Optically Controlled Ultrafast Terahertz Metadevices with Ultralow Pump Threshold

Abstract

Arming metasurface with active materials furnishes a feasible solution to dynamically control over terahertz (THz) waves, which is extremely significant for the realization of upcoming sixth generation telecommunications. However, the present active materials are mainly limited to single external driving field, hindering the capability of metasurface for flexible manipulation of THz waves. Besides, less attention has been paid to the energy question how to significantly reduce the pump threshold for achieving the desired function. Here, a germanium (Ge) hybrid Fano metasurface under dual‐stimulus control is experimentally demonstrated. Photoexcitation of Ge thin film enables 100% modulation depth of Fano resonance and ultrafast switching time within 10 ps. By adding current‐bias, the pump threshold to modulate the metasurface is greatly reduced from 1600 to 200 µJ cm−2. Different from the optical modulation independent of film thickness, it is found that the current function is in proportion with the thickness of Ge thin film. Moreover, it is demonstrated that compared to the single optical‐stimulus, the THz amplitude modulation is increased by 56.3% under dual‐stimulus function. This work naturally improves the flexibility and practicality of Ge‐based metadevice and inspires more innovations to boost the development of switchable sensing, lasing spacer, and nonlinear systems.

Multifield-Controlled Terahertz Hybrid Metasurface for Switches and Logic Operations

“…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 ].…”

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

“…This is because the metallic nature of building meta-atoms always holds immobilized properties, thus fixing the function of devices. [26] Therefore, significant attention has been paid to modulators based on tunable metasurfaces consisting of active materials such as semiconductors, [21,[27][28][29][30][31] 2D materials, [32,33,34] phase change materials, [35][36][37][38][39][40] Dirac semimetal, [41] and perovskites. [42][43][44][45][46] Accordingly, depending on various characteristics of the active materials, a series of external stimuli including optical, [27,28,36,38,42,43] electrical, [21,22,29,34,49] thermal, [35,37,47,48] and mechanical [50] methods jointly promote the development of THz modulators in a more intelligent and multidimensional direction.…”

SnSe2-functionalized ultrafast terahertz switch with ultralow pump threshold

“…To solve this problem, researchers have been devoted to the integration of metasurfaces and active materials, leading to the concept of hybrid active metadevices. 13,14 By applying appropriate external stimuli, such as optical, [15][16][17][18][19][20][21][22][23][24][25][26][27][28] electrical, [29][30][31][32] mechanical 33,34 or thermal excitation, 35,36 the intrinsic properties of the active materials can be reconfigured, which endows the metadevices with functional nature. Among these methods, the optical stimulus exhibits distinct advantages in realizing ultrafast switching, owing to the nanoseconds or even picoseconds relaxation time of the photo-generated carriers.…”

“…[37][38][39][40] To date, a series of ultrafast tunable metadevices have been developed to control the amplitude and phase of THz waves. [15][16][17][18][19][20][21][22][23][24][25] For example, under a pump fluence of 1524 mJ cm À2 , the effective switch-off (modulation depth of 90%) for Fano resonance was achieved via 310 nm-thick germanium (Ge). 16 By coating a 300 nm germanium antimony telluride (GST) layer on the Fano metasurface, Pitchappa et al obtained a complete switching-off of the resonance response, when the laser power was set at 2300 mJ cm À2 .…”