Multi-rate clock signal extracting method and multi-rate clock signal extracting device

A multi-rate clock signal extracting device, comprising:

• a light modulator that modulates a receivable light signal according to a modulating electric signal obtained by mixing an electric signal with frequency f/(2j−1) being 1/(2j−1) of a maximum bit rate frequency f of said light signal (j is an integer of 1 or more) and an electric signal with frequency Δf so as to output a modulated light signal;
• a photoelectric converter that inputs said modulated light signal thereinto and converts the modulated light signal into a first electric signal so as to output the first electric signal;
• a band-pass filter unit that extracts j electric signal components with frequencies (2n−1)×Δf (n is a positive integer from 1 to j) from said first electric signal so as to output the electric signal components as a second electric signal group in parallel;
• an intensity detecting unit that detects intensities of j second electric signals composing said second electric signal group;
• and
• a bit rate detecting unit that compares reference values as the intensity values of the j second electric signals measured for light signals with j bit rates assumed in advance with the intensity values of the j second electric signals output by said intensity detecting unit and finds combinations of matched reference values and intensity values so as to determine and detect bit rates corresponding to the matched reference value as the bit rates of the received light signals;
• a phase comparison unit that comprises j phase comparators for comparing phases of electric signals with equal frequencies between said second electric signal group with frequencies (2n−1)×Δf and a third electric signal group with j frequencies (2n−1)×Δf generated by multiplying a reference signal with frequency Δf generated from a reference signal generator by 2n−1so as to output a group of j difference components as a fourth electric signal group in parallel;
• a bit rate changeover switch that selects one fourth electric signal corresponding to the bit rate detected at said bit rate detecting unit from said fourth electric signal group so as to output the fourth electric signal;
• and
• a modulating electric signal generating unit that inputs said selected fourth electric signal thereinto so as to generate said modulating electric signal.