A micro Fabry-Perot interferometer (M-FPI) is constructed by splicing a short section of polarization-maintaining photonic crystal fiber (PM-PCF) to an end-cleaved single-mode fiber with controllable offset. Due to the high effective optical path difference induced by the solid core of the PCF, the M-FPI has an ultrasmall cavity of approximately 110 \mu m. The temperature sensitivity within a range from 33 oC to approximately 600 oC is measured to be 13.8 pm/oC, which shows good agreement with the theoretical result. This proposed sensor has the advantages of ultracompact size and high stability. Therefore, it is suitable for various space-limited sensing applications in harsh environments.

A simple fiber tip sensor for refractive index (RI) measurement based on Fabry–Perot (FP) interference modulated by Fresnel reflection is proposed and demonstrated. The sensor head consists of an etching-induced micro air gap near the tip of a single-mode fiber. The microgap and the fiber tip function as two reflectors to form a FP cavity. The external RI can be unambiguously measured by monitoring the fringe contrast of the interference pattern from the reflection spectrum. The experimental results show that the proposed sensor achieves temperature-independent RI measurement with good linear response. The proposed sensor achieves a high RI resolution of up to 3.4 \times 10 5 and has advantages of low cost and easy fabrication.

A novel all-fiber temperature-calibrated refractometer based on a compact fiber Bragg grating (FBG) single–multi–single (SMS) structure is proposed and experimentally demonstrated. The sensor head is composed of a FBG combined with a SMS structure, in which the middle multimode fiber (MMF) section is etched by a time-controlled hydrofluoric. The transmission dip of SMS is extremely sensitive to ambient refractive index (RI) variation, whereas the upstream FBG provides the necessary temperature information for RI calibration. All aforementioned functions are performed via a compact FBG-SMS structure not longer than 25 mm. The proposed sensing device provides a linear RI sensitivity over water or waterbased solutions (RI values near 1.33 at optical wavelengths for most biological and many environmental applications), and has temperature-calibration capability. Hence, the said refractometer is a good candidate for sensing in chemical and biological applications.

基于多模干涉效应的单模多模单模(SMS)结构光纤折射率传感器通常需要进行包层腐蚀来提高灵敏度，而且易受环境温度影响。为克服SMS结构的这些不足，提出了一种新型的基于纤芯失配多模干涉的光纤折射率传感器，由单模光纤色散补偿光纤单模光纤(SMF-DCF-SMF)级联光纤布拉格光栅(FBG)构成，长度不超过100 mm。对其灵敏度、线性范围和温度特性等进行了测试，实验结果显示在测量折射率为1.33~1.39的折射率液时，特征波长与折射率呈线性关系，灵敏度为232.8 nm，级联的FBG具有良好的温度校准功能。