An Optical Bandpass Filter Based on a Three-Component Multilayer Structure

摘要

Optical bandpass filters usually represent multilayer dielectric structures in which the layers with high (n_H) and low (n_L) refractive indices [1, 2] alternate. In the case when the optical thicknesses of layers are identical, the structure represents a one-dimensional photonic crystal [3] having periodic transparency windows-passbands with central frequencies multiple to the frequency of the half-wavelength resonance, which are separated by the stopbands-the photonic band gaps. The passband width in such structure is approximately proportional reciprocally to the contrast n_H_L of refractive indices of dielectric layers; therefore, it is relatively wide for a photonic crystal because the highest possible contrast does not exceed four for real optical materials. It should be noted that, when fabricating an optical bandpass filter based on a photonic crystal, it is necessary to change the refractive indices of several external layers in its structure to decrease the passband ripple that may be too high [4, 5].