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Cleaning Up Light For Long Distance Fiber Optics


Developments to Watch

CLEANING UP LIGHT FOR LONG-DISTANCE FIBER OPTICS

Chirping is fine for birds, but it's annoying when it occurs in pulses of light over fiber-optic transmission systems. The reason:

A "chirp" of light is made up of different wavelengths. Short ones travel faster than long ones. So, over 25 to 40 miles, the light pulses become smeared--making it impossible to distinguish the "ones" and "zeroes" of binary computer code.

Bell-Northern Research Ltd., part of Canada's Northern Telecom Ltd., has created a device that precompensates for chirp. That extends the useful transmission range of a light pulse to well over 60 miles. The research arm says the electronic shutter is made of semiconducting materials, so it's smaller and cheaper to manufacture than shutters made of substances such as lithium niobate. It's two to three years from mass production.EDITED BY PETER COY


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