Patent ID: 7830580

Claim:
A semiconductor optical modulator comprising: a heterostructure single mode semiconductor optical waveguide which includes: a stripe optical waveguide in which a lower clad layer formed on a semiconductor substrate and having a first conductivity, an undoped core layer in which a complex refractive index for a signal light propagating therein is changed in response to a strength of an applied electric field, and an upper clad layer having a second conductivity, which are layered in this order from lower layer; and a semi-insulating buried layer formed to sandwich the stripe optical waveguide from its left and right; a below cut-off parallel plates arranged on a side wall of the semi-insulating buried layer on a side to which the stripe optical waveguide is not contacted, and composed of a pair of conductor walls arranged on left and right of the stripe optical waveguide; and a pair of electrodes configured to provide potentials to the lower clad layer and the upper clad layer independently and to form a transmission line in which an RF signal propagates in parallel with a signal light propagating in the undoped core layer.