Chip-Sized Laser Gyroscope Senses Rotation Nearly 2,000 Times More Faintly, Approaching Earth's Spin
A Caltech and UC Santa Barbara team built a Brillouin ring-laser gyroscope that measures rotation as slow as 37 degrees per hour, using only milliwatts of optical power.
Researchers have built a chip-scale optical ring-laser gyroscope that can measure rotation as slow as 37 degrees per hour, a record sensitivity for a device of its kind. The figure approaches Earth's own rotation rate of 15 degrees per hour, and the team says the technology could eventually help with precision navigation and orientation, particularly where GPS is unavailable.
Gyroscopes measure how an object rotates, helping determine its orientation and movement. The chip-based gyroscopes in smartphones and other everyday devices have limited sensitivity, which makes them unsuitable for some demanding uses. Optical gyroscopes are sensitive enough for applications such as aircraft navigation, so scientists have been trying to shrink them onto chips.
The new device is described in the journal Optics Letters. It rests on a special type of low-noise laser built on a photonic integrated circuit made from silicon nitride waveguides. Its sensitivity is a nearly 2,000-fold improvement over the same researchers' earlier silicon nitride Brillouin gyroscope, which measured rotation at 72,000 degrees per hour.
"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 team from the University of California, Santa Barbara. "A fully integrated optical gyroscope would not only be smaller than today's systems but also have no moving parts and thus be very resilient to vibrations and shocks."
The design joins two lines of work. Kerry Vahala's group at the California Institute of Technology developed a Brillouin laser gyroscope approach, in which light interacts with vibrations in the waveguide to produce the low-noise laser signals needed to sense rotation. Blumenthal's group, working with the Air Force Research Laboratory, developed chip-scale Brillouin lasers on a silicon nitride platform that produce highly stable, narrow-frequency light. Silicon nitride guides light with very little loss, and circuits made from it are compatible with standard CMOS manufacturing.
Vahala's approach uses a ring-shaped microresonator that holds light with very little loss and has a high quality, or Q, factor, a measure of how well the ring confines light. That lets light circulate many times, which makes the device extremely sensitive to small changes caused by rotation. Vahala's team demonstrated the technology in 2017 and later used a tiny silica optical resonator to detect the rotation of Earth.
"With more development, this type of optical gyroscope could eventually bring the high-precision sensing of optical gyroscopes to compact, chip-based devices," Vahala said. "That could offer a more mass-manufacturable and rugged device for application in cars, aircraft and spacecraft."
The result is a laboratory demonstration, not a product. The reported sensitivity is still above Earth's rotation rate, so the chip cannot yet sense Earth's rotation the way Vahala's larger silica resonator did. But the combination of CMOS-compatible fabrication, milliwatt power use and no moving parts is what makes the approach attractive for systems that must keep working through vibration and shock when satellite signals are jammed or missing.
