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

摘要

We propose a new photonic crystal (PhC) wavelength demultiplexer based on self-imaging inmultimode interference (MMI) section and on the reflecting filter characteristics of PhC defectsinserted into the MMI section. Because PhC defects with adequate bandgap act as a dichroic mirror,a signal with one wavelength is reflected from the PhC defects, but another signal with a differentwavelength is transmitted. Introduction of PhC defects makes the wavelength demultiplexer muchshorter because there is no need to consider the common beat length for two signals of differentwavelengths. The proposed device was analyzed and optimized using the plane-wave expansionmodel and the finite-difference time-domain method. The multimode section of the optimallydesigned device had a size of 10.3 × 3.2 μm~2and its extinction ratios were -21.7 dB and 16.3 dBfor signals of 1.3 and 1.55 μm, respectively.