SG11201807888XA - Optical modulator - Google Patents

Abstract

OPTICAL MODULATOR In a dual electrode Si optical modulator having a CPW electrode structure according to a related art, a phase difference of return currents propagating through two ground electrodes degrades the modulation frequency characteristic. To prevent this degradation, the modulator length has been shortened to terminate signal propagation before occurrence of a phase difference, or the phase difference has been reduced by reducing the difference between capacitance at a pn junction of an optical waveguide and capacitance between an RF electrode and a ground electrode without an optical waveguide interposed therebetween. However, a short modulator length would reduce an electric field applied to the optical waveguide, thus lowering the modulation efficiency. An air bridge or a wiring line was not compatible with a CMOS-compatible process. An optical modulator according to the present invention includes a bridge wiring that connects two ground electrodes, disposed between an RF electrode and an optical waveguide inside a substrate. The bridge wiring equalizes the potential between the two ground electrodes of the CPW, thereby eliminating a phase difference of return currents induced by a radio-frequency electrical signal to the RF electrode and propagating through the two ground electrodes. It is thus possible to fabricate a Si optical modulator with suppressed degradation of the radio frequency characteristic. Such an optical modulator also deals with the problem of a mask offset during implantation in the fabrication process. (Figure 8)