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The tunability of optical transmittance spectra can be available by mounting one of the mirrors of the Fabry-Perrot cavity on a movable structure. The F-P filter prepared by adopting MEMS process can realize the advantages of miniaturization, array, and high output. The size of the MEMS F-P filter can be reduced to a few hundred micrometers. This feature introduces a new problem for the characterization of optical performance, that is, the incident light needs to be focused onto the mirror with a size of a few hundred micrometers. However, in the actual test, the incident light with a hundred-micron spot is usually a convergent beam with a certain cone angle. It is found that through theoretical analysis, compared to parallel incident light, the convergent light beam passed through the F-P cavity leads to the decrease at peak transmittance and the broadening of full width at half maximum. The reason for that was the converging light with a cone angle passing through the F-P cavity had different incident angles and caused diverse optical path difference. As a result, the light emitting from the cavity with various wavelength would appear in the transmission spectra. In summary, the test results under the converging light could not truly reflect the performance of the F-P cavity and the influence of the cone angle of incident light beam on the performance characterization of MEMS F-P filter was analyzed by theoretical arithmetic and simulation.
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