Cascaded Fiber Mach–Zehnder Interferometers for Sensitivity-Enhanced Gas Pressure Measurement

A simple structured ultra-highly sensitive fiber optic gas pressure sensor with low temperature cross sensitivity is proposed and demonstrated. The sensor is composed of two cascaded Mach-Zehnder interferometers (MZIs), which consist of single mode-multimode-single mode fiber structure with a micro-machined air cavity in each multimode fiber. The micro air cavities are drilled by a femtosecond laser and act as a gas pressure sensing element. Interference happens between the beams transmitting along the air cavity and the remaining silica core of the multimode fiber. The difference between the fringe intervals of the two MZIs are small enough for generating Vernier effect in gas pressure measurement. The same configuration employed in the two MZIs is to obtain the same temperature response, so that preventing the Vernier effect from appearing in temperature changes. Therefore, the proposed sensor can achieve a high gas pressure sensitivity but is insensitive to temperature variation. Experimental results show that the sensitivity for gas pressure measurement is -82.131 nm/MPa.