Single-channel gas concentration measurement method and apparatus using a short-resonator Fabry-Perot interferometer

A single-channel infrared gas concentration measurement apparatus, comprising:

• a measuring
• a radiant source for generating a measuring signal;
• a measurement object containing a gas mixture to be measured and through which said measuring signal is sent;
• a variable bandpass filter for bandpass filtering of the measuring signal on at least two passband wavelengths, said bandpass filter being implemented by means of a single electrostatically tunable, short-resonator Fabry-Perot interferometer fabricated by surface micromachining techniques and having upper and lower resonator mirrors with a distance between said mirrors being equal to n .lambda./2 where n is from 1 to 3, said interferometer further having an aperture integrally provided in an interferometer structure and located adjacent to a side of said lower mirror which is opposite said upper mirror, said aperture being filled with silicon substrate;
• and
• a detector suited for detecting said filtered measuring signals.

An electrically tunable short-resonator Fabry-Perot interferometer fabricated by surface micromachining techniques for infrared gas concentration measurement, said interferometer comprising:

• upper and lower essentially parallel, adjacently aligned, semi-transmissive mirrors spaced at a distance (d) which is designed proportional to a center wavelength (.lambda.) of the interferometer passband according to the formula:
• d=n.lambda./2,
• where n is an integer from 1 to 3 indicating an interferometer order number, said lower mirror having first and second opposite sides, said upper mirror being located closest to said first side of said lower mirror;
• control means for modulating the distance (d) between said resonator mirrors;
• and
• an aperture integrally provided in an interferometer structure and located closest to said second side of said lower mirror, said aperture being filled with silicon substrate.