A confession: I love optical networks. For some reason, the idea of shining light down a thin hair of glass has held a fascination for me ever since I first read about it as a child. There’s a purity, beauty even, about the binary simplicity of a distant light appearing and disappearing that, as a way of communicating over long distances, has probably existed for as long as we’ve been on the planet.
Ultimately, as much optical in the network as possible is the long-term future of information sharing. This is because, when you get down to basic physics, photons travel at much higher speeds than electrons, since they are lighter and encounter less resistance when they move.
People often use analogies for what the optical speeds – such as 40 gigabits per second (Gbps) on one wavelength of light – mean in ‘real terms’.
A common one used in the past was how long it would take to download the entire contents of the library of congress. I actually have trouble picturing that, not only because I’ve not been to the library of congress, but that it seems to contain a tacit assumption that a library’s value lies solely in reproducing and transferring just text or images. But libraries are also about the medium; the physical documents, manuscripts, books, pamphlets and pictures they hold.
I think a better comparison is with content that we’re used to handling in digital form. Digital media. If you have a 32 Gigabyte digital audio player, you’ll know that filling it with content from scratch will take you a while. That is a lot of songs, movies and applications. If it were just high quality audio, you’re looking at 22 days 18 hours of sound. (using AAC at 128kbps where 1MB ≈ 1 minute of recording).
In terms of ‘bits’ 32GB of memory is equivalent to (32 x 8 x 1024 x 1024 x 1024 =) 274 877 906 944 bits. (Let’s say 275 billion). So using a single beam of light pulsing on and off 40 billion times per second (40Gbps), all that 22 days, 18 hours of continuous, high quality audio could be transferred in just under seven seconds (6.871 sec to be precise…). At these data transfer speeds, the problem is getting electronics – silicon – to keep up.
FYI: A bit more calculation can show that this beam of light is 1 339 102 kilometres long. (6.871 seconds x speed of light in optical fibre). So each second of originally recorded sound is spread along a beam of light 681 metres long, That works out at roughly 25 bytes per metre of light, or two bits every ‘beam’ centimetre.
Quite incredible compression.