Patent ID: 7088489

Claim:
A launch arrangement for launching RF energy into an input portion of a coplanar RF energy-coupling electrode structure of an electro-optic modulator, said RF energy-coupling electrode structure including an RF signal electrode and ground electrodes overlying an interaction region containing an optical channel of said electro-optic modulator substrate, said launch arrangement comprising: an RF signal input electrode overlying and dielectrically isolated from said substrate, and having a first RF signal input electrode portion to which an RF signal is applied, and a second RF signal input electrode portion that is joined with said RF signal electrode of said coplanar RF energy-coupling electrode structure, said first RF signal input electrode portion having a first geometry that is sized to provide an impedance-watching connection and maximize confinement of electric field of fundamental coplanar waveguide (CPW) mode with an external RF signal conductor, and said second RF signal input electrode portion having a second geometry, smaller than said first geometry, and sized to provide an impedance-matching connection and maximize confinement of electric field of fundamental coplanar waveguide (CPW) mode with said RF signal electrode of said coplanar RF energy-coupling structure; and at least one ground electrode coplanar with said RF signal input electrode, and having a first ground electrode portion of a third geometry to which a ground potential is applied, and a second ground electrode portion of a fourth geometry that is sized to provide an impedance-matching connection and field confinement of the dominant coplanar waveguide mode with said ground electrode of said RF signal electrode of said coplanar RF energy-coupling structure, and being spaced apart from said RF signal input electrode by a separation geometry that is effective to maximize confinement of propagation energy of dominant CPW mode and mitigate against coupling of RF energy from said launch arrangement into a portion of said substrate outside said interaction region.