Recently, DARPA (Advanced Research Projects Agency of the US Department of Defense) has successfully developed a new type of hollow photonic bandgap fiber, which can transmit light along this material at a speed of 99.7% (or 30% higher than traditional quartz glass fibers). In almost all fiber optic networks, light is transmitted through plastic or glass fibers, and this type of fiber developed using DARPA allows light to pass through the air gap, greatly increasing network speed, bandwidth, and reaching further distances.

The secret of hollow fiber lies in eliminating the cladding and replacing it with photonic crystals. When light passes through the hollow and reaches the edge, the photonic crystal will bounce back photons. After phasing out plastic/glass materials, these hollow fibers can reduce signal loss (extending the distance between repeaters), while increasing the speed of light (about 30% faster than plastic/glass) can also help reduce latency. According to DARPA, these individually separated (single spatial mode) fibers can increase bandwidth and ensure that the polarization characteristics of light are completely unaffected (which is crucial for applications such as sensing and secure communication).

We have no information about the details of how DARPA developed hollow optical fibers, possibly because this is a military project and DARPA is not yet ready to disclose the relevant details. This is very similar to how the University of Southampton in the UK produced hollow optical fibers in March.

DARPA was not the first institution in the United States to develop hollow optical fibers, but it was the first to meet military application standards. You may think that these optical fibers are clearly used for data centers and internet backbone networks, but this technology was actually developed as part of DARPA's Compact Ultra Stable Absolute Reference Gyroscope (COUGAR) project. COUGAR aims to develop a highly accurate gyroscope that can be used for navigation when GPS is ineffective (such as in theater or indoors). After eliminating the complexity of circular laser gyroscopes, simply put, the new type of hollow photonic bandgap fibers should be able to be used to manufacture extremely accurate fiber gyroscopes.

Overall, the United States now has the ability to produce military hollow fiber, but like the Internet that originated from ARPAnet, hollow fiber should ultimately be able to thrive in commercial environments.