Patent ID: 7680418

Claim:
A multi-rate clock signal extracting method, comprising: a light modulating step of modulating a receivable light signal according to a modulating electric signal obtained by mixing an electric signal with frequency f/(2 j−1 ) being 1/(2 j−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 converting step of converting said modulated light signal into a first electric signal; a first band-pass step of extracting j electric signal components with frequencies (2 n−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; a second electric signal intensity detecting step of detecting intensities of j second electric signals composing said second electric signal group; a bit rate detecting step of comparing 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 at said second electric signal intensity detecting step so as to find combinations of matched reference values and intensity values so as to determine and detect bit rates corresponding to the matched reference values as the bit rates of the received light signals; a phase comparing step of comparing phases of electric signals with equal frequencies between said second electric signal group with frequencies (2 n−1 )×Δf and a third electric signal group with j frequencies (2 n−1 )×Δf generated by multiplying a reference signal with frequency Δf generated from a reference signal generator by 2 n−1 so as to output a group of j difference components as a fourth electric signal group in parallel; a bit rate changeover step of selecting one fourth electric signal corresponding to the bit rate detected at the bit rate detecting step from said fourth electric signal group so as to output the fourth electric signal; and a modulating electric signal generating step of inputting said selected fourth electric signal so as to generate and output said modulating electric signal.