Optically CW-mode controlled microwave switches with carrier-confinement on a coplanar waveguide

A new design for optically controlled microwave switches on a semiconductor coplanar waveguide (CPW) with carrier-confinement using a CW laser is presented. The CPWs having a different gap on each signal line are designed and fabricated on a high-resistivity silicon wafer with micro-fabrication technology. To minimize the insertion loss and to obtain a higher on/off ratio with the same optical power, the gap areas between the signal line and the ground plane are etched out using an isotropic-etching technique, and the generated free carriers can be confined. As a result, the insertion loss can be reduced by more than 4 dB with the same optical power. The design for the etching area and the depth are optimized with the numerical simulation results for the generated free-carrier distribution and transmission characteristics.