IEC 62077:2015(E) applies to circulators used in the field of fibre optics bearing all of the following features: - they are non-reciprocal optical devices, in which each port is either an optical fibre or fibre optic connector; - they are passive devices in accordance with the categorization and definition provided in IEC TS 62538; - they have three or more ports for directionally transmitting optical power. An example of optical circulator technology is described in Annex A. This third edition cancels and replaces the second edition published in 2010. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: harmonization of some terms and definitions with other generic specifications, deletion of assessment level. Keywords: optical circulator