Four-state electro-optic switch operating in the short-wave infrared enabled by a dual transparent window C-bar-shaped antenna/AZO metasurface

The short-wave infrared (SWIR) band has become a pivotal spectral window for optical communications, multi-wavelength routing, and integrated photonic logic circuits. Conventional electro-optic switches, however, still face significant challenges in channel count, modulation depth, and insertion loss. To achieve multi-state, broadband, low-loss asynchronous control, we propose a C-shaped split-ring antenna that generates a plasmon-induced-transparency (PIT)-like transparent window through plasmonic coupling between the antenna and the aluminum-doped zinc oxide (AZO) film, and integrate it into a dual-window C-bar-shaped antenna/AZO metasurface. The first window extends approximately 175 nm across the Near-Infrared I and II regions, while the second provides PIT-like transparency over 535 nm, covering the O- and C-telecommunication bands. Consequently, we demonstrate a four-state electro-optic switch realised on this C-bar-shaped antenna/AZO metasurface, in which the modulation of the AZO electron density enables operation from 920 to 1235 nm with a peak modulation depth of 97.08 %, an extinction ratio up to 15.35 dB, and an insertion loss as low as 0.83 dB. These findings offer quantitative design guidelines for next-generation photonic devices.