Infrared modulator for optical sensors based on a vibrating Fabry-Perot interferometer

The paper describes the design of a vibrating Fabry-Perot (FP) modulator for the IR range. A FP modulator is formed by two optical flats from a material of suitable refractive index and reflectivity and low absorption loss for the radiation to be modulated. The inner faces are separated by a parallel gap of controllable width. This gap width is varied sinusoidally with an amplitude 1/8 the wavelength of the radiation modulated. Instead of a two-plate etalon, it is possible to increase the modulation depth by using two etalons connected in series, forming a three-plate FP modulator with resonating center plate attached to a titanium spring. The design of such a tuned three-plate modulator encapsulated for environmental and vibration tests is sketched.