A waveguide-based demultiplexer with two multiple-layer filters

Abstract

SUMMARYAn optical waveguide with multilayer films with the characteristics of 1.31 µm reflection/1.55 µm transmission is analyzed by means of the beam propagation method. First, the power-conservation wide-angle beam propagation method for TM wave analysis is derived. In the process, the evaluation equation for the power is presented and its effectiveness is demonstrated. Next, the characteristics of the filter structure in which the vertex angle of the input and output waveguides is 45° are discussed. After the location of the effective reflection point in the filter is investigated, the wavelength dependence is discussed. It is shown that the difference in the characteristics of the two polarizations can be kept small if the vertex angle is 45°. In order to obtain wavelength separation characteristics with small polarization dependence in a structure with a 90° crossing angle of the input and output waveguides, a structure is presented in which two waveguides with multilayer films and a vertex angle of 45° are cascaded. It is demonstrated that a reflectivity of 98% can be realized for the TE wave and 88% for the TM wave. Finally, it is shown that 98% reflection/98% transmission can be realized for the TE wave and 95% reflection/94% transmission for the TM wave by inserting a spacer layer (1/2 wavelength layer) into the multilayer filter.