National standards of length for high-capacity optical fiber communication systems

Frequency measurement in the optical domain has a number of applications other than the length standard, among which the most important field in a social context is optical fiber communications. In the 1990s, wavelength-division multiplexing began to increase communication capacity, and many specialists anticipate that precise optical frequency management is required in the near future. It was therefore necessary to add a stabilized laser in the 1.5m optical communication band as a frequency standard to the CIPM’s recommendation, and to develop the technology to measure laser frequency in the 1.5m band. In Japan, where the 633nm iodine-stabilized He-Ne laser served as the national measurement standard, the 1.5m stabilized lasers needed to be traceable to the 633-nm national measurement standard.