Researchers have demonstrated a chip-based optical frequency comb that matched bulky tabletop systems in key tests while allowing one device to perform several measurement tasks, a step toward portable atomic clocks and navigation systems that can operate without GPS.

The device uses a new approach called self-aligned parametrically-driven cavity solitons, or SParCS. Optical frequency combs produce a series of precisely spaced frequencies of light, creating a ruler that scientists can use to measure optical frequencies and connect them to electronic signals.

Researchers from the Joint Quantum Institute (JQI), the National Institute of Standards and Technology (NIST), and international partners tested the chip by linking microwave signals, which oscillate billions of times per second, with optical light operating at hundreds of trillions of cycles per second.

In an atomic-clock test, the chip converted an extremely stable optical reference into microwaves that conventional electronics could read. It measured the original optical frequency, which oscillated several hundred trillion times per second, to within about 100,000 oscillations per second of the expected atomic value.

Conventional chip-scale frequency combs typically inject one laser into a tiny ring-shaped resonator. The resulting comb extends to frequencies on either side, but the outer “teeth” can become weak and less well defined, requiring additional equipment to amplify and stabilize them.

SParCS instead uses two lasers at different frequencies as the edges, or bookends, of the comb. Additional frequencies form between them. The researchers combined this approach with a synchronization technique that aligns the frequency lines into a single usable comb.

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