In Fabry - Perot interferon, the distance between the partially reflecting mirrors are varied by using coarse and finely adjustable translation stage driven by micro-meters. One beam splutter is fixed and the other is mounted on the translation stage through a kinematic mount. This two axis kinematic mount is used to correct the parallelism between beam splutters.

The Fabry - Perot design contains plane surfaces that are partially reflecting so that multiple rays of light are responsible for the creation of the observed interference patterns. For high resolution spectroscopy, where a resolution in the range of MHz to GHz is required, a Fabry - Perot interferon (FP) is used. The FP consists of two plane mirrors mounted accurately parallel to each another, with an optical spacing off’s between them.

The enclosed air gap generally varies from several millimeters to centimetres, when the device is used interferometrically. If the gap can be mechanically varied by moving one of the beam splutters, then the device is referred to as an interferon. Its transmission spectrum as a function of wavelength exhibits peaks of transmission corresponding to resonances of the etalon. Fabry - Perot interferometers are widely used in telecommunication, lasers and spectroscopy for controlling and measuring the wavelength of light.