Abstract: A temperature-stable and temperature-tunable composite etalon with an increased field of view is constructed by partially filling the cavity with a transmissive parallel-plate filler. The coefficient of thermal expansion and the index of refraction of the filler material are selected so as to produce the desired rate of change of the optical length of the cavity as a function of temperature. The filler plate is preferably chosen to be significantly thicker than the remaining air gap in the etalon cavity. As a result, the fact that the filler plate occupies a large part of the cavity space increases the acceptance angle of the etalon of the invention in comparison with corresponding conventional air-spaced etalons.