Highly efficient emission from 2-D photonic crystal slab waveguide

Abstract

Since the advent of the photonic crystal waveguide, the connection from or into other optical circuits has been one of the key issues. We propose a method for highly efficient emission, which means high transmission combined with the beaming effect from 2-D photonic crystal slab waveguide. This is achieved via surface mode which resides at the interface between photonic crystal and open space, decaying exponentially into both media and propagating along the boundary. The surface mode in FM direction for each termination is demonstrated using not only Plane Wave Expansion method but also 3-Dimensional Finite Difference Time Domain (FDTD) method. In the FDTD simulation, we make line defect waveguide, terminated in FM direction, and use a sinusoidal source in the waveguide. Using monochromatic source, we calculate reflection and transmission from the waveguide by simulating the flux and find the highest transmission when the mode lies in lower group velocity. Among each termination, high transmission 97% is achieved when the given frequency is met with surface mode above the light line. We show the far field pattern for each termination using near-to-far-field transformation. When we consider the light from the waveguide, we count the quantity within 30˚which corresponds to numerical aperture of 0.5. The collection efficiency is simply calculated by multiplying transmission and the quantity within 30˚ In order to increase the collection efficiency, we apply corrugation effect using the grating theorem which gives additional momentum in the ΓM direction.