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 interferometer (MZI) based on a pair of long-period gratings (LPGs) written on a photonic crystal fiber (PCF). The LPG was fabricated by using a pulsed CO₂ laser to carve grooves periodically along the PCF. The MZI relies on 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/degC and - 2.6 pm/muepsiv, respectively. We also fabricated an MZI on a single-mode fiber, which has a temperature sensitivity of 1215.56 pm/( ^degCmiddotm) and a strain sensitivity of + 0.445 pm/muepsiv.