A Dual-Parameter Sensor Based on the Asymmetry of Alcohol Filling the Photonic Crystal Fiber in Sagnac Loop

This paper proposes a novel temperature and stress sensor based on the asymmetric filling of alcohol into the photonic crystal fiber in a Sagnac loop. First, we etched the photonic crystal fiber and collapsed the air. Then, we filled alcohol into the asymmetric photonic crystal fiber. Next, we connected this structure into a Sagnac interference ring. When the ambient temperature changed, the thermal expansion effect of filled alcohol would lead to the change of birefringence of photonic crystal fiber, which made the interference spectrum of the sensor drift with the change of temperature. Furthermore, after adding transverse stress to the photonic crystal fiber, the fiber's strain changed. With its strain changed, the birefringence of photonic crystal fiber also changed, which made the interference spectrum drift. The experimental results showed that when the temperature or the lateral stress is added, a red shift would occur in the interference spectrum. The temperature sensitivity was found to be 0.1864 nm/°C, and the lateral stress sensitivity was 0.6201 nm/N. The sensor achieved the highly sensitive measurement of temperature and stress. Concurrently, the structure has the advantages of high stability, anti-electromagnetic interference, and easy construction, and it provides a new method for obtaining birefringence of ordinary photonic crystal fiber. In addition, an application system of the sensor has been built. Monochromatic light source with 1554-nm wavelength was used in the experiment. The drift of interference spectrum is transformed into the change of light intensity. The relative error is less than 3%, which indicates a good application prospect.