Study of designing minus filters based on rugate theory

The influence of the rugate filter index profile function parameters, such as refractive index amplitude, film thickness and reference wavelength on the minus filter transmission spectrum, were investigated in this paper. The results show that the rejection bandwidth was affected by the refractive index amplitude, the depth of attenuation region was influenced by the film thickness, and the position of cut-off wavelength was determined by the reference wavelength. The method using the Rugate theory to design minus filters was presented, and several kinds of minus filters were designed using the method.