提出一种基于大空气孔保偏微结构光纤偏振回旋滤波器(PM-MOF-RF)的光微流折射率传感器。保偏微结构光纤(PM-MOF)沿轴向引入周期性往复扭转结构,可实现光纤中正交偏振模的谐振耦合,通过偏振检测,可得到类似于长周期光栅的透射光谱,从而获得偏振回旋滤波器(PRF)。基于耦合模理论,对该器件的透射光谱进行仿真。在该器件两端与单模光纤(SMF)连接处分别接入一小段C形光纤,可将待测液体导入和导出MOF的空气孔而不影响SMF与MOF的光信号耦合,从而得到一个全光纤的光微流折射率传感器。通过有限元分析方法模拟微流折射率在1.333附近变化时PM-MOF的相模式双折射色散曲线,进而可得不同微流折射率的透射光谱,通过追踪光谱波长漂移,得到7196.4 nm/RIU(RIU为折射率单元)的折射率灵敏度,同时可知当按比例缩小光纤尺寸时,可将其灵敏度提升至16754.0 nm/RIU。

An optofluidic refractive index sensor based on large air-hole polarization-maintaining microstructured optical fiber polarization rocking filter (PM-MOF-PRF) is proposed. Resonant coupling between orthogonal polarization modes occurs when a periodic back-and-forth twist is induced by PM-MOF along the axial. Via polarized detection, a transmission spectrum similar to a long-period fiber grating can be observed, and thus a polarization rocking filter (PRF) is obtained. The transmission spectrum of this device is simulated based on mode-coupling theory. When splicing a short piece of C-shaped fiber between the PM-MOF and single-mode fibers (SMF) at both end of the PRF, it allows fluids running into and out of the air hole channels without affecting light coupling between the MOF and SMF. Therefore, an all-fiber optofluidic refractive index sensor can be constructed. Then the phase modal birefringence dispersion curves of the PM-MOF for microfluidics with refractive index around 1.333 is simulated by finite element method, and the transmission spectra of the PRF for different microfluidic refractive index values are obtained. By tracking the wavelength shift of the spectra, a refractive index sensitivity of 7196.4 nm/RIU is achieved, and the value can be improved to 16754.0 nm/RIU when the MOF is tapered to half of the initial diameter.