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Integrated Photodetector Improves Wireless Communications

Photonics Spectra
Mar 1998
Richard Gaughan

Wireless communications of the future may offer better performance, thanks to a photodetector developed by the University of California's Integrated Photonics Laboratory.
The velocity-matched distributed photodetector, developed under the leadership of Professor Ming C. Wu, has a bandwidth greater than 100 GHz and a saturation current of about 60 mA. It combines several photodetectors with microwave and optical waveguides to optimize the detection efficiency. Among its potential applications is "antenna remoting," a practice that separates an Earth station satellite antenna from the processing equipment room.
Saturation current is crucial to maximizing detectable power in photodiodes. Thus, signal volume must be as large as possible. However, as detector size increases, time delays reduce the effective bandwidth. Traditional detector design trades bandwidth against maximum detectable power.
UCLA's device combines up to 10 photodetectors in series. Each photodetector is small enough to retain good high-bandwidth responsivity. The multiple photodetectors increase the detection volume. But they must add exactly in phase or interference will cause responsivity to decrease.
Placing the photodetectors along an optical waveguide parallel to a
microwave coplanar waveguide solves this problem.
Wu anticipates it will be about five years before commercialization.
John Rinks of Ortel Corp. in Alhambra, Calif., said he finds it difficult to extrapolate the demand for a 100-GHz bandwidth device. "Today I couldn't sell it," he said, "But, typically, the industry has underestimated bandwidth demand.

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