Optically Reconfigurable Graphene/Metal Metasurface on Fe:LiNbO₃ for Adaptive THz Optics

Abstract

We demonstrate, experimentally, non-volatile optical control of terahertz metasurfaces comprising of a metallic split ring resonator array sandwiched between monolayer graphene and a photoconductive Fe:LiNbO 3 substrate. We demonstrate frequency selective tuning of THz transmission amplitude, and our results pave the way towards spatially resolved control of THZ metasurfaces for beam-steering, imaging, and sensing applications. The substrate (Fe:LiNbO 3 ) supports non-volatile yet reversible photoinduced charge distributions, which locally modify the electrostatic environment of the nano-thickness graphene monolayer, altering the graphene electrical conductivity and therefore changing the resonance spectra of the metamaterial array. We present lightinduced normalized transmittance changes up to 35% that are non-volatile and persist after the illumination source is removed, yet can be reversed by thermal annealing.

Mechanically Tunable Terahertz Metamaterial Perfect Absorber

“…This work can be used for more efficient THz detection and sensing applications. [13,34] Also, in future, the SRR response may be tuned using active substrates such as photoconductive insulators, [39] in addition to more advanced control over the cavity length using, for example, arrays of microelectromechanical piston actuators [40] to further optimize the maximum absorption and tunability range of the system with potential applications in active phase control.…”

All-Optical Domain Inversion in LiNbO3 Crystals by Visible Continuous-Wave Laser Irradiation

“…Indeed, the ability to generate customized electric field distributions by structured light, without external power supplies or lithography-patterned electrodes, makes Fe:LN a rather versatile and appealing asset. For example, Fe:LN has been successfully employed for the optofluidic manipulation of liquid droplets, − manipulation and patterning of micro/nanoparticles by PV optoelectronic tweezers, − guided locomotion and alignment of liquid crystals, − optical gating of graphene, or hybrid Fe:LN-graphene metasurfaces . All of these applications have been developed with monodomain Fe:LN crystals.…”

“…For example, Fe:LN has been successfully employed for the optofluidic manipulation of liquid droplets, 48−53 manipulation and patterning of micro/nanoparticles by PV optoelectronic tweezers, 54−58 guided locomotion and alignment of liquid crystals, 59−62 optical gating of graphene, 63 or hybrid Fe:LN-graphene metasurfaces. 64 All of these applications have been developed with monodomain Fe:LN crystals. However, multidomain structures could enhance the flexibility and potential of Fe:LN platforms, allowing the light-induced generation of arbitrary 2D bipolar charge distributions on z-cut substrates.…”

Optically Defined Reconfigurable THz Metasurfaces using Graphene on Iron‐Doped Lithium Niobate

“…In this work, we characterized the graphene via Raman spectroscopy to confirm its monolayer thickness and absence of defects, and performed measurements of the electrical resistance of the device with an Agilent probe station in response to optical illumination. Following on from this, in 2020, [ 44 ] we published an experimental demonstration of the graphene on iron‐doped lithium niobate platform for tuning of THz frequency resonances by incorporating a metallic metasurface sandwiched between the graphene and lithium niobate. The effect was demonstrated to be nonvolatile yet reversible upon the application of heat.…”