Compact In-Fiber Interferometer Formed by Long-Period Gratings in Photonic Crystal Fiber

We reported the design and implementation of an in-fiber Mach-Zehnder interferorneter (MZI) based on a pair of long-period gratings (LPGs) written oil a photonic crystal fiber (PCF). The LPG was fabricated by using a pulsed CO2 laser to curve grooves periodically along the PCF. The MZI relies oil the interference between the fundamental core mode and a cladding mode of the PCF. The MZI was further demonstrated as a temperature sensor and a strain sensor. The temperature and strain sensitivities were measured to be 42.4 pm/degrees C . m and -2.6 pm/mu epsilon, respectively. We also fabricated an MZI on a single-mode fiber, which has a temperature sensitivity of 1215.56 pm/(degrees C . m) and a strain sensitivity of +0.445 pm/mu epsilon.