Researchers at the University of California, Santa Barbara, and Caltech have developed a chip-scale optical gyroscope that can detect rotation as slow as 37 degrees per hour, nearly 2,000 times slower than an earlier silicon nitride design.
The result brings the sensor closer to measuring Earth’s rotation rate of 15 degrees per hour. It could eventually help develop compact navigation systems for aircraft, vehicles and spacecraft operating where GPS signals are unavailable.
Unlike conventional gyroscopes that rely on mechanical movement, the new device uses light traveling through a ring-shaped optical circuit to detect rotation. The researchers say the approach could offer high-precision sensing in a smaller, more durable package.
The experimental gyroscope uses silicon nitride, a material compatible with standard CMOS chip-manufacturing processes. Its sensing circuit measures about 24 millimeters across, while the packaged device is only a few centimeters wide.
Light detects tiny rotations
The researchers combined two previously developed technologies: a Brillouin laser gyroscope from Caltech and a low-noise laser-on-a-chip platform developed at UC Santa Barbara with support from the Air Force Research Laboratory.
Inside the device, two semiconductor lasers send light in opposite directions around a ring-shaped circuit. Interactions between the light and vibrations in the material generate two stable laser signals.
When the device rotates, the frequencies of these signals shift slightly relative to each other. Measuring that difference allows the gyroscope to determine the rotation rate.
The ring’s ability to retain light is central to its sensitivity. Its quality factor, a measure of how efficiently an optical resonator stores light, exceeds 163 million.
This allows the device to isolate a narrow 2-megahertz bandwidth from an optical signal operating at approximately 200 terahertz. Photons remain inside the resonator for nearly 100 nanoseconds, allowing light to circulate repeatedly.
The larger ring also improves sensitivity because optical gyroscopes can detect smaller rotations when the light encloses a greater area.
“Our new gyroscope combines several advanced technologies to achieve a high level of sensitivity in a format that can be made with standard CMOS chip-processing methods and uses just milliwatts of optical power,” said Daniel J. Blumenthal, who led the UC Santa Barbara research team.
Testing near Earth’s rotation
To evaluate the device, researchers mounted the packaged chip on a piezoelectric rotation stage that moved it back and forth at controlled frequencies.
A separate optical interferometer measured the stage’s actual movement, providing a reference against which the gyroscope’s readings could be compared.
The sensor produced a linear response and detected rotation as slow as 37 degrees per hour. That compares with 72,000 degrees per hour measured by the researchers’ earlier silicon nitride Brillouin gyroscope.
The improvement demonstrates how low-noise lasers and high-quality optical resonators can increase rotation sensitivity on a photonic chip.
However, the new device has not yet demonstrated direct measurement of Earth’s rotation. It also remains a laboratory prototype rather than a fully integrated navigation sensor.
Researchers are working to reduce unwanted light scattering, which can affect measurement stability. They also plan to integrate the lasers, photodetectors, and other components into a single compact system before testing it outside the laboratory.
The findings were published in Optics Letters.