E. IP, J. Kahn, "Feedforward carrier recovery for optical communication," J. Lightw. Technol. 25, 2675-2692 (2007).

X. Zhou, J. Yu, "Multi-level, multi-dimensional coding for high-speed
and high spectral-efficiency optical transmission," J. Lightw. Technol. 27, 3641-3653 (2009).

X. Zhou, J. Yu, M. Huang, Y. Shao, T. Wang, P. D. Magill, M. Cvijetic, L. Nelson, M. Birk, G. Zhang, S. Ten, H. B. Matthew, S. K. Mishra, "Transmission of 32-Tb/s capacity over 580 km using
RZ-shaped PDM-8QAM modulation format and cascaded multimodulus blind
equalization algorithm," J. Lightw. Technol. 28, 456-464 (2010).

P. J. Winzer, A. H. Gnauck, C. R. Doerr, M. Magarini, L. L. Buhl, "Spectrally efficient long-haul optical networking
using 112-Gb/s polarization-multiplexed 16-QAM," J. Lightw. Technol. 28, 547-556 (2010).

J. Yu, X. Zhou, M. F. Huang, Y. Shao, D. Qian, T. Wang, M. Cvijetic, P. Magill, L. Nelson, M. Birk, S. Ten, H. B. Matthew, S. K. Mishra, "17 Tb/s (161$\,\times\,$114 Gb/s) PolMux-RZ-8PSK transmission over 662 km of
ultra-low loss fiber using C-band EDFA amplification and digital
coherent detection," Proc. ECOC'08 (2008).

H. Takahashi, A. A. Amin, S. L. Jansen, I. Morita, H. Tanaka, "8$\,\times\,$66.8-Gbit/s coherent PDM-OFDM transmission over 640 km of
SSMF at 5.6-bit/s/Hz," Proc. ECOC'08 (2008).

H. Takahashi, A. A. Amin, S. L. Jansen, I. Morita, H. Tanaka, "DWDM transmission with 7.0-bit/s/Hz spectral
efficiency using 8$\,\times\,$65.1-Gbit/s PDM-OFDM," Proc. OFC (2009).

X. Zhou, J. Yu, P. D. Magill, "Cascaded two-modulus algorithm for blind polarization
de-multiplexing of 114-Gb/s PDM-8-QAM optical signals," Proc. OFC'09 (2009).

X. Zhou, J. Yu, M. F. Huang, Y. Shao, T. Wang, L. Nelson, P. D. Magill, M. Birk, P. I. Borel, D. W. Peckham, R. Lingle, "64-Tb/s (640$\,\times\,$107-Gb/s) PDM-36QAM transmission over 320 km using both
pre- and post-transmission digital equalization," Proc. OFC'10 (2010).

A. Sano, T. Kobay, H. Masuda, T. Kobayashi, M. Fujiwara, K. Horikoshi, E. Yoshida, Y. Miyamoto, M. Matsui, M. Mizoguchi, H. Yamazaki, Y. Sakamaki, H. Ishii, "69.1-Tb/s (432$\,\times\,$171-Gb/s) C- and extended L-band transmission over 240 km
Using PDM-16-QAM modulation and digital coherent detection," Proc. OFC'10 (2010).

H. Takahashi, A. Al Amin, S. Jansen, I. Morita, H. Tanaka, "DWDM transmission with 7.0-bit/s/Hz spectral
efficiency using 8$\,\times\,$65.1-Gbit/s coherent PDM-OFDM signals," Proc. OFC'09 (2009).

J. Yu, X. Zhou, Y. K. Huang, S. Gupta, M. F. Huang, T. Wang, P. Magill, "112.8-Gb/s PM-RZ-64QAM optical signal generation and
transmission on a 12.5 GHz WDM grid," Proc. OFC'10 (2010).

A. Sano, T. Kobayashi, A. Matsuura, S. Yamamoto, S. Yamanaka, E. Yoshida, Y. Miyamoto, M. Matsui, M. Mizoguchi, T. Mizuno, "100$\,\times\,$120-Gb/s PDM 64-QAM transmission over 160 km using
linewidth-tolerant pilotless digital coherent detection," Proc. ECOC'10 (2010).

J.-X. Cai, Y. Cai, C. R. Davidson, D. G. Foursa, A. Lucero, O. Sinkin, W. Patterson, A. Philipetskii, G. Mohs, N. S. Bergano, "Transmission of 96$\,\times\,$100 G pre-filtered PDM-RZ-QPSK channels with 400% spectral
efficiency," Proc. OFC'10 (2010).

M. Seimetz, "Laser linewidth limitations for optical systems with
high-order modulation employing feed forward digital carrier phase
estimation," Proc. OFC'08 (2008).

J. G. Proakis, Digital Communication (McGraw-Hill, 1995) pp. 280.