射信号分离输出的功能。实验结果表明,传感系统对动态应变信号有较好的响应,能够测量高达200 kHz的动态应变信号,具备解调MHz频率范围信号的能力,验证了复用解调的可行性。该系统具有结构简单、成本低等特点,可应用于结构健康监测中动态应变信号的检测。

根据动态粒子数光栅形成机理,设计了一种线性双波混频结构的光纤系统。系统中,1490 nm波长分布式反馈(DFB)激光器光源发出的连续激光,通过环形器进入一根3 m长掺铒光纤作为注入光,被与掺铒光纤另一端光学耦合的压电振动镜反射后形成反射光。掺铒光纤中注入光与后向传播的反射光干涉形成驻波场,通过空间烧孔效应沿光纤纵向形成动态粒子数光栅。压电振动镜对反射光波进行相位调制时,环形器反射端口输出的双波混频(TWM)信号可视作输出光波的强度调制。实验中通过此双波混频系统对压电换能器产生的机械振动进行检测,结果表明:光纤双波混频检测系统具有良好的动态响应特性,能够测量50 Hz~10 kHz 的振动信号,采集到的输出信号频率与压电驱动信号频率很好地吻合。

A high-sensitivity long-period fiber grating (LPFG) methane sensor that contains a compact and uniform styrene-acrylonitrile (SAN)/cryptophane A nanofilm is presented. The sensor is prepared by using an automatic dip-coater in a solution of cryptophane A, SAN resin dissolved in ortho-dichlorobenzene, a low-volatile solvent. The effect of film thickness on the LPFG's resonant wavelength is thoroughly investigated. The optimum sensor among the three LPFGs with different film thicknesses is directly used to detect the methane concentration in a coal mine gas sample. The results indicate that the sensors with film thicknesses of 484 to 564 nm exhibit a redshifted resonant wavelength when the methane concentration is increased from 0% to 3.5% (vol). The data demonstrates that the sensor with a film thickness of 484 nm has remarkable sensitivity (～0.633 nm%-1), and its detection limit can reach 0.2%. The methane concentrations determined by our sensor are consistent with those obtained by gas chromatography.

A novel long-period fiber grating (LPFG) film methane sensor is designed and applied successfully. The sensor is constructed by depositing a thin styrene-acrylonitrile (SAN) film containing the new compound cryptophane-E-(OEt)6 onto the cladding surface of the LPFG. This film is sensitive to methane gas. Methane causes a change in the refractive index of the sensing film, which can be measured by shifting the resonance wavelength. Experimental results show that the resonant wavelength shifts to the longer wavelength, with increasing methane concentration at a range of 0.0%–3.5% (v/v). A linear relationship is obtained within the test range. Detection limit is estimated at 0.2%, and response time is 60 s. No significant interference is detected from dry air, O2, CO, CO2, and H2. This novel methane sensing material has great application potential due to its advantages.