Patent ID: 7245787

Claim:
A bias adjustment method for an optical SSB modulator or an optical FSK modulator including a first sub Mach-Zehnder waveguide, a second sub Mach-Zehnder waveguide and a main Mach-Zehnder waveguide equipped with the first and second Mach-Zehnder waveguides, comprising the steps of: supplying a predetermined signal to the main Mach-Zehnder waveguide; adjusting bias signals supplied to the first and second Mach-Zehnder waveguides so as to lower an amplitude of an output light of the main Mach-Zehnder waveguide; wherein the predetermined signal supplied to the main Mach-Zehnder waveguide is an alternating current signal having an amplitude higher than amplitudes of the bias signals supplied to the first and second Mach-Zehnder waveguides.