Patent ID: 7873283

Claim:
An optical transmission system in which an optical signal is transmitted from an optical transmission apparatus to an optical receiving apparatus via an optical transmission path, comprising: a degree of polarization measurement section that measures a degree of polarization of said optical signal; and an optical SNR calculation section that stores an initial value of said degree of polarization of said optical signal, and determines a change amount in an optical signal to noise ratio of said optical signal according to a change between a measured value of the degree of polarization obtained in said degree of polarization measuring section relative to said stored initial value, wherein said degree of polarization measurement section that measures said degree of polarization of said optical signal after a predetermined amount of time has elapsed from a time when said initial value was stored, and said predetermined amount of time is set so that said degree of polarization measurement section to measure the change in said degree of polarization due to a change in the optical signal to noise ratio, when a change in said degree of polarization due to a change in a polarization mode dispersion is compensated.