A thermally stabilized optical filter device includes a multilayer optical bandpass filter on a transparent substrate, with the transparent substrate being composed of a material having a first coefficient of thermal expansion. An encasement surrounds the transparent substrate such that the bandpass filter is exposed for transmission of predetermined optical wavelengths there through. The encasement is composed of a material having a second coefficient of thermal expansion that is different than the first coefficient of thermal expansion. The encasement provides thermal stability to the optical properties of the bandpass filter by compensating for changes in the filter that occur with temperature variations. In another embodiment, a collet assembly provides means for selectively compressing a filter chip to tune the filter response.