20 dB -enhanced coupling to slot photonic crystal waveguide using multimode interference coupler

Abstract
The authors experimentally demonstrate a slot photonic crystalstructure for guiding light in a sub- 100 - nm -wide low-index region. A multimode interference-based coupling structure is introduced to couple light into such a narrow slot photonic crystal waveguide. A coupler of 1.26 μ m long enhances the coupling efficiency by 20 dB for the quasi-transverse-electric mode over 35 nm optical bandwidth centered at 1562 nm . The measured transmission spectra are in good agreement with the simulated band diagram.