Anello Photonics is a Silicon Valley based startup developing next generation navigation technologies. The heart of the Anello’s products is the silicon photonics optical gyro, the SiPhOG™ which is a 10X reduction in SWAP-C compared to current products.
This paper describes the progress made in developing a resonant optical gyroscope fabricated with a silicon-nitride (SiN) waveguide using CMOS-compatible processes. The ultra-low loss of SiN waveguides allows ring resonators to be fabricated with small footprints (~1 cm2) while achieving higher Q-factors (~108) than similar resonators made from other materials. For this reason, SiN is a very promising platform for developing a miniaturized optical gyroscope with tactical-grade specifications, which require an angular random walk (ARW) of 0.05 deg/h/√Hz and a drift of 10 deg/h. Our first-generation SiN ring gyro, reported in 2022, had an affective diameter of 11.6 mm, a perimeter of 37 mm and a finesses of 1270. When interrogated with a 10-kHz linewidth laser, it had a measured ARW of 1.3 deg/h/√Hz and a drift of 4000 deg/h, and its dominant noise was backscattering noise. In this paper, we present a second-generation of SiN gyro with a longer ring waveguide and a lower finesse to reduce the backscattering noise. This multi-turn ring has the shape of a spiral with 33 turns and an average diameter of 12.2 mm, a waveguide length of 1.2 m, and a finesse of 30. The laser linewidth was also decreased to 100 Hz to reduce the dominant noise sources, including laser frequency noise and backscattering noise. The reported ARW of this new gyro is 0.28 deg/√h, which is a factor of 4.5 lower than that of the first-generation gyro. After splicing several of the components together to reduce instabilities due to mechanical connectors, the drift was reduced to 500 deg/h. This work provides an incentive to move towards integrating more components on the chip. With continued research, this technology could soon meet the performance requirements of a wide variety of navigation-related applications.
Anello photonic is a silicon valley based startup developing next generation navigation technologies. The heart of the Anello’s products is the silicon photonics optical gyro, the SiPhOG™ which is a 10X reduction in SWAP-C compared to current products.
Advancements in silicon photonics technology have resulted in significant progress toward tactical-grade chip-scale optical gyroscopes for applications such as inertial navigation for a range of self-driving vehicles. Our first generation of gyro, reported a year ago, was a resonant ring gyro fabricated with an ultra-low-loss silicon-nitride waveguide in a racetrack shape with a perimeter of 37 mm and a finesse of 1270. When the laser frequency was tuned to interrogate the resonance with the lowest backscattering coefficient, and balanced detection was implemented to reduce common noise in the two output signals, the angular random walk (ARW) was measured to be 80 deg/h/√Hz, and the gyro output was dominated by backscattering noise. The second-generation reported here utilizes a longer ring to further reduce backscattering noise. The ring resonator is a circular spiral with 33 turns, a length of 1.2 m, and a finesse of 29. When interrogated with a narrow-linewidth laser like the racetrack gyro, it has a measured ARW of 210 deg/h/√Hz dominated by laser-frequency noise. The ARW is higher than that of the racetrack gyro because the balanced detection was not as effective (13.2 dB of common noise rejection compared to 18 dB in the racetrack gyro). Tests in a vacuum indicate that environmental fluctuations do not contribute to the noise, and that most of the measured drift (3,500 deg/h) has an optical and/or electronic origin. We also report the noise performance of the racetrack gyro interrogated in a Sagnac interferometer probed with broadband light. This configuration was inspired by a recent publication from Shanghai Jiao Tong University that reports a resonant fiber optic gyroscope interrogated with broadband light with a measured ARW that meets tactical-grade requirements. The advantages of this interrogation technique are that it eliminates the need to stabilize the resonator, it reduces the component count, and by making use of incoherent light, it reduces the backscattering noise. The measured ARW of the racetrack gyro interrogated with broadband light was dominated by excess noise at large detected powers, and it was a factor of ~900 larger than the ARW of the same racetrack gyro interrogated with the laser. The reason for this increase in ARW is that the advantage of having a high-finesse resonator is lost when the ring is interrogated with broadband light, and the sensitivity is reduced by a factor of the finesse compared to the same ring resonator interrogated with a laser. This reduction in sensitivity is demonstrated experimentally. Achieving tactical-grade requirements will require returning to a laser interrogation, improving the balanced detection scheme to achieve a noise cancellation of 25 dB or better, and optimizing the laser linewidth to minimize both laser frequency noise and backscattering noise.
Recent breakthroughs in silicon photonics technology may soon lead to mass-producible chip-scale tactical-grade (or better) gyroscopes by using a CMOS-compatible fabrication process to print highly integrated high-sensitivity optical gyroscopes. This paper reports our progress on designing and building an optical gyro out of an SiN racetrack resonator of 37-mm perimeter with 1270 finesse (108 intrinsic quality factor) using off-the-shelf fiber components (circulators, splitters, and modulators) and a semiconductor laser to achieve an angular random walk (ARW) of 80 deg/h/Hz, or 1.3 deg/h. To our knowledge, it is a record by a factor of 2 for the ARW per footprint area of a Sagnac-effect-based gyroscope on a chip. A balanced-detection scheme is employed to cancel 18 dB of gyroscope noise caused by laser phase noise converted into amplitude noise by residual backscatterers in the resonator. The backscattering coefficient was found to be very sensitive to wavelength, and therefore to the resonance used to probe the resonator. The lowest backscattering coefficient was measured to be more than 1,000 times lower than the mean. The use of this resonance, as well as an asymmetric phase-modulation scheme, greatly reduced the gyroscope’s backscattering noise. Achieving this gyro’s theoretical minimum ARW of 16 deg/h/Hz will likely require a lower backscattering coefficient or better means of cancelling backscattering noise. Further improvements to tactical-grade performance (and better) will likely require a larger resonator area, further reduction of backscattering, and/or a laser with reduced frequency noise.
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