ITU-T G.655 recommends which type of singlemode optical fiber?

DSF (Dispersion-Shifted Fiber) is defined by ITU-T G.653, which shifts the zero-dispersion wavelength to 1550 nm, causing severe four-wave mixing crosstalk in DWDM systems.

N-DSF (Non-Dispersion-Shifted Fiber) corresponds to ITU-T G.652, the standard singlemode fiber with zero dispersion near 1310 nm, not G.655.

ITU-T G.655 specifically standardizes Non-Zero Dispersion-Shifted Fiber (NZ-DSF), which intentionally keeps chromatic dispersion slightly above zero in the C-band to prevent phase-matching of nonlinear effects like four-wave mixing that degrade DWDM signals. Unlike pure DSF (G.653), NZ-DSF avoids the zero-dispersion point at the operating wavelength, making it the preferred fiber for long-haul dense wavelength-division multiplexing networks. This controlled dispersion profile is the core technical innovation the G.655 recommendation addresses.

SF is not a recognized ITU-T singlemode optical fiber designation and does not correspond to any standard fiber category in the G.65x series.