Patent ID: 8000612

Claim:
An optical transmission device for outputting a single-sideband optical intensity-modulated signal with suppressed optical carrier component, the optical transmission device comprising: first and second Mach-Zehnder interferometers each for receiving one of two optical signals obtained by branching an optical carrier having a frequency f 0 outputted from a light source and outputting a phase-modulated signal obtained by modulating a phase of the input optical signal with an inputted electrical signal having a frequency f 1 ; a third Mach-Zehnder interferometer for further phase-modulating and combining together the two phase-modulated signals outputted from the first and second Mach-Zehnder interferometers, respectively; a light branching section for branching the optical intensity-modulated signal into an optical signal transmitted along an optical transmission path and a monitoring optical signal; a photodetector section for converting the monitoring optical signal to an electric signal and outputting the electric signal as a monitoring signal; a branching section for branching the monitoring signal into two signals; an optical carrier component extracting section for passing therethrough only a signal component of one of the branched monitoring signals that is in a vicinity of the frequency f 1 ; an optical carrier component level detecting section for detecting a level of the signal outputted by the optical carrier component level extracting section to output an optical carrier component monitoring signal according to the detected level; a vestigial sideband component extracting section for passing therethrough only a signal component of the other one of the branched monitoring signals that is in a vicinity of a frequency 2×f 1 ; a vestigial sideband component level detecting section for detecting a level of the signal outputted by the vestigial sideband component level extracting section to output a vestigial sideband component monitoring signal according to the detected level; an optical carrier component suppressing section for suppressing an optical carrier component of the optical intensity-modulated signal by controlling bias voltages to be applied to the first and second Mach-Zehnder interferometers and causing a level of the optical carrier component monitoring signal to be less than or equal to a reference value; and a vestigial sideband component suppressing section for suppressing an unnecessary one sideband component of the optical intensity-modulated signal by controlling a bias voltage to be applied to the third Mach-Zehnder interferometer and causing a level of the vestigial sideband component monitoring signal to be less than or equal to a reference value.