Unrepeatered long haul optical fiber transmission systems

A long haul optical fiber transmission system comprising:

• a transmitter comprising a modulated bit rate of at least 40 Gb/s;
• a receiver optically coupled to the transmitter with a composite optical fiber span, the composite optical fiber span comprising:
• a first optical fiber optically coupled to the transmitter and comprising an effective area Aeff1 of at least 120 μm2, an attenuation α1 of less than 0.180 dB/km, a nonlinear refractive index n21, and a length L1 from about 60 km to about 90 km;
• and
• a second optical fiber optically coupled to the first optical fiber and comprising an effective area Aeff2 of less than 120 μm2, an attenuation α2 of less than 0.180 dB/km, a nonlinear refractive index n22 and a length L2, wherein a sum of the length L1 and the length L2 is at least 160 km, the composite optical fiber span does not comprise a repeater between the transmitter and the receiver, and the composite optical fiber span does not contain any rare earth dopants, , wherein a total length of the composite optical fiber span is 400 km or less.