* Single-spatial-mode: light can take only a single path, enabling higher bandwidth over longer distances;
* Low-loss: light maintains intensity over longer distances;
* Polarization control: the orientation of the light waves is fixed in the fiber, which is necessary for applications such as sensing, interferometry and secure communications.
Hollow-core fiber can also be bent and coiled while guiding light at speeds 30 percent faster than conventional fiber. The hollow fiber also will enable higher intensity optical beams.
The real breakthrough with COUGAR (Compact Ultra-Stable Gyro for Absolute Reference) fiber is that it can achieve a single-spatial-mode, maintain polarization and provide low loss, all while keeping more than 99 percent of the optical beam in the air.
The intensity of light that propagates through glass optical fiber is fundamentally limited by the glass itself. A novel fiber design using a hollow, air-filled core removes this limitation and dramatically improves performance by forcing light to travel through channels of air, instead of the glass around it. DARPA’s unique spider-web-like, hollow-core fiber, design is the first to demonstrate single-spatial-mode, low-loss and polarization control—key properties needed for advanced military applications such as high-precision fiber optic gyroscopes for inertial navigation.
“While we are still working on integrating this new technology into a gyroscope, the fiber itself is revolutionary,” added Conway. “This type of technology may also lend itself to other types of high-power sensors and additional applications where intense optical beams are required. Hollow-core fiber is also naturally radiation hardened, so it may open up fiber applications to space systems.”
Speeds of light
Speed of light in a vacuum is -: 2.99 x 10^8 ms^-1
Speed of light in air = 2.99 x 10^8 / 1.003 = 2.981 x 10^8 ms^-1 [0.3% slower than light in a vacuum]
Speed of light in water = 2.99 x 10^8 / 1.333 = 2.2431 x 10^8 ms^-1 [similar to speed in glass. 30% slower]