Patent ID: 7657176

Claim:
A method of evaluating a faulty point in a multi-stage optical amplifying and repeating transmission line where a plurality of optical amplifying repeaters are inserted at predetermined intervals in an optical cable, comprising the steps of: monitoring, at an optical spectrum monitoring function unit, an optical spectrum of an optical noise signal successively amplified through a chain of optical amplifying repeaters at a downstream side of the faulty point at a light receiving end of the optical cable and judging, at a faulty point judging function unit, the location of the faulty point from the monitored optical spectrum of the optical noise signal, wherein said judging step estimates the number of repeaters from the degree of change of the optical spectrum characteristic curve which changes from a flat shape to a projection shape successively depending on the increase in the number, from the faulty point, of the repeaters, wherein the optical spectrum characteristic curve is depicted on a graph which is defined by a wavelength (λ) on an axis of an abscissa and an optical power (Pi) on an axis of an ordinate.