Graphene light modulator based on hybrid surface plasmon

Abstract

The invention discloses a graphene optical modulator based on hybrid surface plasmon, which comprises a split-ring-like resonance strip waveguide, a graphene layer, a dielectric spacer layer, a substrate and a bottom electrode from top to bottom, and is characterized in that two sides of the split-ring-like resonance strip waveguide are respectively provided with a gate electrode; the cross section of the split-ring-like resonant strip waveguide is of a split-ring-like resonant structure; the open end of the split resonant ring structure is in contact with the graphene layer; the thickness of the dielectric spacer layer is 5-50 nm; the gate electrodes on the two sides are a source electrode and a drain electrode respectively, the bottom electrode is a gate electrode, and incident light is modulated by controlling the voltage of the source electrode, the drain electrode and the gate electrode; to-be-modulated input light is incident perpendicular to the cross section, and hybridized surface plasmons are excited at the opening end face of the split-ring-like resonant ring strip-shaped waveguide and the interface, close to the graphene layer, of the dielectric spacer layer. The on-off ratio, the bandwidth and various modulation performances of the modulator based on the graphene material are improved.

Description

Technical Field

[0001] The present invention relates to a modulator based on graphene materials in the field of optical communication, and in particular to a graphene optical modulator based on hybrid surface plasmons. Background Art

[0002] Silicon-based modulators are core devices in optical communications, but traditional silicon-based waveguide modulators (such as silicon optical modulators) are limited by the optical modulation of silicon-based materials themselves. Their theoretical bandwidth limit is less than 70 GHz, and the energy consumption is only a few dozen fJ / bit, which is already a relatively low figure. The silicon-based ridge waveguide integrated optical modulator based on single-layer graphene achieves modulation by actively tuning the Fermi level of the single-layer graphene sheet. The 3dB bandwidth of the modulator is about 1GHz. This bandwidth is limited by the parasitic response of the device, not the carrier transmission time. Due to the extremely high carrier mobility and saturation velocity of graphene, the bandwidth is limited by the parasitic response and is about 1GHz. Due to the very thin thickness of graphene, its absorption and modulation capabilities of light are limited, so the effect of single-layer graphene in optical modulation is limited, especially for common silicon-based dielectric waveguides, where the light field is mainly distributed in the center of the medium, greatly reducing the interaction with the surface graphene. In order to enhance the interaction between graphene and light, researchers combined graphene with plasmon waveguides and designed a hybrid graphene waveguide modulator based on plasmon angular modes. However, through research, it was found that although the mode field of surface plasmons can be flexibly regulated by metal micro-nanostructures within the subwavelength range, due to the ohmic loss of metal, plasmon waveguides have large propagation losses, and the main field component of traditional surface plasmons is perpendicular to the graphene plane, and the proportion of components parallel to graphene is very low, so it cannot effectively interact with graphene, resulting in the difficulty in improving the switching ratio of pure plasmon-based graphene optical modulators and accompanied by large energy consumption, limiting its application potential. Summary of the invention

[0003] Purpose of the invention: In view of the above problems, the present invention proposes a graphene optical modulator based on hybrid surface plasmons, which improves the switching ratio, bandwidth and various modulation performances of the modulator based on graphene materials.

[0004] Technical solution: The technical solution adopted by the present invention is a graphene optical modulator based on hybrid surface plasmon, which includes a quasi-open resonant ring strip waveguide, a graphene layer, a dielectric spacer layer, a substrate and a bottom electrode from top to bottom, and a gate electrode is provided on each side of the quasi-open resonant ring strip waveguide above the graphene layer; the quasi-open resonant ring strip waveguide is a metal waveguide, and the cross section of the quasi-open resonant ring strip waveguide is an open resonant ring structure, and the open end of the open resonant ring structure is in contact with the graphene layer; the thickness of the dielectric spacer layer is 5-50nm. The graphene layer is a two-dimensional material, and the thickness of the graphene layer is generally the thickness of a single atomic layer. The input light to be modulated is incident perpendicular to the cross section, and the light field excitation with the electric field polarization direction horizontal or the magnetic field polarization direction along the propagation direction is used to excite the hybrid surface plasmons at the interface between the open end face of the quasi-open resonant ring strip waveguide and the dielectric spacer layer close to the graphene layer; the gate electrodes on both sides are the source and the drain respectively, and the bottom electrode is the gate, and the incident light is modulated by controlling the voltage of the source, the drain and the gate.

[0005] A better solution is that the arm width of the split resonant ring structure is the main factor affecting the modulation depth, and the arm width w of the split resonant ring structure is 5-40nm. Further optimizing other structural parameters of the split resonant ring structure, the width d of the split resonant ring structure x 40-150nm, height d y It is 40-150nm.

[0006] Placing the graphene layer where the light field is strongest can further enhance the interaction between light and graphene.

[0007] The graphene layer can also be replaced by other broadband Dirac semimetal type two-dimensional materials, that is, the graphene layer can be replaced by other materials such as transition metal chalcogenides with a band gap, black phosphorus, etc.

[0008] The graphene layer is designed as a single layer, a double layer or a multi-layer. Adding multiple layers can improve the modulation performance.

[0009] The quasi-open resonant ring strip waveguide adopts a plasmon material, and the plasmon material includes a noble metal material or aluminum.

[0010] The interior of the quasi-open resonant ring strip waveguide is filled with an insulating medium / oxide with a lower refractive index, including air, porous silicon dioxide, etc.

[0011] The dielectric spacer layer is made of insulating oxide; the dielectric spacer layer is made of aluminum oxide.

[0012] The gate electrode is a gold electrode, the substrate is a silver layer, and the bottom electrode is a silver electrode.

[0013] The present invention provides an optical communication chip, which modulates optical signals through the hybrid surface plasmon-based graphene optical modulator.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following advantages: In order to further improve the interaction between light and graphene, in addition to placing graphene at the position where the light field is strongest, the present invention also makes the polarization of light conform to the surface conductivity plane of graphene. The present invention combines an open resonant ring structure with a metal waveguide to propose a quasi-open resonant ring strip waveguide, and enhances the interaction between graphene and light through a composite structure of a quasi-open resonant ring strip waveguide and a metal flat waveguide with a dielectric insulating layer in between. The composite structure proposed by the present invention excites hybrid surface plasmons at the interface between the open end face of the quasi-open resonant ring strip waveguide and the dielectric spacing layer close to the graphene layer, and at the same time cleverly combines the circular current of the quasi-open resonant ring, significantly improving the in-plane component of the surface conductivity plane of graphene and enhancing the interaction between graphene and light. By enhancing the interaction between graphene and light, the switching ratio, bandwidth and various modulation performances of the modulator based on graphene materials are improved.

[0015] The composite structure proposed in the present invention utilizes the strong light field binding ability of hybrid surface plasmons to confine the light field within a very small spatial range, thereby realizing sub-wavelength scale light field confinement. Traditional metal plasmon waveguides have high transmission losses due to the ohmic loss of metals, which limits their application in long-distance transmission and large-scale integrated photonic systems. The composite structure proposed in the present invention reduces the transmission loss to a certain extent by coupling the dielectric waveguide mode with the surface plasmon mode, and can realize longer-distance light transmission, making it more suitable for practical optical communications and integrated optical systems. The hybrid surface plasmons are selective for the polarization state of light, and only allow light with a specific polarization direction to propagate. By using high-quality polarizers to ensure that the incident light has a specific and stable polarization direction, this characteristic can effectively regulate polarization, and has potential application value in the fields of optical signal processing and optical sensing.

[0016] The graphene optical modulator based on hybrid surface plasmon proposed in the present invention achieves modulation depth (more than 20dB / μm) in the working wavelength range of 800-1650nm, covering the entire communication frequency band, showing excellent modulation performance, and demonstrating a design of a graphene optical modulator based on a special hybrid plasma waveguide. At a wavelength of 1310nm, the modulation depth of the modulator is 20.46dB / μm, and can be further optimized through adjustable parameters. Its insertion loss is only 0.248dB / μm, the 3dB modulation bandwidth is 200GHz, and the energy consumption is only 0.43fJ / bit. At 850nm, the modulation depth reaches an astonishing 33.9dB / μm, showing excellent performance at shorter communication wavelengths and occupying less space. Compared with other single-layer graphene optical modulators, the present invention not only shows excellent modulation capabilities, but also has the advantages of wide working bandwidth (from visible light to infrared light), fast modulation rate, and low power consumption. This is of great significance to the basic design of graphene plasmon modulators and provides a feasible solution for the miniaturization and high integration of next-generation optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is the structure of the hybrid surface plasmon-based graphene light modulator of the present invention, (a) is a side view, (b) is a front view;

[0018] Figure 2 It is the surface current distribution corresponding to the two-dimensional structural cross section of the quasi-open resonant ring strip waveguide described in the present invention;

[0019] Figure 3 The modulation depth of the present invention varies with the trend curve of various structural parameters;

[0020] Figure 4 is the change of transmission coefficient at different Fermi levels and the electric field distribution in the off and on states;

[0021] Figure 5 It is the variation of modulation depth of broadband response with wavelength (λ=800-1650nm) in 2D guided wave mode analysis and 3D propagation mode analysis;

[0022] Figure 6 It is a comparison chart of various indicators of the modulators of the present invention and those in the literature.

[0023] In the figure: 1-type open resonant ring strip waveguide, 2-substrate, 3-gate electrode, 4-aluminum oxide dielectric spacer layer, 5-graphene layer, 6-bottom electrode. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0025] Example 1

[0026] The graphene optical modulator based on hybrid surface plasmon of the present invention has a structural schematic diagram as shown in FIG. Figure 1 As shown. A graphene optical modulator based on hybrid surface plasmon includes a quasi-open resonant ring strip waveguide 1, a gate electrode 3, a graphene layer 5, an aluminum oxide dielectric spacer layer 4, a substrate 2, and a bottom electrode 6 is provided at the bottom of the substrate 2. The quasi-open resonant ring strip waveguide 1 and the gate electrode 3 are in the same layer. The quasi-open resonant ring strip waveguide 1 is made of silver, the gate electrode is made of gold, and the bottom electrode and the substrate are made of silver. The present invention defines the width of the quasi-open resonant ring strip waveguide as d x , height d y , the arm width is w, and the thickness of the dielectric layer is defined as h. The width d of the open resonant ring structure x and height d y The thickness of the dielectric layer should be in the range of 5 to 50 nm. When the thickness of the dielectric layer h exceeds 50 nm, the local field enhancement effect of the hybrid surface plasmon is too weak, and the modulation performance of the optical modulator deteriorates rapidly. When the thickness of the dielectric layer is less than 5 nm, more complex changes occur due to the nano effect. Placing the graphene layer at the position where the light field is strongest can further enhance the interaction between the composite structure and light. The specific parameters in this example are: width d x =60nm, height d y =60nm, arm width w=10nm, dielectric layer thickness h=10nm, and the width of the entire modulator p=500nm. The refractive index of the aluminum oxide dielectric layer is set to 1.75. The calculated modulation depth is 14.25dB / μm. The gate electrode is preferably a gold electrode, the substrate is preferably a silver layer, and the bottom electrode is preferably a silver electrode. The input light to be modulated is incident perpendicular to the cross section, and the light field excitation with the electric field polarization direction horizontal or the magnetic field polarization direction along the propagation direction is used to excite the hybrid surface plasmon at the interface between the open end face of the quasi-open resonant ring strip waveguide and the dielectric spacer layer close to the graphene layer. The gate electrodes on both sides are the source and the drain, respectively, and the bottom electrode is the gate. The incident light is modulated by controlling the voltages of the source, drain, and gate.

[0027] In order to comprehensively study the performance of the modulator, the current density of the three-dimensional propagation model of the modulator was simulated and calculated using a finite element solver. Generally speaking, the hybrid surface plasmon waveguide has a strong mode field localization capability at the gap (where graphene is placed). Due to the unique geometric structure of the quasi-open resonant ring, a circulating current can be generated at the waveguide cross section, resulting in an electric field tilt at the opening. The parallel component at the opening of the quasi-open resonant ring is greatly enhanced, matching the carrier migration direction in graphene. Therefore, this structure is expected to improve the interaction between surface plasmons and graphene and further improve the modulation performance.

[0028] This scheme utilizes the excellent optoelectronic properties of graphene, including high carrier mobility, special band structure, good conductivity and high transmittance. As a dynamic control material for on-chip waveguide modulation, it has the advantages of wide working bandwidth coverage (from visible light to infrared light), fast modulation rate, low insertion loss and strong high-density integration capability.

[0029] The modulator is an integrated all-optical modulator based on hybrid plasmon enhancement. Plasmon waveguides can provide smaller propagation mode area and greater local field enhancement, and the enhanced mode localization based on the hybrid waveguide of plasmon angle mode can achieve higher modulation depth. The hybrid surface plasmon waveguide has excellent mode field localization capability at the dielectric insulating layer, and at the same time, it cleverly combines the circular current of the open resonant ring, significantly improving the in-plane component of the electric field at the opening, so that the interaction between graphene and light is enhanced, and the modulation performance of the optical modulator is improved.

[0030] The metal-like open resonant ring design is an extension of the metal particle localized mode to the hybrid plasmon waveguide. Through the special metal structure size design, under the excitation of specific light polarization, a magnetic resonance mode field with ultra-high localization capability can be obtained in the metal localized mode. And the current distribution of this mode has a ring distribution, and has a parallel electric field with ultra-high localization capability at the metal opening. In the process of extending the localized mode to the hybrid plasmon waveguide, the waveguide mode continues to maintain the low loss and high localization characteristics of the hybrid plasmon waveguide, while taking into account the characteristics of the ring distribution of the current of the quasi-open magnetic resonance mode, forming an ultra-high localized parallel electric field at the metal opening, which improves the interaction with the carriers in the graphene plane.

[0031] Example 2

[0032] The structure of the graphene light modulator based on hybrid surface plasmon described in Example 1 is the same as that of the graphene light modulator based on hybrid surface plasmon described in Example 1, and the structural parameter d is set to x =40nm,d y =40nm, w=40nm, h=10nm. The width of the modulator p=500nm. The refractive index of the aluminum oxide dielectric layer is 1.75. The calculated modulation depth is below 5dB / μm.

[0033] Example 3

[0034] The structure of the graphene light modulator based on hybrid surface plasmon described in Example 1 is the same as that of the graphene light modulator based on hybrid surface plasmon described in Example 1, and the structural parameter d is set to x =40nm,d y=60nm, w=5nm, h=10nm. The width of the modulator p=500nm. The refractive index of the aluminum oxide dielectric layer is 1.75. The calculated modulation depth can reach 22.45dB / μm. It can be seen that as the arm width decreases from 40nm to 5nm, the modulation depth increases rapidly. In addition to the modulation depth, the insertion loss and quality factor are also calculated. The results show that at this high modulation depth, the insertion loss is only 0.248dB / μm, and the quality factor is as high as 90.5.

[0035] Example 4

[0036] The structure of the hybrid surface plasmon-based graphene optical modulator is the same as that of Example 1, except that the air in the middle of the silver open ring is replaced with porous silica, and the structural parameters are set to dx=60nm, dy=60nm, w=5nm, and h=10nm. The width of the modulator p=500nm. The refractive index of the alumina dielectric layer is 1.75. The refractive index of the porous silica is 1.05. The calculated modulation depth is 19.97dB / μm.

[0037] Example 5

[0038] The structure of the graphene light modulator based on hybrid surface plasmon described in Example 1 is the same as that of the graphene light modulator based on hybrid surface plasmon described in Example 1, and the structural parameter d is set to x =80nm,d y =80nm, w=10nm, h=10nm. The width of the modulator p=500nm. The refractive index of the aluminum oxide dielectric layer is 1.75. The calculated modulation depth is 11.34dB / μm.

[0039] Example 6

[0040] The structure of the hybrid surface plasmon-based graphene optical modulator is the same as that of the embodiment 1. The graphene layer can also be replaced by other broadband Dirac semimetal type two-dimensional materials, such as transition metal chalcogenides with band gaps, black phosphorus, etc. The quasi-open resonant ring strip waveguide uses plasmon materials, such as precious metal materials gold and silver, or metal aluminum. The dielectric spacer layer can also use other insulating oxides instead of aluminum oxide.

[0041] Next, the intrinsic modes, modulation performance and electrical performance of the structure of the hybrid surface plasmon-based graphene optical modulator are further studied, and a more detailed analysis is given below.

[0042] In order to study the mode field distribution of the graphene waveguide modulator in detail and analyze its performance, a full-field electromagnetic wave simulation was performed, and the eigenmode analysis of the two-dimensional structure of the quasi-open resonant ring hybrid surface plasmon waveguide without graphene was performed. The operating wavelength was set to 1310nm. The geometric parameters of the quasi-open resonant ring strip waveguide were defined, and the width d of the waveguide cross sectionx =60nm, height d y =60nm, arm width w=5nm, dielectric layer thickness h=10nm, and the width of the entire modulator p=500nm. In addition, the refractive index of the dielectric layer is set to 1.75, and the dielectric constant of silver can be obtained using experimental data. The calculated modulation depth is 20.46dB / μm.

[0043] First, the performance of the waveguide eigenmode needs to be measured, including the localization of the mode field and the propagation loss. The real part of the effective refractive index represents the degree of localization of the mode field, and the imaginary part represents the Ohmic loss in the metal. The electric field distribution of the antisymmetric mode is analyzed in detail as the parameters change, and the changes in the real and imaginary parts are further analyzed to describe the mode field distribution of the electric field intensity and the three components of the electric field. The mode field distribution of the electric field in the vertical and horizontal directions represents the degree of localization of the electric field in the plane where the graphene is placed. The electric field distribution along the vertical arrow direction at the bottom of the quasi-open resonant ring strip waveguide in the dielectric layer is analyzed, and it is found that with the increase of the arm width, the effective mode area gradually expands in the z direction. However, the electric field distribution along the horizontal arrow on the contact surface of the quasi-open resonant ring strip waveguide with the dielectric layer and graphene shows an opposite trend. These two observations are contradictory, so the real part generally shows a trend of decreasing first and then increasing. Subsequently, we studied the changes in the imaginary part, which is mainly due to the Ohmic loss in the metallic silver. Figure 2 The electric field distribution along the horizontal arrow inside the metal of the left arm of the quasi-open resonant ring strip waveguide is depicted in the figure. Considering the small arm width, the metal can be regarded as a uniform material, so the absorption coefficient is approximately a constant, making the loss proportional to the electric field strength. As the arm width increases, the valley value of the electric field amplitude decreases, indicating that the field intensity enhancement is also gradually decreasing, so the loss gradually decreases, which leads to a decrease in the imaginary part of the effective refractive index. Next, we studied the transmission loss and mode area of ​​the quasi-open resonant ring strip waveguide as the arm width changes. The transmission loss at w=5nm (~3dB / μm) is much smaller than the modulation depth of the structure designed by the present invention, so the present invention can achieve effective modulation in a very compact device, so the transmission loss can be ignored. As the arm width increases, the propagation distance is also extended. The effective mode area of ​​the waveguide is always maintained at 10 -4 This indicates that the mode field is well localized near the plane of graphene. This indicates that when the open-ring resonant strip waveguide is used as a modulator, there will be a good interaction between light and matter.

[0044] Next, we focus on analyzing the parallel components near the graphene plane in the mode field. In order to study the potential physical mechanism of the enhanced interaction between light and matter at the upper surface of the open-ring resonant strip waveguide and the dielectric spacer layer (graphene plane), we study the polarization degree γ of the eigenmode. ∥ and locality η c , where E / / is the parallel component of the mode field on the dielectric surface (including E x and E y mode field component), S is the effective area of ​​graphene, polarization degree γ ∥ Represents the proportion of parallel components in the mode field. Locality η c It is the ratio of the mode field in the block near the graphene to the total mode field, indicating the degree of enhancement of the local field strength at the graphene plane. The volume of this block V = h c *S, when calculating, considering that graphene is a two-dimensional material, h c When the arm width w is 5nm, the polarization degree is as high as 68.4%, and the parallel component is greatly increased, which is conducive to the coupling of the hybrid plasmon waveguide mode with graphene. Since the strip waveguide of the quasi-open resonant ring waveguide generates a circular current, there are many inclined components, which increases the parallel component, such as Figure 2 As shown in the figure, the parallel component at the graphene plane is the highest, which is exactly what we expect and can greatly improve the modulation performance of the modulator. At the same time, as the arm width w gradually decreases, the polarization degree and localization degree are improved, which points out the direction for optimizing the modulation performance of the modulator.

[0045] Then, we introduce graphene to study the related performance of dynamic modulation. First, the introduction of graphene has little effect on the mode field distribution of the optical waveguide because the layer is very thin at the atomic level, which reduces the optical losses caused by undesirable mode mismatch and reflection. Secondly, the regulatory effect of graphene is usually achieved through the evanescent field coupling of the optical waveguide mode. The clever design of the waveguide mode of this hybrid waveguide can greatly improve the localization of its mode and enhance the in-plane component near the graphene plane. By introducing anisotropic graphene, we focus on the changes in the imaginary part of the waveguide mode accompanied by the graphene Fermi level to characterize the modulation performance of graphene light modulation.

[0046] A thin layer of graphene is covered on the dielectric layer of the plasmon modulator to study the modulation performance. The graphene conductivity is calculated with the Fermi level at an incident light wavelength of 1310nm using a formula. In the simulation process, an anisotropic graphene model with in-plane conductivity is used, and its conductivity can be described by linear response theory. Both the real and imaginary parts of the propagating waveguide mode change significantly by changing the chemical potential, proving that both absorption and refraction are affected by the surface carrier concentration. The effective refractive index is a quantitative value of phase shift and light absorption in an optical waveguide, which is very important for the study of waveguide modulators. Therefore, the plasmon silver-like open resonant ring strip waveguide with graphene added is simulated, and the real and imaginary parts of the effective refractive index are calculated as the Fermi level changes. It can be seen that the conductivity and the effective refractive index have a good match.

[0047] The modulation depth can be estimated by using the change in the imaginary part of the eigenmode of the silver-like open-loop resonant ring strip waveguide after the introduction of graphene. The Fermi level of graphene is changed by applying different gate voltages. At low voltages, the Fermi level of graphene is lower than the transition threshold, and the external photons of graphene will be absorbed, resulting in interband transitions. This causes the eigenmode of the waveguide to have a large mode field loss, and the corresponding effective refractive index has a large imaginary part, which is defined as the closed state (the Fermi level is set to 0.4eV). On the contrary, when under a very high voltage, the Fermi level will exceed the transition threshold. Since the absorption has reached saturation, external photons cannot be absorbed. At this time, graphene is almost equivalent to non-existence, and the absorption loss of the eigenmode is very low. The corresponding effective refractive index is a very small imaginary part, which is defined as the ON state (the Fermi level is set to 0.6eV). Therefore, the modulation depth can be estimated by the difference between the two imaginary parts of the on state and the off state. In order to facilitate calculation, the width d of the quasi-open-loop resonant ring strip waveguide is first calculated. x With length d y Set to the same length. Under the initial setting of structural parameters (d x =80nm,d y =80nm, w=10nm, h=10nm), the calculated modulation depth is 8.79dB / μm.

[0048] From the analysis of the intrinsic modes, it can be seen that the quasi-open resonant ring strip waveguide forms a circular current at the cross section, which significantly enhances the electric field component parallel to the plane, especially the electric field component in the x direction, and significantly improves the performance of the hybrid surface plasmon quasi-open resonant ring strip waveguide modulator. However, the potential of the quasi-open resonant ring strip waveguide structure modulator has not been fully explored, and its structural parameters can still be further optimized to increase the effective polarization component of the electric field at the graphene plane, thereby increasing its modulation depth. In order to find the optimal structural parameters, the width d of the two arms of the quasi-open resonant ring strip waveguide is adjusted by the control variable method. x , height d y and arm width w were parametrically scanned, such as Figure 3 As shown, the trend curves of the modulation depth changing with each structural parameter are obtained. It can be seen that the modulation depth decreases to varying degrees as the three structural parameters decrease. It is worth noting that as the arm width decreases from 40nm to 5nm, the modulation depth increases by 5 times, which shows that among the structural parameters of the quasi-open resonant ring waveguide, the arm width is the main factor affecting the modulation depth. As previously analyzed, the mode field distribution of the eigenmode changes with the arm width. As the arm width decreases, the polarization degree and localization degree are optimized, confirming the calculated modulation depth results. Therefore, the main direction to increase the modulation depth by optimizing the structural parameters is to reduce the arm width. Due to the mode cutoff, the three structural parameters cannot be reduced at the same time. The structural parameter d is selected by scanning the parameters.x =60nm,d y =60nm, w = 5nm, the modulation depth reaches 20.46dB / μm. Then the arm length d of the quasi-open resonant ring strip waveguide is fixed. y The width d of the open ring resonator is 60nm. x The modulation depth is calculated by jointly scanning the arm width w, such as Figure 3 (d) As the arm width and width become smaller, the modulation depth becomes larger and larger. x =40nm, w=5nm, the modulation depth can reach 22.45dB / μm. In addition to the modulation depth, the insertion loss and quality factor are also calculated. The results show that at this high modulation depth, the insertion loss is only 0.28dB / μm, and the quality factor is as high as 73. These parameters show that the performance of the modulator is excellent.

[0049] It is not comprehensive to explain the modulation performance of the hybrid surface plasmon-like open ring resonator waveguide modulator only from a two-dimensional model. In order to verify the correctness of the modulation performance of the two-dimensional waveguide mode analysis, a three-dimensional modulator model needs to be established. Therefore, a three-dimensional hybrid open ring resonator waveguide propagation model was established using finite element software for simulation. In the three-dimensional propagation model, the modulation depth does not need to be calculated using a complex formula for the imaginary part of the effective refractive index. It only requires the transmission coefficient of the waveguide and the propagation distance to obtain it. In both the off and on states, the ratio of the energy at the coupling end and the coupling end of the waveguide light field is calculated, and then the modulation depth can be calculated by a simple calculation with the propagation distance. Figure 4 It is the transmission coefficient of the three-dimensional waveguide model of the quasi-open ring resonator waveguide at different Fermi levels when the propagation distance is 1μm. According to the transmission coefficient ratio of the on state and the off state, the modulation depth of the three-dimensional model is calculated to be 20.17dB / μm, the insertion loss is 0.26dB / μm, and the quality factor is 78, which matches the two-dimensional model very well, proving the reliability and authenticity of the above calculation. From the transmission coefficient curve, the Fermi level greater than 0.48eV corresponds to the off state of the modulator, and the Fermi level less than 0.48eV corresponds to the on state of the modulator. Figure 5As shown in the figure, the broadband response of the hybrid surface plasmon-like open resonant ring strip waveguide modulator is calculated. In the broadband wavelength range (800nm-1650nm), the modulation depth of the two-dimensional model is basically consistent with that of the three-dimensional model, and the modulation depth is above 20dB / μm. For the polarization direction of the incident light, it should be ensured to remain relatively stable over the entire wavelength range. The incident light is ensured to have a specific and stable polarization direction by using high-quality polarizers. In addition, the intensity of the incident light should also be kept consistent within a reasonable range. Fluctuations in intensity may affect the accuracy of the model, especially when it comes to optical phenomena that are sensitive to light intensity. A constant incident light intensity is achieved by using a stable light source and an appropriate light intensity regulator to ensure that the results of the two-dimensional model and the three-dimensional model are comparable. From these parameters, it can be seen that the modulation depth of the two-dimensional model is basically consistent with that of the three-dimensional model. The modulator has a good broadband response and exhibits excellent modulation performance.

[0050] like Figure 6 As shown in the figure, the performance of modulators in recent years is compared from six aspects: number of graphene layers, modulation depth, insertion loss, area of ​​active devices, energy consumption and 3dB bandwidth modulation rate. It can be seen from the performance comparison chart that the modulator of the present invention not only improves the modulation depth, but also has lower insertion loss and energy consumption, and has a relatively small device area, which makes the modulator of the present invention more compact and highly integrated, which helps to play an advantage in application scenarios such as micro-nano photonic chips. The modulator has the characteristics of wide bandwidth, which provides a wider working range and higher data transmission rate for high-speed optical communication and data processing.

[0051] The present invention realizes a hybrid plasmon-like open resonant ring waveguide modulator with a modulation depth of 20.46 dB / μm, an insertion loss of only 0.28 dB / μm, and a quality factor of 73, with excellent modulation performance and good broadband response. In addition, the electrical performance of the modulator is also very good. Finally, the performance of the modulator in recent years is compared from six aspects: the number of graphene layers, modulation depth, insertion loss, area of ​​active devices, energy consumption, and 3dB bandwidth. It can be seen that the single-layer graphene modulator designed by the present invention has great advantages, which can promote the commercialization of tunable graphene optical modulators based on hybrid plasmon-like open resonant ring strip waveguides.

[0052] These advantages can make the present invention applicable to many fields, such as in the field of optical communication, it can realize high-speed optical signal modulation and improve the data transmission rate of the optical communication system. In the wavelength division multiplexing system, optical signals of different wavelengths can be modulated independently to increase the communication capacity. In the field of integrated optics, the present invention can be integrated into photonic integrated circuits to realize miniaturized, high-performance optical devices, etc.

Claims

1. A graphene light modulator based on hybrid surface plasmon, characterized in that: The optical modulator comprises, from top to bottom, a quasi-open resonant ring strip waveguide, a graphene layer, a dielectric spacer layer, a substrate and a bottom electrode, wherein a gate voltage electrode is respectively arranged above the graphene layer and on both sides of the quasi-open resonant ring strip waveguide; the quasi-open resonant ring strip waveguide is a metal waveguide, the cross section of the quasi-open resonant ring strip waveguide is an open resonant ring structure, and the open end of the open resonant ring structure is in contact with the graphene layer; the thickness h of the dielectric spacer layer is 5-50nm; the input light to be modulated is incident perpendicular to the cross section, and the light field excitation with the electric field polarization direction horizontal or the magnetic field polarization direction along the propagation direction is used to excite the hybrid surface plasmon at the interface between the open end face of the quasi-open resonant ring strip waveguide and the dielectric spacer layer close to the graphene layer; the gate voltage electrodes on both sides are the source and the drain respectively, and the bottom electrode is the gate, and the incident light is modulated by controlling the voltages of the source, the drain and the gate.

2. The hybrid surface plasmon-based graphene optical modulator according to claim 1, characterized in that: The width d of the split ring resonator structure x 40-150nm, height d y It is 40-150nm, and the arm width w is 5-40nm.

3. The graphene optical modulator based on hybrid surface plasmon according to claim 1, characterized in that: The graphene layer is placed at the position where the light field is strongest.

4. The hybrid surface plasmon-based graphene optical modulator according to claim 1, characterized in that: The graphene layer is replaced by other broadband Dirac semimetal type two-dimensional materials, and the broadband Dirac semimetal type two-dimensional materials include transition metal chalcogenides with band gaps and black phosphorus.

5. The hybrid surface plasmon-based graphene optical modulator according to claim 1, characterized in that: The graphene layer adopts a single-layer, double-layer or multi-layer design.

6. The hybrid surface plasmon-based graphene optical modulator according to claim 1, characterized in that: The quasi-open resonant ring strip waveguide adopts a plasmon material, and the plasmon material includes a noble metal material or aluminum.

7. The graphene optical modulator based on hybrid surface plasmon according to claim 1, characterized in that: The interior of the quasi-open resonant ring strip waveguide is filled with an insulating medium with a lower refractive index, and the insulating medium includes air and porous silicon dioxide.

8. The graphene optical modulator based on hybrid surface plasmon according to claim 1, characterized in that: The dielectric spacer layer is made of insulating oxide; the dielectric spacer layer is made of aluminum oxide.

9. The hybrid surface plasmon-based graphene optical modulator according to claim 1, characterized in that: The gate electrode is a gold electrode, the substrate is a silver layer, and the bottom electrode is a silver electrode.

10. An optical communication chip, characterized in that: The chip modulates optical signals through the hybrid surface plasmon-based graphene optical modulator as claimed in claim 1.

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