Multi-Parameter Sensing Based On Two Order Loyt-Sagnac Interf Erometry

The optical fiber sensors are widely used in various fields because of its unique advantages. Recent years, the sensor based on high birefringent fiber Sagnac interferometer has been widely studied, because the sensor structure is more flexibility and the sensor sensitivity is higher.The one order Saganc interferometer based on high birefringent fiber can be applied in optical filters, fiber sensors and so on, and there are many correlational researches. While the research of high order Sagnac interferometer is limited to narrow band pass filter.In this paper, the second order Loyt-Sagnac interferometer structure was designed and be used in sensing area, based on the structure and principle of the common one order Sagnac interferometer. The second order Loyt-Sagnac interferometer was constructed by inserting two PCs and two sections of HBFs into the fiber loop. One of HBF act as the reference fiber, and the other is sensor fiber. The output spectrum of Loyt-Sagnac interferometer exhibits peaks at wavelengths where two interference peaks of the individual Sagnac loops of the two HBFs partially overlap, and the height of each peaks will be determined by the amount of overlap part. The polarization angle of input light and the lengths of HBFs were optimized to enhance the sensitivity in the second order Loyt-Sagnac configuration.The main research contents of this paper include:1. The transmission fields of one order Sagnac interferometer and two order Loy-Sagnac interferometer were calculated by using the Jones matrix analysis.2. The sensing principle of second order Loyt-Sagnac interferometer was analysed and the temperature sensing, pressure sensing and twist sensing were simulated based on two different Sagnac interferometer structures. The result shows that second-order Loyt-Sagnac interferometer has higher sensitivity in both temperature sensing and pressure sensing.3. According to above analysis, the experiment platform is set up. The temperature sensing and twist sensing are respectively experimented. Because of different mechanisms of two sensors, twist and temperature sensing are experimented simultaneously in the Loyt-Sagnac interferometer structure. The results show that second-order Loyt-Sagnac interferometer has higher sensitivity in temperature sensing than one order Saganc interferometer, and the relationship between the fringe visibility of spectrum and the twist angle follows Sine function in twist sensing.