| 摘要 |
To provide an optical modulator whereby low-voltage driving and stable modulation characteristics are maintained over a wide band. An optical modulator having a substrate 10, an optical waveguide (not illustrated) formed on the substrate 10, modulating electrodes (signal electrode 11, ground electrode 12) for modulating light waves propagating through the optical waveguide, and an external signal line (not illustrated, only connection connector 4 shown) for supplying a modulation signal to the modulating electrodes, the external signal line being provided outside the substrate, wherein the optical modulator is characterized in that the impedance value in an active region S of the modulating electrodes in which an electric field formed by the modulating electrodes is applied to the optical waveguide is set so as to be lower than the impedance value of the external signal line, and an impedance adjusting part 21 configured from a lumped constant circuit and provided with a function for adjusting impedance mainly for modulation signals in a low-frequency region, and an impedance matching line L provided with a function for adjusting impedance mainly for modulation signals in a high-frequency region are arranged between the external signal line and the active region of the modulating electrodes. |
