Gas sensor based on plane annular micro-cavity

The invention relates to a gas detection method and a gas sensor based on planar annular microcavities. The method is mainly characterized in that two couplers consisting of the planar annular microcavities and biconical optical fibers are adopted, one is a gas detection coupler, and the other is a coupler in a vacuum environment. The gas detection method comprises the following steps: based on aprinciple that the absorption effect of evanescent wave on different gases changes the peak value of a transmitted spectrum, a transmitted spectrum of the gas detection coupler of gas to be detected and a transmitted spectrum of the coupler in the vacuum environment are utilized to contrast; and the detection of the variety and the concentration of the gas to be detected is realized through spectral changes of the transmitted spectrums. The gas sensor designed by the method has the advantages of short response time, relatively simple structure, extremely high sensitivity to virulent harmful gas with extremely low conc