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![Three-dimensional schematics of optical modulators. (a) Graphene ridge waveguide modulator; (b) graphene buried waveguide modulator. $W$ W , waveguide width; $L$ L , graphene length; $h$ h , waveguide height; ${d_{\rm hBN}}$ d h B N , hBN thickness; $s$ s , spacing between the electrode and the waveguide. The refractive index of graphene can be calculated according to the conductivity model [12].](profile/Xiaoying-He-4/publication/338438344/figure/fig1/AS:11431281253744369@1718924318544/Three-dimensional-schematics-of-optical-modulators-aGraphene-ridge-waveguide.jpg)
Three-dimensional schematics of optical modulators. (a) Graphene ridge waveguide modulator; (b) graphene buried waveguide modulator. $W$ W , waveguide width; $L$ L , graphene length; $h$ h , waveguide height; ${d_{\rm hBN}}$ d h B N , hBN thickness; $s$ s , spacing between the electrode and the waveguide. The refractive index of graphene can be calculated according to the conductivity model [12].
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For exploring a strong electro-optic effect from a graphene/hexagonal boron nitride (hBN) structure, here a comprehensive study for investigating the integrated broadband graphene/hBN modulators has been presented. Two representative configurations with a ${{\rm Si}_3}{{\rm N}_4}$ S i 3 N 4 waveguide were compared, focusing on optimizing the hBN th...
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In order to solve the defects of the high driving voltage and a large volume of the existing electro-optical modulators, a double-waveguide stacked graphene optical modulator based on a Mach-Zehnder Interferometer structure is designed in this paper. First, the modulator size of traditional planar structure is effectively reduced by stacking two mo...
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Citations
... This calculation is carried out under the specific condition where the chemical potential μ c significantly exceeds the temperature T and applied voltage [35]. The surface conductivity of a single graphene layer in equation (1) can be given by the Kubo formula for considering the intraband transition terms in equations (2) and (3), where σ intra is intraband conductivity and σ inter is interband conductivity [35,36,38] ...
... These results correspond to the Im(n eff ) in figures 2(a) and (d) for the designed waveguides related to the application of V D on the graphene layer and TiO 2 with high permittivity [38,46]. The optical absorption of graphene is determined by the position of the Fermi level, which is tuned by applying the drive voltage for the graphene/TiO 2 waveguides, resulting in modulation depths of 0.02, 0.42, 0.34, and 0.27 dB μm −1 for h TiO2 values of 10, 30, 50, and 70 nm, respectively, as shown in figure 3. ...
... In figure 4, the electro-optical modulator devices are simulated by driving different voltages over the graphene layer with the FDE. The modulation depth (α) can be described by the ratio of the maximum to the minimum absorption or the modulation efficiency in decibels per micro unit length (dB/μm) which is α 100% − α 5% [38,50]. At an h (3)TiO2 of 30 nm, thin TM mode absorption of the devices as a function of voltages ranging between −5 and 4.5 V is shown in figure 4 for different waveguide widths. ...
A novel way to enhance modulation performance is through the design of a hybrid plasmonic optical modulator that integrates multi-layer graphene and TiO2 on silicon waveguides. In this article, a design is presented of a proposed modulator based on the use of the two-dimensional finite difference eigenmode solver, the three-dimensional eigenmode expansion solver, and the CHARGE solver. Leveraging inherent graphene properties and utilizing the subwavelength confinement capabilities of hybrid plasmonic waveguides (HPWs), we achieved a modulator design that is both compact and highly efficient. The electrical bandwidth f 3dB is at 460.42 GHz and it reduces energy consumption to 12.17 fJ/bit with a modulator that functions at a wavelength of 1.55 μm. According to our simulation results, our innovation was the optimization of the third dielectric layer’s thickness, setting the stage to achieve greater modulation depths. This synergy between graphene and HPWs not only augments subwavelength confinement, but also optimizes light–graphene interaction, culminating in a markedly enhanced modulation efficiency. As a result, our modulator presents a high extinction ratio and minimized insertion loss. Furthermore, it exhibits polarization insensitivity and a greater bandwidth. Our work sets a new benchmark in optical communication systems, emphasizing the potential for the next generation of chip-scale with high-efficiency optical modulators that significantly outpace conventional graphene-based designs.
... The designed waveguides are functions of the waveguide widths of 300 nm, 400 nm, 500 nm, and 600 nm while the parameters, HSi, tTiO2, λ0, T, and the scattering rate, are 250 nm, 10 nm, 1550 nm, 300 K and 15 meV, respectively. The absorption depth can be described by the ratio of the maximum to the minimum absorption or the absorption coefficient in decibels per micro unit length (dB/µm) is ⍺100% -⍺5% [43], [44]. ...
... A 600 nm width reduces its efficiency, compared to the other modulators, and increases with modulator length. Furthermore, the extinction ratio (ER) and insertion loss (IL) were calculated as ( α100% / α5% ) ×L and ( α5% − α100% ) ×L, respectively [43], [44], and are shown in Fig. 4(c) and 4(d). The obtained ER values correspond with the calculated efficiency, but the IL values show the opposite behavior, in which a 300 nm width exhibits higher excess loss for a waveguide length. ...
... respectively, which decrease with increasing tTiO2. Such dielectric thicknesses affect the absorption distribution at higher voltages with an increasing full width at the half maximum (FWHM) value, which is related to the equivalent capacitance per unit area of the devices [44]. Moreover, modulator efficiencies decrease with the dielectric thickness, but increase with the modulator length, as shown in Fig. 5(b). ...
This work presents a novel contribution to graphene/TiO2 electro-optical modulators based on silicon-on-silica waveguide with a hybrid plasmonic waveguide to achieve ultrafast switching and low-voltage states. Waveguide structure consists of a rectangular silicon core covered by a high relative permittivity TiO2 dielectric layer with two layers of graphene, air-clad, and silica lower cladding. Effective refractive indices can be tailored to support the propagation of the transverse magnetic mode with a suitable design related to an electro-absorption modulator for simulation results. Modulation depth and bandwidth were enhanced by the waveguide width and dielectric thickness, respectively. Maximum and minimum absorption depths at the driving voltage states can determine modulators. The simulation produced the highest efficient modulator with high speed at 3dB bandwidth of 93.7 GHz using a low energy consumption of 210.6 fJ/bit, a small footprint (24 μm
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), and a broad operating spectrum range from 1310 to 1550 nm. This is because the physical process acts according to the modulator at the Fermi energy of graphene and the structure of the waveguide. These modulators can have practical applications due to their distinctive advantages, including a small device footprint, low voltage operation, ultrafast modulation switching across a broad wavelength range, and low-energy operation.
... 237 Generally, the optimum configuration of graphene upon a dielectric waveguide/resonator and the estimation of the upper performance metrics of amplitude and phase modulators is an open topic in the literature. 214,[323][324][325][326] All publications converge that graphene has the potential for ultra-high-speed modulation with high ER and acceptable ILs. ...
Electro-optic modulators are an indispensable part of photonic communication systems, largely dictating the achievable transmission rate. Recent advances in materials and fabrication/processing techniques have brought new elements and a renewed dynamic to research on optical modulation. Motivated by the new opportunities, this Perspective reviews the state of the art in integrated electro-optic modulators, covering a broad range of contemporary materials and integrated platforms. To provide a better overview of the status of current modula-tors, an assessment of the different material platforms is conducted on the basis of common performance metrics: extinction ratio, insertion loss, electro-optic bandwidth, driving voltage, and footprint. The main physical phenomena exploited for electro-optic modulation are first introduced, aiming to provide a self-contained reference to researchers in physics and engineering. Additionally, we take care to highlight topics that can be overlooked and require attention, such as the accurate calculation of carrier density distribution and energy consumption, the correct modeling of thin and two-dimensional materials, and the nature of contact electrodes. Finally, a future outlook for the different electro-optic materials is provided, anticipating the research and performance trends in the years to come.
In this paper, an electro-absorption modulator based on a hybrid plasmonic structure is designed and analyzed for wavelengths ranging from 1300 to 1800 nm and chemical potentials ranging from 0 to 0.65 eV for graphene. This modulator has a high modulation depth (19.9 dB/µm) in the broad wavelength range of 1300–1800 nm. The proposed modulator comprises three graphene layers and two Hexagonal Boron Nitride (h-BN) layers. Silver nano-ribbons are placed on the structure and inside the silicon layer. The silver nano-ribbons create a spatially confined plasmonic mode along its edge. The edge is covered by graphene sheets, which is isolated by a layer of h-BN. A silver nano-ribbon with sharp rectangular edges can serve as a guide for a spatially confined plasmonic mode. There are two edges involving in the presence of transverse electric field components that contribute to the interaction. Our results show a high amount of light confinement and surface plasmon polaritons. The proposed modulator has a 11.8 dB/µm modulation depth with 1.7 dB/µm loss at 1550 nm and a 19.9 dB/µm modulation depth with 2.9 dB/µm loss at 1300 nm.
