A capacity crunch at the fiber optic level?

In the last EIF meeting on innovation, I had the pleasure of listening to a brief talk by Prof. Sergei K. Turitsyn who spoke of a capacity crunch for current fiber optic technology in the near future. Mostly, discussions of capacity crunch center around available spectrum. In contrast, this talk was about capacity crunch at the fiber optic level due to nonlinear properties of optical fiber

It has been while since I looked at fiber optic technology(since college) and the domain is not directly related to my PhD research, but the talk highlights an interesting scenario which I suspect needs to be discussed more.

Thus, since I am not an expert in this domain, I am using this blog to create a discussion on a topic which I suspect needs to be highlighted to policy makers. Sergei referred to a paper by David J Richardson and David was kind enough to send me a copy of this paper for this analysis.

The issue:

In October 2010 David J. Richardson, from the Optoelectronics Research Centre at the University of Southampton, published an article called “Filling the Light Pipe”. According to David’s analysis, we face a “possible capacity crunch” in 2020 for optic fiber technology. This indicates an urgent need for research and development into higher bandwidth fibre optic cables. David Richardson claims improvements must be made to the key physical properties of fibre cables and optical amplifiers, which are used to transmit data across long distances.

He made further comments when he spoke to BBC News (here) :

“The thought that the current fibre technology has infinite capacity is not true – we are beginning to hit the fundamental limits of the current technology”

“We need to be looking at the next big breakthrough to allow us to continue to scale as we have traditionally done.”

“It’s likely we’re going to have to go right back to the fundamentals of the optics, the actual light pipes. And if you want to develop the next generation of cable, you want to be doing that 10 years in advance, not for tomorrow.

Background

An optical fiber (or optical fibre) is a flexible, transparent fiber made of a pure glass (silica) not much wider than a human hair. It functions as a waveguide, or “light pipe”, to transmit light between the two ends of the fiber. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference.

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. While fiber optic communications have taken on a lot of usage, they are not new. In 1880 Alexander Graham Bell and his assistant Charles Sumner Tainter created a very early precursor to fiber-optic communications, the Photophone, at Bell’s newly established Volta Laboratory inWashington, D.C. Bell considered it his most important invention. The device allowed for the transmission of sound on a beam of light.

However, the promise of infinite capacity in Alexander graham bell’s time now appears to have hit a limit based on current and projected usage at a fiber optic level

In information theory, the Shannon–Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise.

Considering all possible multi-level and multi-phase encoding techniques, the Shannon–Hartley theorem states the channel capacity C, meaning the theoretical tightest upper bound on the information rate (excluding error correcting codes) of clean (or arbitrarily low bit error rate) data that can be sent with a given average signal power S through an analog communication channel subject to additive white Gaussian noise of power N, is:

where

C is the channel capacity in bits per second;

B is the bandwidth of the channel in hertz (passband bandwidth in case of a modulated signal);

S is the total received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e. modulated carrier), measured in watt or volt2;

N is the total noise or interference power over the bandwidth, measured in watt or volt2; and

S/N is the signal-to-noise ratio (SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the Gaussian noise interference expressed as a linear power ratio (not as logarithmicdecibels).

 

Now , based on David Richardson’s paper – Shannon’s law applies also to optic fiber communication because the data-carrying capacity of a single optical fiber is determined by the spectral bandwidth over which suitably low-loss signal transmission can be achieved.

Recent developments have led to an impressive demonstration of within a factor of ~2 of the nonlinear Shannon limit for the current fiber technology. Although these are still experimental (ie not commercially deployed), the results in experimental setting provide room to grow current usage for a few years. However, beyond that, the path is unknown because once the capacity of conventional single-mode fiber-based systems is exhausted, the only option will be to add additional parallel, which is expensive

Hence, the paper argues that further innovation/breakthroughs are needed and that since we are already stretching the limits of Shannon’s law, that need is urgent for the near term time frame.

Conclusions:

I am using this blog to articulate the problem and create some discussion. While not being an expert in this exact domain, based on the analysis above, I think a discussion is needed at a policy level.

Optic fiber image – wikipedia

A capacity crunch at the fiber optic level?