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Abstract
The active modulation of the Fano resonance is rare but desirable. However, recent studies mostly focused on a single modulation method and few reported the use of three photoelectric control methods. A tunable graphene DNA-like metamaterial modulator with multispectral Fano resonance is demonstrated. In experimentally fabricated metamaterials with six photoelectric joint modulation patterns, each joint shows different optoelectrical response characteristics. Ultrahigh modulation depth (MD) up to 982% was achieved at 1.5734 THz with a 1.040 A external laser pump by involving combined optoelectrical methods. These results show that the metasurface modulator is a promising platform for higher-order Fano resonance modulation and communication fields.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Two-dimensional metamaterials, known as metasurfaces, are periodic two-dimensional artificial materials that have specific properties that natural materials cannot surpass [1–5]. Metasurfaces have promising applications, e.g., as absorbers [6,7], antennas [8], stealth cloakings [9], and sensors [10–12]. Fano resonance, which was first reported by Fano in 1961, gives an asymmetric line shape, which can be observed in the electromagnetic spectrum. Fano resonance originates from the interaction between a continuum state and a discrete quantum-level state. It has many important applications, e.g., in slow-light devices [13], biosensing [10–12], plasmonic switching, plasmon rulers [14], and Fano modulators [15–18]. The applications of multiple Fano resonance switching are more diverse and flexible than those of a single Fano resonance, and they can be integrated into photonic devices such as wavelength division multiplexers [19], multicolor nonlinear processes [20,21], solar cells [22], and plasmon rulers [14] and so on. There have been few reports of multiple Fano resonances based on metasurface, although research in this area is important. Higher-order Fano resonances have better tuning performances over lower-order Fano resonances when used in cooperation with optoelectronic modulation. Higher-order Fano resonances such as the quadrupolar (Q), octupolar (O), hexadecapolar (H), and triakontadipolar (T) [23–25] modes have a higher Q factor. Until now, the line shape, position, sharpness, resonant modes, and depth of a Fano resonance have been passively restricted by the properties of the metasurface, e.g., shape, position, and materials. Recent reports have indicated that active modulation of the characteristics of the Fano resonance are rare but desirable. Three types of modulation have been proposed for achieving delicate control of metadevices, namely electrical modulation, light modulation, and combined electrical–optical modulation. There have been few reports that discussed the use of three photoelectric control methods based on metasurface. These three methods can give three different kinds of responses, which can be used to obtain modulation devices that accurately control the optoelectrical response. Most modulation functions of tunable devices are achieved by external excitation with a magnetic field [26] or thermal field [27,28], and by electrical [29,30] and optical [31–34] methods through using a photoelectric-adjustable material.
Graphene is a two-dimensional material with specific optical and electrical properties such as high transferred electron mobility and tunable conductivity and is a promising photoelectronic material for external excitations [19,35,36]. These properties can be considerably and rapidly changed by varying the electric gating. In 2020, Li et al. obtained an active Fano metasurface by using a graphene-based asymmetric split ring metasurface [37]. The active tunable function was achieved by using a combination of optical pump illumination and a biased voltage. In 2020, Zhen et al. theoretically investigated multiple Fano resonances in an asymmetric hybrid graphene–metal metamaterial [38].
Recently, the split ring shape and its many variations were widely employed for metasurface design for a variety of uses, such as the gradient metasurface [39] and the fields of structural experimental mechanics [40]. In this study, one tunable graphene metasurface which is composed of periodic structures of twisted DNA-like split rings was developed. The metasurface exhibited multiple Fano resonance points in the y-polarized direction when graphene is not used. Three modulation methods were applied to obtain the tunable transmission characteristics of the metasurface experimentally. We experimentally identified the advantages and disadvantages of these three modulation methods. The results show that the Fano modulator with a combination of electrical and optical modulation has the best modulation characteristics. The maximum modulation depth (MD) was 982%. These results indicate the metasurface modulator is a promising platform for higher-order Fano resonance modulation and communication fields.
2. Materials and methods
2.1 Design of metal−polyimide-integrated terahertz metasurfaces
In Fig. 1(a), the red electromagnetic wave represents the incident terahertz wave and the green electromagnetic wave represents the laser wave in Fig. 1(b) and 1(c). In the experiments, a terahertz time-domain spectrometer (TDS) (DaHeng Company) was used to obtain the transmission characteristics of the designed Fano metasurface in the absence of a graphene layer. In the experiments with optical modulation alone. The instruments shown in Fig. 1(b) were assembled and used. Figure 1(b) shows the terahertz optical dynamic transmission characteristics observed in this type of experimental environment when the optical laser pump current setting was varied from 0 mA to 1360 mA with a terahertz optical excitation pulse.
Fig. 1. Schematic diagrams of DNA-like metasurfaces. (a) Metasurface without external stimuli. (b) Metasurface with optical stimuli. (c) Metasurface with electrical stimuli or combined optoelectrical stimuli. (d) Geometric parameters of the unit cell of the metasurface are px = 248 µm, py = 300 µm, l1 = 218.96 µm, l2 = 105 µm, d1 = 10.5 µm, d2 = 14.04 µm, w1 = 6 µm, w2 = 4 µm. (e) Fabricated microscopy image of the metasurface. (f) Raman spectra of three-layer graphene at three different locations on the JGS1 substrate. (g) Capacitor effects of the unit cell. (h) Comparison of measured y-polarized transmission spectra of metasurface with or without graphene. (i) Simulated transmission spectra of y-polarized incident terahertz waves.The y direction is defined according to the coordinate system in Fig. 1(a) and the electric field is propagating along the y direction.
As shown in Fig. 1(c), external biased voltages were applied to the graphene layer on the metasurface. The applied voltage equipment consisted of an adjustable DC voltage source. The source was connected to two metallic probes, which served as positive and negative electrodes. The terahertz electronic dynamic transmission properties were investigated by varying the external biased voltage in the range 0–8 V. After these two experiments, the terahertz optical electronic dynamic transmission characteristics were determined by using a combination of external biased voltages and an external optical laser pump. We still used the instruments shown in Fig. 1(c). In Fig. 1(b) and 1(c), a graphene layer was applied to the metasurface.
A schematic diagram of the metasurface, which consists of DNA-like twisted split rings (DTSRs), is shown in Fig. 1(d). The structure originates from the topology of a small fragment of the DNA projection. There is a small bulge at the lower end of the DTSR structure, which is a linking section that simulates one DNA projection and another DNA projection [41]. The geometric parameters of the DTSR unit cell are shown in Fig. 1(d). A microscopy image of the 1 cm × 1 cm periodic array in the designed and fabricated metasurface is shown in Fig. 1(e). The fabricated MM samples were prepared by the following steps. First, a 500-µm-thick z-cut far-ultraviolet optical quartz glass (JGS1) was prepared as a substrate, then a 10-µm-thick polyimide film was spin-coated on the substrate. The permittivity of the polyimide film was 3.1, and its loss tangent was 0.05. Magnetron sputtering [42] process was used to grow a 0.2-µm thick gold layer on the polyimide layer. A photolithography process was used to etch periodic DTSR patterns on the gold layer. In the next step, a second 10-µm-thick polyimide film was spin-coated and the graphene layer was transferred onto it. To accomplish electric modulation, a thin ionic gel [43] film was transferred onto the graphene layer for charge accumulation and storage. Multilayered (three to five layers) graphene was prepared and the graphene layers were transferred onto the new polyimide layer. Raman spectroscopy with a 514 nm excitation laser (Fig. 1(f)) was used to investigate the properties of the three-layer graphene. The anisotropic structure of the unit cell led to the small gaps between the DTSR arrays being filled with polyimide. Figure 1(g) shows that the small gaps in each unit cell acted as capacitors. We obtained the y-polarized transmission spectra with and without graphene in the absence of external stimuli (Fig. 1 h). The two curves show similar trends, except for some discrepancies in the resonant valleys and transmission amplitudes, which can be attributed to fabrication deviations of the metasurface.
2.2 Simulated y-polarized transmission spectra and physical mechanism
The black curve in Fig. 1(i) represents the y-polarized transmission spectrum without graphene and external stimuli. It contains five resonant valleys. CST software was used to simulate the E-field distribution in the absence of graphene and obtained the E-field distribution maps shown in Fig. 2(a)–(d). The Max, Min denotation goes from a minimum negative value to a maximum positive value.The designed Fano resonance of the metasurface resulted from interference caused by the coupling effect between the super-radiant bright mode and the sub-radiant dark mode. Because of the broken symmetry, there are p nodes in the electromagnetic field distribution of the DTSRs. The relationship between the node number, p, and the number of the mode order, n, is n = 2p. The 2p-order electromagnetic Fano resonance is produced [23–25] when the node number is p. When the order 2p is larger than 4, it is defined as higher-order modes, or it is defined as lower order modes.
In Fig. 2(a), at 0.196 THz, the red region indicates the positive part of the dipoles and the blue region indicates the negative part. The node number is 1. This indicates that there is one pair of dipole modes in the inner region of the DTSR unit cell structure. This resonant mode is not a higher-order Fano resonance mode. Also, it is not a Fano resonance point.
Figure 2(b) shows that at 0.36 THz the node number is 2. This resonant mode is a quadrupole mode, not a higher-order mode. Figure 2(c) shows that at 0.932 THz, the node number is 3. This indicates that this resonant valley is a higher-order octupolar (O) mode. As shown in Fig. 2(d) at 1.536 THz, the node number is 4. This resonant valley has a super-higher-order hexadecapolar (H) mode. These resonant frequencies in Fig. 2(b) to 2(d) are all Fano resonance points.
2.3 Dynamic physical mechanism under different Fermi-level changes
The electrical dynamic transmission characteristics of the graphene–polyimide terahertz metasurface were determined by using a TDS instrument (Fig. 1(c)). The y-polarized dynamic transmission spectrum changed with increasing positive voltage, as shown in Fig. 3(a). Without graphene, the simulated y-polarized transmission spectrum showed five resonant valleys. The y-polarized transmission spectrum with graphene was simulated; the resonant valleys and their corresponding amplitudes and frequencies are shown in Table S1 (Supplement 1). The number of resonant valleys in the simulated transmission spectrum was 12. These numbers of simulated resonant valleys in Fig. 3(b) are much greater than the number of experimentally identified resonant valleys in Fig. 3(a).
Fig. 3. (a) Measured y-polarized transmission spectra with only biased voltage ranging from 0 V to 7 V. (b) Simulated y-polarized transmission spectra when the Fermi level of graphene was set at 0 eV to 0.30 eV.
The tenability of the transmission spectra of multispectral Fano resonances was clarified by simulating the transmission spectra under different Fermi levels, from 0 to 0.30 eV. Figure 3(a) shows the experimental y-polarized transmission spectra with a biased voltage on graphene that increased from 0 to 7 V. Figure 3(b) shows the simulated y-polarized transmission spectra with biased Fermi levels on graphene increasing from 0 to 0.30 eV. These two figures show similar trends; differences are inevitable because of experimental errors or fabrication discrepancies.
3. Results and discussion
3.1 Dynamic electrical modulation of Fano resonance on the metasurface
The three strategies are used to achieve ultrasensitive modulation of the higher-order Fano resonances, using an external minor-power laser pump with the terahertz-TDS measurement system shown in Fig. 1(b). The first modulation uses only light. The second modulation uses only electricity, an external weak DC adjustable voltage source was applied to the graphene film and the terahertz-TDS measurement system in Fig. 1(c). In the third method, an external laser pump and the external DC voltage source were both applied to the graphene film, the third method uses electricity as well as light.The terahertz-TDS measurement system in Fig. 1(c) was also used. For electrical modulation in the y-polarized directions, the biased voltages were varied in the range 0–7 V. The y-polarized transmission curves were obtained and they were shown in Figs. 3(a), Fig. 4 and 5.
Fig. 4. Measured transmission spectra under only optical stimuli, the current of laser pump varied from 0 mA to 1360 mA
Fig. 5. Measured transmission spectra under four photoelectric combined settings. (a) Biased voltage was fixed at 1.03 V and laser pump current was varied from 20 mA to 1360 mA. (b)Biased voltage was fixed at 2.03 V and laser pump current was varied by the same configuration as in Fig. 5(a). (c)Biased voltage was fixed at 4.03 V and laser pump current was varied by the same setting as in Fig. 5(a). (d) Biased voltage was fixed at 7.03 V and laser pump current was varied by the same configuration as in Fig. 5(a).
In Fig. 3(a), under electrical modulation, Fano resonant frequencies were observed, three resonant frequencies(A1-A3) were selected to illustrate the trend. These resonant valleys showed a similar pattern as those in Fig. 2. To compare and comprehend the modulation effects clearly, the amplitude data and corresponding three frequencies were recorded in Tables S2–S7 (Supplement 1). The MDs and frequency shifts were also calculated at the corresponding frequencies. The modulation depth [44] was defined as MD = (TVi – TV0)/TV0, where TVi represents the transmission coefficient when external excitation is applied (biased voltage or optical pump), and TV0 represents the transmission coefficient without external excitation. When the MD is positive, it is increasing relative to the initial state. When the MD is negative, it is decreasing relative to the initial state. The data in Fig. 3(a) show that the maximum negative MD was −53.4% at A3 when the biased voltage was 0.03 V. When the biased voltage was 1 V, the maximum positive MD was 3.22% at A1. Figure 3(a) shows that when the biased voltage was increased from 0 to 0.51 V, the transmission curve in different sections experienced two different stages. In one stage, the transmission initially increased and then decreased, and then the changes were repeated (FITDR). In the other stage, the transmission initially decreased and then increased, and then the changes were repeated (FDTIR). The FITDR stage occurred at frequency points A1 and A3. The FDTIR stage occurred at some other frequency points. In the transmission spectra, many resonant frequencies disappeared and reappeared. The transmission decreased when the voltage was increased from 0 to 0.03 V. When the biased voltage was increased from 0.03 to 1 V, it increased. When the biased voltage increased from 1 to 4 V, it decreased. When the biased voltage increased from 4 to 7 V, it increased. Figure 3(a) shows that overall, the transmission went through the FDTIR process. The maximum frequency shift was 0.05 THz, when the biased voltage was 0.03 V at 1.8731THz. Two large decreases in amplitude were observed, namely when the biased voltage was increased from 0 to 0.03 V, and when the voltage was increased from 1 to 4 V. In the other periods, the amplitude was always increasing relative to the initial state. This can be explained by two important factors. One is the strength of the graphene Fermi-level [44] enhancement. The other is the capacitance effect in the DTSR unit cell. Initially, when the biased voltage was increased from 0 to 0.03 V, the Schottky effect had not been established in the graphene film via a connection between the electrodes and the ionic gel. The holes and electrons inside the graphene film accumulated at opposite sides with increasing biased voltage. However, the number of carriers [45] was not large enough to induce a Fermi-level transition of the graphene layer. The capacitance effects therefore dominated. As the biased voltage was increased from 0.03 to 4 V, carriers accumulated inside the gaps and the capacitance acted as a barrier to increases in transmittance. In this period, the carrier strength dominated, therefore the transmittance was always increasing. Until this balance was broken, the capacitance effect dominated, and the transmittance decreased when the voltage was 4 V. As the biased voltage increased from 4 to 7 V, sufficient carriers accumulated, Fermi-level enhancement dominated the modulation process, and therefore the transmittance was increasing.
3.2 Dynamic optical modulation of Fano resonance on the metasurface
As shown in Fig. 1(b), the minor optical pump current was varied from 0 to 1360 mA. The y-polarized transmittance curves (Fig. 4 and Table S3 in Supplement 1) were acquired. Figure 4 showed that there were higher-order Fano resonant frequencies, three resonant frequencies (B1-B3) were selected to illustrate the trend. This pattern is similar to that of the higher-order Fano resonant modes in Fig. 2. Figure 4 shows that the transmission spectra involved three types of stages. The first was an initial increase followed by a decrease and then an increase (FITDI) at B2 and B3. The second stage was an initial decrease followed by an increase (FDTI) at B1. The third was FITDR at some other frequencies. The data in Fig. 6(b) show that the MD was −85.90% at B3 and 67.35% at B2.
Fig. 6. The illustration of modulation depth trend with the change of frequency. (a) The modulation depth when only under only optical stimuli. (b) The modulation depth when under only electrical stimuli. (c) The modulation depth when the biased voltage is 1.03V under the combined optical and electrical stimuli (d) The modulation depth when the biased voltage is 2.03V under the combined optical and electrical stimuli (e) The modulation depth when the biased voltage is 4.03V under the combined optical and electrical stimuli (f) The modulation depth when the biased voltage is 7.03V under the combined optical and electrical stimuli.
The data in Table S3 in Supplement 1 show that the maximum frequency shift was 120 GHz at 1.1988 THz, when the external pump current was 640 mA. The overall trend in Fig. 4 shows that when the pump power current was increased from 0 to 80 mA, the transmission was increased. When the pump power current was increased from 80 to 1360 mA, the transmission was always decreasing relative to the initial state. This can be explained by the two factors mentioned in the previous section. One factor is the capacitance effect shown in Fig. 1. The other factor is the strength of the Fermi-level enhancement of the graphene layer. Initially, when the biased voltage increased from 0 to 80 mA, the capacitance effect had not been established in the graphene layer. With increasing laser pump power current, because a minor laser pump was used, a low Fermi level was needed to overcome the weak capacitance effect, and it dominated the process. When the laser pump power current was increased from 80 to 1360 mA, the minor laser pump had insufficient strength to reach a higher Fermi level. The capacitance effect was enhanced and the barrier to transmittance was enhanced, therefore the transmittance was always decreasing.
3.3 Combined dynamic electrical and optical modulation of Fano resonance on the metasurface
Precise modulation of the terahertz response was achieved by using the cooperative and joint photoelectric modulation method shown in Fig. 1(c). As shown in Fig. 5, the external voltage at 1.03, 2.03, 4.03, and 7.03 V was fixed first, and then changed the external optical pump current from 0 to 1360 mA. Four different patterns were observed in the transmission spectra. Also, in Fig. 4 and 5, higher-order resonant frequencies were observed, three resonant frequencies in each pattern as C1-C3, D1-D3, E1-E3, and F1-F3 were selected to illustrate the trend. Figure 5(a) and the data in Table S4 in Supplement 1 show that there were three resonant frequencies, namely C1, C2, and C3, and the modulation effect was weak. As shown in Fig. 6(c), the negative MD was −28.07% at C3 when the biased pump current was 560 mA. The positive MD was 4.16% at C2 when the biased pump current was 560 mA. The frequency shift was initially blue, then red, and then blue (FBTRB) at C2. The maximum frequency shift (40 GHz) occurred at both C2 and C3. The weak modulation effect can be explained by the weak Fermi-level effect and the weak capacitor effect induced by the change of the dielectric constant in this environment. Figure 5(b) and the data in Table S5 in Supplement 1 show that the transmission spectra went through stages of three types. The first involved an initial decrease, then an increase, then a decrease (FDTID) at D1. The second involved an initial decrease and then an increase (FDTI) at D2 and D3. The third involved repeatedly involved an initial decrease, then an increase, and then a decrease (FITDR) at some other resonant frequencies. The data in Fig. 6(d) show that the maximum positive MD was 5.22% at D2, when the biased pump current was 1360 mA, and the maximum negative MD was −44.25% at D3, when the biased pump current was 1120 mA.
The frequency shift was initially red, then blue, and then red (FRTBR) at D2.The maximum frequency shift (120 GHz) occurred at D2. The transmittance was always decreasing relative to the initial state. The transmittance at frequencies greater than 1 THz fluctuated more than the one observed in Fig. 5(a). This is because the Fermi level was higher than that in Fig. 5(a). However, the capacitance effect was still dominant. Because of the barrier to transmittance, the curve kept decreasing relative to the initial state. The higher Fermi level pushed the fluctuation of the higher-order Fano resonances at higher frequencies. Figure 5(c) and the data in Table S6 in Supplement 1 show that the transmission spectra went through stages of three types. The first, at E1, involved an initial increase, then a decrease, and then an increase; the changes were then repeated (FITDR). The second involved an initial increase and then a decrease (FITD) at E3. The third involved an initial decrease and then an increase (FDTI) at some other resonant frequencies. The data in Fig. 6(e) show that the maximum negative MD was −44.47% at E2, when the biased pump current was 240 mA, and the maximum positive MD was 982% at E3, when the biased pump current was 1040 mA. The maximum frequency shift (130 GHz) occurred at E2. The transmittancefirst decreased and then was always increasing relative to the initial state.
The transmittance at frequencies greater than 1 THz was more flexible than that in Fig. 5(b). This is because the Fermi level was higher than that in Fig. 5(b). When the optical pump current was increased from 0 to 240 mA, the capacitance effect was still dominant, therefore the transmittance was decreasing relative to the initial state. With increasing optical pump current, the Fermi-level strength dominated the next process. A higher Fermi level drove the strong fluctuations of higher-order Fano resonances at higher frequencies. Figure 5(d) and the data in Table S7 in Supplement 1 show that the transmission spectra involved stages of three types. The first was an initial decrease, then an increase, and then a decrease (FDTID) at F1. The second involved an initial increase, then a decrease, and then an increase (FITDI) at F3. The third involved an initial increase and then a decrease (FITD) at F2. The data in Fig. 6(f) show that the maximum positive MD was 139.96% at F3, when the biased pump current was 1360 mA, and the maximum negative MD was −51.26% at F2, when the biased pump current was 1040 mA. The maximum frequency shift (100 GHz) occurred at 1.8731THz, the frequency shift was blue.
The transmittance first decreased and then was always increasing relative to the initial state. The transmittance at frequencies greater than 1 THz was less flexible than that in Fig. 5(c). Although the Fermi level reached was higher than that in Fig. 5(c), the capacitance effect was weaker than that in Fig. 5(c). Initially, the Fermi level was beyond the Dirac point; the Fermi level increased with increasing applied current. The strength of the Fermi level was dominant, therefore the transmittance was increasing relative to the initial state. When the external laser pump current was increased from 0.2 A to 0.8 A, the Fermi-level strength dominated the process, therefore the transmittance was increasing. When the external laser pump current was increased from 0.8 A, the balance was broken and the capacitance effect dominated the process. When the external laser pump current was switched from 0.8 to 1.36 A, because of the high external voltage (7 V), the capacitor in the ionic gel broke down and the capacitor effect of the ionic gel was weakened. The carriers could not further accumulate in the graphene layers and the number of carriers are limited, therefore the strength of the Fermi level was limited. If the external voltage exceeds 7 V, the same situation will happen. The strength of the higher Fermi level can only drive moderate fluctuations of higher-order Fano resonances at higher frequencies. A comparison of the four combined optical-electric modulation patterns is shown in Fig. 5. Figure 5 shows that the maximum MD occurred when the external biased voltage was 4 V and the external laser pump current was 1360 mA. In this case, the modulation strength was stronger than in those in the other three cases.
Also, we have drawn the figures of the modulation depth trend with the frequency change in Fig. 6. As seen from Fig. 6(a), the slope of 0.03 V is the sharpest in this method, it indicated the modulation depth is always decreasing and it decreased dramatically than the other voltage settings. As observed from Fig. 6(b), the slope of modulation depth is increasing at 20 mA and 320 mA, while the other’s modulation depth is decreasing overall. It is seen in Fig. 6(c) that the slope of the modulation depth at 560 mA is negative and sharpest in this pattern. The other slopes are flat. As found in Fig. 6(d), the slope of 1120 mA is always decreasing. The other slopes in this pattern experienced decreasing followed by an increased stage. Also, it is found in Fig. 6(e) that the slope of 240 mA and 1360 mA have the same trend. The slope of 560 mA and the slope of 1040 mA experienced an increase followed by decreased stage. However, the other slopes are always increasing. In Fig. 6(f), the slope of 1040 mA experienced fluctuation. The other slopes are always increased followed by decreased stage.
According to the Table 1 in the supplementary material, the MD range can be sorted from the largest to the smallest, MD Range (Mixed method and at 4.03 V)> MD Range(Mixed method and at 7.03 V)> MD Range(Only Light)> MD Range(Only Electricity)> MD Range(Mixed method and at 2.03 V)>MD Range (Mixed method and at 2.03 V). The modulation effect of only electricity is not as good as that of only light. The best modulation effect can be achieved when the biased voltage was set to 4.03 V. The worst modulation effect can be achieved when the biased voltage was set to 1.03 V.
Table 1. The comparison between all the six optic-electric modulating methods
4. Conclusion
In this study, an active terahertz Fano DNA-like metasurface based on a graphene–JGS1 hybrid interface has been designed, fabricated and evaluated. A combination of external stimuli, i.e., a biased voltage and an optical pump, induced modulation of the higher-order Fano resonances. Different patterns of electromagnetic responses were obtained under six photoelectric settings. Ultra-high modulation depth (MD) up to 982% was achieved by involving combined optoelectrical methods. The proposed approach of modulation by three types of stimulus with graphene–JGS1 hybrid material platform has potential applications in the active tuning of terahertz devices at low gate voltages and low optical powers. Such a scheme could also be used for three-stimuli-based modulation of on-chip-guided terahertz waves on graphene–JGS1 platform.
Funding
Natural Science Foundation of Shandong Province (ZR202102180769, ZR2021MF014, ZR2020FK008); National Natural Science Foundation of China (61735010, U1831211); Special Funding of the Taishan Scholar Project (tsqn201909150); Shanghai Sailing Program (20YF1454800).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
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