Patent ID: 6947218

Claim:
An etalon optical interference filter comprising: a) a first reflector, having an internal end and an external end, said reflector comprising a first sequence of thin dielectric layers comprising alternating high and low indices of refraction layers and a absentee layer; and b) a second reflector positioned a selected distance from the internal end of said first reflector, having an internal end and an external end, said second reflector comprising a second sequence of thin dielectric layers comprising alternating high and low indices of refraction layers, wherein said first reflector and said second reflector are located in substantially parallel planes with respect to one another and thereby form a resonance cavity between the first reflector and the second reflector; wherein the position of said absentee layer in said first sequence of thin dielectric layers, composition of said absentee layer or both is selected to provide a selected cumulative reflectance phase dispersion, and wherein selection of the cumulative reflectance phase dispersion and the optical path length of said resonance cavity provides substantially independent control of the resonance frequency and free spectral range of said etalon optical interference filter.