Experimental demonstration of high coupling efficiency between wide ridge waveguides and single-mode photonic Crystal waveguides

The experimental demonstration of a high efficiency coupling technique based on setting a single defect within a photonic crystal (PhC) taper is reported. The samples were fabricated on a Silicon-on-insulator substrate and a 3-μm-wide ridge waveguide was used to couple the light into and out of a single-mode PhC waveguide. Transmission efficiencies higher than 70% for wavelengths at 1.55 μm are demonstrated which sharply improves the transmission efficiency achieved with butt-coupling and conventional PhC tapers.