Patent ID: 7522844

Claim:
An optical modulation apparatus which modulates plural input lightwaves having different frequencies by their respective modulation signals, and in which with respect to a natural number n that is not higher than a number N of modulation signals that are varied and is not lower than a number of the plural input lightwaves, for each varied n, fn is an input light component of a channel n, Fn is a modulation frequency, An is a lower sideband order and Bn is an upper sideband order corresponding to sideband channels generated by modulation, the apparatus comprising: an input filter, an optical modulator configured to receive the plural modulation signals applied simultaneously thereto, and an output filter disposed on a single optical path; a multiple round-trip optical path formed by the plural input lightwaves that are input through the input filter, modulated into a signal having the input light component fn with a sideband by the optical modulator using a modulation signal having the modulation frequency Fn, reflected in round trips by the input filter and output filter, and subjected to a modulation performed by the optical modulator each time the lightwaves make a round trip, wherein an optical signal with a sideband having a frequency which has reached a frequency determined by the output filter or the input filter from among sidebands An and Bn generated by the modulation is output through the output filter or the input filter, wherein the modulation frequency Fn is determined by a transmission time of the input filter, a reflection time of the output filter, and a length of an optical path between the input filter and the output filter, and wherein the time required for each light component of channel n to make a round trip is an integer multiple of one period of each modulation signal (=1/Fn).