Multifield Controlled Terahertz Modulator Based on Silicon‐Vanadium Dioxide Hybrid Metasurface

Abstract

Despite flourishing and deepening trend in the terahertz (THz) field, there are still challenges in high‐performance active system components, such as THz modulators. Present THz modulators are typically limited to a single external driving field and the fixed switching speed, hindering the ability to flexibly manipulate THz waves. Here, an optically and thermally controlled THz modulator based on silicon (Si) and vanadium dioxide (VO2) hybrid metasurface is proposed to overcome these limitations. The modulator enables the dynamical control of the transmitted amplitude in the range of 0.4–1.8 THz. Under thermal management, a maximum modulation depth (MD) of 97.2% at 0.9 THz can be acquired, thanks to the phase transition of VO2. Once excited with an 800 nm pump light at 1600 µJ cm−2, the device achieves a maximum MD of 91.5% at 0.87 THz accomplished with an ultrafast speed of 2 ps, resulting from photogenerated carriers in the Si substrate. Furthermore, the findings of this study propose a promising strategy for developing multifield controlled active THz components, which would be a new paradigm to design switchable metasurface devices.

Multifield-Controlled Terahertz Hybrid Metasurface for Switches and Logic Operations

“…In the common long side of SRR I and SRR II , an embedded VO 2 bridge was precisely connected to the electrodes and resonators, which could undergo a reversible phase transition triggered by the heat generated from external currents. The dielectric permittivity of VO 2 can be described using a Drude model [ 51 ]: where and are usually assumed to be 12 and 5.75 × 10 13 rad/s, plasma frequency is dependent on conductivity, and σ is proportional to the free carrier density [ 44 , 52 ]. Additionally, to properly manipulate resonance intensity, semiconductor layers made of Ge were selected to wrap SRR III and SRR IV .…”

“…The linear plane waves are normally incident with Y polarization along the negative Z direction. To imitate the phase transition of VO 2 induced by electrical voltage, conductivity was varied from 2 × 10 2 to 2 × 10 5 S/m [ 50 , 52 , 53 ]. Similarly, the conductivity of Ge was varied from 1 to 4 × 10 3 S/m to simulate the influence of optical pump irradiation [ 49 , 54 ].…”

“…Similarly, the conductivity of Ge was varied from 1 to 4 × 10 3 S/m to simulate the influence of optical pump irradiation [ 49 , 54 ]. It is essential to mention that a 400 nm optical pump (3.1 eV) is typically used to activate the photoinduced carriers in Ge (0.66 eV), and the pump frequency enables the Ge conductivity change to 4 × 10 3 S/m that only leads to a slight alteration in undoped VO 2 conductivity, thus ensuring independence between the two modulation approaches [ 52 , 55 , 56 , 57 ]. The normalized transmission spectra were calculated via the formula: |T(ω)| = |E s (ω)/E r (ω)| with E s (ω) and E r (ω) representing the amplitude of THz waves transmitted through the device and the thickness of bare sapphire, respectively [ 58 ].…”

Terahertz modulation characteristics of three nanosols under external field control based on microfluidic chip

“…Based on a Si/VO 2 hybrid metasurface, Zhao et al proposed a photothermally controlled THz modulator capable of dynamically controlling the transmission amplitude in the range of 0.4-1.8 THz. With the improvement of application requirements, the preparation of broadband flexible THz modulators has become a research hotspot (Zhao et al, 2022). Several two-dimensional materials have been applied to develop flexible THz devices.…”

Reassessing Fano Resonance for Broadband, High‐Efficiency, and Ultrafast Terahertz Wave Switching

“…[ 14 , 15 ] Due to its adjustable and on‐demand optical qualities, THz microcavities in the form of artificially constructed subwavelength metamaterials have received considerable attention in the THz photonics field. [ 16 , 17 , 18 , 19 ] Recent developments in functional THz metadevices have drawn attention toward versatile modulations by using mechanical, [ 20 , 21 , 22 , 23 ] electrical, [ 24 , 25 ] thermal, [ 26 , 27 ] magnetic, [ 28 ] and optical [ 29 , 30 ] approaches. To fully exploit the potential of terahertz radiation, the urgent application‐side demands have propelled this topic ahead swiftly and elevated active metadevices to be the frontier of metasurface research.…”