Optically tunable millimeter-wave attenuator based on layered structures

A new type of optically controllable, millimeter-wave (MMW) attenuator base d on high-resistivity (high-R) silicon (Si) wafers and a layered structure is developed. A high-R float-zone Si wafer is a lossless dielectric materia l at microwave frequency without optical excitation. When an Si wafer is op tically excited, free carriers are generated, and the Si wafer becomes a lo ssy dielectric. This property is combined with a layered structure to devel op a simple optically tunable MMW attenuator. A more than 20 dB attenuation with a 10% bandwidth of the center frequency is obtained at W-band. The pr oposed structure is useful for developing low-cost attenuators and switches in the MMW region. (C) 2000 John Wiley & Sons, Inc.