Unrepeatered Transmission over 670.64km of 50G BPSK, 653.35km of 100G SP-QPSK, 601.93km of 200G 8QAM and 502.13km of 400G 64QAM

We report the results of 50G, 100G, 200G, 400G unrepeatered transmission aimed at achieving the longest distance without any inline active elements, this system realizes record single-carrier at 50 Gb/s (PM-BPSK), 100 Gb/s (SP-QPSK), 200Gb/s (PM-8QAM) and 400 Gb/s (PM-64QAM) unrepeatered transmission over 670.64 km with 103.95 dB span loss, 653.35 km with 101.27 dB span loss, 601.93 km with 93.3 dB span loss, and 502.13 km with 77.83 dB span loss, respectively. This was achieved using optimized high order Raman amplifiers, cascaded RGUs and optimal coherent modulation format with concatenated FEC. G.654.E fiber with ultra low-loss & 130 $mu text{m}^2$ effective area is used as span fiber.