Patent ID: 8014684

Claim:
An optical frequency shift keying modulator utilizing a reciprocating modulation, comprising: an optical modulator ( 2 ) modulating a light outputted by controlling a frequency of a modulating signal to generate a signal having side band frequencies of and f 0 −n 1 f m and f 0 +n 2 f m wherein f 0 is frequency of input light, n 1 and n 2 are modulation order, and f m is frequency of modulation signal; a first optical filter ( 3 ) transmitting a light of a predetermined frequency domain among a light inputted to the optical modulator ( 2 ) and a light outputted from the optical modulator ( 2 ) while reflecting a light of other frequencies; a second optical filter ( 4 ) transmitting a light of a predetermined frequency domain among a light inputted to the optical modulator ( 2 ) and a light outputted from the optical modulator ( 2 ) while reflecting a light of other frequencies; and an RF signal source ( 5 ) generating the modulating signal inputted to the optical modulator ( 2 ); wherein said optical modulator ( 2 ) inputs said side band frequencies f 0 −n 1 f m and f 0 +n 2 f m to said second optical filter ( 4 ), and wherein said side band frequencies f 0 −n 1 f m and f 0 +n 2 f m are controlled by said optical frequency shift keying modulator by controlling the frequency of the modulating signal, f m , inputted to the optical modulator ( 2 ) in such a way that only one of the side band frequencies f 0 −n 1 f m and f 0 +n 2 f m falls within the predetermined frequency domain in which the second optical filter ( 4 ) transmits and said second optical filter of the optical frequency shift keying modulator outputs only one of the side band frequencies, and wherein the RF signal source controls the frequency of the modulating signal to be 1/T multiplied by an even number or an odd number, the T being a time for the light to be transmitted between the two optical filters.