Microsoft Backed Research Breaks The Optical Loss Barrier Using Hollow Core

For decades optical power loss of the best performing solid core fibre has hovered around .14dB per kilometer. So it comes as a surprise and a shock that the Microsoft owned hollow core fibre optic company, Lumensity, has designed a hollow core that beats all solid core glass in minimizing optical loss. The new hollow core design was tested using a 15 kilometer spool and the result was .091 dB loss at the standard long haul 1550 nanometer wavelength. Even more impressive was the fact that the optical loss remains under .1 from 1481 nanometers wavelength to 1625 nm. This range represents about 18 Terahertz of raw spectrum. But even that is not the end of the story. Light intensity loss remains under .2 dB all the way from 1250 nm to 1750 nm. In other words, it encompasses the O, E, S, C, L, and U bands. In contrast, attenuation varies with frequency for solid core silica fibre with a global minimum at 1550 nm. Loss is simply too high in the O, E, S, and U bands. This limits usable spectrum to the C + L bands.

Upshot Of This Hollow Core Breakthrough

1. Optical attenuation is low enough to use the O, E, S, C, L, and U bands for long haul optical networks versus just the C and L bands. These latter two bands represent about 10 THz of usable spectrum versus 66 THz for the new hollow core fibre. So the new technology enables a quantum leap in available bandwidth.

2. Hollow core does not suffer from nonlinearities such as chromatic distortions. This eliminates the need for expensive digital signal processing and lowers equipment costs.

3. The lower light loss in hollow core glass doubles the optical amplifier spacing and halved the number required for any long haul span.

4. Signal latency was 41% lower than standard G.652d solid core glass.

Magic Behind The Performance

The hollow core design uses a serious of glass rings in the hollow core to prevent optical loss. Why is this necessary? In solid core fibre light bounces off the cladding because the refractive index of the core fibre is greater than the cladding. But the refractive index of air is always less than the cladding's. So light will always escape. This very thin glass tubes confine the light

Caveats

1. It is far more challenging to manufacture hollow core fibre given the very thin walls of these glass tubes. Doubtless, the challenges will be overcome. But to do so in an economical way in order to produce a price competitive product means that large scale commercial deployments will probably just start around 2030.

2. The other problem is fragility. The absence of a solid core means that mechanical stress can be redistributed as efficiently. Hence the fibre is more fragile. This may be a big drawback at the installation stage. It certainly means the fibre optic technicians will need to be retrained to handle it.