Through DARPA's Compact Ultra-Stable Gyro for Absolute Reference (COUGAR) program, hollow-core fiber technology design and production is now in the United States.
Using a hollow, air-filled core dramatically improves light's performance by forcing it to travel through channels of air -- and DARPA’s unique spider-web-like, hollow-core fiber design demonstrates single-spatial-mode, low-loss and polarization control.
Single-spatial-mode means that light can take only a single path, enabling higher bandwidth over longer distances; low-loss means that light maintains intensity over longer distances; and polarization control means that the orientation of the light waves is fixed in the fiber, which is necessary for applications such as sensing, interferometry and secure communications.
These properties, according to DARPA, are key in advanced military applications such as high-precision fiber optic gyroscopes for inertial navigation.