Light focusing via Rowland concave surface of photonic crystal

This letter investigates the focusing characteristics of lightwaves emitted from photonic crystal waveguide aperture using a concave corrugated surface. Based on Rowland's theory, the concave structure is applied to the photonic crystal output surface. The field distribution pattern of the emitted lightwaves demonstrates the focusing effect. The focusing distance agrees with Rowland's theory. By optimizing the surface structures, the focused beam has a full wave at half maximum width of 1.6a. This suggests that the concave corrugated surface could substitute conventional optical lens for focusing and coupling subwavelength devices. Similarly, by inverting the surface structures, the lightwaves splits at the same focusing location.