I am attending an introductory course of optics and photonics and we just started to study optical fibers for digital communications. However, I have started wondering about using optical fibers to transmit energy. I have done some research on the internet and I have found some insights on power-over-fiber technologies but there isn't really a lot of material, so here I am.

Is power-over-fiber a technology which in the future can be develop in order to compete with electrical power transfer or there are physical limits?

As far as I know we have an efficent device to convert electrical to optical power, namely the laser. Optical fibers can transmit power with an attenuation as low as 0.18 dB/Km which seem pretty good to me. Maybe the problem can be the efficency of photodiodes at the end of the line?

P.S. I'm in the final year of my bachelor degree course in Engineering Physics and I'm trying to understand which technologies are likely to be developed in the future in order to invest my time studying something promising.

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    $\begingroup$ The conversion from electrical to optical is not near 100%, and the conversion back to electrical is also not near 100%. Power-over-fiber makes sense in some specific cases. As a large scale distribution network, I'll stick with efficient, easy-to-use wiring, not finicky optical fiber. $\endgroup$ – Jon Custer Nov 8 '16 at 17:21
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    $\begingroup$ Cost is usually a significant factor too, not just efficiency. $\endgroup$ – Real Nov 8 '16 at 17:22
  • $\begingroup$ Have you asked your course lecturer this question? What was his/her answer? What other research have you done to find an answer? $\endgroup$ – sammy gerbil Nov 8 '16 at 17:26
  • $\begingroup$ @sammygerbil Not yet, I asked this on SE before because I try to avoid silly questions with people who will give me a mark. $\endgroup$ – skdys Nov 8 '16 at 17:31
  • $\begingroup$ Why do you think the question is silly? Isn't it possible that asking a question could gain marks? $\endgroup$ – sammy gerbil Nov 8 '16 at 17:36

There are several practical limits to power-over-fiber.

The first is absorption: even the best fibers have some limited absorption, so at high power levels they will get hot.

The next is power conversion: even after you have transmitted power over the cable, turning it into something useful (electricity) will incur a significant loss of efficiency.

Finally, there is spontaneous Brillouin scattering (SBS): at sufficiently high power densities, optical media become nonlinear and this will lead to spontaneous conversion of some of the optical power to phonons. Quoting from the RP photonics encyclopedia:

SBS introduces the most stringent power limit for the amplification and the passive propagation of narrow-band optical signals in fibers.

That same link explains the mechanism in more depth. SBS puts an upper limit on the power you can send through a fiber, regardless of the losses you can tolerate.

  • $\begingroup$ Of course, its not like one can send an arbitrary amount of power over a copper wire either... It might be an interesting back-of-the-envelope calculation to determine how much power Netflix distributes every day in the US... $\endgroup$ – Jon Custer Nov 8 '16 at 17:54

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