Hybrid metasurface for ultra-broadband terahertz modulation

Jane E. Heyes*, Withawat Withayachumnankul, Nathaniel K. Grady, Dibakar Roy Chowdhury, Abul K. Azad, Hou Tong Chen

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    40 Citations (Scopus)

    Abstract

    We demonstrate an ultra-broadband free-space terahertz modulator based on a semiconductor-integrated metasurface. The modulator is made of a planar array of metal cut-wires on a silicon-on-sapphire substrate, where the silicon layer functions as photoconductive switches. Without external excitation, the cut-wire array exhibits a Lorentzian resonant response with a transmission passband spanning dc up to the fundamental dipole resonance above 2 THz. Under photoexcitation with 1.55 eV near-infrared light, the silicon regions in the cut-wire gaps become highly conductive, causing a transition of the resonant metasurface to a wire grating with a Drude response. In effect, the low-frequency passband below 2 THz evolves into a stopband for the incident terahertz waves. Experimental validations confirm a bandwidth of at least 100%, spanning 0.5-1.5 THz with -10 dB modulation depth. This modulation depth is far superior to -5 dB achievable from a plain silicon-on-sapphire substrate with effectively 25 times higher pumping energy. The proposed concept of ultra-broadband metasurface modulator can be readily extended to electrically controlled terahertz wave modulation.

    Original languageEnglish
    Article number181108
    JournalApplied Physics Letters
    Volume105
    Issue number18
    DOIs
    Publication statusPublished - 3 Nov 2014

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