Thermally stable air-gap etalon for dense wavelength-division multiplexing applications

摘要

A thermally stable etalon Fabry-Perot etalon and method for making such etalons is disclosed. Particularly, a re-entrant etalon having an etalon gap which may be several times thicker than the etalon riser is presented. The riser and a spacer have differing dimensions and are constructed of materials having different coefficients of thermal expansion such that as the spacer expands increasing the etalon gap the riser expands a corresponding amount to keep the etalon gap in a thermally stable equilibrium. It is required that the etalon gap be formed to a very high degree of precision. In a preferred method of fabrication etalon plates and risers are provided. The etalon plates and risers are manufactured to ordinary precision optical standards. The riser and etalon plate are kept in a spaced apart relationship by spacers. To increase etalon gap precision, the spacer thicknesses are adjusted to high degrees of precision using special coatings. Once a coating of appropriate thickness is formed on the spacers, a plurality of thermally stable highly precise etalons having a free spectral range of 100 GHz and a thermal expansion coefficient of less than 5×10^−8 may be assembled. The method of the present invention may also be used to adjust the etalon gap of telescopic etalon filters.