Phase-shifted Photonic Crystal Waveguide Gratings and Their Application for Wavelength Demultiplexing

Standard photonic crystal (PC) waveguide gratings show a stopband only in reflection. By incorporating single or multiple phase-shift regions into the PC waveguide gratings, an extremely narrow transmission peak opens up in the reflection band. Using coupled-mode theory together with transfer-matrix formalism, it is shown that by properly choosing the magnitudes of the phase shifts, the transmission spectrum can be tailored into a nearly rectangular line shape. As a specific application, the designed phase-shifted PC waveguide gratings can be used as a filter in dense wavelength-division-multiplexed (DWDM) optical communication systems with a 100-GHz channel spacing. The theoretically calculated results are numerically verified by using two-dimensional (2-D) finite-difference time-domain (FDTD) method.