"Father of Fiber Optics" Wins Nobel Prize

alphadogg writes "Charles Kao, whose work in the 1960s laid the foundation for today's long-distance fiber-optic networks, has won a share of this year's Nobel Prize in Physics (PDF). Kao, sometimes referred to as the 'father of fiber-optic communications,' was formally honored by the Nobel Foundation in Stockholm, Sweden 'for groundbreaking achievements concerning the transmission of light in fibers for optical communication.' Kao's breakthrough discovery in 1966 was to determine how to transmit light over long distances using ultrapure optical glass fibers. This would extend the distance of such transmissions to 62 miles vs. the mere 65 feet allowed under previous technology held back by impurities. The first ultrapure fiber was created in 1970."

Comments

No love for the inventors of the CCD?

[viking099]

These guys also got the Nobel prize this year for their work on the CCD. That's worth a mention too, I think!

Re:No love for the inventors of the CCD?

[IWannaBeAnAC]

Umm, the Nobel prizes are not all announced at the same time. The Medicine prize was announced yesterday. The Physics prize was announced today.

Re:62 miles in the 70's

[olsmeister]

The equipment I work with can do about 90 miles. Say 7 dBm transmit, -30 dBm receive. If you use around 0.25 dBm attenuation per kilometer at 1550 nanometers, that'll get you to around 150 km.

This is at 2.5 Gbps.

I don't know if that's a lot or not, but that's around where we max out.

Fiber optics took about 20 years to arrive

[Terje Mathisen]

I did my MSEE thesis in 1981, working on mono-mode optical fibers. This was still pretty cutting edge at the time, but the first semi-automatic splicing units had started to arrive.

The most fascinating feature of very pure optical fibers is that they have two minima not too far apart:

At around 1200 nm the frequency dispersion is very close to zero, which means that a single pulse traveling along the fiber will suffer minimum smearing, which maximizes the possible bandwidth.

At around 1500 nm the optical damping (i.e. sum of scattering & absorption) has a minimum, which means that by using this frequency you can maximize the distance between repeaters.

Anyway, it took about 20 years (i.e. around 2001) before mono-mode fibers become standard in all new installations here in Norway, it seems like this is the normal time to go from lab prototypes to SOP.

Terje

Re:Shares of the Nobel Prize

[Late Adopter]

The Nobel Prize in Physics has never been awarded to more than 3 people, and that was first done in its third year, in 1903, to Becquerel and the Curies.

Re:Why 62 miles?

[TheRaven64]

The quality of the cylinder. With a fibre-optic link, you have a tube of glass. You put a photon in one end, it travels along, and then it comes out the other end. If it is perfectly straight and you aim perfectly, then the photon travels straight through the glass. In this case, you could just use a laser and skip the whole glass thing. If you aim slightly off centre, or the path is curved, then the photon will hit the inside wall and, using the power of total internal reflection, bounce back. It may bounce quite a lot of times over the length. The next photon you send in may bounce a different number of times (because it went in at a very slightly different angle) and this is where the problems start. Both photons will be going at exactly the same speed, so if they have different paths with different distances, they will take different amounts of time to reach the far end. The longer the fibre, the greater this difference can be. This limits the transmission rate through the fibre, because you need to delay photons (or small groups of photons) sufficiently that you can tell the order in which they were sent. If you send one, then send the next one, and the second arrives before the first, then you have a problem. You could say this is to do with the speed of light: if it were infinite then this problem would not exist.

The other problem is that total internal reflection relies on the photons hitting the inside of the glass at quite a sharp angle. Impurities in the manufacturing can result in places where photons fail to reflect and just leak out (you can see this by shining a light in one end of a drum of fibre optic cables in the dark and watching the entire length glow slightly). If you are sending individual photons this is a big problem, but you're probably sending little bursts of them. When you do that, some proportion will be lost over each unit length of the fibre and after a certain distance insufficient will be left to be detectable at the far end.