To minimize chromatic dispersion at 1550nm, a new fiber called dispersion-shifted fiber (DSF) was introduced. By changing the index profile and reducing the core radius, fiber designers were able to move lambda-0 from the 1310nm window to the 1540 to 1560nm window. Though effective in greatly reducing chromatic dispersion effects, which limits bandwidth, the positioning of lambda-0 in close proximity to the operating wavelengths resulted in a tendency to a nonlinear distortion effect called four wave mixing (FWM). This is especially troublesome in DWDM applications with more than eight wavelengths. Typical losses range from 0.25 to 0.30dB/km.