Abstract: A method is provided for automatically identifying a system fault in an optical communication system that includes first and second transmission paths for supporting bidirectional communication. In accordance with the method, measurements are made of a plurality of optical gain values respectively generated by a plurality of optical amplifier units disposed in respective loop back paths extending through the first and second transmission paths of the optical communication system. A gain signature is obtained by subtracting a plurality of baseline values from the plurality of optical gain values. Directional state changes are located along the gain signature to identify a plurality of directional states. Each of the directional states is assigned a pre-established state such that the gain signature is represented by a sequence of pre-established states. The sequence of pre-established states of said gain signature is compared to a plurality of predetermined sequences of pre-established states.