Design of 50 G nonpolarizing dense wavelength division multiplexer angle-tuning bandpass filter

Transmission characteristic differences of a narrow bandpass filter between p- and s-polarized light, especially the central wavelength separation, will corrupt the performance of the filter when the incidence is oblique. In this paper, by adding high-index materials asymmetrically to both sides of a low-index spacer, which tunes the equivalent index of the spacer, the central wavelengths of the two polarizations coincide perfectly when in 20° incidence; with different reflected layers on the two sides of the spacers and replacing some reflected layers with equivalent layers, the 0.5 dB normalized passband width is kept at 0.2 nm, which meets the requirement of the 50 G dense wavelength division multiplexer filter.