Patent ID: 8620160

Claim:
An optical transmission apparatus, comprising: a receiver that receives a wavelength division multiplexed (WDM) signal reached via one or more relay nodes being connected in a ring shape, each of the relay nodes including an optical amplifier, the receiver including a variable optical attenuator (VOA) that makes a tilt-correction to the received WDM signal in accordance with a given amount; a monitor that measures an optical power level of each wavelength of the WDM signal received by the receiver; a distributed Raman amplifier (DRA) pump laser that makes a tilt-correction to the WDM signal received by the receiver in accordance with a given amount; a first processor that determines whether a tilt amount indicating an amount of tilt of the WDM signal calculated based on measurement results of the monitor is suitable or not, and calculates a node tilt-correction amount to be applied to tilt-correction processing performed by the optical amplifier of the each relay node when the tilt amount is not suitable; and a second processor that performs transferring the calculated node tilt-correction amount to the each relay node, wherein the first processor calculates the tilt amount and the node tilt-correction amount in such a manner that: short and long wavelength bands are defined so that the short wavelength band includes wavelengths shorter than wavelengths included in the long wavelength band; first and second average power levels are calculated by averaging the monitored optical power levels of wavelengths included in the short and long wavelength bands, respectively; the tilt amount is obtained by subtracting the first average power level from the second average power level; the node tilt-correction amount is obtained by dividing the tilt amount by the number of the one or more relay nodes between an optical add drop multiplexer (OADM) transmitting node and an OADM receiving node plus 1; and the first processor selects, depending on each of predetermined time periods, one of the VOA and the DRA pump laser so that a tilt-correction to the received WDM signal is made, by the selected one of the VOA and the DRA pump laser, in accordance with the calculated node tilt-correction amount, during the each of the predetermined time periods.