Patent ID: 7957652

Claim:
An optical modulator comprising: a first sub Mach-Zehnder waveguide (MZ A ) ( 2 ); a second sub Mach-Zehnder waveguide (MZ B ) ( 3 ); a main Mach-Zehnder waveguide (MZ C ) ( 8 ) including: an input part ( 4 ) of an optical signal; a branching part ( 5 ), wherein the optical signal is branched at the branching part to the first sub Mach-Zehnder waveguide (MZ A ) and the second sub Mach-Zehnder waveguide (MZ B ); the first sub Mach-Zehnder waveguide (MZ A ); the second sub Mach-Zehnder waveguide (MZ B ); a combining part ( 6 ) being configured to connected to the first sub Mach-Zehnder waveguide (MZ A ) and the second sub Mach-Zehnder waveguide (MZ B ), wherein the optical signal outputted from the first sub Mach-Zehnder waveguide (MZ A ) and the optical signal outputted from the second sub Mach-Zehnder waveguide (MZ B ) are combined at the combining part; an output part ( 7 ) outputting the optical signal combined at the combining part, the output part being configured to be connected to the combining part; a first electrode (RF A electrode) ( 9 ) for inputting radio frequency (RF) signals to two arms composing the first sub Mach-Zehnder waveguide (MZ A ); a second electrode (RF B electrode) ( 10 ) for inputting radio frequency (RF) signals to two arms composing the second sub Mach-Zehnder waveguide (MZ B ); a main Mach-Zehnder electrode (electrode C) ( 11 ) for applying voltage to the main Mach-Zehnder waveguide (MZ C ), thereby controlling a phase difference between an output signal from the first sub Mach-Zehnder waveguide (MZ A ) and an output signal from the second sub Mach-Zehnder waveguide (MZ B ); a first intensity modulator ( 12 ), the intensity modulator being provided on waveguide portion between a combining part of the first sub Mach-Zehnder waveguide (MZ A ) and the combining part ( 6 ) of the main Mach-Zehnder waveguide (MZ C ), the intensity modulator modulating intensity of the optical signal propagating through the waveguide portion; an asymmetric directional coupler provided at the branching part ( 5 ) of the main Mach-Zehnder waveguide (MZ C ) ( 8 ), the asymmetric directional coupler controlling intensity of the optical signal branched to the first sub Mach-Zehnder waveguide (MZ A ) so that intensity of the optical signal branched to the first sub Mach-Zehnder waveguide (MZ A ) becomes higher than intensity of the optical signal branched to the second sub Mach-Zehnder waveguide (MZ B ); and an intensity modulator provided on a waveguide portion between a combining part of the second sub Mach-Zehnder waveguide (MZ B ) and the combining part ( 6 ) of the main Mach-Zehnder waveguide (MZ C ), the intensity modulator modulating intensity of the optical signal propagating through the waveguide portion.