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So I have heard that using photons to compute is faster than electrons. I was wondering why exactly that is? Is it because light travels through a waveguide faster than electricity through a wire?

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    $\begingroup$ Are you more concerned with propagation or computation? Your title and text are slightly different from one another. $\endgroup$
    – garyp
    May 11 '17 at 16:13
  • $\begingroup$ Specifically just the time for propagation. I already know computing is faster because optical transistors can make switches faster than regular transistors $\endgroup$
    – Tyler
    May 11 '17 at 20:30
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Whether light travels faster in a waveguide or an electrical signal on a wire depends entirely on the dielectric materials of the waveguide and in the space around the wire, as well as on the exact geometry of the waveguide and the wire relative to the return path for signals travelling on it.

A typical optical waveguide is made of glass with an index of refraction of about 1.5, so optical signals will travel along it at about 66% of c.

Some common electrical waveguides (coaxial cable) can be made to have propagation velocities in the range of 80 - 90% of c.

The propagation velocity on a wire in an IC will be slower because semiconductors typically have much higher index of refraction than teflon; but the same applies to an optical signal traveling in a waveguide made of a semiconductor material.

The people who hoped to achieve faster computation using optical computing mostly hoped to do that with certain tricks like using optics to "calculate" a Fourier transform physically. This is essentially a form of analog computing, though, which has limitations of its own. So far, optical computing has not had much (any?) commercial success.

A further limitation of optical computing elements is that the smallest structure that can contain a photon is roughly the same size as the wavelength of that photon. For photons with low enough energy not to be strongly absorbed by typical semiconductor materials, this is on the order of 1 $\mu{\rm m}$, nearly a hundred times larger than state of the art transistors used for electrical computing.

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Yes, a photon traveling inside a waveguide is a lot faster than an electron inside a wire. A photon propagates in the transverse direction to the dimension of the waveguide. Electrons face resistance inside of a wire. This resistance causes Joule heating effect to take place. This decreases the rate of transmission of energy. But in the case of photons and waveguides, there is very slight energy loss due to penetration of electromagnetic wave in the conducting walls (remember skin depth!). This makes the waveguide mechanism to be superior to the wire and electron mode of data transmission.

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    $\begingroup$ How fast an electron moves inside a wire is irrelevant to how fast an electrical signal can propagate along a wire. $\endgroup$
    – The Photon
    May 12 '17 at 5:58
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Light travels faster than electricity because photons has no mass, but electrons do

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    $\begingroup$ Unless you are just thinking of a wire with a DC voltage, then the thing carrying information that is propagating is an EM field just like light. $\endgroup$ May 11 '17 at 16:14
  • $\begingroup$ I thought that electricity and light both traveled at the speed of light? $\endgroup$
    – Tyler
    May 11 '17 at 20:31

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