Optical resonators, or whispering gallery resonators, are the optical analog of an acoustic tuning fork. They confine light in circular orbits around their periphery. The efficiency of confinement or photon lifetime depends on the material and geometry of the cavity as well as the surface roughness.
Silica toroidal resonators, such as the one shown here, have demonstrated photon lifetimes greater than 100ns.(1-2) This value corresponds to approximately 10meters of optical fiber coiled into a 100micron (1E-6m) footprint. To achieve this performance requires a combination of very low material loss and defect-free toroidal resonator surface. These devices are fabricated using a combination of standard photolithography, buffered oxide etching, XeF2 etching and CO2 laser reflow. (1-2)
As a result of their small geometry and high performance, these devices have applications in biodetection of single molecules, integrated microlasers, non-linear optics, and studying fundamental physics phenomena. Current research in the Armani group at the University of Southern California is focused on developing visible and near-IR microlasers integrated on a silicon wafer(3) and ultra-sensitive biosensors for detection of methylated DNA and single cells.(4)
A scanning electron micrograph of the toroidal resonant cavity taken with the desktop SEM. As can be observed, the surface of the toroidal resonator is defect free. Image courtesy of the Armani Research Group at the University of Southern California.
- D. K. Armani, T. J. Kippenberg, S. M. Spillane, K. J. Vahala, Nature 421, 925 (Feb 27, 2003).
- X. Zhang, H.-S. Choi, A. M. Armani, Applied Physics Letters 96, 153304 (2010).
- H.-S. Hsu, C. Cai, A. M. Armani, Optics Express 17, 23265 (2009).
- H. K. Hunt, C. Soteropulos, A. M. Armani, Sensors 10, 9317 (2010).