Reinventing the Optical Gyroscope with Silicon Photonics
ANELLO Photonics is bringing optical gyros to the mass market using silicon photonics, changing the game for autonomous navigation.
Optical gyroscopes sense angular rate using the Sagnac effect, which was discovered in the early 1900’s. It wasn’t until several decades later that this concept was commercialized with the production of fiber-optic gyros (FOGs). With measurement accuracies better than one part in a billion, inertial sensing expert Anthony Lawrence describes:
“Nature is rarely that cooperative.”
Optical gyros are the sensor of choice for inertial navigation when GPS is unavailable for extended periods. Since their invention, a few million optical gyroscopes have been manufactured and used in select high-performance applications which can afford their hefty price tag.
In contrast, micro electro-mechanical systems (MEMS)-based sensors are now produced in billion-unit quantities annually. These sensors consist of a 3D micromachined mechanical structure that uses physical displacement to sense motion.
Given MEMS gyros are so common today, why is ANELLO Photonics reinventing the optical gyroscope? Can the silicon photonic optical gyro (SiPhOG™) compete with MEMS sensors?
The short answer is YES. There are three primary factors that will drive an exponential increase in usage of optical gyroscope in the mass market:
1. Industrial Vehicle Automation Requires Precision and Integrity
The autonomous car will eventually revolutionize passenger transportation, but truly autonomous vehicle usage is currently being led by industrial applications.
“Autonomous Driving” in the industrial context includes precise vehicle operations that are often dangerous, expensive, and repetitive. Industrial autonomy is conducted on a wide variety of platforms such a drones, construction equipment, and farming.
According to Yole’s research, the industrial segment of the $3B high-performance inertial measurement unit (IMU) market is growing five times faster than high-performance aerospace and defense applications. Autonomous development is a top strategic priority at major industrial conglomerates around the world.
For example, John Deere showcased the need for intelligent robotic machines to “Feed and Build the World” during its CES 2023 keynote presentation. John Deere has recognized the need for new sensing technologies, and it has recently selected ANELLO as one of the start-ups in its Technology Incubation Program.
Globally, industrial vehicle production represents millions of units per year, and the opportunity to economically retrofit existing machines is even larger. The deployment of autonomy in the industrial context delivers a faster return on investment with lower regulatory complexity, but it requires superior positioning performance with continuous centimeter precision in extremely harsh environments. This is an excellent fit for what a mass-produced optical gyroscope like the SiPhOG™ can deliver.
2. MEMS Sensors have Important Limitations
Commercial and government entities have worked extensively on performance improvements to MEMS-based inertial sensors since their commercial launch in the early 1990’s. Today, there are several premium-quality MEMS solutions in the marketplace. These premium MEMS devices have in-run bias instability (i.e., short-term drift) of less than 1 deg/hr; however, there are several common challenges with these devices.
First, the 1 deg/hr drift is short-lived. To maintain this performance requires continuous on-line calibration with external sensors. This means every 10 to 100 seconds, the device will begin to drift faster than the specified bias instability value and requires an update from GPS or other sensors to remain “fully calibrated”.
Second, many of these more sensitive MEMS devices have achieved their lowered noise floor by using a larger and more compliant mechanical structure, which in turn has increased susceptibility to vibration and the potential for “stiction failure” under shock.
Third, these premium MEMS sensors are not necessarily low-cost or small. Typically, high-performance MEMS sensors require larger device structures combined with vacuum packaging, both of which drives up the cost significantly as compared to the MEMS sensor found in an iPhone. Moreover, the performance improvement of MEMS devices has plateaued, where the most prominent solutions were introduced about a decade ago.
3. Silicon Photonics is Ready
ANELLO is utilizing Silicon Photonics to dramatically reduce the size, power, and cost of the fiber-optic gyroscope.
ANELLO’s CEO, Dr. Mario Paniccia, helped pioneer optical transceivers utilizing integrated photonics, and brought these devices to high-volume production while at Intel. Now at ANELLO Photonics, Mario’s team has architected two unique silicon photonic integrated circuits (PICs).
The first PIC integrates ANELLO-designed active optical components with specific performance adaptation suitable for optical gyro requirements.
In a second PIC, ANELLO has developed a unique silicon nitride waveguide process that has world-record optical loss. Utilizing this process, ANELLO can fabricate integrated waveguides up to 50 meters long that feature minimal insertion loss and small size.
ANELLO’s custom silicon nitride waveguide process is now available as a standard process from Tower Semiconductor and it is also being utilized in applications like LiDAR and quantum computing.
Conclusions
When I graduated from UC Berkeley almost thirty years ago, the LN-200 FOG-based IMU was just introduced by Northrop Grumman. At the time, the LN-200 was revolutionary for its combination of small-size, high-performance, and low-drift. Last year, I dropped my eldest daughter off at UC Santa Cruz, and still to this day the same LN-200 remains popular for high-end applications. What other electronic device do you know that has remained both popular and largely unchanged for thirty years?
ANELLO seeks to drive a new revolution in inertial sensing with optical gyros using silicon photonics, which will allow many more applications to experience the optical gyroscope’s exquisite performance.