Bullseye-shaped MEMS couples light and mechanical modes

January 31, 2017 // By Julien Happich
Researchers from the University of Campinas (Brazil) have developed a new type of optomechanical device able to confine both optical and mechanical waves.

The CMOS-compatible device obtained through conventional lithography consists of a silicon microdisk on a pillar, with a circular mechanical grating. While the optical waves are confined at the disk edge in whispering gallery-like modes due to total internal reflection, mechanical modes are confined as an edge state lying within a phononic bandgap of the circular grating.

Schematic of a bullseye optomechanical cavity (green)
supported by a central pedestal (blue).
The inset illustrates the mechanical motion
localized at the disk’s edge.

Publishing their results in the Optics Express journal under the title "Hybrid confinement of optical and mechanical modes in a bullseye optomechanical resonator", the researchers explain how the two unrelated confining mechanisms relax the need for simultaneous optical and mechanical bandgaps, easing design rules across numerous materials while minimizing both optical and mechanical losses.

The tiny MEMS, about 24 microns wide, can be easily mass-produced and their particular opto-mechanical properties could turn them into highly sensitive force and motion sensors, beyond the capabilities of today's accelerometers and gyroscopes.

a) Scanning electron microscope (false color) images
of typical bullseye cavities from side b) and top.

The radial groves effectively couple mechanical and optical waves, meaning that mechanical motion can be detected through the changes in optical modes. Reversely, if the disk was made out of a lasing material, the changes in mechanical modes could alter the laser pulses, the whole mechanical structure acting as an optical modulator.

Next, the researchers hope to combine the optomechanical disk with an integrated optical waveguide that would bring light to and from the device, all in one package.