Optical modulator with wirings of equal length

An optical modulator comprising, on a substrate, an optical waveguide and a control electrode for controlling light waves propagating through the optical waveguide,

• wherein the optical waveguide includes a first branch section that branches one input light beam into two, each of first and second modulation portions, which are connected to two branched waveguides branched in the first branch section, having a structure in which one or more Mach-Zehnder type optical waveguides are combined,
• the control electrode includes signal electrodes that apply a modulation signal to the first and second modulation portions,
• input portions of all the signal electrodes that are configured to input modulation signal to the first and second modulation portions and that are arranged on any one of the left and right sides of the substrate in a propagation direction of the light waves,
• output portions of the signal electrodes that are configured to output the modulation signal from the first and second modulation portions and that, in the propagation direction of the light waves, are arranged on both sides of the substrate on which the first or second modulation portion is arranged, wherein each of the signal electrodes has at least one of the output portions located on one side of the substrate,
• at least two termination substrates, each of the termination substrates including a termination circuit connected to each output portion is arranged near the output portion, wherein one of the termination substrates is disposed on the side on which the first modulation portion is arranged and another one of the termination substrates is disposed on the other side on which the second modulation portions is arranged, the output portions of a part of the signal electrodes are extended from the first modulation portion to the one of the terminal substrates, and the output portions of another part of the signal electrodes are extended from the second modulation portion to the other one of the terminal substrates,
• a DC wiring that is not electrically connected to the signal electrode is included to apply a bias voltage to the modulation portion or an optical waveguide in a stage subsequent to the modulation portion,
• a light reception element that monitors some of the light waves derived from the modulation portion and is arranged on the substrate, and a monitor wiring that derives an output signal from the light reception element are included, and
• at least a portion of the DC wiring or the monitor wiring is forming in a portion of the termination substrate,
• wherein lengths of wirings from a start portion of an interaction region in the modulation portion to the output portion are set to be equal between the different signal electrodes.