Researchers at Facebook and intelligent transport network solutions provider Infinera have developed transmitting and receiving equipment that could squeeze 26.2 terabits per second through the MAREA cable, which currently can carry up to 20 terabits per second on each of eight fiber pairs.
While this is not a huge increase, it sets a record for the most bits per second squeezed through a limited fiber bandwidth.
The new method, called 16QUAM (quadrature amplitude modulation), digitally modulates a four-bit code so it can have one of 16 values at every interval.
This allowed the researchers to transmit a record 6.21 bits per second per hertz of bandwidth.
This high-data-rate transmission pushed the cable close to the Shannon noise limit (the theoretical maximum information transfer rate of a channel for a particular noise level).
In order to circumvent the Shannon limit, Facebook wants to increase the fiber count in cables, which will require redesigning cables so they can provide more electrical power for repeaters situated along their routes, and so the cables can fit more than 25 fiber pairs.
From IEEE Spectrum
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