ITU G.652 is the first single-mode fiber standard specified by the ITU-T. It includes four revisions which are G.652.A, G.652.B, G.652.C, and G.652.D. Among them, G.652.A and G.652.B fibers are rarely used now due to inferior performance in modern WDM applications. While G.652.C and G.652.D fibers feature a reduced water peak (ZWP – Zero Water Peak), which allows them to be used in the wavelength region between 1310nm and 1550nm supporting Coarse Wavelength Division Multiplexed (CWDM) transmission. G.652.D fiber is the most up-to-date technology today, which provides not only the maximum return of your investments but also affords the best protection and is recommended as the fiber of choice when deploying single-mode optical fiber in most of the application cases currently.