A fiber optical sensor that operates based on the phase change of light waves due to external physical quantities is known as a phase modulation optical fiber sensor. In this type of sensor, phase modulation is primarily achieved through the use of a fiber interferometer, which is a method of interferometry. Optical fiber interferometry is a measurement method characterized by high sensitivity and a very large dynamic range. In principle, optical fiber interferometers can be categorized into dual-beam interferometers and multi-beam interferometers. Common interference structures include the Mach-Zehnder interferometer (MZI), Michelson interferometer, Fabry-Perot interferometer (FPI), ring resonator interferometer, and Sagnac interferometer, among others, all of which have been utilized in optical fiber sensing applications.