title: Robust 9-QAM digital recovery for spectrum shaped coherent QPSK signal.
abstract: 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.
authors.affiliation: Wuhan National Laboratory for Optoelectronics, School of Optoelectronics Science and Engineering, Huazhong University of Science and Technology, Wuhan, 430074, Hubei, China. yellowbo@gmail.com
authors.forename: Bo
authors.initials: B
authors.lastname: Huang
authors.forename: Junwen
authors.initials: J
authors.lastname: Zhang
authors.forename: Jianjun
authors.initials: J
authors.lastname: Yu
authors.forename: Ze
authors.initials: Z
authors.lastname: Dong
authors.forename: Xinying
authors.initials: X
authors.lastname: Li
authors.forename: Haiyan
authors.initials: H
authors.lastname: Ou
authors.forename: Nan
authors.initials: N
authors.lastname: Chi
authors.forename: Wen
authors.initials: W
authors.lastname: Liu
mesh_terms: D000465:Algorithms; D016247:Information Storage and Retrieval / Q000379:methods*; D055096:Optical Devices; D012815:Signal Processing, Computer-Assisted; D013685:Telecommunications