nm

One billionth (10 -9 , or 1 / 1,000,000,000 ) of a meter. The wavelength of an optical signal is measured in nanometers.The wavelength of a typical optical signal in a long haul fiber optic transmission system (FOTS) is in the 1550 nm window, for example. Just to put it in perspective, an average molecule is about a nanometer in diameter, a human DNA molecule is about 2.5 nm wide, and a human hair is in the range of 5,000