Optimization of a Photonically Controlled Microwave Switch and Attenuator

A silicon-based photoconductive switch and attenuator for microwave signals has been demonstrated and optimized for low insertion loss and high attenuation response upon illumination from a standard infrared LED. This device is fabricated within a coplanar waveguide for easy integration into a planar antenna for photonic control of an array. A general tradeoff exists between the goals of low insertion loss and high attenuation range. However, design and process enhancements are found to improve the device performance. A device that offers up to 20-dB attenuation with insertion loss of only 0.6 dB at 2.0 GHz is demonstrated. These devices show a frequency range where the insertion phase shift upon attenuation is significantly less than 1°/dB.