Scientists have developed a compact optical ‘isolator’, capable of sending light in one direction at a time. The device, made with silicon nanophotonic structures will be highly important for future optical circuitry on a chip.
The development of sophisticated integrated photonic circuits has been hindered by the difficulty of performing ‘on-chip’ complete optical isolation ― a perfect one-way valve for light propagation. Backwards-propagating light, commonly caused by reflections, is often problematic in photonic devices and can severely degrade the performance of optical communication systems. Devices for quenching backwards-propagating light, known as optical isolators, already exist. The problem is that these isolators rely on magneto-optical materials that are not compatible with integrated circuit manufacturing techniques, in particular silicon complementary metal-oxide-semiconductor (CMOS) technology.
Online this week in Nature Photonics, Shanhui Fan and Zongfu Yu propose an on-chip optical isolation scheme using photonic structures composed of silicon waveguides and ring-resonators. By modulating the refractive index of the structures in time and space, energy and momentum are imparted to the forwards-propagating, (but not to the backwards-propagating) light, allowing them to be separated. The result is an ultra-compact complete optical isolator that can be built using CMOS-compatible materials systems.