Limitations of NRZ transmission using SM Fiber
Attenuation lowest near ?=1550 nm wavelength. (0.2 dB/km means the signal has 50% of the initial power after traveling 15 km)
Chromatic dispersion near ?=1550 nm wavelength limits 2.5 Gb/s spans to around 45 km
Regenerator spacing can be increased by using dispersion shifted fiber or by dispersion management