1 Nanophotonic Devices, Department of Photonics Engineering, Technical University of Denmark2 High-Speed Optical Communication, Department of Photonics Engineering, Technical University of Denmark3 Department of Photonics Engineering, Technical University of Denmark4 Diode Lasers and LED Systems, Department of Photonics Engineering, Technical University of Denmark5 Fudan University6 ZTE Corporation7 Huazhong University of Science and Technology8 Fudan University9 Huazhong University of Science and Technology
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.
Optics Express, 2013, Vol 21, Issue 6, p. 7216-7221