Microgenetic-algorithm-based design of combined conventional waveguide and photonic crystal devices

Abstract

We have proposed the hybrid integration of photonic crystals (PhCs) and conventional index-guided waveguides (CWGs) as a potentially attractive method of realizing compact waveguide elements for large-scale planar lightwave circuits (PLCs). In this paper we briefly review the properties of PhC/CWG 90° bends in low index, low index contrast waveguides and then extend them to waveguides with high index and low index contrast. We find that diffraction from the boundary of the PhC region limits the optical efficiency of the bend. To overcome this we use a rigorous design tool based on a micro-genetic algorithm (microGA) and a finite difference time domain (FDTD) method to optimize the boundary layer to suppress the unwanted diffraction. We find that this approach yields an improvement in the bend efficiency for light at 1.55 micron from 80% to 95%.