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Photons can travel from the other side of the universe and can reach us because they do not interfere among themselves. We exploit this characteristics in optical fibres, using photons to transport data.
Light is also very good to transport data because its frequency is really high (physicists talks in terms of wavelength when dealing with light and frequency when dealing with radio waves, although they are both electromagnetic waves that can be defined both in terms of wavelength and frequency). Red light has a frequency around 430 trillion Hz, violet light goes up to 750 trillion Hz. Compare this with the frequency we use in radio transmission, in the range of GHz (even in the highest frequencies now considered for 5G we stay below the 100GHz). This means that the light frequency is over 10,000 times higher than the radio frequency we use (closer to 100,000 times higher) and this means that we can pack 10,000 times more data.
Additionally, since they don’t interfere they use very little power (and dissipate very little heat.
All these wonderful characteristics makes it very difficult to use photons also for computation, since in computation you need to interact quickly and effectively to get a result. That is why the light flowing into an optical fibre has to be converted into electrons for computation.
Optical computers would be faster, use much less power. A pity we can’t build them.
Well, researchers are working to turn the seemingly impossible into something that is feasible. In a paper with the cryptic title “Giant nonlinear response at a plasmonic nanofocus drives efficient four ways mixing ” researchers at the Imperial College in London describe a way to make photon interact at a micrometer scale (that means that interaction takes place in the range of a trillionth of a second compare this with the switching time of a transistor that is roughly one thousand times slower!) by forcing photons to squeeze into a cavity some 25nm wide and having them interacting in a micrometer space using plasmonic effects.
We are still far from developing an optical computer, but at least a path to explore has been found.
