Patent ID: 7869715

Claim:
An apparatus that performs dispersion compensation on an optical signal according to a control signal of a predetermined frequency, the apparatus comprising: a demodulating unit that demodulates the optical signal subjected to the dispersion compensation; a monitoring unit that monitors a change of a bit error rate of the optical signal demodulated by the demodulating unit against an amount of the dispersion compensation, and outputs an error signal indicating the change of the bit error rate; a filtering unit that filters the error signal and allows a component to pass through, wherein the component has a frequency substantially equal to or less than the predetermined frequency; a generating unit that generates a modification signal by comparing the component of the error signal with the control signal; and a superposing unit that superposes the modification signal on the control signal to change the amount of the dispersion compensation wherein the generating unit includes: a multiplying unit that multiplies the component of the error signal and the control signal and outputs a product signal; and a low pass filtering unit that filters the product signal and allows a component to pass through, wherein the component has a frequency less than the predetermined frequency.