Researchers at the University of California, Santa Barbara and Caltech have developed a chip-scale optical gyroscope that can detect rotations as low as 37 degrees per hour, nearly 2,000 times slower than an earlier silicon nitride design.
The result brings the sensor closer to measuring the Earth’s rotation rate of 15 degrees per hour. It could ultimately help develop compact navigation systems for aircraft, vehicles and spacecraft used where GPS signals are not available.
Unlike traditional 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 sensors in a smaller, longer-lasting package.
The experimental gyroscope uses silicon nitride, a material compatible with standard CMOS chip manufacturing processes. Its sensor circuit measures around 24 millimeters in diameter, 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 light and vibrations in the material create two stable laser signals.
As the device rotates, the frequencies of these signals shift slightly relative to each other. By measuring this difference, the gyroscope can determine the rotation rate.
The ring’s ability to store light is central to its sensitivity. Its quality factor, a measure of how efficiently an optical resonator stores light, is over 163 million.
This allows the device to isolate a narrow 2 megahertz bandwidth from an optical signal operating at around 200 terahertz. Photons remain in the cavity for almost 100 nanoseconds, allowing light to circulate repeatedly.
The larger ring also improves sensitivity because optical gyroscopes can detect smaller rotations as the light covers a larger area.
“Our new gyroscope combines several advanced technologies to achieve high levels of sensitivity in a format that can be manufactured using standard CMOS chip processing methods and consumes only milliwatts of optical power,” said Daniel J. Blumenthal, who led the UC Santa Barbara research team.
Tests near the Earth’s rotation
To evaluate the device, the researchers mounted the packaged chip on a piezoelectric rotating stage that moved it back and forth at controlled frequencies.
A separate optical interferometer measured the actual movement of the table and provided a reference against which the gyroscope readings could be compared.
The sensor produced a linear response, detecting a rotation of only 37 degrees per hour. This compares to 72,000 degrees per hour measured with the researchers’ previous silicon nitride Brillouin gyroscope.
The improvement shows how low-noise lasers and high-quality optical resonators can increase rotation sensitivity on a photonic chip.
However, the new device has not yet been able to demonstrate a direct measurement of the Earth’s rotation. Additionally, it remains more of a laboratory prototype 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 lab.
The results were published in Optics letters.
