Design of a Compact Wavelength Demultiplexer Based on Multimode Interference and Filtering of a Photonic Crystal Structure

Abstract

We propose a new photonic crystal (PhC) wavelength demultiplexer based on self-imaging in multimode interference (MMI) section and on the re ecting lter characteristics of PhC defects inserted into the MMI section. Because PhC defects with adequate bandgap act as a dichroic mirror, a signal with one wavelength is re ected from the PhC defects, but another signal with a di erent wavelength is transmitted. Introduction of PhC defects makes the wavelength demultiplexer much shorter because there is no need to consider the common beat length for two signals of di erent wavelengths. The proposed device was analyzed and optimized using the plane-wave expansion model and the nite-di erence time-domain method. The multimode section of the optimally designed device had a size of 10.3 3.2 m2 and its extinction ratios were {21.7 dB and {16.3 dB for signals of 1.3 and 1.55 m, respectively.