Optical fiber interferometry is a sophisticated technique leveraging the principles of interference to perform high-precision measurements and sensing applications in fiber optics. Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology. This book highlights the key technology of fiber optic interferometers (FOI), providing a systematic overview of their principles and applications. What is a Fiber Optic Interferometer? A fiber optic.