When you want to isolate communications between two devices or locations, a fiber optic link is one of the best ways to go. Under some circumstances, however, you might also want to isolate the transmission of power - in situations where traditional copper wire might prove unsafe or impractical, for instance. That's why researchers at Sandia National Laboratories are developing a power-over-fiber (PoF) communications cable. It carries not only data, but also optical power.

Invented by Sandia's Titus Appel and Steve Sanderson, PoF is currently limited to a fairly low capacity, so don't expect it to be delivering power to your house any time soon. It could, however, supply power to small electrical devices such as sensors, for which it would also be providing data transfer.

In the cable's present incarnation, optical power goes through a single glass fiber. A laser diode at one end of that fiber emits light, while a miniaturized photovoltaic cell at the other end converts it into electricity. Power is only delivered on demand, in order to save energy.

Data is carried by plastic optical fibers, connected to stacked circular circuit boards with LEDs, mounted in the backshell connector housings at either end of the cable. The next version of the PoF will use less-bulky glass fibers for both power and communications. It should also have the ability to provide power to outside devices, whereas the present prototype uses the optical power solely to run its own communications electronics.

So, where would such a cable find use? Appel and Sanderson believe it would be useful in applications relating to safety, such as security, explosives, explosion-proof devices, aviation and medical devices. "The key issue here is to maintain total electrical isolation from any stray electrical energy and high-voltage electrical surges caused by such things as lightning strikes," said Sanderson.

The team have already tested a PoF-based low-energy detonator firing cable, which carries data regarding detonator resistance, temperature and charging voltages, while also delivering power to the detonator. They are now working on reducing the size, weight and cost of the technology, and making it rugged enough to stand up to everyday use.