Breakthrough in Optical Frequency Synthesizer Using Integrated Photonics

(Originally published by The Kavli Nanoscience Institute at Caltech)

April 30, 2018

Micrograph images and fabrication process for integrated ultrahigh-Q optical resonator.

Much like how radio frequency synthesis allows for the precise targeting of a specific radio signal, optical frequency synthesis would allow light to be generated on demand at exact wavelengths with incredible precision. And just like how radio frequency synthesis now has wide ranging applications in today's consumer products (from smartphones to tv remotes), optical frequency synthesis will have a significant impact across consumer, scientific and military applications - from observing distant planets to LIDAR technology, atomic clocks, testing fundamental theories and more.

However, optical frequency synthesis must overcome certain barriers before it can competitively enter the market, including cost and size parameters. These challenges sparked DARPA's Direct On-Chip Digital Optical Synthesizer program (DODOS) in 2014, and now its researchers—including The Kavli Nanoscience Institute's faculty board member Kerry Vahala—have released a publication in Nature. Titled "An Optical-Frequency Synthesizer Using Integrated Photonics", it details the researchers' progress in miniaturizing components of optical synthesizers via chip-based integrated photonics and nonlinear optics.

Through the combination of a pair of frequency combs, optoelectronics and tunable miniature lasers, the researchers have successfully reduced the capabilities of a tabletop-sized optical frequency synthesizer down to a few silicon chips measuring 5 mm x 10 mm in size. Vahala's contribution to this project was in developing an ultrahigh-Q chip with an integrated resonator having a record Q factor over 200 million. This milestone demonstrated proper UHQ resonator integration with components in photonic circuits on silicon at the wafer-scale. The integrated UHQ resonator was developed in part at the Kavli Nanoscience Institute's multi-user cleanroom facilities.

Press releases:

DARPA: Achieving Unprecedented Frequency Control in Miniature Lasers

NIST: NIST Team Shows Tiny Frequency Combs Are Reliable Measurement Tools

Read more on Kerry Vahala's UHQ Resonator Development:

KiYoul Yang, Dong Yoon Oh, et al., Nature Photonics, "Bridging Ultrahigh-Q Devices and Photonic Circuits"

"News & Views" article by Joyce K. S. Poon in Nature Photonics, "Integrated Ultra-Low-Loss Resonator on a Chip"