In the book Nonlinear Optics, it is stated that the nonlinear effects start to become a problem in WDM systems (around 1550 nm) after about 1 mW of optical power. However, I measured the optical power at transmission of a transmitting laser of a 10GBASE-ZR on a short, 2 km link, and found that it was 2.5 mW.
What is the operating optical power of telecommunications lasers? Does it differ for inter-continental links compared to short links, i.e. between buildings on a campus? If they are above 1 mW, are nonlinear effects a concern?