2.38 Tbit/s, 1.49 bit/s/Hz, and (160 Gbit/s) RZ-DQPSK polarization division multiplex transmission over 273 km of fiber
A. Abas, B. Milivojevic, A. Hidayat, S. Bhandare, D. Sandel, H. Zhang, R. Noé, ELECTRICAL ENGINEERING 88 (2006) 211–214.