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Power over Fiber

Definition: delivery of power for electronic devices via light in an optical fiber

German: Leistungsübertragung über Glasfasern

Category: fiber optics and waveguides

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Optical fiber cables can be used for transmitting optical power from a source to some application. The term power over fiber or photonic power implies that the optical power is generated from electric power with a laser diode and at the end converted back to electrical power for some electronic device. That conversion can be done with a photovoltaic cell, i.e., a semiconductor device based on a material such as gallium arsenide, indium phosphide, or indium gallium arsenide. A typical system contains a laser diode emitting a few watts of optical power, a multimode fiber of a few hundred meters length, and a photovoltaic cell with an active area of several square millimeters.

Although an insulated copper wire is a simpler technology for transferring electric power, power over fiber offers advantages in specific situations:

  • Non-conducting fiber cables (based on glass fibers or plastic fibers) can be installed where high electric voltages exists. For example, a fiber can transmit power for a current transducer in a high-voltage transmission line. Such current sensors with an optical power isolator can replace bulky transformer systems.
  • The insulating property is also useful when a device (e.g. some radio signal receiver) is connected to an antenna, which could be hit by lightning. There is then no risk that the lightning is transmitted via the cable.
  • Optical delivery of power avoids any sensitivity to strong magnetic fields (e.g. in magnetic resonance imaging) and to electromagnetic interference. Conversely, no electromagnetic radiation can be emitted, which might disturb other devices.
  • There is no risk that explosive materials (e.g. in a fuel tank of an airplane) can be ignited, as could occur e.g. via an electric spark.
  • In a system for optical fiber communications, there may be spare fibers which can be used for transmitting power when an electrical connection does not exist.
  • A fiber can have a far lower weight than an electrical cable, and may tolerate higher temperatures.
  • The same fiber may be used to send back data e.g. from a sensor, using some other wavelength channel.

Therefore, a number of applications can be envisaged in areas such as industrial sensors, aerospace, and optical communications.

Obvious disadvantages are the cost of optical components and the limited potential in terms of available power and conversion efficiency. There may also be a laser safety issue associated with several watts of optical power, which can leave the fiber when it is broken.

Choice of Wavelength and Power Efficiency

For short-range transmission, laser diodes emitting around 750–850 nm can be used in combination with GaAs-based photovoltaic cells. The power efficiency of a photovoltaic cell can easily be around 40–50%, i.e. significantly higher than for a normal solar cell, because the photon energy of the light is well matched to the band gap energy of the photovoltaic cell. The electrical-to-electrical efficiency can then be of the order of 20–30% for systems with a short fiber.

Optical losses in the fiber, mostly due to scattering, limit the transmission distance and power efficiency of the system. Longer transmission distances (possibly several kilometers) can be realized with systems operating at longer optical wavelengths, because this drastically reduces Rayleigh scattering.

Suppliers

The RP Photonics Buyer's Guide contains 3 suppliers for power over fiber systems.

Questions and Comments from Users

2021-02-04

Can a single-mode fiber withstand 1 W from a semiconductor laser, or are there limitation on the fiber? For example, would it have to be made out of quartz instead of silica?

Answer from the author:

Yes, a single-mode fiber can carry that power in the infrared region which is usually used for such purposes. You could also easily use a multimode fiber.

Note that quartz is a crystalline material, from which one can hardly make flexible fibers. But maybe you mean “fused quartz”, a term sometimes used for amorphous material. That would be the same as fused silica.

2021-02-14

What kind of optical fiber is best suited for PoF – single-mode or multimode?

How can you transmit data and power using the same cable?

What software can simulate PoF?

Answer from the author:

Generally, it will depend on the used laser source which kind of fiber is most suitable. It is a (spatially) single-mode laser, you may well work with single-mode fiber, otherwise with multimode fiber.

Yes, you could at the same time transmit data, e.g. on a separate optical wavelength. But that is probably unusual.

Concerning simulations, I am not sure what aspect you would like to simulate. If it is just light propagation in the fiber, various software tools are available, including our RP Fiber Power.

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See also: fibers, fiber cables, laser diodes, fiber optics
and other articles in the category fiber optics and waveguides

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