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If photons and electrons travel at the same speed am I right in thinking that the benefits of optical computing would be limited to parallel processing?

by mentos 11y ago

programmer_dude 11y ago
>If photons and electrons travel at the same speed "If" - they do not! https://en.wikipedia.org/wiki/Electron_mobility https://en.wikipedia.org/wiki/Electron_mobility Quoting from the above source... >Typical electron mobility for Si at room temperature (300 K) is 1400 cm2/ (V·s) and the hole mobility is around 450 cm2/ (V·s).[2] However this is besides the point since electric fields in a conductor do move at the speed of light.
pronoiac 11y ago
The article refers to lower power requirements. One of the problems of higher clock rates is heat dissipation; if this runs a lot cooler, then it might be able to clock much higher.
dogma1138 11y ago
Electrons have mass they can't move at the speed of light. Photons also have other nice properties such as wavelength which open a whole suit of possibilities e.g. like having a logic gate which can operate in different mods based on the wavelength and polarization of the light. While this is technically possible with electronics as well by setting a different voltage limit it's much more effective with photonic computing and doesn't not increase the complexity of your base components as much. The current designs for a photonic computer are also much more parallel most of them basically layers of LED's and detectors with a very fast LCD matrix which serves as a mask between them. if you have a 256x256 pixel screen you can perform an operation on 65536 bits in a single clock, if you stack them up you basically getting 1 order of magnitude with each layer this isn't something you could ever achieve with current solid state electronics.
- mentos 11y ago
  What fraction of the speed of light are electrons moving at in the most advanced silicon chip we have? Trying to understand how much speed is left on the table for us to pick up in serial processing?
  - dogma1138 11y ago
    It's not that easy to define because were talking about semi-conductors after all;) They don't move at a constant speed like say in a conductor (which isn't the case either because electric field causes resistance e.g. eddy currents, but lets say a super-conductor) You have quite a few concepts with semiconductors primarily saturation velocity (which in most cases is the peak velocity, but not necessarily attained in actual operation) which is also affected by the drift velocity due to any electric fields in your components. https://en.wikipedia.org/wiki/Saturation_velocity https://en.wikipedia.org/wiki/Saturation_velocity Light speed in vacuum is 29979245800 cm/s Saturation velocity in Si based SC is 10000000 cm/s So there's quite a bit of difference there ;)
    - mentos 11y ago
      So does this imply an opportunity to improve computing speed by 2997?
      - dogma1138 11y ago
        No because the speed of the components with the current designs is still limited by the switching speed of the masking matrix. And in any case you will still need to transform photons back to electrons twice. The speed of electrons or EM wave propagation vs photons isn't a player in why photonic computing might be better. The ability to encode more data into the photons, a much more power efficient and inherently parallel design are. Also because light has much more shorter wavelength than "electricity" electromagnetic waves in conductors (kilometers vs nano-meters) you can have a much higher throughput with light even if you use it to replace the carrier wires in electronics (which is what Intel is working on they want to keep electronic switching but make all carriers photonic). https://en.wikipedia.org/wiki/Speed_of_electricity https://en.wikipedia.org/wiki/Speed_of_electricity
Veratyr 11y ago
Might be worth reading up to understand how much the speed Electrons can move at matters: https://en.wikipedia.org/wiki/Speed_of_electricity https://en.wikipedia.org/wiki/Speed_of_electricity TL;DR: "The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic wave, not the movement of electrons. Electromagnetic wave propagation is fast and depends on the dielectric constant of the material. In a vacuum the wave travels at the speed of light and almost that fast in air."
- dogma1138 11y ago
  While that's true for simple conductive cables that's not the case for semi-conductors. https://en.wikipedia.org/wiki/Saturation_velocity https://en.wikipedia.org/wiki/Saturation_velocity Especially since there are some semi-conductors which actually require you to move electrons, like e.g. flash memory ;)

If photons and electrons travel at the same speed am I right in thinking that the benefits of optical computing would be limited to parallel processing?

by mentos 11y ago

If photons and electrons travel at the same speed am I right in thinking that the benefits of optical computing would be limited to parallel processing?

programmer_dude 11y ago

>If photons and electrons travel at the same speed "If" - they do not! https://en.wikipedia.org/wiki/Electron_mobility https://en.wikipedia.org/wiki/Electron_mobility Quoting from the above source... >Typical electron mobility for Si at room temperature (300 K) is 1400 cm2/ (V·s) and the hole mobility is around 450 cm2/ (V·s).[2] However this is besides the point since electric fields in a conductor do move at the speed of light.

pronoiac 11y ago

The article refers to lower power requirements. One of the problems of higher clock rates is heat dissipation; if this runs a lot cooler, then it might be able to clock much higher.

dogma1138 11y ago

Electrons have mass they can't move at the speed of light. Photons also have other nice properties such as wavelength which open a whole suit of possibilities e.g. like having a logic gate which can operate in different mods based on the wavelength and polarization of the light. While this is technically possible with electronics as well by setting a different voltage limit it's much more effective with photonic computing and doesn't not increase the complexity of your base components as much. The current designs for a photonic computer are also much more parallel most of them basically layers of LED's and detectors with a very fast LCD matrix which serves as a mask between them. if you have a 256x256 pixel screen you can perform an operation on 65536 bits in a single clock, if you stack them up you basically getting 1 order of magnitude with each layer this isn't something you could ever achieve with current solid state electronics.

mentos 11y ago
What fraction of the speed of light are electrons moving at in the most advanced silicon chip we have? Trying to understand how much speed is left on the table for us to pick up in serial processing?
- dogma1138 11y ago
  It's not that easy to define because were talking about semi-conductors after all;) They don't move at a constant speed like say in a conductor (which isn't the case either because electric field causes resistance e.g. eddy currents, but lets say a super-conductor) You have quite a few concepts with semiconductors primarily saturation velocity (which in most cases is the peak velocity, but not necessarily attained in actual operation) which is also affected by the drift velocity due to any electric fields in your components. https://en.wikipedia.org/wiki/Saturation_velocity https://en.wikipedia.org/wiki/Saturation_velocity Light speed in vacuum is 29979245800 cm/s Saturation velocity in Si based SC is 10000000 cm/s So there's quite a bit of difference there ;)
  - mentos 11y ago
    So does this imply an opportunity to improve computing speed by 2997?
    - dogma1138 11y ago
      No because the speed of the components with the current designs is still limited by the switching speed of the masking matrix. And in any case you will still need to transform photons back to electrons twice. The speed of electrons or EM wave propagation vs photons isn't a player in why photonic computing might be better. The ability to encode more data into the photons, a much more power efficient and inherently parallel design are. Also because light has much more shorter wavelength than "electricity" electromagnetic waves in conductors (kilometers vs nano-meters) you can have a much higher throughput with light even if you use it to replace the carrier wires in electronics (which is what Intel is working on they want to keep electronic switching but make all carriers photonic). https://en.wikipedia.org/wiki/Speed_of_electricity https://en.wikipedia.org/wiki/Speed_of_electricity

Veratyr 11y ago

Might be worth reading up to understand how much the speed Electrons can move at matters: https://en.wikipedia.org/wiki/Speed_of_electricity https://en.wikipedia.org/wiki/Speed_of_electricity TL;DR: "The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic wave, not the movement of electrons. Electromagnetic wave propagation is fast and depends on the dielectric constant of the material. In a vacuum the wave travels at the speed of light and almost that fast in air."

dogma1138 11y ago
While that's true for simple conductive cables that's not the case for semi-conductors. https://en.wikipedia.org/wiki/Saturation_velocity https://en.wikipedia.org/wiki/Saturation_velocity Especially since there are some semi-conductors which actually require you to move electrons, like e.g. flash memory ;)