SF Technotes

A Revolutionary Fiber-Optic Cable

By Michael Castelluccio
September 21, 2021
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Thomas Edison took more than 6,000 tries to come up with a suitable filament that would both glow and not quickly disintegrate inside his first light bulb.

 

He tried everything from platinum to human hair, as well as scores of different plant fibers. The filament he finally selected to be the first to go into mass production was made of fine strips of carbonized bamboo. That was in 1880. The modern tungsten filament didn’t follow until more than two decades later in 1904.

 

For some perspective on the long journey contemporary physics has taken in its effort to pipe not only light into our homes, but also sound, images, and data using filament structures, consider the current optical fiber that we now have in the ground, strung between telephone lines, and even within lighting systems for our homes.

 

Remarkable advancements of fiber technology today include the thin cables that can be introduced into a lung to light a pulmonary examination to the larger versions of those same glass bundles that are fed down into multistory buildings to deliver natural light to spaces within the building’s interior. Glass cabling that carries pulsing light loaded with telecommunication and network information covers the planet and lies beneath the oceans. The filaments in these can be thinner than a human hair, yet they accommodate near-light-speed transfers because they transmit light through clear glass or plastic.

 

GLASS VS. TWISTED COPPER

 

We’ve had fiber-optic cable since 1952 when the U.K.-based physicist Narinder Singh Kapany invented the first working prototypes. The many advantages of optical fiber begin with the fact that the cables aren’t metallic and that they carry signals that move as pulses of light. They aren’t affected by electrical noise around them, such as EMI (electromagnetic interference) or RFI (radio frequency interference), as copper can be. That noise can slow transmissions as data can be corrupted by it.

 

Fiber-optic cables can’t generate sparks, and that can be a critical advantage in explosive industrial environments. And attenuation loss (loss of power) is lower in optical fiber, and it rarely needs amplification, in contrast to copper cables.

 

Encased in glass, the hollow-core Lumenisity’s fiber is filled with air. Image courtesy: BT/Lumenisity

HOLLOW-CORE FIBER CABLE

 

A new high-performance hollow-core fiber-optic cable is currently being tested by British Telecommunications (BT) for its global communications services and solutions. The company told ZDNet’s Daphné Leprince-Ringuet that “hollow core fiber enables data to travel up to 50% faster than in traditional optical cables.” BT’s press release explains, “Hollow core fibre doesn’t have internal material—it’s filled with only air—so there is less light scattering and less crosstalk between channels, even at a single photon level.” Photons traveling through air are one step closer to the ideal medium of a vacuum, through which the flows can almost reach the actual speed of light.

 

After three months of recent hollow-core trials, BT recorded improved transmission of data due to “wonderful properties like low latency [time delay] and low scattering [diffusion of the light beam].” In its tests, BT used six-kilometer-long fiber created and manufactured by Lumenisity Limited, a company that developed out of research projects at Southampton University.

 

But an even more surprising result was published by BT in the second week of September 2021. The company revealed the results of its test transmission of quantum key distribution (QKD) information over hollow-core fiber cable. QKD is seen as a game-changing development for cryptography that will enable a post-quantum cryptography that’s safe from cryptanalytic attack by a quantum computer.

 

A current method for testing QKD involves sending the qubits that have the cryptographic key and the encrypted message over fiber-optic cables. Leprince-Ringuet explains the problems that arise using conventional optical fiber: “When using traditional optical fiber, which is made of glass, the effectiveness of the protocol is limited. This is because the light signals that carry information are likely to spread their wavelengths when travelling through glass, an effect called ‘crosstalk’ that causes channels of light to leak into other channels.” The result is that the qubits carrying the key can’t be sent along over the same cable with the encrypted message. BT draws the analogy of trying to have a whispered conversation next to a playing orchestra.

 

But if you have an air-filled channel that inhibits scattering and limits crosstalk, Leprince-Ringuet explains, “there can be a clear separation between the encrypted data stream and the faint quantum signal that carries the encryption key—even if they are both travelling over the same fiber.” This elevates hollow-core optical fiber as a potential “all-in-one” QKD solution.

 

From glowing room lights to glowing monitors, advances in filament materials have fired revolutions from the first extended days of clean interior lighting in Edison’s time to possibilities that now might hasten a quantum internet. And all of this has happened in, historically, a relatively short period of time.



Michael Castelluccio has been the technology editor for Strategic Finance for 26 years. His SF TechNotes blog is in its 23rd year. You can contact Mike at mcastelluccio@imanet.org.


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