Optomechanics Promise Integrated All-Optical Switching

Yvonne Carts-Powell

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A microscale mechanical switch on a silicon chip uses light from a microring to deflect a cantilevered light guide (foreground), thus modulating the signal.

An optical switch might be the first step towards faster optical communications. At the tiny sizes of integrated photonics, an optical signal can generate enough mechanical force to physically move a small object, such as the tip of a cantilever. Researchers at the University of Minnesota used this property to create an optomechanical force to deflect the cantilever. Because the cantilever contained an optical waveguide, they were able to modulate the optical signal passing through the cantilever using only optically passive materials (Nat. Comm. 3:1091, 2 Oct 2012).
The force is supplied by an optical control coupled into a microring resonator. The cantilever acts like a spring, thus creating an intensity sine wave in the output 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. "This is the first time that this novel optomechanical effect is used to amplify optical signals without converting them into electrical ones," group leader Mo Li said.
This is different from previous work because many wavelengths can be modulated—as long as they are not near the microring’s resonance. The researchers demonstrated modulating two wavelengths at once in the signal channel.
The researchers used silicon waveguides on standard silicon wafers. The signal waveguide was 420 nm wide, and the maximum displacement of the cantilever was limited to the distance between the signal waveguide and the microring. Many different wavelengths can be multiplexed in the signal light guide, as long as they are far from the microring’s resonant wavelengths.
Currently, the device operates one million times per second. Researchers expect to improve it to several billion times per second—into radio frequencies. This could allow RF devices to be connected directly with fiber optics for broadband communication.

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