Investigation and Demonstration of a WR-4.3 Optically Controlled Waveguide Attenuator

We report the design and demonstration of a compact WR-4.3 (170-260 GHz, equivalent to WR-4 band in Electronics Industries Alliance band designation) optically controlled waveguide attenuator using an E-plane tapered high-resistivity micromachined silicon absorber. Variable attenuation is realized by illuminating the silicon absorber with different light intensities from a fiber-guided infrared laser diode. Finite element method simulation has shown that high attenuator performance can be potentially achieved. For a prototype demonstration, a WR-4.3 optically controlled attenuator has been designed and implemented using an E-plane split waveguide configuration. The attenuator has been characterized in the WR-4.3 waveguide band using a vector network analyzer and the results show that a 0.6-dB insertion loss, greater than 10-dB return loss, and an average of approximately 25-dB tuning range have been achieved over most of the WR-4.3 band (i.e., 170-230 GHz). This approach is promising for developing high-performance variable waveguide attenuators into the millimeter-wave and terahertz regime.