Tunable and reconfigurable bandstop filters enabled by optically controlled switching elements

Abstract

The authors report a novel approach for designing tunable and reconfigurable bandstop filters by employing bias-free optically-controlled photoconductive radio frequency (RF) switching elements. To verify the effectiveness of the approach, a bandstop filter with two stopbands centred at 4.05 and 4.75 GHz was designed using a split-ring-coupled microstrip transmission line on RO3010 substrates. To enable reconfigurability, a micromachined Si chip with a thickness of ∼73 μm was embedded in the gap of each resonator. The tuning and reconfiguring of the filter are accomplished by selectively illuminating the Si chips using fibre-coupled laser diodes with a wavelength of 808 nm. By turning on and off each laser diode, the filter stop bands can be dynamically reconfigured. In addition, the suppression of each stop band can be continuously and independently tuned by changing the light intensity from 0 to 20 W/cm2. With geometric scaling, this approach is promising for realizing a novel class of compact and high-performance tunable and/or reconfigurable circuits from the microwave to mmW-THz region.