Optical modulator

An optical modulator comprising a plurality of optical modulation sections which are arranged in parallel on a same main substrate having an electro-optic effect, in the respective optical modulation sections, a Mach-Zehnder type optical wave guide is formed on the main substrate, and a signal electrode and an earth electrode are provided along a pair of branching waveguides that are disposed between an optical branching section and an optical multiplexing section of the Mach-Zehnder type optical waveguide, that perform modulation of light that propagates on the Mach-Zehnder type optical waveguide by applying an electric signal corresponding to modulation data to the signal electrode that is a travelling wave electrode, wherein:

• the optical modulator comprises, arranged on the main substrate;
• an output light multiplexing section that multiplexes modulation light that has been respectively output from the optical modulation sections,
• an intermediate substrate that is provided separately to the main substrate, and
• a plurality of signal lines formed on the intermediate substrate respectively corresponding to the optical modulation sections,
• and in the signal electrodes of the respective optical modulation sections on the main substrate, each of the input ends to which an electric signal is applied are arranged side by side on one side face of the main substrate,
• and in the respective signal lines on the intermediate substrate, each of the input ends to which an electric signal is applied from outside, respectively corresponding to the optical modulations sections, are arranged side by side with a predetermined spacing on one side face of the intermediate substrate, and each of the output ends that are electrically connected to the input ends of the signal electrodes of the corresponding optical modulation section on the main substrate are arranged side by side on the other side face of the intermediate substrate, and each of the electrical lengths from the input end to the output end are different to each other,
• and wherein the construction is such that, when on the branching wave guides that run along the signal electrodes, of the pair of branching wave guides of the respective optical modulation sections, base points where optical path lengths from the output light multiplexing sections are equal to each other, are set individually, the electrical lengths of the signal lines respectively corresponding to the optical modulation sections, from the input end of the signal line on the intermediate substrate through the input end of the signal electrode on the main substrate connected to the output end of the signal line, to the base point on the signal electrode, become equal to each other.