Patent ID: 7756422

Claim:
A measurement system which measures, in an optical communication system for transmitting WDM light in a predetermined signal wavelength band from a transmitting station to a receiving station, a span loss between the transmitting station and the receiving station, comprising: a reference light generation unit, provided in the transmitting station, for generating reference light having a wavelength component in the signal wavelength band; a first photo detector, provided in the transmitting station, for detecting the optical power of the signal wavelength band; a second photo detector, provided in the receiving station, for detecting the optical power of the signal wavelength band; a third photo detector, provided in the transmitting station, for detecting the optical power of control light having a wavelength which is allocated out of the signal wavelength band; a fourth photo detector, provided in the receiving station, for detecting the optical power of the control light; a first calculation unit for calculating a reference span loss from results detected by said first and second photo detectors when the reference light is being generated; a second calculation unit for calculating correction data from results detected by said third and fourth photo detectors; and a third calculation unit for calculating a span loss in the signal wavelength band by correcting the reference span loss using the correction data, wherein said second calculation unit outputs, as the correction data, a difference between a first correction value determined during initial start-up of the optical communication system and a second communication correction value determined during operation of the optical communication system.