Numerical Study of Transmission Improvement in a Photonic Crystal Waveguide Bend by Mode-Matching Technique

An approach to improve the transmission efficiency of photonic crystal (PC) waveguide bends through maximization of the overlap integral of fields between the straight waveguide and the waveguide bend is presented. By shifting the lattice points around the bend corner, the bound state in the waveguide bend and the guided mode in the straight waveguide are matching, and the transmission of a PC waveguide bend can be significantly improved. The transmission of a 120^deg PC waveguide bend with mode matching is dramatically improved from 5.7% to 87.5%. The bound state in a PC waveguide bend is similar to a cavity mode; therefore, the PC waveguide bend performs a narrowband transmission. Frequency shift of the spectra for a PC waveguide bend due to this lattice shifting can also be observed.