OPTICAL TRANSMISSION SYSTEM

PROBLEM TO BE SOLVED: To provide an optical transmission system which is capable of obtaining high frequency utilization efficiency and suppresses transmission quality deterioration caused by XPM between optical signals of different modulation modes mixed in the same optical fiber transmission line.SOLUTION: The optical transmission system uses together two single-core bidirectional transmission systems in which double-core fiber transmission lines are used and optical signals in two directions of uplink and downlink directions are accommodated in one optical fiber transmission line. A wavelength arrangement is configured in such a manner that the modulation mode of optical signals accommodated in a downlink direction of one optical transmission line in the two systems is only a first modulation mode and that the modulation mode of optical signals accommodated in an uplink direction is only a second modulation mode. The wavelength arrangement is configured in such a manner that the modulation mode of optical signals accommodated in a downlink direction of the other optical transmission line in the two systems is only the second modulation mode and that the modulation mode of optical signals accommodated in an uplink direction is only the first modulation mode. 【課題】高い周波数利用効率が得られ、かつ簡易な構成で、同一の光ファイバ伝送路で混在する異なる変調方式の光信号間のＸＰＭによる伝送品質劣化を抑圧した光伝送システムを提供する。【解決手段】二芯ファイバ伝送路を使用し、一本の光ファイバ伝送路に上下２方向の光信号を収容する一芯双方向伝送方式を２式併用する。２式併用されたうちの一方の光伝送路の下り方向に収容される光信号の変調方式は第１の変調方式単一となるようにし、同上り方向に収容される光信号の変調方式は第２の変調方式単一となるよう波長配置を構成する。また、２式併用されたうちのもう一方の光伝送路の下り方向に収容される光信号の変調方式は第２の変調方式単一となるようにし、同上り方向に収容される光信号の変調方式は第１の変調方式単一となるよう波長配置を構成する。【選択図】図１