Hollow-core Fibers Improve Stability of Light-Based Gyroscopes

Researchers at the University of Southampton’s Optoelectronics Research Centre, collaborating with researchers from Honeywell, have applied nodeless antiresonant fibers (NANFs) — a distinct class of hollow-core optical fiber with low attenuation — to improve the stability of resonator fiber optic gyroscopes. By confining light in a central void of the hollow-core fiber, filled with air or gas, the fibers eliminated many of the nonlinear effects that negatively influence the performance of sensor devices such as resonator fiber optic gyroscopes.

When paired with NANFs, the light-based gyroscopes, which boast applications in civil aviation, autonomous vehicle transportation, and other forms of navigation, demonstrated a long-term bias stability of 0.05 degrees per hour — a value that is close to levels required for civil aircraft aviation, the researchers said.

A device’s bias stability is defined as performance under stable rotation conditions, such as in the presence of Earth’s rotation only.

Resonator fiber optic gyroscopes use the pulses from two lasers traveling at opposite directions through a coil of optical core fiber. The ends of the fiber are connected, forming an optical resonator, to allow the majority of the produced light to recirculate around the coil. When the coil is rotating, as opposed to at rest, the shift in resonance frequencies relative to one another are different and can be measured to calculate the direction of movement or positioning for a device on which the gyroscope may be attached.

In tests that revealed the NANFs-incorporated gyroscope’s long-term bias stability, the researchers mounted the device on a stable, static pier.

Resonator fiber optic gyroscopes require ultrafine laser linewidths, though, and identifying an optical fiber capable of withstanding even modest required laser power levels without causing performance-degrading nonlinear effects has posed a challenge for scientists and engineers.

Researchers have incorporated a new type of hollow-core optical fiber known as a nodeless antiresonant fiber to boost the performance of resonator fiber optic gyroscopes. These gyroscopes could one day form the basis of navigation technologies that are more compact and more accurate than today’s systems. Courtesy of Gregory T. Jasion, Optoelectronics Research Centre, University of Southampton.

NANFs exhibit even lower levels of nonlinear effects than other hollow-core fibers and, due to their corresponding low level of optical attenuation, allow light to maintain intensity over extended lengths of propagation through the fiber.

In applications involving resonator fiber optic gyroscopes, in which light must travel in only a single path through the fiber, NANFs provide another essential benefit: They eliminate backscattering, polarization coupling, and modal impurities. Each can cause noise that contributes to optical errors in fiber technology performance.

“Although the backbone of this sensor is the new type of optical fiber, we also worked to greatly reduce noise when sensing the resonance frequency with unprecedented accuracy,” said Glen A. Sanders, who led the research team from Honeywell International. “This was crucial for enhancing the performance and moving toward miniaturizing the sensor.”

Sanders said Honeywell proposed using a hollow-core fiber for resonator fiber optic gyroscopes in 2006.

The researchers are now attempting to develop a prototype gyroscope featuring a more compact and stable configuration. They also plan to use the latest generation of NANFs; the fibers exhibit improved (decreased) optical loss as well as improved modal and polarization purity.

The research was published in Optics Letters (www.doi.org/10.1364/OL.410387).