Investigation of Optically Controlled Millimeter Wave Coplanar Waveguide Photoconductive Device

Devices based on photoconductive materials are promising solutions for future reconfigurable millimeter-wave communication systems. So far, there are several examples of photoconductive radio-frequency switches in the literature, however, their operating frequency and performance are low compared to other radio-frequency switching techniques. In this paper, we propose different photoconductive switch topologies based on the coplanar waveguide, which is more suitable for millimeter-wave applications than the published solutions. The utilization of germanium as the photoconductive element is also evaluated. The main advantages of germanium are its high carrier mobility and lifetime, which facilitates the creation of efficient devices, uniform carrier concentration in thick layers, which enhances interaction with the electromagnetic field in transmission line as well as sensitivity in 1.5 mu m spectral region, which simplifies the integration of radio-frequency equipment based on photoconductive devices with existing telecommunication networks. The construction of the switch was evaluated using full-wave electromagnetic simulations based on the finite-difference time-domain method. The influence of the photoconductive substrate conductivity changes on the transmission and reflection characteristics of the coplanar waveguide was investigated. Additionally, the feasibility of the utilization of thin-film photoconductive materials in the proposed switch was examined.