Design of optical bandpass filters based on a two-material multilayer structure

An easy method for designing filters with equalized passband ripples of a given magnitude is proposed. The filter, which is made of two dielectric materials, comprises coupled half-wavelength resonators and multilayer mirrors. The filter design begins with the synthesis of the multimaterial filter prototype whose mirrors consist of quarter-wavelength layers. Optimal refractive indices of the layers in the prototype are obtained by a special optimization based on universal rules. The thicknesses of the mirrors' layers in the final filter are computed using derived formulas. A design procedure example for silicon-air bandpass filters with a fractional bandwidth of 1% is described.