少模光纤倾斜光栅制备及扭转传感研究

设计了一种基于少模光纤倾斜布拉格光栅的反射型扭转传感器，小角度倾斜光栅中的纤芯基模与二阶模在光栅处发生互耦，通过测量该过程形成的反射峰强度变化实现扭转测量。分析了光栅倾斜角度对模式耦合效率的影响，采用相位掩模板法在线刻写光栅技术，在少模光纤上刻写了不同的小角度倾斜光栅；在此基础上选择倾斜角度为1°的光栅进行了单点、双点扭转传感实验，实验表明其反射光谱中基模与二阶模的互耦合峰(LP₀₁-LP₁₁)对光纤扭转敏感，可以实现对扭转角度大小的测量。在-50°～-150°逆时针扭转过程中，扭转灵敏度为0.52 dB/(rad·m^-1),而在40°～190°顺时针扭转的角度范围内，扭转灵敏度为0.34 dB/(rad·m^-1)。这种传感器具有在单根光纤上实现多点扭转传感的潜力，在多点扭转监测方面具有应用前景。

Fabrication and twist sensing characteristics of tilted Bragg gratings in few-mode fiber

A reflective torsion sensor based on the few-mode fiber tilted Bragg grating is designed. The fundamental mode and the secondorder mode in the fiber core can be mutually coupled at the small-angle tilted grating. Through analyzing the couple reflection peak intensity, the torsion angle can be detected. The influence of the tilt angles on the mode coupling efficiency is analyzed with different small-angle tilted gratings written on the few-mode fiber. The tilted gratings are on-line written by using the phase mask method on a fiber drawing tower. The gratings with title angle of 1° is selected to perform single-point and double-point torsion experiments. Experimental results show that the reflection peak of the cross coupling between the fundamental mode (LP01 ) and the second-order mode (LP11 ) is sensitive to the twisting of the optical fiber. Thus, the twisting angle can be measured. The torsional sensitivity is 0. 52 dB/ (rad·m -1 ) during the counterclockwise twist from -50° ~ -150°, while the torsional sensitivity is 0. 34 dB/ (rad·m -1 ) in the 40° ~ 190° clockwise twist angle range. The sensor has the potential to realize multi-point torsion sensing with a single fiber, which has application prospects for multi-point torsion monitoring.