In single-mode fiber-oriented data transmission systems we use the spectral range of 1260 ~ 1675 nm. This spectrum is divided into several standardized ranges: Historically, the first range to be used was the O-band. This band laid the groundwork for optical transmission without the need for. In fiber-optic communication, a single-mode optical fiber, also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode of light - the transverse mode. By selecting the. As fiber optic networks have developed for longer distances, higher speeds and wavelength-division multiplexing (WDM), fibers have been used in new wavelength ranges, now called "bands," where fiber and transmission equipment can operate more efficiently.