Study on the fir bandpass filters consisting of two resonant grids

A series of interference filters composed of two resonant grids, with resonant wavelengths λ_m <200μm, were constructed, and the dependence of the spectral characteristics on the separation of the two grids was studied experimentally in detail. The multiple-beam interference theory was applied to analyse the experimental results. The theoretical calculations and the experimental results are in good agreement. A method is presented, by which double-grid interference filters can be designed with the computer aid.