6 Tb/s unrepeatered transmission of 60 × 100 Gb/s PDM-RZ QPSK channels with 40 GHz Spacing over 437 km

We present a 60 × 100 Gb/s unrepeatered transmission experiment at 2.5 b/s/Hz spectral efficiency over a record distance of 437 km of ultra-low loss fibre, with a high power booster and third-order Raman pumping. We also assess the penalty of 40 GHz compared to 50 GHz channel spacing.