Patent ID: 7693427

Claim:
A modulator for modulating an input signal, comprising: a phase inverting unit that produces an inverted signal with an inverted phase of the phase of a first input signal transferred within a first frequency bandwidth; a first semiconductor laser that FM-modulates the first input signal to produce a first FM-modulated light beam; a second semiconductor laser that FM-modulates the inverted signal to produce a second FM-modulated light beam; an optical phase-modulating unit that changes the phase of one of the first FM-modulated light beam and the second FM-modulated light beam on the basis of a second input signal transferred within a second frequency bandwidth to produce a phase-modulated light beam; an optical merging unit that merges the phase-modulated light beam and the other of the first FM-modulated light beam and the second FM-modulated light beam to produce a modulated light beam; and a photoelectric converting unit that converts the modulated light beam in a modulated signal by optical heterodyne detection, wherein the second frequency bandwidth is higher than the first frequency bandwidth.