Open Access
Add to BibSonomy
Abstract
Surface plasmon resonance (SPR) enables strong field confinement, opening thereby new avenues for device miniaturization and reducing energy consumption. Plasmonic devices with electrical tunability attract tremendous interest for various applications. Most of the current researches achieved SPR modulation with relatively large driving voltages, or by other relatively low-speed tuning approaches, such as thermo-optic, magneto-optic, acousto-optic etc. In this paper, we propose and demonstrate an efficiently electrical SPR modulation based on lithium niobate (LN) with gold nanolayer (~81 nm) via electron-plasmon interaction. Efficient intensity modulation and wavelength shift (in visible band) of ~5.7 dB/V and ~36.3 nm/V are respectively obtained with low DC current. More importantly, modulation phenomenon of field distribution dependent is also observed and experimentally unveiled. Further performance is analyzed in terms of AC modulation and polarization characteristics. This key achievement opens up opportunities for applications such as optical interconnection, electric field sensing, electrically plasmonic modulation, etc.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
The need for plasmonic devices is keenly felt as miniaturized photonic circuits are increasingly prevalent for optical interconnection. Surface plasmon (SP) is a result of resonant interaction between the light waves that are trapped on the surface and free electrons. The electromagnetic fields of the SP waves are strongly concentrated in the vicinity of a metal–dielectric interface. Surface plasmon resonance (SPR) provides electromagnetic field enhancement and nanoscale light confinement [1]. It allows the realization of on-chip miniaturization of all-optical circuits and high-density integration with low energy consumption [2–4]. The attractive properties of SPR have encouraged and led to research and developments in various applications such as plasmonic emitters [5–7], plasmonic modulator [8–10], sensing [11,12], hot electron photodetection [13], and plasmonic focusing [14]. Dynamic control and manipulating of a plasmonic resonance would be applied in spectroscopy, sensing and subwavelength optoelectronics. Based on controlling, guiding and detecting the SPR, high-speed and ultra-compact devices have been realized such as detectors, switches and modulators [15–17]. Dynamic manipulation of SPR based on different mechanisms has been demonstrated, such as acousto-optic effect [18], magnetooptic effect and all optical modulation [8,19]. In addition, controlling SPR in a gold–ferromagnet–gold system using an external magnetic field has been reported [20]. The modulation speed is in the order of gigahertz frequencies which is limited by control of the external magnetic field. It is desirable to be able to dynamically tune the SPR by applying an electrical bias. Electronic control over SPR has two advantages. Firstly, high field confinement can be obtained based on SPR at the metal–dielectric interface. Secondly, simultaneous electric and optical functions can be performed in the same structure. Controlling of plasmonic resonances with hybrid semiconductor−metal nanostructures have been demonstrated [21,22]. However, plasmonic devices using electrostatic gating can be tuned only at terahertz frequencies because large responses of the gate-induced free electrons in semiconductors only exists at the terahertz frequency. Electrical control of plasmon resonance at optical frequencies is a challenge because the free electron response is reduced dramatically. Tacking advantage of the strong and gate-tunable optical transitions of graphene, electrical control of the plasmon resonance has been achieved using a hybrid graphene-gold nanorod structure and a graphene–mica heterostructure [23,24]. Electro-optic modulation with a tunability of 0.13 dB μm−1 was achieved in low-loss plasmonic waveguides with graphene [25]. However, the interband loss of graphene is large in the near-IR and visible wavelength range [26]. Other two-dimensional nanomaterials have also been applied for SPR because of their exceptional plasmonic properties [27]. For example, a nanoplasmonic modulator was constructed by combining the Au nanodisk with MoS2 monolayers which has a wavelength shift of ~5 nm with a voltage of 8 V [28]. In addition, thermo-optic effect of benzocyclobutene has been exploited to realize Mach–Zender interferometric modulators and switches based on long-range SPR [29]. Electronic control over plasmonic resonance using a metal-oxide-silicon geometry has also been reported, which depends on carrier-induced refractive index change in the silicon layer [30]. However, the modulation speed is limited by the electron mobility in the silicon layer. In addition, these devices are limited in small refractive index change and a larger device footprint. Electronic control over SP dispersion and transmission of gold nanohole arrays has been demonstrated by combining liquid crystals with nanostructured metal films [31], which is also limited in modulation speed. Modulation of the intensity of the longitudinal SPR by 100% based on liquid crystals with an applied voltage of 4 V has been reported [10]. However, SPR wavelength modulation is not available with liquid crystals. Electro-optic polymer has been applied for SP modulation taking advantage of its large electro-optic coefficient and fast modulation speed. For example, a surface-normal plasmonic modulator with sub-wavelength metal grating on electro-optic polymer thin film has been reported, which showed an optical transmission drop of 1.2% and a wavelength shift of ~2 nm at 1522 nm under 20 V [32]. A metasurface modulator based on electro-optic polymer using bimodal plasmonic resonance can achieve intensity modulation of 15 dB and a wavelength tuning of ~5 nm under 4.7 V [33]. However, electro-optic polymers are sensitive to fatigue and solvent, and have limited temperature usability [34]. The reported works on electronic control over SPR are limited in weak intensity modulation, small wavelength tuning, and large driving voltage.
Lithium niobate (LN) have attracted tremendous interests because of their nonlinear, electro-optic, acousto-optic, piezoelectricity, and ferroelectricity properties. Compared with other electro-optic materials, LN has advantages of wide transparency window (400–5000 nm), large electro-optic coefficient and strong optical nonlinearity. In our previous works, an electro-optically controllable add-drop filter with an amplitude tunability of ~0.139 dB/V provided by LN has been reported [35]. The electro-optic effect of LN provides a significant opportunity to realize fast electro-optic control of SPR. In addition to telecom wavelengths, LN has been exploited for applications in visible wavelength range. Recently, ultra-low-loss integrated photonics using thin-film LN in visible wavelength range have been demonstrated [36]. With LN, the low-loss waveguides, Y splitters, ultra-high-Q microring resonators and electro-optical modulators operating at 600–900 nm wavelength range were fabricated which have superior performance. Besides, Gao et al. have demonstrated that the metasurfaces are capable of showing high-efficiency transmission structural colors as a result of structural resonances and intrinsic high transparency of LN in visible spectral range [37]. By means of micro and nanostructured gold layer on top of LN, one can tailor the spectral modulation behavior form visible to near infrared (NIR). Therefore, LN is available and can be used for electrical SPR modulation at visible wavelengths. In addition, the input power of our SPR modulation experiment is relative low. The LN can support relative high power with respect to the liquid crystal, electro-optic polymer, etc. The plasmonic structure provides strong confinement of both electrical and optical fields [20]. The rapid advances in plasmonics and LN have revealed the great potential of realizing ultra-compact, high-speed, low power consumption plasmonic devices with a combination of LN with SPR. Therefore, the combination of metallic nanostructure and LN to realize SPR control could potentially generate broad interest in developing of electronically tunable modulators with strong and fast modulation. An integrated-optic biosensor using LN for electro-optical modulation of SPR has been demonstrated, the intensity and wavelength modulation were ~0.3 dB and ~3.5 nm with 200 V, respectively [11].
Here, we demonstrate electronic modulation of SPR based on lithium niobate (LN) with gold nanolayer (~81 nm) via electron-plasmon interaction (EPI). The Au electrodes on top of LN enable strong confinement of both electrical and optical fields near the metal-dielectric interface. The advantages of strong field confinement of EPI and electro-optic characteristics of LN are combined to modulate SPR with low DC current. Efficient intensity modulation of SPR and wavelength shift of ~5.7 dB/V and ~36.3 nm/V are respectively achieved with low DC current (<1.2V) in the visible window which are much larger than the reported works. More importantly, modulation phenomenon of electric field distribution dependent is experimentally demonstrated, which has not been reported to the best of our knowledge. In addition, our experiment of SPR modulation is demonstrated by using low input power. In addition, AC modulation and polarization characteristics are further analyzed.
2. Device structure
The Au electrode is used for bias voltage control, which is on top of the LN substrate. The optical microscopy of the fabricated device is shown in Fig. 1(a). The electrode deposited by Plasma-enhanced chemical vapor deposition (PECVD) includes a square of 50 μm × 50 μm in the middle. The Au electrodes provide strong coupling between the guided mode and SP mode. Between the LN and Au film, there is a layer of 5 nm Cr for good adhesion. The parameters of this device are selected based on numerical simulations using COMSOL Multiphysics. The locations of applying voltage for modulation are shown in Fig. 1(a). The calculated electric field of the electrode is shown in Fig. 1(b). Note that the electric field distribution is different at different regions of the electrodes. It is obvious the electric field is strongly confined at two corners of the square electrodes. The normalized electric field intensities are calculated to be 0.09, 0.27 and 1 for Regions 1, 2, and 3, respectively. By applying voltage on the Au electrodes, the required electric field can be produced. The electric field amplitude enhancement in LN provides good overlap with modulating electric field that can be changed by applying voltages to the electrodes. The induced electric field by the voltage changes the refractive index of LN. High-resolution scanning electron microscopy (SEM) images of the electrodes are shown in Fig. 2. The zoom in shown in Fig. 1(b) indicates the high quality of the Au electrodes with uniform and smooth structures. The thickness of the metal film (Cr and Au) was measured to be ~80.7 nm. The transmission spectrum for SPR was calculated in the wavelength range from 0.4 to 1.1 μm using the finite-difference time-domain (FDTD). As shown in Fig. 3, the transmission spectrum indicates SPR at 582 nm. The resonance is attributed to coupling of the guided modes in the LN and the SP modes.
Fig. 1 (a) Optical microscopy of the fabricated device. (b) Calculated electric field distribution of the electrode.
Fig. 2 (a) SEM image of the fabricated Au electrode. (b) SEM image showing thickness of the electrode.
3. Device fabrication
The fabrication process of the electro-optic plasmonic modulation device is shown in Fig. 4. Firstly, the photoresist (S1805) was spin coated on to the LN substrate with a spin speed of 4000 rpm for ~30 s. After that, a layer of photoresist with a thickness of ~500 nm was formed. The sample was baked at 115 °C for ~1 min until it was completely dry. Then the geometric patterns of the mask were transferred to the photoresist after photolithography and development. During the photolithography process, the sample was exposed to UV radiation at 365 nm with 150 mJ/cm2 for ~4 s. Then the sample was soaked in the developing solution (ZX238). After that, the photoresist patterns were formed with designed structures. In the next step, a layer of Cr with a thickness of 5 nm was deposited on the LN substrate through PECVD. Then the Au film was grown on top of the Cr with a thickness of ~80 nm using PECVD. Next, ultrasonic stripping process was performed in acetone. After that, the Au electrodes with desired structures were formed.
4. Results and discussion
The electro-optical modulation characteristics are investigated using the experimental setup as shown in Fig. 5. The Kretschmann configuration is used to meet the phase matching condition between the incident light and SP wave. The LN substrate is attached to the flat surface of a prism. In order to reduce the loss caused by reflection, the gap between the LN and prism is filled with the index matched fluid with refractive indices of 1.5148-1.5152. Firstly, the SPR spectra are measured using a supercontinuum spectrum laser with a wavelength range of 450-2400 nm (NKT Photonics, Superk Compact). The light from the laser becomes collimated light after passing through the collimator (Thorlabs, RC08FC-P01). By tuning the polarizer, the TM polarized light is obtained for exciting SPR. After the convex lens, the light is focused on to the prism with an incident angle of 45°. The total reflection at the interface of LN and air provides phase matching condition for SPR. Finally, the output light from the prism is coupled into the fiber-based spectrometer (Ocean Optics, USB2000 + VIS-NIR-ES) by the convex lens for spectral measurement. The fiber holder can be regarded as a receiving screen. By adjusting the positions of the prism, convex lens and fiber holder, a clear image of the micro electrodes on the LN is obtained on the screen. The SPR spectrum is recorded by the spectrometer with a wavelength range of 540-780 nm. The multimode fiber is connected to the spectrometer.
To investigate the field distribution dependent modulation of SPR, the output spectra of the device are tested when the light from supercontinuum spectrum laser is focused to Regions 1, 2, and 3 of the electrode. Figure 6(a) shows the SPR spectra when different voltages (0 to 1.2 V) are applied to the electrodes for light illumination of Regions 3. The SPR dip appears at 525.1 nm when the voltage is 0.6 V. SPR requires that the phase matching condition is satisfied. Applying voltage can compensate for the phase mismatch between the guided mode and SP mode. Therefore, the SPR characteristics can be tuned electrically by changing the applied voltage. Figure 6(a) indicates both the intensity variation and resonance wavelength shift occur in the presence of applied voltage. With the voltage changed from 0 to 1.2 V, the intensity at resonance dip is increased and the resonance dip is red-shifted. Note that there is a resonance peak on the left side of the resonance dip. As the voltage increases, intensity increase and red shift of the resonance peak are observed. To see more clearly the relation between the SPR spectrum change and voltage, the resonance peaks on the left side of the dips are extracted. Figure 6(b) shows the dependence of resonance peak wavelength shift on applied voltage for light illumination of Regions 1, 2 and 3. The wavelength shift increases with applied voltage. The resonance peak wavelength shifts are 9.3, 11.4 and 43.6 nm under 1.2 V for light illumination of Regions 1, 2 and 3, respectively. This wavelength shift results from increase of the propagation constant of the guided mode when the voltage increases [11]. The intensity increase and wavelength shift of Region 3 are much larger, which is attributed to stronger field distribution from the electrodes in Region 3. The obtained results confirm electro-optical modulation of SPR depends on the field distribution of the electrode. When voltage is applied to the electrode, different regions of the electrode have different electric field distribution. The SPR modulation characteristics are different when light is focused to different regions of the electrode. Region 3 has much stronger electric field, the refractive index change induced by applying voltage in this region is lager. Therefore, stronger SPR intensity and wavelength modulation can be obtained in Region 3. The difference in shape of the experimental spectrum compared with the calculated spectrum is attributed to the imperfection of fabrication of the Au film with Cr adhesion layer, the imperfect collimation and exciting of the SP mode. The electro-optical modulation is mainly contributed from two effects. Firstly, the external DC current propagating in the Au film contributes to the modulation of SPR. The EPI can be changed by varying the external current, which has been exploited to control SPR [38]. Besides, the phase matching condition for SPR is changed by electro-optic effect of LN. The refractive index of LN is modulated when the voltage is applied on the micro electrodes which produces electric field [11]. The propagation constant of the guided mode in LN is changed with applied voltage. Therefore, the EPI and change of phase matching condition work together to realize efficient SPR electro-optical modulation.
Fig. 6 (a) SPR spectra measured with the supercontinuum spectrum laser for light illumination of Region 3. (b) Dependence of the SPR resonance peak wavelength shift on the applied voltage for three regions.
To investigate the SPR intensity modulation characteristics, green (532 nm) and red (661 nm) lasers are used as light sources. As the voltage applied on the electrode is varied from 0 to 1.2 V, the output spectrum is recorded by the spectrometer. Figures 7(a)–7(c) show the variation of intensity for green light illumination of Regions 1, 2, and 3, respectively. The spectrum intensity increases with the applied voltage. Figure 7(d) plots the spectrum peak intensity at 532 nm as a function of applied voltage for the three regions. The intensities increased by 1.40, 2.41 and 4.48 folds for light illumination of Regions 1, 2 and 3 under 1.2 V, respectively. Region 3 has the best performance due to stronger electric-field intensity. The increase of intensity with higher voltage is due to the moving away of the SPR wavelength from the wavelength of the light source (532 nm).
Fig. 7 SPR spectrum intensity modulation with the 532 nm laser for light illumination of Regions (a) 1, (b) 2 and (c) 3. (d) SPR spectrum intensity at 532 nm as a function of voltage for light illumination of Regions 1, 2 and 3.
Then the red laser at the wavelength of 661 nm is used as light source for SPR modulation. Figures 8(a)–8(c) show the measured SPR spectra with voltage varied from 0 to 1.2 V when Regions 1, 2 and 3 of the electrodes are illuminated, respectively. The SPR spectrum intensity increases with the applied voltage. The relation between the spectrum peak intensity and applied voltage is plotted in Fig. 8(d). Intensity increases of 1.65, 1.71 and 2.12 folds are obtained under 1.2 V for light illumination of Regions 1, 2 and 3, respectively. The experimental results measured with the green and red lasers confirm that the SPR spectrum intensity can be modulated by applying voltage, which depends on the field distribution of the electrode. Then the polarization characteristics of this device are investigated. The state of polarization of input light is tuned by adjusting the polarizer. The output light is recorded by the spectrometer at a series of incident angles (every 10°). The 0–2π phase change is obtained by tuning the polarizer. Figures 9(a) and 9(b) show the output power as a function of the polarization angle with the 532 and 661 nm laser sources, respectively. In Fig. 9, 0° is the TM polarization. Polarization effect is observed in Fig. 9. The polarization-extinction ratios are 8.0 and 6.8 dB for the 532 and 661 nm, as shown in Figs. 9(a) and 9(b), respectively.
Fig. 8 SPR spectrum intensity modulation with the 661 nm laser for light illumination of Regions (a) 1, (b) 2 and (c) 3. d) SPR spectrum intensity at 661 nm as a function of voltage for light illumination of Regions 1, 2 and 3.
Figure 10(a) shows the experimental setup for AC modulation measurement. The green laser of 532 nm is used for electric response measurement. A photodetector (Daheng Optics, DH-GDT-D020V) and an oscilloscope (Siglent, SDS1102CFL) are used to monitor the output. The voltage variation is monitored by the oscilloscope. A square wave with peak-to-peak voltages of 0.88 V and 1.12 V are applied to the Au electrode. The modulation frequency is 50 Hz. Figure 10(b) shows electro-optical modulation responses with different modulation depth, which can accurately follow the two above electric modulation signal. Modulations in higher frequencies can be achieved by the desired electrodes with impedance matching. The SPR modulation characteristics for various configurations are compared in Table 1. As listed in Table 1, The LN, liquid crystal, MoS2 and electro-optic polymer are exploited for SPR modulation with various structures. The maximum intensity and wavelength modulation of the reported works are 3.2 dB/V and 1.1 nm/V, respectively, which are obtained in a metasurface modulator based on electro-optic polymer [31]. In comparison, the intensity and wavelength modulation of our device are 1.8 and 33 times lager, respectively. Therefore, our device can provide much larger intensity modulation and wavelength shift with much lower voltages.
Fig. 10 (a) Experimental setup for response time measurement. (b) Electric response for electro-optical modulation.
Table 1. Comparison of various SPR modulation methods
5. Conclusions
In conclusion, we have demonstrated efficient SPR modulation with low driving DC based on lithium niobate (LN) with gold nanolayer (~81 nm) via EPI. For a driving voltage of 1.2 V, ~4.5 fold of SPR intensity modulation and ~44 nm resonance wavelength shift in the visible window are achieved. The SPR spectrum modulation is different when the input light is focused to different regions of the electrode, this field distribution dependent modulation is experimentally unveiled. Further measurements such as AC modulation and polarization characteristics are also accomplished. The proposed device provides an effect path to manipulate SPR with low energy consumption, which offers a possible solution for miniaturization of electro-optically modulation device, electric field remote sensing, and plasmonic device etc.
Funding
National Natural Science Foundation of China (61775084,61705089,61705087,61505069, 61475066, 61405075); National Major Project of China (J-GFZX0205010501.12, GFZX0205010501.24-J); Guangdong Special Support Program (2016TQ03X962); Natural Science Foundation of Guangdong Province (2015A03036046, 2016A030310098, 2016A030311019, 2014B090905001);
References
1. J. A. Schuller, E. S. Barnard, W. Cai, Y. C. Jun, J. S. White, and M. L. Brongersma, “Plasmonics for extreme light concentration and manipulation,” Nat. Mater. 9(3), 193–204 (2010). [CrossRef] [PubMed]
2. Z. Zhang, Y. Fang, W. Wang, L. Chen, and M. Sun, “Propagating Surface Plasmon Polaritons: Towards Applications for Remote-Excitation Surface Catalytic Reactions,” Adv. Sci. (Weinh.) 3(1), 1500215 (2015). [CrossRef] [PubMed]
3. E. Ozbay, “Plasmonics: merging photonics and electronics at nanoscale dimensions,” Science 311(5758), 189–193 (2006). [CrossRef] [PubMed]
4. C. Genet and T. W. Ebbesen, “Light in tiny holes,” Nature 445(7123), 39–46 (2007). [CrossRef] [PubMed]
5. S. Kim, J. Jin, Y. J. Kim, I. Y. Park, Y. Kim, and S. W. Kim, “High-harmonic generation by resonant plasmon field enhancement,” Nature 453(7196), 757–760 (2008). [CrossRef] [PubMed]
6. D. M. Koller, A. Hohenau, H. Ditlbacher, N. Galler, F. Reil, F. R. Aussenegg, A. Leitner, E. J. W. List, and J. R. Krenn, “Organic plasmon-emitting diode,” Nat. Photonics 2(11), 684–687 (2008). [CrossRef]
7. A. Hryciw, Y. C. Jun, and M. L. Brongersma, “Plasmon-enhanced emission from optically-doped MOS light sources,” Opt. Express 17(1), 185–192 (2009). [CrossRef] [PubMed]
8. D. Pacifici, H. J. Lezec, and H. A. Atwater, “All-optical modulation by plasmonic excitation of CdSe quantum dots,” Nat. Photonics 1(7), 402–406 (2007). [CrossRef]
9. M. J. Dicken, L. A. Sweatlock, D. Pacifici, H. J. Lezec, K. Bhattacharya, and H. A. Atwater, “Electrooptic modulation in thin film barium titanate plasmonic interferometers,” Nano Lett. 8(11), 4048–4052 (2008). [CrossRef] [PubMed]
10. S. Khatua, W. S. Chang, P. Swanglap, J. Olson, and S. Link, “Active modulation of nanorod plasmons,” Nano Lett. 11(9), 3797–3802 (2011). [CrossRef] [PubMed]
11. T. J. Wang, W. S. Lin, and F. K. Liu, “Integrated-optic biosensor by electro-optically modulated surface plasmon resonance,” Biosens. Bioelectron. 22(7), 1441–1446 (2007). [CrossRef] [PubMed]
12. P. Mulpur, S. Yadavilli, A. M. Rao, V. Kamisetti, and R. Podila, “MoS2/WS2/BN-Silver Thin-Film Hybrid Architectures Displaying Enhanced Fluorescence via Surface Plasmon Coupled Emission for Sensing Applications,” ACS Sens. 1(6), 826–833 (2016). [CrossRef]
13. C. Clavero, “Plasmon-induced hot-electron generation at nanoparticle/metal-oxide interfaces for photovoltaic and photocatalytic devices,” Nat. Photonics 8(2), 95–103 (2014). [CrossRef]
14. J. Becker, I. Zins, A. Jakab, Y. Khalavka, O. Schubert, and C. Sönnichsen, “Plasmonic focusing reduces ensemble linewidth of silver-coated gold nanorods,” Nano Lett. 8(6), 1719–1723 (2008). [CrossRef] [PubMed]
15. D. K. Gramotnev and S. I. Bozhevolnyi, “Plasmonics beyond the diffraction limit,” Nat. Photonics 4(2), 83–91 (2010). [CrossRef]
16. M. Kauranen and A. V. Zayats, “Nonlinear plasmonics,” Nat. Photonics 6(11), 737–748 (2012). [CrossRef]
17. Z. Fang, Z. Liu, Y. Wang, P. M. Ajayan, P. Nordlander, and N. J. Halas, “Graphene-antenna sandwich photodetector,” Nano Lett. 12(7), 3808–3813 (2012). [CrossRef] [PubMed]
18. D. Gérard, V. Laude, B. Sadani, A. Khelif, D. Van Labeke, and B. Guizal, “Modulation of the extraordinary optical transmission by surface acoustic waves,” Phys. Rev. B Condens. Matter Mater. Phys. 76(23), 235427 (2007). [CrossRef]
19. K. J. Chau, S. E. Irvine, and A. Y. Elezzabi, “A gigahertz surface magneto-plasmon optical modulator,” IEEE J. Quantum Electron. 40(5), 571–579 (2004). [CrossRef]
20. V. V. Temnov, G. Armelles, U. Woggon, D. Guzatov, A. Cebollada, A. Garcia-Martin, J.-M. Garcia-Martin, T. Thomay, A. Leitenstorfer, and R. Bratschitsch, “Active magneto-plasmonics in hybrid metal–ferromagnet structures,” Nat. Photonics 4(2), 107–111 (2010). [CrossRef]
21. H.-T. Chen, W. J. Padilla, J. M. O. Zide, A. C. Gossard, A. J. Taylor, and R. D. Averitt, “Active terahertz metamaterial devices,” Nature 444(7119), 597–600 (2006). [CrossRef] [PubMed]
22. H.-T. Chen, W. J. Padilla, M. J. Cich, A. K. Azad, R. D. Averitt, and A. J. Taylor, “A metamaterial solid-state terahertz phase modulator,” Nat. Photonics 3(3), 148–151 (2009). [CrossRef]
23. J. Kim, H. Son, D. J. Cho, B. Geng, W. Regan, S. Shi, K. Kim, A. Zettl, Y.-R. Shen, and F. Wang, “Electrical Control of Optical Plasmon Resonance with Graphene,” Nano Lett. 12(11), 5598–5602 (2012). [CrossRef] [PubMed]
24. H. Hu, X. Guo, D. Hu, Z. Sun, X. Yang, and Q. Dai, “Flexible and Electrically Tunable Plasmons in Graphene-Mica Heterostructures,” Adv. Sci. (Weinh.) 5(8), 1800175 (2018). [CrossRef] [PubMed]
25. Y. Ding, X. Guan, X. Zhu, H. Hu, S. I. Bozhevolnyi, L. K. Oxenløwe, K. J. Jin, N. A. Mortensen, and S. Xiao, “Efficient electro-optic modulation in low-loss graphene-plasmonic slot waveguides,” Nanoscale 9(40), 15576–15581 (2017). [CrossRef] [PubMed]
26. M. Jablan, H. Buljan, and M. Soljačić, “Plasmonics in graphene at infrared frequencies,” Phys. Rev. B Condens. Matter Mater. Phys. 80(24), 245435 (2009). [CrossRef]
27. Y. Li, Z. Li, C. Chi, H. Shan, L. Zheng, and Z. Fang, “Plasmonics of 2D Nanomaterials: Properties and Applications,” Adv. Sci. (Weinh.) 4(8), 1600430 (2017). [CrossRef] [PubMed]
28. B. Li, S. Zu, J. Zhou, Q. Jiang, B. Du, H. Shan, Y. Luo, Z. Liu, X. Zhu, and Z. Fang, “Single-Nanoparticle Plasmonic Electro-optic Modulator Based on MoS2 Monolayers,” ACS Nano 11(10), 9720–9727 (2017). [CrossRef] [PubMed]
29. T. Nikolajsen, K. Leosson, and S. I. Bozhevolnyi, “Surface plasmon polariton based modulators and switches operating at telecom wavelengths,” Appl. Phys. Lett. 85(24), 5833–5835 (2004). [CrossRef]
30. J. A. Dionne, K. Diest, L. A. Sweatlock, and H. A. Atwater, “PlasMOStor: a metal-oxide-Si field effect plasmonic modulator,” Nano Lett. 9(2), 897–902 (2009). [CrossRef] [PubMed]
31. W. Dickson, G. A. Wurtz, P. R. Evans, R. J. Pollard, and A. V. Zayats, “Electronically Controlled Surface Plasmon Dispersion and Optical Transmission Through Metallic Hole Arrays Using Liquid Crystal,” Nano Lett. 8(1), 281–286 (2008). [CrossRef] [PubMed]
32. F. Ren, M. Li, Q. Gao, W. Cowell III, J. Luo, A. K. Y. Jen, and A. X. Wang, “Surface-normal plasmonic modulator using sub-wavelength metal grating on electro-optic polymer thin film,” Opt. Commun. 352, 116–120 (2015). [CrossRef]
33. J. Zhang, Y. Kosugi, A. Otomo, Y. Nakano, and T. Tanemura, “Active metasurface modulator with electro-optic polymer using bimodal plasmonic resonance,” Opt. Express 25(24), 30304–30311 (2017). [CrossRef] [PubMed]
34. Z. Ma, Z. Li, K. Liu, C. Ye, and V. J. Sorger, “Indium-Tin-Oxide for High-performance Electro-optic Modulation,” Nanophotonics 4(1), 198–213 (2015). [CrossRef]
35. S. Zhou, J. Dong, D. He, Y. Wang, W. Qiu, J. Yu, H. Guan, W. Zhu, Y. Zhong, Y. Luo, J. Zhang, Z. Chen, and H. Lu, “Interlinked add-drop filter with amplitude modulation routing a fiber-optic microring to a lithium niobate microwaveguide,” Opt. Lett. 42(8), 1496–1499 (2017). [CrossRef] [PubMed]
36. B. Desiatov, A. Shams-Ansari, M. Zhang, C. Wang, and M. Lončar, “Ultra-low-loss integrated visible photonics using thin-film lithium niobate,” Optica 6(3), 000380 (2019). [CrossRef]
37. B. Gao, M. Ren, W. Wu, H. Hu, W. Cai, and J. Xu, “Lithium Niobate Metasurfaces,” Laser Photonics Rev. 13(5), 1800312 (2019). [CrossRef]
38. N. Noginova, A. V. Yakim, J. Soimo, L. Gu, and M. A. Noginov, “Light-to-current and current-to-light coupling in plasmonic systems,” Phys. Rev. B Condens. Matter Mater. Phys. 84(3), 035447 (2011). [CrossRef]
39. M. V. Gorkunov, I. V. Kasyanova, V. V. Artemov, M. I. Barnik, A. R. Geivandov, and S. P. Palto, “Fast Surface-Plasmon-Mediated Electro-Optics of a Liquid Crystal on a Metal Grating,” Phys. Rev. Appl. 8(5), 054051 (2017). [CrossRef]
