An optically controlled coplanar waveguide phase-shifter

Phase-shift measurements of an optically controlled coplanar waveguide phase shifter were performed at various illuminating intensities. This device is based on the interaction between the guided wave on a coplanar waveguide (CPW) and an optically induced electron-hole plasma in a semiconductor substrate. A prototype device consisting of a CPW on a heterojunction substrate of AlGaAs/GaAs/AlGaAs was fabricated and tested. The measured phase-shift obtained with the total illuminating optical power in the -20 dBm range was as large as 50 degrees for a 1 cm-long line at 10 GHz. Although the SWF (slow wave factor) at the higher frequencies is small in comparison to the one at lower frequencies, studies suggest that the SWF at the higher frequencies can be improved by changing the doping concentration of the substrate. The measured results and the advantages of using this approach suggest that optical control is an attractive alternative to the Schottky contacted phase-shifter approach.<>