Low-Powered, Electrically Controllable Tamm Plasmons for High On/Off Ratio Optical Switch

Recent advances in reconfigurable photonics have attracted attention for enabling the active manipulation of light, facilitating rapid information transfer and high-density multi-spectral operations. The fundamental requirements of active photonics are the photonic structure, which confines a specific wavelength range at the target resonance, and the active material that modifies the condition of light-matter interaction using external stimuli or control mechanisms [1]. To confine and propagate electromagnetic waves effectively, these resonators rely on photonic structures. Specifically, in metasurfaces-driven reconfigurable photonics, photonic structures have emerged as highly promising, leveraging resonant properties to interact with light and enable localized manipulation, detection, or confinement at subwavelength scales. However, the intricate design and complexity of fabrication processes have posed challenges. Alternatively, thin-film-based optical modulators have shown significant potential for strong light-matter interaction, even with simplified configurations. Tamm plasmon (TP) structures, as powerful planar plasmonics, offer efficient light absorption. Optical TPs can occur at the interface between distributed Bragg reflectors (DBRs) and an absorbing layer with layers of optical thickness half the light wavelength [2]. While the lossy layer efficiently absorbs the confined electric field density at the interface in the Tamm plasmon state, complete elimination of the lossy property is necessary to deactivate the absorption. To unlock their active functionality, the ability to perform optical mode conversion between lossless and absorption states is essential.<br/><br/>In this study, we introduce the active Tamm resonator, which utilizes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as the active material for optical modulation. By applying a voltage range of ±1 V, the resonator transitions from a Tamm resonant state (complete absorption) to a mirror state (total reflection). PEDOT:PSS possesses optical characteristics that enable efficient and rapid conversion of the optical mode between a lossless state (dielectric) and an absorption state (metallic) through a redox electrochemical reaction [3]. This conversion is achieved through an electrochemical redox reaction involving proton exchange, facilitated by self-aligned Au nanocolumns acting as a membrane between TPs and electrode for fast proton permeability. The active Tamm resonator exhibits reversible and fast response, characterized by triggered stimulation. Notably, cyclical writes and erase states generate a hysteresis loop, enabling the development of a non-volatile memory device. By sequentially programming the input electrical signal, the fabricated device demonstrates optically readable information with excellent retention. Moreover, by designing a circuit that can address each pixel, we have developed an information storage system that uses square pulsed potentials for optical recording and reading. Overall, this research emphasizes the design of optical structures and material selection for the active Tamm resonator as a powerful tool in reconfigurable photonics.<br/><br/>[1] J. Karst, M. Floess, M. Ubl, C. Dingler, C. Malacrida, T. Steinle, S. Ludwigs, M. Hentschel, H. Giessen, " Electrically switchable metallic polymer nanoantennas," Science. 374, 612-616 (2021).<br/>[2] S. H. Kim, J. H. Ko, Y. J. Yoo, M. S. Kim, G. J. Lee, S. Ishii, Y. M. Song, “Single-Material, Near-Infrared Selective Absorber Based on Refractive Index-Tunable Tamm Plasmon Structure,” Adv. Opt. Mater. 10, 2102388 (2022).<br/>[3] J. H. Ko, Y. J. Yoo, Y. Lee, H.-H. Jeong, Y. M. Song, “A review of tunable photonics: Optically active materials and applications from visible to terahertz,” iScience 25, 104727 (2022).