The femtosecond laser has emerged as a powerful tool for micro- and nanoscale device fabrication. Through nonlinear ionization processes, nanometer-sized material modifications can be inscribed in transparent materials for device fabrication. This paper describes femtosecond precision inscription of nanograting in silica fiber cores to form both distributed and point fiber sensors for sensing applications in extreme environmental conditions. Through the use of scanning electron microscope imaging and laser processing optimization, high-temperature stable, Type II femtosecond laser modifications were continuously inscribed, point by point, with only an insertion loss at 1 dB m^-1 or 0.001 dB per point sensor device. High-temperature performance of fiber sensors was tested at 1000 ℃, which showed a temperature fluctuation of ±5.5 ℃ over 5 days. The low laser-induced insertion loss in optical fibers enabled the fabrication of a 1.4 m, radiation-resilient distributed fiber sensor. The in-pile testing of the distributed fiber sensor further showed that fiber sensors can execute stable and distributed temperature measurements in extreme radiation environments. Overall, this paper demonstrates that femtosecond-laser-fabricated fiber sensors are suitable measurement devices for applications in extreme environments.

为满足油浸式变压器在线监测的需求,根据非共振光声光谱和无孔膜油气分离理论,将直径为40 mm的聚全氟乙丙烯(FEP)高分子膜与体积仅为0.3 mL的光声气室结合,设计了集成光声气体传感器和油气分离膜的微型传感模块,该模块具有体积小、油气分离时间短及可实时在线检测的优点。油中溶解的故障特征气体扩散进入气室中,利用近红外激光光声光谱技术、波长调制和二次谐波检测技术对气室中的气体进行高灵敏度检测。对特征气体C2H2检测的实验结果表明,在油温为60 ℃时,油中溶解气体传感系统可在3 h内实现油气分离平衡,其中对于体积分数为10 -6的油中溶解C2H2气体的体积分数测量误差在±30%之内。

A trace ammonia (NH3) detection system based on the near-infrared fiber-optic cantilever-enhanced photoacoustic spectroscopy (CEPAS) is proposed. A fiber-optic extrinsic Fabry-Perot interferometer (EFPI) based cantilever microphone has been designed to detect the photoacoustic pressure signal. The microphone has many advantages, such as small size and high sensitivity. A near-infrared tunable erbium-doped fiber laser (EDFL) amplified by an erbium-doped fiber amplifier (EDFA) is used as a photoacoustic excitation light source. To improve the sensitivity, the photoacoustic signal is enhanced by a photoacoustic cell with a resonant frequency of 1624 Hz. When the wavelength modulation spectroscopy (WMS) technique is applied, the weak photoacoustic signal is detected by the second-harmonic detection technique. Trace NH3 measurement experiments demonstrate that the designed fiber-optic CEPAS system has a linear response to concentrations in the range of 0-20 ppm at the wavelength of 1522.448 nm. Moreover, the detection limit is estimated to be 3.2 ppb for a lock-in integration time of 30 s.

H2S是SF6气体绝缘设备中放电故障诊断的特征组分之一; 针对H₂S在红外波段吸收系数小, 传统光学检测方法对H2S检测灵敏度较低的问题, 结合大功率光纤激光放大技术、共振式激光光声光谱技术、波长调制光谱技术和二次谐波检测技术, 提出了一种基于光纤放大激光光声光谱的SF6分解组分H2S气体的超高灵敏度检测方法; 采用近红外可调谐窄线宽分布反馈激光二极管级联高饱和输出功率掺饵光纤放大器作为光声激发光源, 搭建具有超高灵敏度的激光光声光谱微量H2S气体检测系统。结果表明：当测量时间为100 s时, 该系统对SF6背景中H2S气体的检测极限达到1.5×10-8。

结合光纤声波传感技术、纵向共振式光声探测技术、波长调制技术和二次谐波检测技术, 提出了一种基于光纤法布里-珀罗干涉传感器的悬臂梁增强型光声信号检测方法。针对光纤耦合近红外激发光的特点, 对共振式光声池进行了优化设计, 搭建了一套超高灵敏度的激光光声光谱微量乙炔气体检测系统。实验结果表明, 当测量时间为60 s时, 该系统对乙炔气体的检测极限达到8×10-10。

Weak signal detection for single-mode fiber-optic distributed temperature sensor (DTS) is a key technology to achieve better performance. A hybrid technique combining the incoherent optical frequency domain reflectometry (IOFDR) and the three-channel simultaneous radio-frequency (RF) lock-in amplifier (LIA) is presented to improve the signal-to-noise ratio (SNR) of the measured spontaneous Raman backscattered light. The field programmable gate array (FPGA) based RF-LIA is designed with a novel and simple structure. The measurement frequency range is achieved from 1 kHz to 100 MHz. Experimental results show that the backscattered light signal of picowatt level can be detected with high SNR. With a 2.5 km single-mode fiber, a 1064 nm laser source, and the measurement time of 500 s, this sensing system can reach a spatial resolution of 0.93 m and a temperature resolution of about 0.2℃.

利用小功率40 kHz的CO2脉冲激光对25 μm厚的超薄熔石英玻璃与熔石英毛细管端面进行热熔焊接，研究和分析了占空比(脉冲激光功率)、离焦激光预热、离焦激光退火对熔石英玻璃热熔焊接的影响。结果表明，实现超薄熔石英玻璃与毛细管端面无气化穿孔、密封、牢固焊接的占空比为37%；占空比为20%的+2 mm离焦脉冲激光预热对超薄熔石英玻璃无裂纹/裂缝的焊接起到了关键作用；适当占空比的-2 mm离焦脉冲激光退火能够释放超薄熔石英玻璃在热熔焊接过程中产生的残余热应力，提高熔石英器件的性能，经激光焊接的光纤法布里珀罗传感器的压力和温度曲线的线性度分别为0.9995和0.9991，而且重复性好。

采用全矢量有效折射率法计算光子晶体光纤的色散系数，深入分析了光子晶体光纤色散系数与结构参数之间的关系，发现色散系数随着结构参数的变化具有双极值特性：1)当Λ值保持不变时，随着d/Λ值的减小，零色散波长向长波方向移动，在达到极大值后，则转向短波方向移动，例如当Λ=2.3 μm时，极大零色散波长出现在约d/Λ=0.24处，约为1728.9 nm，当Λ取不同值时，较小的Λ值，会对应有较大的极大零色散波长；2) 当d/Λ值保持不变时，随着Λ值的减小，零色散波长向短波方向移动，在达到极小值后，则转向长波方向移动，例如当d/Λ=0.9时，极小零色散波长出现在约Λ=0.6 μm处，约为564.29 nm，当d/Λ取不同值时，该比值越大，则会对应着越小的极小零色散波长。这一发现对于优化设计特种光子晶体光纤具有一定的价值。

Pressure sensors based on fiber-optic extrinsic Fabry-Perot interferometer (EFPI) have been extensively applied in various industrial and biomedical fields. In this paper, some key improvements of EFPI-based pressure sensors such as the controlled thermal bonding technique, diaphragm-based EFPI sensors, and white light interference technology have been reviewed. Recent progress on signal demodulation method and applications of EFPI-based pressure sensors has been introduced. Signal demodulation algorithms based on the cross correlation and mean square error (MSE) estimation have been proposed for retrieving the cavity length of EFPI. Absolute measurement with a resolution of 0.08 nm over large dynamic range has been carried out. For downhole monitoring, an EFPI and a fiber Bragg grating (FBG) cascade multiplexing fiber-optic sensor system has been developed, which can operate in temperature 300 ℃ with a good long-term stability and extremely low temperature cross-sensitivity. Diaphragm-based EFPI pressure sensors have been successfully used for low pressure and acoustic wave detection. Experimental results show that a sensitivity of 31 mV/Pa in the frequency range of 100 Hz to 12.7 kHz for aeroacoustic wave detection has been obtained.

文章采用全矢量有效折射法深入分析了光子晶体光纤结构参数及比例系数对波导色散、总色散的作用，总结了光子晶体光纤色散特性的调整方法，探索出特定色散特性光子晶体光纤的设计方法，并且设计了在800 nm处具有近零平坦色散的光子晶体光纤，该光纤对于研究飞秒激光的传输特性和应用具有一定的价值。