The automatic control of the spacing of Fabry-Perot interferometers to transmit at a given wavelength is discussed, and an interferometer is described in which the plates are maintained parallel to within the accuracy of the plates themselves and at a preset spacing. The variation in mean spacing over test periods of several hours has not exceeded ± 0.7 nm despite temperature fluctuations and other uncontrolled environmental conditions.
J. V. Ramsay, "Automatic Control of the Spacing of Fabry-Perot Interferometers," Appl. Opt. 5, 1297-1301 (1966)