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Proceedings Paper

Advances in coherent optical modems and 16-QAM transmission with feedforward carrier recovery
Author(s): Reinhold Noé; Sebastian Hoffmann; Christian Wördehoff; Ali Al-Bermani; Mohamed El-Darawy
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Paper Abstract

Polarization multiplexing and quadrature phase shift keying (QPSK) both double spectral efficiency. Combined with synchronous coherent polarization diverse intradyne receivers this modulation format is ultra-robust and cost-efficient. A feedforward carrier recovery is required in order to tolerate phase noise of normal DFB lasers. Signal processing in the digital domain permits compensation of at least chromatic and polarization mode dispersion. Some companies have products on the market, others are working on them. For 100 GbE transmission, 50 GHz channel spacing is sufficient. 16ary quadrature amplitude modulation (16-QAM) is attractive to double capacity once more, possibly in a modulation format flexible transponder which is switched down to QPSK only if system margin is too low. For 16-QAM the phase noise problem is sharply increased. However, also here a feedforward carrier recovery has been implemented. A number of carrier phase angles is tested in parallel, and the recovered data is selected for that phase angle where squared distance of recovered data to the nearest constellation point, averaged over a number of symbols, is minimum. An intradyne/selfhomodyne synchronous coherent 16-QAM experiment (2.5 Gb/s, 81 km) is presented.

Paper Details

Date Published: 24 January 2011
PDF: 9 pages
Proc. SPIE 7960, Coherent Optical Communication: Components, Subsystems, and Systems, 79600L (24 January 2011); doi: 10.1117/12.881542
Show Author Affiliations
Reinhold Noé, Univ. of Paderborn (Germany)
Sebastian Hoffmann, Univ. of Paderborn (Germany)
Christian Wördehoff, Bielefeld Univ. (Germany)
Ali Al-Bermani, Univ. of Paderborn (Germany)
Mohamed El-Darawy, Univ. of Paderborn (Germany)

Published in SPIE Proceedings Vol. 7960:
Coherent Optical Communication: Components, Subsystems, and Systems
Guifang Li; Dieter Stefan Jäger, Editor(s)

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