ABSTRACT: This document provides the view of Telcordia on generic criteria for single-mode fiber optic isolators and circulators intended for use in Local Exchange Carrier (LEC) systems and other telecommunications networks. An optical isolator is a two-port passive component that allows light (in a given wavelength range) to pass through with low attenuation in one direction, while isolating (providing a high loss for) light propagating in the reverse direction.