Codirectional couplers in GaAs-based planar photonic crystals

Several designs for codirectional couplers in planar photonic crystals etched into GaAs-based heterostructures were investigated both theoretically and experimentally. Two different numerical techniques, i.e., plane wave expansion and finite difference time domain, were used to calculate the coupling lengths. Both methods are shown to be in good agreement with the experimental results. The measured coupling lengths are in the order of 350 periods, leading to a physical length of the order of 80μm, much smaller than what is achieved in classical integrated optics couplers.