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What if power could be delivered over optical fiber instead of copper wire, without fear of short circuits and sparks?


Electricity Over Glass By Anna Basanskaya
Running a live wire into a passenger jet's fuel tank seems like a bad idea on the face of it. Still, sensors that monitor the fuel tank have to run on electricity, so aircraft makers previously had little choice. But what if power could be delivered over optical fiber instead of copper wire, without fear of short circuits and sparks? In late May, the big laser and optics company JDS Uniphase Corp., in San Jose, Calif., bought a small Silicon Valley firm with the technology to do just that.

Photonic Power Systems Inc., in nearby Cupertino, has developed a system that uses a laser to inject power in the form of light into a fiber-optic cable and a photovoltaic (PV) array to convert the light back into electricity for powering devices. This method of transferring power can be highly advantageous in situations where sparks or shorts can be a fatal problem [see photo, "Fatal Short"], where electromagnetic interference is more than just an inconvenience—in cellphone base stations, for example, or in pacemakers—and where conventional methods are bulky and cumbersome.

Already, a Photonic Power device is replacing instrument transformers used in the power grid to measure high currents. But lacking the backing of a big company, aircraft makers and other potential customers have been hesitant to design power over optical fiber into their systems, says Jan-Gustav Werthen, the founder of the company and now the engineering director for the photonic power unit at JDS Uniphase. After all, power over fiber is still a relatively unfamiliar technology.

At the heart of the system is an array of PV cells on a 2-by-2- or 1-by-1-millimeter chip of gallium arsenide, indium phosphide, or indium-gallium arsenide, depending on the wavelength of the laser to be used. With an efficiency of 40 to 50 percent, the array is twice as good at turning light into electricity as the typical silicon PV cells found on the sides of buildings and significantly better than the advanced-material cells used in solar concentrators. The high efficiency is achieved partly because the lasers providing power are tuned to produce light at the frequencies best converted to electricity by the chip, while PV arrays have to convert light at whatever frequencies the sun provides.

Complete Article:
http://spectrum.ieee.org/oct05/1863