Patent ID: 7630650

Claim:
A multi-level modulation receiving device for receiving a multi-level modulated optical signal, comprising: an optical splitter for receiving a multi-level modulated optical signal transmitted thereto via a transmission line, and splitting the multi-level modulated optical signal into n optical signals; equalizers associated with n channels, respectively, each of the equalizers including a demodulator for demodulating a corresponding channel of the split optical signal and converting the optical signal to an electrical channel signal, an equalizing filter having at least one variable parameter as a weight therefor, for equalizing waveform of the channel signal in accordance with an averaged variable parameter value, a discriminator for discriminating a waveform-equalized filter output signal output from the equalizing filter, a signal quality monitor for monitoring signal quality of the filter output signal, and a variable parameter value calculator for calculating a variable parameter value to be set as the variable parameter, in accordance with the signal quality; and a variable parameter averaging unit for averaging the variable parameter values calculated for the respective channels, to generate the averaged variable parameter value, and sending the averaged variable parameter value to the equalizing filters such that an identical weight is set in the equalizing filters associated with the n channels.