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I'm not super well versed on this topic. But the basic physics of photon and electron make light a poor source for computing compared to electricity. Photons

by ww520 5y ago

I'm not super well versed on this topic. But the basic physics of photon and electron make light a poor source for computing compared to electricity. Photons don't interact with each other much when crossed, while electrons interfere each other greatly. It's really difficult to build logic gates out of photons while electrons work great with semiconducting materials to build gates. Light is good for communication due to its non-interfering nature to pump up the bandwidth. There's a saying light is great for data transmission while electricity is great for computing. So when people claim making supercomputer out of optical computing, take it with a grain of salt.

aidenn0 5y ago
Photons may not interact with themselves much, but they interact with other materials in significant and useful ways, and there are plenty of materials that change their optical properties in response to an electric field (which can be either electronic or optical in origin, given that light, particularly coherent light can have fairly strong electric fields). There are millions of things that an electronic digital computer can do that are unlikely to be replaced by photonics, but a hybrid approach may offer advantages in computing specific things. As we have slowed down getting perf/watt advantages from shrinking processes, more and more specialized hardware has been used for performing calculations. It's not that far-fetched to think that photonics might have a niche where it has performance advantages.
- ww520 5y ago
  You're right that photons interact with many materials. However, few exhibit semiconducting properties that's useful for building logic gates. Silicon has a kind of perfect energy band gap for its valence band electrons jumping to conducting band free elections to allow electricity flow. The gap is not too small to introduce ambiguity or too big to require too much energy to move from non-conductive to conductive state. Photonics needs to find a semiconducting material/alloy that beats silicon to be a viable option. Most research in building logic gate with light is a combination of light and electricity. The most promising recently is using Josephson junction in a superconducting electric current loop. A photon hitting the loop adds energy to the superconducting current. With enough energy the current becomes critical current, which moves the Josephson junction from 0 voltage to a voltage. The raised voltage gives off the energy and the current falls back to non-critical. Continuous photons hitting the loop causes the Josephson junction to have an extremely high frequency AC voltage. That's a photon controlled gate. But the research is still really early and it requires low temperature superconductivity. It's still a long way to be competitive in reality.
  - aidenn0 5y ago
    I think we are both in agreement that photonics will not replace silicon for logic gates (at least with current technology). However both what I was talking and in the specific example from TFA photonics are being used for analogue computing which does not necessarily require logic gates. The simplest example would be AM modulating a laser with a signal and passing the result through a prism. This calculates a Fourier transform on the signal. This is not a great example because, for most domains, the output is too noisy to be of great use and ADCs/DSPs can do this fairly efficiently already. I believe the computer mentioned in TFA involves matrix projections.
krasin 5y ago
As other commenter said, the magic happens not just between photons, but between photons and non-linear optical materials, in which these photons travel. While not directly related to computing, I was fascinated to learn that lasers routinely use crystals to cut wavelength of the light by half ([1], [2]). 1. https://en.wikipedia.org/wiki/Second-harmonic_generation https://en.wikipedia.org/wiki/Second-harmonic_generation 2. https://en.wikipedia.org/wiki/Potassium_dideuterium_phosphate https://en.wikipedia.org/wiki/Potassium_dideuterium_phosphat...
- ww520 5y ago
  That's true but so far none of those materials found, to be competitive with electricity+silicon.

by ww520 5y ago

aidenn0 5y ago

Photons may not interact with themselves much, but they interact with other materials in significant and useful ways, and there are plenty of materials that change their optical properties in response to an electric field (which can be either electronic or optical in origin, given that light, particularly coherent light can have fairly strong electric fields). There are millions of things that an electronic digital computer can do that are unlikely to be replaced by photonics, but a hybrid approach may offer advantages in computing specific things. As we have slowed down getting perf/watt advantages from shrinking processes, more and more specialized hardware has been used for performing calculations. It's not that far-fetched to think that photonics might have a niche where it has performance advantages.

ww520 5y ago
You're right that photons interact with many materials. However, few exhibit semiconducting properties that's useful for building logic gates. Silicon has a kind of perfect energy band gap for its valence band electrons jumping to conducting band free elections to allow electricity flow. The gap is not too small to introduce ambiguity or too big to require too much energy to move from non-conductive to conductive state. Photonics needs to find a semiconducting material/alloy that beats silicon to be a viable option. Most research in building logic gate with light is a combination of light and electricity. The most promising recently is using Josephson junction in a superconducting electric current loop. A photon hitting the loop adds energy to the superconducting current. With enough energy the current becomes critical current, which moves the Josephson junction from 0 voltage to a voltage. The raised voltage gives off the energy and the current falls back to non-critical. Continuous photons hitting the loop causes the Josephson junction to have an extremely high frequency AC voltage. That's a photon controlled gate. But the research is still really early and it requires low temperature superconductivity. It's still a long way to be competitive in reality.
- aidenn0 5y ago
  I think we are both in agreement that photonics will not replace silicon for logic gates (at least with current technology). However both what I was talking and in the specific example from TFA photonics are being used for analogue computing which does not necessarily require logic gates. The simplest example would be AM modulating a laser with a signal and passing the result through a prism. This calculates a Fourier transform on the signal. This is not a great example because, for most domains, the output is too noisy to be of great use and ADCs/DSPs can do this fairly efficiently already. I believe the computer mentioned in TFA involves matrix projections.

krasin 5y ago

As other commenter said, the magic happens not just between photons, but between photons and non-linear optical materials, in which these photons travel. While not directly related to computing, I was fascinated to learn that lasers routinely use crystals to cut wavelength of the light by half ([1], [2]). 1. https://en.wikipedia.org/wiki/Second-harmonic_generation https://en.wikipedia.org/wiki/Second-harmonic_generation 2. https://en.wikipedia.org/wiki/Potassium_dideuterium_phosphate https://en.wikipedia.org/wiki/Potassium_dideuterium_phosphat...

ww520 5y ago
That's true but so far none of those materials found, to be competitive with electricity+silicon.