Silicon photonic crystal nanostructures for refractive index sensing

The authors present the fabrication and optical investigation of silicon on insulator photonic crystal drop filters for use as refractive index sensors. Two types of defect nanocavities (L3 and H1-r) are embedded between two W1 photonic crystal waveguides to evanescently route light at the cavity mode frequency between input and output waveguides. Optical characterization of the structures in air and various liquids demonstrates detectivities in excess of Δn/n=0.018 and Δn/n=0.006 for the H1-r and L3 cavities, respectively. The measured cavity frequencies and detector refractive index responsivities are in good agreement with simulations, demonstrating that the method provides a background free transducer signal with frequency selective addressing of a specific area of the sensor chip.