Photonics Reduces Switch Size

Photonic crystal technology has been used to reduce the size of an optical switch to only a few wavelengths of light. The technology may eventually be used in small consumer devices that connect homes or offices to communication networks via ultrafast optical fibers for high bandwidth applications.

The University of St. Andrews team's optical switch beside a human hair (left). The actual switch is the tiny rectangular area in the center of the image. (Images courtesy the Microphotonics Group at the University of St Andrews)

A team of researchers based in the School of Physics and Astronomy at the University of St. Andrews in Scotland developed the tiny optical switches, which are only about one-tenth of the width of a human hair.

Switching light is one of the most fundamental functions of an optical circuit, and many types of optical switches have been created. Most operate by imposing a phase shift between two sections of the device in order to direct light from one port to another or to switch it on and off. The constraint to this method is that typical refractive index changes are very small. This issue is usually addressed by making the devices longer, which increases the overall footprint, or by using resonant enhancement, which reduces the bandwidth.

A scanning electron micrograph of the optical switch.

The device created by the St. Andrews team is a slow-light-enhanced optical switch 36 times shorter than a conventional device with the same refractive index change and a switching length of 5.2 µm.

Professor Thomas Krauss, who led the research, said, "The switch is aimed at applications in telecommunications where we foresee its use in routing of optical signals. The idea of using fiber in the home or office requires small optical circuits that operate with low power. When these can be mass-produced in a cost-effective way it helps to keep the cost of the products down. At the moment, optical switches tend to be millimeters in size. It is difficult to state which is the smallest optical switch ever made -- but this is certainly one of them."

By focusing on silicon as the material platform, the photonic devices developed by the group can be mass-produced in a similar way as computer chips for the microelectronics industry, and integrated with electronic circuitry on the same chip.

The St. Andrews team inspects one of their devices. From left: Thomas Krauss, Liam O'Faolain, Thomas White and Daryl Beggs.

The group aims to address the increasing need for optical components at all levels of the communications network that carries the ever-increasing flow of data over the Internet.

The work, which will be published in the Optical Society of America's Optics Letters, is part of the UK Silicon Photonics project, a consortium led by Surrey University. The project recently received a funding boost from EPSRC (Engineering and Physical Sciences Research Council), with £1.4 million (about $2.8 million) awarded to St. Andrews.

For more information, visit: www.st-andrews.ac.uk