Design, fabrication, and characterization of coupling-strength-controlled directional coupler based on two-dimensional photonic-crystal slab waveguides

A directional coupler (DC) with a coupling-strength control defect (CCD) based on a two-dimensional photonic-crystal slab waveguide is numerically and experimentally studied. The structure consists of two parallel-coupled single-defect waveguides separated by a triple-line air-hole array, with some missing air holes in the middle of the triple line. Using a two-dimensional finite-difference time-domain method, a 50% coupler was designed and almost 50% coupling performance was experimentally confirmed at a wavelength of ∼1.3 μm with a coupling length of about 7 μm, about 1/3 in length as compared to the DC without the CCD.© 2003 American Institute of Physics.