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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 6 — Mar. 25, 2013
  • pp: 7216–7221

Robust 9-QAM digital recovery for spectrum shaped coherent QPSK signal

Bo Huang, Junwen Zhang, Jianjun Yu, Ze Dong, Xinying Li, Haiyan Ou, Nan Chi, and Wen Liu  »View Author Affiliations

Optics Express, Vol. 21, Issue 6, pp. 7216-7221 (2013)

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We propose 9-ary quadrature amplitude modulation (9-QAM) data recovery for polarization multiplexing-quadrature phase shift keying (PM-QPSK) signal in presence of strong filtering to approach Nyquist bandwidth. The decision-directed least radius distance (DD-LRD) algorithm for blind equalization is used for 9-QAM recovery and intersymbol interference (ISI) compression. It shows the robustness under strong filtering to recover 9-QAM signal rather than QPSK. We demonstrate 112 Gb/s spectrum shaped PM-QPSK signal by wavelength selective switch (WSS) in a 25-GHz channel spacing Nyquist wavelength division multiplexing (NWDM). The final equalized signal is detected by maximum likelihood sequence decision (MLSD) for data bit-error-ratio (BER) measurement. Optical signal-to-noise ratio (OSNR) tolerance is improved by 0.5 dB at a BER of 1x10−3 compared to constant modulus algorithm (CMA) plus post-filter algorithm.

© 2013 OSA

OCIS Codes
(060.1660) Fiber optics and optical communications : Coherent communications
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.4510) Fiber optics and optical communications : Optical communications

ToC Category:
Fiber Optics and Optical Communications

Original Manuscript: December 20, 2012
Revised Manuscript: January 24, 2013
Manuscript Accepted: February 7, 2013
Published: March 14, 2013

Bo Huang, Junwen Zhang, Jianjun Yu, Ze Dong, Xinying Li, Haiyan Ou, Nan Chi, and Wen Liu, "Robust 9-QAM digital recovery for spectrum shaped coherent QPSK signal," Opt. Express 21, 7216-7221 (2013)

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