.The output signal of the fiber interferometer has periodic and nonlinear characteristics, and complex signal processing methods are required to demodulate the phase signal. Good interference signal processing technology has the following basic characteristics: a linear relationship between the interferometer phase change and the measured physical quantity, uniform sensitivity across the entire measurement range, and the ability to automatically distinguish the direction of phase change when it exceeds 2π. This chapter discusses three types of interferometers: double-beam, multi-beam, and long-range, explores various demodulation technologies suitable for different interference types through relative and absolute measurement methods, deeply analyzes the impact of the interferometer light source spectrum on system performance and introduces two typical photodetector modes: single-ended detection and differential balanced detection.