Fabry Perot Interferometer by JFC UCL (2016)
Source. Description only, reasonable animations. Considers the case of two nearby beam splitters.Fabry-Perot Introduction by Williams College Physics (2020)
Source. Shows a working device. Confocal optical cavity, one of the mirrors scans back and forward moved by a piezoelectric motor, this is called a "scanning Fabry-Perot interferometer".
Does not produce an interference pattern, only an on/off blob, which is then fed into an oscilloscope for analysis. The oscilloscope shows both the mirror displacement (which is given by a voltage) and the light detector output.
Articles by others on the same topic
An interferometer splits or combines coherent wave amplitudes so that an observable depends on their relative wave phase. A Michelson interferometer sends light through two reflected paths before recombination; moving one mirror changes the round-trip optical path difference.
For two detected contributions, under ideal mutual coherence and matched polarization. The varying cross term turns tiny path changes into measurable intensity changes. Stable interpretation requires control of vibrations, beam overlap and optical coherence. A lack of visible fringes can result from those limitations rather than from a lack of light in one path.