Terahertz Optical Switches With Movable Silicon Waveguides Monolithically Fabricated on High-Resistivity Single-Crystal Silicon Substrates

Abstract

Photonic integrated circuits (PICs) based on dielectric waveguides are being developed for beyond 5G/6G communication systems. Variable passive elements, essential for PICs, present challenges for downsizing and low power consumption in the terahertz range. Variable passive elements based on microelectromechanical systems (MEMS) are promising solutions; however, the previous terahertz variable passive elements based on MEMS have complex structures processed on all layers of silicon-on-insulator (SOI) substrates. They can be fabricated on a single layer of silicon substrate, which is cheaper than an SOI substrate. However, to the best of the authors’ knowledge, there have been no demonstrations. We proposed a terahertz optical switch, which is one of the variable passive elements, based on comb-drive actuators fabricated on a single layer of silicon substrate. A comb-drive actuator was designed for 200 µm displacement at 104.5 V. An optical switch was designed for an extinction ratio of 18.9 dB at 300 GHz. The device was fabricated on a single layer of high-resistivity single-crystal silicon substrate, achieving a displacement of 185.4 µm at 93 V and an extinction ratio of 13.69 dB at 300 GHz. The optical switch part measured 5.65 mm long and power consumption was only 3.6 mW, outperforming previous works. While conventional comb-drive actuators are fabricated on SOI substrates, our design was fabricated on a single layer of silicon substrate. The proposed single-layer comb-drive actuator can be applied to variable phase shifters, directional couplers, and add/drop filters. This work addresses key challenges in terahertz variable passive elements and contributes to the advancement of terahertz PICs for beyond 5G/6G communications.