Patent ID: 7376348

Claim:
An optical communication system having a sending unit transmitting multiplexed optical signals, in which optical signals are multiplexed with wavelength division multiplexing, to a receiving unit through either one of a main transmission line or a backup transmission line, and a receiving unit receiving the optical signal transmitted from a sending unit from either one of the main transmission line or the backup transmission line, the said sending unit comprising: a pre-emphasis section adjusting signal levels of each wavelength; a transmitter multiplexing each wavelength signal of which level is adjusted by the pre-emphasis section, and sending the multiplexed wavelength signal; and a controller controlling the pre-emphasis section to adjust each wavelength signal level, based on control data transmitted from the receiving unit for adjusting each wavelength signal level, and the said receiving unit comprising: a measurement section measuring signal quality of each wavelength included in received optical signals; a memory storing the initial value of the signal quality of each wavelength measured by the measurement section before the transmission line is switched over either from the main transmission line to the backup transmission line or from the backup transmission line to the main transmission line; and a transmitter ordering the measurement section to measure the signal quality of each wavelength included in optical signals received after a switchover when a transmission line switchover is performed, and generating control data based on both the initial quality value and the post-switchover quality value, and sending the generated control data to the sending unit.