PhD Defenses


Thu April 28th 2022, 11:00am - 12:00pm
Stanford overview

Photo by Linda Cicero

Ph.D. Candidate:  Matthew Grant

Research Advisor: 
Michel Digonnet

Thursday, April 28

Time: 11 AM PDT

Location: Room 101X (auditorium) in Paul Allen Building

Zoom Link:

Zoom Password: email nickswan@stanford for password


Avenues to miniaturize optical gyroscopes

The emergence of self-driving cars and other small autonomous vehicles has created an enormous demand for a new compact navigation system. Global positioning systems (GPS) can surely function in this capacity, but relying solely on GPS for navigation is unfortunately highly unsafe because signals can be blocked by tunnels, buildings, terrain, etc., or intentionally jammed or spoofed. The typical solution is to supplement GPS with precise gyroscopes, but no current gyro meets this application’s criteria for size, cost, and ease of mass producing while maintaining sufficient precision. Recent breakthroughs in silicon photonics technologies offer a potential solution by printing highly integrated high-sensitivity optical gyros on silicon chips at CMOS fabrication foundries.


In the first part of this defense, I will discuss novel optical gyro architectures intended to fundamentally enhance rotation sensing to meet these stringent requirements on gyro noise and drift with current and prospective silicon photonics technologies. Specifically, I will present the results of the sensitivity of optical gyros consisting of two coupled ring resonators operated at an exceptional point (EP), where the rotation-induced shift of resonance frequency is enhanced by several orders of magnitude over the conventional resonant gyro. I will present in particular a novel EP gyro design utilizing optical gain in one of the resonators, a device with a predicted sensitivity ~2400-fold larger than that of a conventional resonant gyro utilizing a single ring resonator. Interestingly, despite the enormous EP enhancement of resonance splitting, this sensitivity enhancement is attributed entirely to the presence of optical gain, and not to the presence of an EP. One way or another, the EP enhancement cancels itself out in an optical sensor’s output.


In the second part of this defense, I will discuss my effort to build and test a competitive compact gyro made of an on-chip silicon-nitride racetrack ring resonator with an equivalent radius of 5.7 mm and a quality factor of 200 million.  The measured angular random walk of the gyro (or minimum detectable rotation rate) is 80 deg/h/ÖHz. The noise was determined experimentally to be limited by the very small amount of residual backscattering in the ring, with a backscattering coefficient of -98 dB/mm at the optimal resonance of the device. This noise and ARW are a record (by a factor of two) for a chip-scale gyro of this size.