从理论和实验上研究了一种操作简单、价格低廉、灵敏度高的折射率光纤传感器。该传感器采用光纤回波强度调制原理, 用半导体激光器作为光源, 普通光功率计作为光电探测器, 传感头为普通光纤端面。根据回波损耗随界面物质折射率不同而发生变化的机制, 导出相对回波强度与折射率之间的对应关系。计算证明相对回波强度参量的引入能够有效地消除仪器的不稳定性、内部损耗和环境影响带来的测量误差, 提高测量精度。灵敏度分析表明, 对于具有0.01 dBm的仪器测量精度, 相应的折射率分辨率可达2×10-4折射率单位。实验结果表明在液体折射率1.30～1.45的范围内, 测量值均能很好地与理论值相符合, 且相对偏差低于5%。

A new refractive index fiber sensor with simple operation, low cost and high sensitivity has been explored. The new refractive index fiber sensor is based on the principle of return strength modulation. A laser diode module and two optical power meters are used as the light source and photo-detectors, respectively. The relationship between relative return strength and refractive index is derived from the mechanism that the return loss from the end reflection interface of an optical fiber varies with the refractive index of the material contacted with the fiber. The relative return strength technology can improve measuring accuracy effectively and eliminate the measuring error resulted from the instability and internal loss of the instrument, as well as environmental effect. The sensitivity analysis of the sensor shows that the resolution of refractive index is 2×10-4 index-unit, with measurement precision of 0.01 dBm. It is found that the experimental data agree well with the theory values, and the relative error is smaller than 5% within the refractive index ranging from 1.30 to 1.45.