Zhu Yi, Guo Anbo, Xu Jiangtao, Zhang Zhengwei, Pang Fufei, Zhang Weijian, Zeng Xianglong, Sun Jianfeng
The Key Lab of Specialty Fiber Optics and Optical Access Network, Joint International Research Laboratory of Specialty Fiber Optics and Advanced Communication, Shanghai University, Shanghai 200444, China.
Shanghai Satellite Network Research Institute Co., Ltd, Shanghai, China.
Nanophotonics. 2023 Jun 23;12(16):3229-3242. doi: 10.1515/nanoph-2023-0092. eCollection 2023 Aug.
In this study, we experimentally showcase the microfiber evanescent-field photothermal gas detection by exploiting all-fiber MHz-level frequency shift scheme. Based on the acousto-optic interaction effect, the low-frequency shifts of 0.9 MHz and 1.83 MHz can be obtained through the cyclic conversion between the transverse core modes LP and LP in the few-mode fiber. Our proposed all-fiber frequency shifters show flexible MHz-level up(down) frequency shifts with superior sideband rejection ratio (over 40 dB) and low insertion loss (less than 1 dB). Furthermore, an all-fiber heterodyne interferometric detection system is implemented by leveraging the above low-frequency shifters, in which around 1-μm-diameter microfiber is investigated for photothermal gas detection. A pump-probe configuration is employed to obtain the photothermal effect induced by the gas absorption of the modulated evanescent field. By demodulating the phase of the beat signal output by the interferometer, an equivalent detection limit (1) of 32 ppm and a response time of 22 s are achieved for ammonia, as well as 0.24 % instability within 48 pump cycles. Given its compact all-fiber configuration and high sensitivity with fast response, the experimental results can pave the way for widespread applications like heterodyne detection, fiber optical sensors, and interplanetary coherent communications.
在本研究中，我们通过利用全光纤兆赫兹级频移方案，实验展示了微光纤倏逝场光热气检测。基于声光相互作用效应，通过少模光纤中横向纤芯模式LP和LP之间的循环转换，可获得0.9 MHz和1.83 MHz的低频移。我们提出的全光纤频移器展示了灵活的兆赫兹级向上（向下）频移，具有出色的边带抑制比（超过40 dB）和低插入损耗（小于1 dB）。此外，利用上述低频移器实现了全光纤外差干涉检测系统，其中对直径约1μm的微光纤进行光热气检测研究。采用泵浦-探测配置来获得由调制倏逝场的气体吸收引起的光热效应。通过解调干涉仪输出的拍频信号的相位，对于氨气实现了32 ppm的等效检测限(1)和22 s的响应时间，以及在48个泵浦周期内0.24 %的不稳定性。鉴于其紧凑的全光纤配置以及快速响应的高灵敏度，实验结果可为外差检测、光纤光学传感器和星际相干通信等广泛应用铺平道路。
