Augmented All-Optical Active Terahertz Device Using Graphene-Based Metasurface

Geunchang Choi, Tuan Khanh Chau, Sung Ju Hong, Dasom Kim, Sung Hyuk Kim, Dai Sik Kim, Dongseok Suh, Young Mi Bahk, Mun Seok Jeong

Research output: Contribution to journalArticlepeer-review

Abstract

Photo-excited graphene has a positive (semiconductor-like) or negative (metal-like) response depending on the Fermi level, which is tuned by gate control, doping, and growth. Both negative and positive photoconductive responses have a potential application as an ultrafast optical modulator in the control of light transmission. However, it is challenging to achieve a high on/off ratio in the photo-excited graphene because of a small absorption of electromagnetic waves and a limitation of photo-induced conductivity change. Here, the negative-type high on/off ratio and ultrafast terahertz modulation are experimentally demonstrated using graphene/metal nanoslot antennas. When the graphene covers the nanoslot antennas, the terahertz waves are completely blocked (off-state). This perfect extinction results from the enhanced intraband absorption in graphene by strong localized fields near the nanogap. However, once the optical pump is applied to the graphene/nanoslot antennas, terahertz transmission becomes recovered resonantly (on-state) due to the photo-induced transparency of graphene that leads to a distinctive modulation from off- to on-resonance. Furthermore, the fast carrier relaxation induced by strong terahertz field-driven carrier redistribution is responsible for the faster modulation of transient terahertz transmission. The results will open up pathways toward negative-response terahertz modulation applications with high on/off ratio and ultrafast time scale.

Original languageEnglish
Article number2100462
JournalAdvanced Optical Materials
Volume9
Issue number16
DOIs
StatePublished - 2021 Aug 18

Keywords

  • graphene
  • metasurfaces
  • optical pump terahertz probe spectroscopy
  • terahertz modulation
  • ultrafast dynamics

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