Design of the filter with flattening spectral transmittance

Abstract

A new method to produce flattening spectral transmittance for birefringent chain filter based on the interference of polarized light is presented. In previous publications, each birefringent crystal must be of equal thickness and only one group of azimuth angles of the crystals was obtained. Besides, the shape of spectral transmittance is not enough flat and the flatness width of the passband and the stopband is not wide enough. Our method is more advantageous than that of the previous publications. It is based on Fourier transform. The thickness of each crystal can be different. We can obtain all the numerical solutions of the azimuth angles of the crystals when ripples are relative small in both the relative wide passband and stopband. In this paper, three birefringent crystals are used and all the azimuth angles of the crystals are obtained when ripples are limited to a uniform 0.1% in both the passband and the stopband with the widths of greater than 2/11 period. The influence of the change of the azimuth angles and thickness of the crystals on the spectral transmittance of the system is discussed as well.