Ultra-high sensitivity gas pressure sensor based on cascaded Mach-Zehnder interferometer and Sagnac interferometer

A highly sensitive optical fiber gas pressure sensor based on Vernier effect of cascaded optical fiber Sagnac interferometer (SI) and Mach Zehnder interferometer (MZI) is proposed, and the sensing characteristics are verified. The SI consists of a 3 dB coupler and a section of panda fiber, and SI is used as a filter. As the sensing part, MZI has high sensitivity and good stability. It is composed of single-mode fiber, multimode fiber and quartz capillary. By controlling the length of two interferometers, their free spectrum ranges (FSR) are similar but not equal. Therefore, the cascade structure produces the Vernier effect, which can amplify the gas pressure sensitivity of the sensor. The experimental results show that the gas pressure sensitivity of a single MZI is only − 7.75 nm/MPa. The cascade structure can amplify the sensitivity to − 211.9 nm/MPa, and the magnification factor is 27.3, which is consistent with the theoretical analysis results. In addition, the proposed sensor has excellent repeatability and stability.