Device uses light to rapidly turn a switch on and off

A team of scientists and engineers at Minnesota University has invented a microscale optical device that could increase the speed of downloading information online and reduce the cost of internet transmission.

According to a statement, the device uses light to turn a mechanical switch of light on and off at high speed — a development that could lead to advances in computation and signal processing.

The research results were published in the online journal Nature Communications.

’This device is similar to electromechanical relays but operates completely with light,’ said Mo Li, an assistant professor of electrical and computer engineering in the university’s College of Science and Engineering.

The new study is based on a previous discovery by Li and collaborators in 2008 where they found that nanoscale light conduits can be used to generate a strong enough optical force with light to mechanically move the optical waveguide.

In the new device, the researchers found that this force of light is so strong that the mechanical property of the device can be dominated completely by the optical effect rather than its own mechanical structure.

The effect is amplified to control additional coloured light signals at a much higher power level.

‘This is the first time that this novel optomechanical effect is used to amplify optical signals without converting them into electrical ones,’ Li said.

Different-coloured light channels

Glass optical fibres carry many communication channels using different colours of light assigned to different channels.

In optical cables, these different-coloured light channels do not interfere with each other and it is this non-interference characteristic that ensures the efficiency of a single optical fibre to transmit more information over long distances.

But this advantage is also said to harbour a disadvantage: when considering computation and signal processing, optical devices could not allow the various channels of information to control each other easily.

The researchers’ new device has two optical waveguides, each carrying an optical signal. Placed between the waveguides is an optical resonator. In the optical resonator, light can circulate hundreds of times, gaining intensity.

Using this resonance effect, the optical signal in the first waveguide is enhanced in the resonator and generates a very strong optical force on the second waveguide.

The second waveguide is released from the supporting material so that it moves in oscillation when the force is applied on it. This mechanical motion of the waveguide alters the transmission of the optical signal.

Because the power of the second optical signal can be many times higher than the control signal, the device functions like a mechanical relay to amplify the input signal.

Currently, the new optical relay device operates one million times per second. Researchers expect to improve it to several billion times per second. The mechanical motion of the current device is sufficiently fast to connect radio-frequency devices directly with fibre optics for broadband communication.