Patent ID: 7302188

Claim:
A dispersion equalizer comprising: an error detection unit that detects a transmission error of an optical signal, wherein the optical signal is coded based on an error-correction code and transmitted on an optical fiber transmission line; an alarm detection unit that detects alarm information on transmission of the optical signal; a variable dispersion equalization unit provided at an earlier stage with respect to the error detection unit and the alarm detection unit, wherein variable dispersion equalization unit adjusts a parameter for restricting a transmission length of the optical fiber transmission line based on a control signal; and a control unit that generates the control signal based on the transmission error information obtained from the error detection unit and the alarm information obtained from the alarm detection unit, wherein if the control unit does not receive the alarm information, the control unit controls the variable equalization unit such that the transmission error becomes smaller, and if the control unit receives the alarm information, the control unit switches control over the variable equalization unit from an ordinary control to a search mode control for searching an optimal dispersion equalization value in a wide range to thereby search the optimal dispersion equalization value at a higher speed.