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Fiber Polisher Polishes Performance of Optical Amplifier

Photonics Spectra
Aug 1999
Daniel C. McCarthy

Video-on-demand, real-time Internet gaming, telecommuting. The consumer applications that fiber to the home will one day enable admittedly are much sexier than its enabling component technologies. Nevertheless, the market awaits for those who would produce, among other things, better optical amplifiers for tele- and datacommunications. In an innovative approach to increase the performance of one such optical amplifier, researchers at Lawrence Livermore National Laboratory are using a fiber polishing machine from Ultra Tec Manufacturing Inc.

The polishing heads of Ultra Tec's fiber polishers provide three-axis control. Their protractor head enables them to deliver the fine control required to taper and polish optical fibers. Courtesy of Ultra Tec Manufacturing Inc.

"A lot of datacom problems are associated with signal processing," said Phillip Stephan, a senior mechanical technologist at Livermore. "[Erbium-doped fiber amplifiers] have to process signals when they come in and again when they go out."

The GaAs-based amplifier Livermore is cultivating streamlines the signal processing function. Also, its saturation level is much higher than erbium-doped devices, which means it can shoulder a higher volume of signals.

But these capabilities of Livermore's amplifier fade if it cannot efficiently be coupled to a standard 25- to 127-µm-diameter optical fiber. Or as Stephan explained, "The more energy you can couple from the chip, the more signal you can send."

In evaluations of his amplifier, he found that unpolished fibers generally capture 30 percent of the laser energy. However, by polishing a cone-shaped lens into the fiber tip, he increased coupling efficiency to 50 percent.

The technique is not peculiar to Livermore, and commercial lens fibers are available. But the evaluative and sensitive nature of the work at the lab requires continued experimentation to optimize the fiber lens. "It takes some finesse to take the machine to the limits of its polishing abilities," Stephan said. "The angles are critical to establish focus and clearances."

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