Multiplexing: Wavelength-Division or Spatial Division
Satcom needs the kind of attention fiber gets from the corporate research community. They’ve reached a new record: 100 Tbps. Dude, that’s huge!
Via New Scientist…
Today’s fibre optics use several tricks to enhance bandwidth. Like the radio band, the optical spectrum can be sliced into many distinct channels that can simultaneously carry information at different frequencies. The laser light is pulsed on and off rapidly, with each pulse further sliced up into different polarities, amplitudes and phases of light, each of which contains a bit of information. The trick is to pack all these signals together in one fibre so that they hit the receiver as one pulse without interference.
At the Optical Fiber Communications Conference in Los Angeles last month, Dayou Qian, also of NEC, reported a total data-sending rate of 101.7 terabits per second through 165 kilometres of fibre. He did this by squeezing light pulses from 370 separate lasers into the pulse received by the receiver. Each laser emitted its own narrow sliver of the infrared spectrum, and each contained several polarities, phases and amplitudes of light waves to code each packet of information.
At the same conference, Jun Sakaguchi of Japan’s National Institute of Information and Communications Technology in Tokyo also reported reaching the 100-terabit benchmark, this time using a different method. Instead of using a fibre with only one light-guiding core, as happens now, Sakaguchi’s team developed a fibre with seven. Each core carried 15.6 terabits per second, yielding a total of 109 terabits per second. “We introduced a new dimension, spatial multiplication, to increasing transmission capacity,” Sakaguchi says.
Multi-core fibres are complex to make, as is amplifying signals for long-distance transmission in either technique. For this reason, Wang thinks the first application of 100-terabit transmission will be inside the giant data centres that power Google, Facebook and Amazon.
