652 fiber is designed to have a zero-dispersion wavelength near 1310 nm, therefore it is optimized for operation in the 1310nm band and can also operate at 1550 nm. A . There are 19 different single mode optical fiber specifications defined by the ITU-T, among which G. 652 fiber is the most commonly used. 2 µm mode field diameter for backward compatibility with legacy networks. Quality and proven performance. 652 is an international standard that describes the geometrical, mechanical, and transmission attributes of a single-mode optical fibre and cable, developed by the Standardization Sector of the International Telecommunication Union (ITU-T) that specifies the most popular type of single-mode. G. 657 are ITU-T standardized singlemode fiber types used across long-haul, metro, ODN, and FTTH networks.