Above – Illustration of a pair of silicon high contrast gratings that can be used to guide visible light on a chip with low losses despite large absorption by the silicon material.
Nanostructures were used to make high contrast gratings. Such a grating consists of nanometer-sized 'posts' lined up to form a 'fence' that prevents light from escaping. The posts are 150 nanometers in diameter and are spaced so that light passing through them interferes destructively with light passing between them. Destructive interference is a phenomenon where waves – including electromagnetic waves such as visible light – that oscillate out of sync cancel each other out. This way, no light can "leak" through the grating and most of it gets reflected back inside the waveguide.
The next step is to engineer the efficient coupling of the light out of the waveguides into other components. That's a crucial step in our research, with the ultimate goal of integrating the all-optical transistors into integrated circuits that would be able to perform simple logic operations.