New Mode of Transmission May Double Fiber Optic Capacity

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A new approach to transmitting data signals could more than double the amount of data that optical fibers can carry, claim scientists at the University of California, San Diego. The researchers suggest their work, which was published in in the June 26 issue of the journal Science, could "completely redefine the economy on which the present data traffic rests." 

Data signals traveling as laser pulses through an optical fiber are vulnerable to optical distortions resulting from interference among multiple signals of different wavelengths traveling down the same fiber.

These nonlinear wave interactions mean that data signals can degrade over great distances unless they regularly get regenerated along the way — that is, converted to electrical signals, subjected to computer analysis to weed out any distortions, and then converted back to optical signals. This process not only slows data traffic, but also accounts for most of the cost of setting up new optical network infrastructure.

Now UC-San Diego researchers say they may have discovered a way to easily get rid of these distortions, greatly reducing the need for constant and expensive signal regeneration. The research team told Science magazine this could lead to a two- to four-fold boost to either the amount of data a fiber can carry or the distance that signals travel before they need to be regenerated.

The lasers used to transmit signals through optical fibers typically vary in wavelength by hundredths of a percent as they operate. This variation is normally random, and the noise it adds to data streams makes it virtually impossible to isolate and filter out the distortions resulting from nonlinear wave interactions. Instead, the researchers suggest making the variations in the laser wavelengths predictable rather than random.

Whereas telecommunication networks typically use several lasers to generate the different wavelengths sent down optical fibers, the researchers converted light of a single wavelength from one laser into pulses of many different wavelengths. Experiments with optical fibers more than a thousand meters long showed that when the primary laser fluctuated in wavelength, its subsidiary pulses changed by matching amounts, making this variation simple to account for. This in turn made it easier to filter out distortions from nonlinear wave interactions.


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