From EETimes: Increase fiber optic capacity in existing networks by 10-times just by switching to a new kind of transmitter -- that's the claim of a research group at EPFL (École Polytechnique Fédérale de Lausanne, Switzerland). Using sinc-shaped Nyquist pulses, information can be encoded on pulses that overlap in the time domain and use a minimum of spectral bandwidth, thus maximizing optical capacity, according to the EPFL research team of Camille Brès and Luc Thévenaz.
Other groups have tried to produce Nyquist sinc pulses to minimize inter-symbol interference, but had to resort to complex signal generators. Brès and Thévenaz claim their spectral synthesis technique works better, plus is the only one that will be easy to implement for commercial optical transmitters.
"We synthesize a spectrum that gives the perfect pulse shape. We do it by using a simple intensity modulator to generate a set of spectral lines, regularly spaced and showing exactly the same amplitude and the same phase. This gives automatically in the time domain the sinc pulse shape," Thévenaz told us. "This is very simple and straightforward, but nobody thought to do it this way before.
The EPFL team claims that in the lab a laser and a modulator -- to produce wide-spectrum pulses -- are all that's needed to generate Nyquist pulses that are 99 percent perfect.
The researchers claim that designing a transmitter chip that realizes their encoding technique should be a straightforward exercise for optical chipmakers, and would include "the modulators required to generate the square shaped spectrum and a set of short delay lines and modulators to generate data sequences and to interleave them in the temporal sequence, to increase the data rate," said Thévenaz.
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