Patent ID: 7957004

Claim:
Interference filter, especially for use in gas detection, using infrared light within a chosen range of wavelengths, comprising at least two essentially parallel reflective surfaces with a chosen distance between them thus defining a resonator delimited by the reflective surfaces between which the light may oscillate, and wherein at least one of said reflective surfaces is partially transparent for transmission of light to or from said resonator, wherein the filter comprises: a first transparent material having a refractive index comparable to the refractive index of silicon or higher, positioned in at least a part of said resonator and the first transparent material being provided with at least one of said reflective surfaces, wherein one of said reflective surfaces includes a pattern being divided into at least two surface parts disposed in different planes at different distances from another reflective surface, thus providing at least two different optical path lengths between the reflective surfaces giving resonance at different wavelengths, and wherein said filter comprises an additional pattern on at least one of said reflective surfaces, the additional pattern comprising a diffracting relief pattern adapted to provide a diffractive grating for diffraction of at least two wavelengths in at least two directions.