A group of researchers from Lumenisity — department The University of Southampton’s Optoelectronics Research Center, with the support of Microsoft, has created a cable with a hollow core.
According to the developers at Lumenisity, their cable provides the lowest level of signal delay, ever recorded in fiber optics. According to the researchers, they managed to achieve 0.091 dB/km at 1550 nm, using double-nested anti-resonant node-free fiber (DNANF).
This figure is lower, than the minimum — 0.14 dB/km, typical for advanced modern quartz fibers. There has been no significant improvement in this indicator since the 1980s. The researchers emphasize, that this is one of the most important improvements in waveguide technology over the past 40 years.
Traditional single-mode fiber directs light through the glass, slowing the signals to about 200 million m/s. This is two-thirds of the potential speed of these signals in a vacuum. Meanwhile, hollow-core fibers direct light primarily through the air, which reduces the delay by about half and minimizes nonlinear effects.
However, there is a significant drawback. Such hollow-core structures lose energy at a rate exceeding 1 dB/km. This limits their use to short specialized communication lines.
The design, proposed by Lumenisity developers, DNANF overcomes these limitations, by using concentric glass tubes only a few microns thick. They act like tiny mirrors, reflecting light back into the air core and suppressing higher-order modes.
Testing of two-nested antiresonant knotless fiber on 15 km long coils using several measurement methods confirmed, that attenuation is less than 0.1 dB/km. It is also important, that the loss remained below 0.2 dB/km in the 66 THz spectral range. This range is much wider, than the narrow telecommunications “windows”, that work best with silicon.
The developers also noted, that chromatic dispersion — the propagation of different wavelengths at different speeds in the same medium, was 7 times lower, than in older versions of fiber optics. This makes it possible to simplify the design transceiver and reduce energy consumption by network equipment.
Microsoft acquired Lumenisity in 2022, aiming to bring the technology DNANF from the laboratory to the level of commercial use. At that time, the optical fiber, created by the researchers, achieved a signal loss of about 2.5 dB/km, which was incomparable to the traditional minimum of 0.14 dB/km for glass fiber.
According to the results of the pilot project, which was conducted in parallel with the research of Lumenisity scientists, Microsoft said, that about 1,200 km of the new fiber successfully transmitted real traffic. In 2024, at the Microsoft Ignite conference, CEO Satya Nadella said, that the company plans to deploy 15 thousand kilometers of fiber optics in the Azure network over the next two years to support AI connectivity.
According to one of the developers Francesco Poletti, the low level of signal loss, will allow operators to eliminate one of the two or three amplifier sites and thus significantly reduce capital and operating costs. Scaling up production will require new equipment, and standards have not yet been developed. But for the first time, fiber, that transmits light through the air is faster and has lower losses, than the glass it is trying to replace.
Information about the development was published in the journal Nature Photonics
Source: Tom’sHardware
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