Hybrid surface plasmon based graphene optical modulator

Abstract

The application discloses a graphene optical modulator based on hybrid surface plasmons, which comprises, from top to bottom, an open-like resonant ring strip-shaped waveguide, a graphene layer, a dielectric spacer layer, a substrate and a bottom electrode, and one gate voltage electrode is arranged on each side of the open-like resonant ring strip-shaped waveguide; the cross section of the open-like resonant ring strip-shaped waveguide is in an open-like resonant ring structure; the open end of the open-like resonant ring structure is in contact with the graphene layer; the dielectric spacer layer has a thickness of 5-50 nm; the two gate voltage electrodes are respectively a source electrode and a drain electrode, and the bottom electrode is a gate electrode, and the incident light is modulated by controlling the voltage of the source electrode, the drain electrode and the gate electrode; the input light to be modulated is incident perpendicularly to the cross section, and the hybrid surface plasmons are excited at the open end surface of the open-like resonant ring strip-shaped waveguide and the interface between the dielectric spacer layer and the graphene layer close to each other. The application improves the on-off ratio, bandwidth and various modulation performances of the modulator based on the graphene material.

Description

TECHNICAL FIELD

[0001] The application relates to a graphene material-based modulator in the field of optical communication, in particular to a graphene optical modulator based on hybrid surface plasmons. BACKGROUND

[0002] Silicon-based modulators are core devices in optical communication, but traditional silicon-based waveguide modulators (such as silicon optical modulators) are limited by the limitations of silicon-based materials in optical modulation, and the theoretical bandwidth limit is less than 70 GHz, and the energy consumption of several tens of fJ / bit is already relatively low data. A silicon-based ridge waveguide integrated optical modulator based on single-layer graphene realizes modulation by actively tuning the Fermi energy level of the single-layer graphene sheet, and the 3dB bandwidth of the modulator is about 1GHz. This bandwidth is limited by the parasitic response of the device, not the carrier transport time. Because the carrier mobility and saturation speed of graphene are extremely high, the bandwidth is limited by the parasitic response, about 1GHz. Because the thickness of graphene is very thin, its absorption and modulation capacity for light are limited, so the effect of single-layer graphene in optical modulation is limited, especially for common silicon-based dielectric waveguides, the light field is mainly distributed in the center of the dielectric, greatly reducing the interaction with the surface graphene. In order to enhance the interaction between graphene and light, researchers combine graphene with plasmonic waveguides and design a hybrid waveguide modulator based on plasmonic angular mode mixing graphene. However, through research, it is found that although the mode field of surface plasmons can be flexibly controlled by metal micro-nano structures in the subwavelength range, due to the ohmic loss of metal, the plasmonic waveguide has a large propagation loss, and the main field component of the traditional surface plasmon is perpendicular to the graphene plane, and the parallel component of the graphene is very low, which cannot effectively interact with the graphene, thereby making it difficult to improve the on-off ratio of the graphene optical modulator based on pure plasmons and accompanied by large energy consumption, limiting its application potential. SUMMARY

[0003] The application aims at the above problems, and provides a graphene optical modulator based on hybrid surface plasmons, which improves the on-off ratio, bandwidth and various modulation performances of the graphene material-based modulator.

[0004] Technical solution: The technical scheme adopted by the present application is a graphene optical modulator based on hybrid surface plasmons, which comprises, from top to bottom, a strip waveguide with an open resonant ring structure, a graphene layer, a dielectric spacer layer, a substrate and a bottom electrode, and a gate voltage electrode is arranged on the graphene layer and on both sides of the strip waveguide with an open resonant ring structure; the strip waveguide with an open resonant ring structure is a metal waveguide, the cross section of the strip waveguide with an open resonant ring structure 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 5-50 nm. 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 vertically to the cross section, and a light field with a horizontal electric field polarization direction or a magnetic field polarization direction along the propagation direction is used to excite hybrid surface plasmons at the open end of the strip waveguide with an open resonant ring structure and the interface between the dielectric spacer layer and the graphene layer; the two gate voltage electrodes are a source electrode and a drain electrode respectively, and the bottom electrode is a gate electrode, and the voltage of the source electrode, the drain electrode and the gate electrode is controlled to modulate the incident light.

[0005] More preferably, the arm width of the open resonant ring structure is the main factor affecting the modulation depth, and the arm width w of the open resonant ring structure is 5-40 nm. Further optimization of other structural parameters of the open resonant ring structure, the width d of the open resonant ring structure is 40-150 nm, and the height d of the open resonant ring structure is 40-150 nm. x y

[0006] The graphene layer is placed at the position where the light field is the strongest, which can further improve the interaction between light and graphene.

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

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

[0009] The strip waveguide with an open resonant ring structure uses plasmonic materials, and the plasmonic materials include noble metal materials or aluminum.

[0010] The inside of the strip waveguide with an open resonant ring structure is filled with an insulating dielectric / oxide with a lower refractive index, including air, porous silica and the like.

[0011] The dielectric spacer layer uses an insulating oxide; the dielectric spacer layer uses aluminum oxide.

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

[0013] ​​The application provides an optical communication chip, which modulates an optical signal through the hybrid surface plasmon-based graphene optical modulator.

[0014] Beneficial effects: Compared with the prior art, the application has the following advantages: in order to further improve the interaction between light and graphene, in addition to placing graphene at the position of the strongest light field, it is more important to make the polarization of light consistent with the surface conductive plane of graphene. The application combines the open resonant ring structure with the metal waveguide, proposes a kind of open resonant ring strip waveguide, and through the composite structure of the intermediate insulating layer of the open resonant ring strip waveguide and the metal flat plate waveguide, the interaction between graphene and light is enhanced. The composite structure proposed in the application excites hybrid surface plasmons at the open end face of the open resonant ring strip waveguide and the interface of the intermediate insulating layer close to the graphene layer, and ingeniously combines the annular current of the open resonant ring, which significantly improves the in-plane component of the surface conductive plane of graphene and enhances the interaction between graphene and light. By enhancing the interaction between graphene and light, the on-off ratio, bandwidth and various modulation performances of the modulator based on graphene material are improved.

[0015] The composite structure proposed in the application uses the strong light field binding ability of hybrid surface plasmons to limit the light field in a very small spatial range, realizing subwavelength scale light field confinement. The traditional metal plasmonic waveguide has high transmission loss due to the ohmic loss of metal, which limits its application in long-distance transmission and large-scale integrated photonic systems. The composite structure proposed in the application couples the dielectric waveguide mode with the surface plasmon mode to a certain extent, reduces the transmission loss, realizes long-distance optical transmission, and is more suitable for practical optical communication and integrated optical systems. Hybrid surface plasmons have selectivity to the polarization state of light, only allowing light with a specific polarization direction to propagate, and the use of high-quality polarizing plates ensures that the incident light has a specific and stable polarization direction. This characteristic can effectively regulate the 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 plasmons proposed in this invention achieves a modulation depth (exceeding 20 dB / μm) within the operating wavelength range of 800-1650 nm, covering the entire communication frequency band and exhibiting excellent modulation performance. It demonstrates a graphene optical modulator design based on a special hybrid plasmonic waveguide, achieving a modulation depth of 20.46 dB / μm at 1310 nm, which can be further optimized through adjustable parameters. Its insertion loss is only 0.248 dB / μm, with a 3 dB modulation bandwidth of 200 GHz and power consumption of only 0.43 fJ / bit. At 850 nm, the modulation depth reaches an astonishing 33.9 dB / μm, demonstrating superior performance at shorter communication wavelengths and occupying less space. Compared with other single-layer graphene optical modulators, this invention not only exhibits excellent modulation capabilities but also boasts advantages such as a wide operating bandwidth (from visible light to infrared light), high modulation rate, and low power consumption. This is of great significance to the fundamental design of graphene plasma modulators, providing a feasible solution for the miniaturization and high integration of next-generation optoelectronic devices. Attached Figure Description

[0017] Figure 1 The structure of the graphene optical modulator based on hybrid surface plasmons described in this invention is shown in (a) as a side view and (b) as a front view.

[0018] Figure 2 This refers to the surface current distribution corresponding to the two-dimensional structural cross-section of the quasi-open resonant ring-strip waveguide described in this invention.

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

[0020] Figure 4 It refers to the changes in the transmission coefficient at different Fermi levels and the electric field distribution in the off and on states;

[0021] Figure 5 The modulation depth of the broadband response varies with wavelength (λ = 800-1650 nm) under two-dimensional guided wave mode analysis and three-dimensional propagation mode analysis.

[0022] In the figure: 1-Class open resonant ring strip waveguide, 2-Substrate, 3-Gate voltage electrode, 4-Alumina dielectric spacer layer, 5-Graphene layer, 6-Bottom electrode. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Example 1

[0025] The hybrid surface plasmon based graphene light modulator has a structure diagram as shown in the figure. Figure 1 The hybrid surface plasmon based graphene light modulator comprises an open-like resonant ring strip waveguide 1, a gate voltage electrode 3, a graphene layer 5, an alumina dielectric spacer layer 4, a substrate 2, and a bottom electrode 6 provided at the bottom of the substrate 2. The open-like resonant ring strip waveguide 1 and the gate voltage electrode 3 are in the same layer, the open-like resonant ring strip waveguide 1 is composed of silver, the gate voltage electrode is composed of gold, and the bottom electrode and the substrate are composed of silver. The width of the open-like resonant ring strip waveguide is defined as d x , the height is d y , the arm width is w, and the thickness of the dielectric layer is h. The width d x and the height d y of the open-like resonant ring structure are in the range of 40-150 nm. The thickness of the dielectric layer should be in the range of 5-50 nm. When the thickness h of the dielectric layer exceeds 50 nm, the localized field enhancement effect of the hybrid surface plasmon is too weak, and the modulation performance of the light modulator deteriorates rapidly. When the thickness of the dielectric layer is less than 5 nm, more complex changes are caused by the nanometer effect. Placing the graphene layer at the position of the strongest light field can further enhance the interaction between the composite structure and the light. In this example, the specific parameters are as follows: the width d x = 60 nm, the height d y = 60 nm, the arm width w = 10 nm, the dielectric layer thickness h = 10 nm, and the width p of the entire modulator = 500 nm. The refractive index of the alumina dielectric layer is set to 1.75. The calculated modulation depth is 14.25 dB / μm. The gate voltage 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 vertically to the cross section, and the light field is excited using an electric field polarization direction horizontally or a magnetic field polarization direction along the propagation direction, so as to excite the hybrid surface plasmon at the open end surface of the open-like resonant ring strip waveguide and the interface of the dielectric spacer layer close to the graphene layer. The two side gate voltage electrodes are respectively a source electrode and a drain electrode, and the bottom electrode is a gate electrode. The incident light is modulated by controlling the voltages of the source electrode, the drain electrode and the gate electrode.

[0026] In order to comprehensively study the performance of the modulator, the current density of the three-dimensional propagation model of the modulator is simulated by using a finite element solver. Under normal circumstances, the hybrid surface plasmon waveguide has strong mode field localization ability at the gap (where the graphene is placed). Due to the unique geometry of the open-like resonant ring, circulating current can be generated at the waveguide cross section, resulting in the tilting of the electric field at the opening. The parallel component at the opening of the open-like resonant ring is greatly improved, which matches the direction of the carrier migration in the graphene, so that the structure is expected to improve the interaction between the surface plasmon and the graphene and further improve the modulation performance.

[0027] The scheme utilizes the excellent photoelectric performance of graphene, including high carrier mobility, special energy band structure, good conductivity and high light transmittance, as a dynamic modulation material for on-chip waveguide modulation, and has the advantages of wide working bandwidth (from visible light to infrared light), fast modulation rate, low insertion loss and high-density integration capability.

[0028] The modulator is an integrated all-optical modulator based on hybrid plasmonic enhancement. The plasmonic waveguide can provide smaller propagation mode area and larger local field enhancement, and the mode localization based on hybrid plasmonic angular mode waveguide is enhanced to realize higher modulation depth. The hybrid surface plasmonic waveguide has excellent mode localization capability at the dielectric insulating layer, and the ring current of the open resonant ring is ingeniously combined to significantly improve 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.

[0029] The metal-like open resonant ring design is a generalization of the metal particle local mode to the hybrid plasmonic waveguide. Through special metal structure size design, under the excitation of a specific light polarization, a magnetic resonance mode field with ultra-high localization capability can be obtained in the metal local mode. And the current distribution of this mode has a ring-shaped distribution, and the parallel electric field at the metal opening has ultra-high localization capability. In the generalization process of the local mode to the hybrid plasmonic waveguide, the waveguide mode continues to have the characteristics of low loss and high localization of the hybrid plasmonic waveguide, while taking into account the ring-shaped distribution of the current of the open magnetic resonance mode, forming a parallel electric field with ultra-high localization at the metal opening, which is the loading layer of graphene, thereby improving the interaction with the in-plane carriers of graphene.

[0030] Example 2

[0031] The structure of the graphene optical modulator based on hybrid surface plasmons described in Example 1 is the same, and the structure parameters d x = 40 nm, d y = 40 nm, w = 40 nm, h = 10 nm. The width of the modulator p = 500 nm. The refractive index of the aluminum oxide dielectric layer is 1.75. The calculated modulation depth is below 5 dB / μm.

[0032] Example 3

[0033] The structure of the graphene optical modulator based on hybrid surface plasmons described in Example 1 is the same, and the structure parameters d x = 40 nm, d y= 60 nm, w = 5 nm, h = 10 nm. The width of the modulator p = 500 nm. The refractive index of the alumina dielectric layer is 1.75. The calculated modulation depth is up to 22.45 dB / μm. It can be seen that the modulation depth increases rapidly as the arm width decreases from 40 nm to 5 nm. In addition to the modulation depth, the insertion loss and the quality factor are also calculated, and the results show that at such a high modulation depth, the insertion loss is only 0.248 dB / μm, while the quality factor is as high as 90.5.

[0034] Example 4

[0035] The structure of the hybrid surface plasmonic graphene optical modulator described in Example 1 is the same, the air in the silver open ring is replaced by porous silica, and the structure parameters dx = 60 nm, dy = 60 nm, w = 5 nm, h = 10 nm are set. The width of the modulator p = 500 nm. 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 19.97 dB / μm.

[0036] Example 5

[0037] The structure of the hybrid surface plasmonic graphene optical modulator described in Example 1 is the same, and the structure parameters dx = 60 nm, dy = 60 nm, w = 5 nm, h = 10 nm are set. x = 80 nm, d y = 80 nm, w = 10 nm, h = 10 nm. The width of the modulator p = 500 nm. The refractive index of the alumina dielectric layer is 1.75. The calculated modulation depth is 11.34 dB / μm.

[0038] Example 6

[0039] The structure of the hybrid surface plasmonic graphene optical modulator described in Example 1 is the same, and the graphene layer can also be replaced by other wide-band Dirac semimetal type two-dimensional materials, such as transition metal chalcogenides with band gaps, black phosphorus, etc. The strip waveguide of the quasi-open resonant ring adopts plasmonic materials, such as noble metal materials gold and silver, or adopts metal aluminum. The dielectric spacer layer can also be replaced by other insulating oxides instead of alumina.

[0040] The intrinsic mode, modulation performance and electrical performance of the structure of the hybrid surface plasmonic graphene optical modulator described above are further studied, and more detailed analysis is given below.

[0041] In order to study the mode field distribution of the graphene waveguide modulator in detail and analyze its performance, full-field electromagnetic wave simulation is carried out, and the intrinsic mode analysis is carried out on the two-dimensional structure of the quasi-open resonant ring hybrid surface plasmonic waveguide without placing graphene. The working wavelength is set to 1310 nm. The geometric parameters of the quasi-open resonant ring strip waveguide are defined, and the width of the waveguide cross section dx = 60 nm, height d y = 60 nm, arm width w = 5 nm, dielectric layer thickness h = 10 nm, width p = 500 nm of the whole modulator. In addition, the refractive index of the dielectric layer is set to 1.75, and the dielectric constant of silver can be obtained by using experimental data. The calculated modulation depth is 20.46 dB / μm.

[0042] First, the performance of the waveguide eigenmode needs to be measured, including the localization of the mode field and the propagation loss, etc. 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 with the change of the parameters, and the real part and the imaginary part are further analyzed, which describes the mode field distribution of the electric field intensity and the electric field three components. The mode field distribution of the electric field in the vertical direction and the horizontal direction represents the degree of localization of the electric field in the plane of the graphene. By analyzing the electric field distribution along the vertical arrow direction at the bottom of the dielectric layer of the strip waveguide with a split-ring resonator, 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 strip waveguide with a split-ring resonator and the dielectric layer and the graphene shows an opposite trend. These two observations are contradictory, so the real part shows a trend of first decreasing and then increasing. Subsequently, we studied the change of the imaginary part, which is mainly due to the ohmic loss in the metal silver. Figure 2 The electric field distribution along the horizontal arrow direction inside the metal of the left arm of the strip waveguide with a split-ring resonator is depicted. Considering that the arm width is small, the metal can be regarded as a homogeneous material, so the absorption coefficient is approximately constant, thereby making the loss proportional to the electric field intensity. With the increase of the arm width, the valley value of the electric field amplitude decreases, indicating that the field intensity is also gradually decreasing, so the loss is gradually decreasing, which leads to the decrease of the imaginary part of the effective refractive index. Next, we study the trend of the transmission loss and the mode area of the strip waveguide with a split-ring resonator with the change of the arm width. The transmission loss (~3 dB / μm) when w = 5 nm is much smaller than the modulation depth of the structure designed in the present application, so the present application can realize effective modulation in a very compact device, and then the transmission loss can be ignored. With the increase of the arm width, the propagation distance is also prolonged. While the effective mode area of the waveguide always remains in the order of 10 -4 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 with the change of the parameters, and the real part and the imaginary part are further analyzed, which describes the mode field distribution of the electric field intensity and the electric field three components. The mode field distribution of the electric field in the vertical direction and the horizontal direction represents the degree of localization of the electric field in the plane of the graphene. By analyzing the electric field distribution along the vertical arrow direction at the bottom of the dielectric layer of the strip waveguide with a split-ring resonator, 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 strip waveguide with a split-ring resonator and the dielectric layer and the graphene shows an opposite trend. These two observations are contradictory, so the real part shows a trend of first decreasing and then increasing. Subsequently, we studied the change of the imaginary part, which is mainly due to the ohmic loss in the metal silver.

[0043] Next, the parallel component near the graphene plane in the mode field is analyzed. In order to study the potential physical mechanism of the enhanced interaction between light and matter at the surface of the dielectric spacer layer (graphene plane) of the strip waveguide with a split-ring resonator, the polarization degree γ ∥ and the localization degree η c of the eigenmode are studied, where E / / is the parallel component of the mode field on the surface of the dielectric layer (including E x and E y , S is the effective area of graphene, and the degree of polarization γ ∥ represents the proportion of the parallel component of the mode field. The localization degree η c is the ratio of the mode field in the body block near the graphene to the total mode field, indicating the degree of enhancement of the localized field strength at the graphene plane. The volume of this body block is V = h c *S, and when calculating, considering that graphene is a two-dimensional material, h c is set to 1 nm. When the arm width w is 5 nm, the degree of polarization is as high as 68.4%, and the parallel component is greatly increased, which is conducive to the coupling of the hybrid plasmonic guided mode and graphene. Because the strip waveguide of the open-ring resonator waveguide produces a ring current, it results in many inclined components, thereby increasing the parallel component, as shown in Figure 2 , the parallel component at the graphene plane is the highest, which is 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 degree of polarization and the localization degree are improved, which indicates the direction for optimizing the modulation performance of the modulator.

[0044] 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 loss caused by unwanted mode mismatch and reflection. Second, the regulation of graphene is usually realized through the evanescent field coupling of the optical guided mode. By skillfully designing the guided mode of this hybrid waveguide, the localization of the mode can be greatly improved, and the in-plane component near the graphene plane can be enhanced. By introducing anisotropic graphene, we focus on the change of the imaginary part of the guided mode with the Fermi level of graphene to characterize the modulation performance of graphene optical modulation.

[0045] A thin layer of graphene is covered on the dielectric layer of the plasmonic modulator to study the modulation performance. The change trend of the graphene conductivity with the Fermi level at the incident light wavelength of 1310 nm is calculated by using the formula. In the simulation process, an anisotropic graphene model with in-plane conductivity is used, and its conductivity can be described by the linear response theory. The real part and the imaginary part 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 the phase shift and light absorption in the optical waveguide, and it is very important for the study of waveguide modulators. Therefore, the real part and the imaginary part of the effective refractive index are calculated by simulating the plasmonic silver open-ring resonator strip waveguide with graphene, and it can be seen that the conductivity and the effective refractive index have a good matching degree.

[0046] The modulation depth can be estimated using the change in the imaginary part of the eigenmodes of a silver-based open-loop resonant strip waveguide after the introduction of graphene. By applying different gate voltages to change the Fermi level of graphene, at low voltages, the Fermi level of graphene is below the transition threshold, and external photons of graphene will be absorbed, resulting in interband transitions. This leads to a large mode field loss in the waveguide's eigenmodes, and the corresponding effective refractive index has a large imaginary part; this state is defined as the off state (setting the Fermi level to 0.4 eV). Conversely, at a very high voltage, the Fermi level will exceed the transition threshold. Since absorption has reached saturation, external photons cannot be absorbed, and graphene is almost non-existent. The absorption loss of the eigenmodes is very low, and the corresponding effective refractive index has a very small imaginary part; this state is defined as the ON state (setting the Fermi level to 0.6 eV). Therefore, the modulation depth can be estimated by the difference between the two imaginary parts of the on and off states. For ease of calculation, the width d of the quasi-open-loop resonant strip waveguide is first... x With length d y Set to the same length. Under the initially set structure parameters (d) x =80nm, d y =80nm, w=10nm, h=10nm), the calculated modulation depth is 8.79dB / μm.

[0047] Eigenmode analysis reveals that the quasi-slit resonant ring-strip waveguide forms a ring current at its cross-section, significantly enhancing the electric field component parallel to the plane, particularly the electric field component in the x-direction. This substantially improves the performance of the hybrid surface plasmon resonance quasi-slit resonant ring-strip waveguide modulator. However, the potential of the quasi-slit resonant ring-strip waveguide modulator has not yet been fully explored, and its structural parameters can be further optimized to increase the effective polarization component of the electric field at the graphene plane, thereby increasing its modulation depth. To find the optimal structural parameters, the controlled variable method is used to optimize the width d of the two arms of the quasi-slit resonant ring-strip waveguide. x Height d y Parametric scans were performed on the arm width w, as follows: Figure 3 As shown, the modulation depth (MDD) varies with each structural parameter. It can be seen that the MMD decreases to varying degrees as all three structural parameters decrease. Notably, the MMD increases fivefold as the arm width decreases from 40 nm to 5 nm, indicating that arm width is the primary factor influencing the MMD in the quasi-opening resonant ring waveguide. As previously analyzed, the mode field distribution of the intrinsic modes changes with arm width; decreasing the arm width optimizes the polarization degree and localization, confirming the calculated MMD results. Therefore, the main direction for improving the MMD by optimizing structural parameters is to reduce the arm width. Due to mode cutoff, the three structural parameters cannot be reduced simultaneously; therefore, a parameter d is selected through parameter sweep.x = 60 nm, d y = 60 nm, w = 5 nm, the modulation depth reaches 20.46 dB / μm. Then the arm length d y = 60 nm, d x The modulation depth is calculated by jointly sweeping the arm width d Figure 3 (d), the smaller the arm width and the width, the greater the modulation depth becomes, in d x = 40 nm, w = 5 nm, the modulation depth reaches 22.45 dB / μm. In addition to the modulation depth, the insertion loss and the quality factor are also calculated, the results show that at such a high modulation depth, the insertion loss is only 0.28 dB / μm, while the quality factor is as high as 73. Through these parameters, it can be seen that the performance of the modulator is very excellent.

[0048] It is not enough to explain the modulation performance of the hybrid surface plasmon resonance ring waveguide modulator only from the two-dimensional model, in order to verify the correctness of the two-dimensional waveguide mode analysis of the modulation performance, it is necessary to establish a three-dimensional modulator model. Therefore, a three-dimensional hybrid waveguide propagation model of the ring resonator is established by using finite element software. In the three-dimensional propagation model, the modulation depth does not need to be calculated by the complex effective refractive index imaginary part formula, only the transmission coefficient of the waveguide and the propagation distance can be obtained. In the on and off states, the ratio of the energy of the light field at the input and output ends of the waveguide is calculated, and then the modulation depth is calculated by simply operating with the propagation distance. Figure 4 is the transmission coefficient of the three-dimensional waveguide model of the ring resonator waveguide at different Fermi levels when the propagation distance is 1 μm. According to the ratio of the transmission coefficients of the on and off states, the modulation depth of the three-dimensional model is calculated as 20.17 dB / μm, the insertion loss is 0.26 dB / μm, and the quality factor is 78, which is very good match with the two-dimensional model, proving the reliability and authenticity of the calculation above. From the transmission coefficient curve, it can be seen that the Fermi level greater than 0.48 eV corresponds to the off state of the modulator, and the Fermi level less than 0.48 eV corresponds to the on state of the modulator. As Figure 5As shown, the broadband response of the hybrid surface plasmon polariton-like open resonant ring strip waveguide modulator is calculated, and the modulation depth of the two-dimensional model and the three-dimensional model basically coincides in the wideband wavelength range (800nm-1650nm), and the modulation depth is all above 20dB / μm. For the polarization direction of the incident light, it should be ensured that it remains relatively stable in the entire wavelength range. By using high-quality polarizers, the incident light with a specific and stable polarization direction can be ensured. In addition, the intensity of the incident light should also be kept consistent within a reasonable range. The fluctuation of the intensity may affect the accuracy of the model, especially when it comes to optical phenomena sensitive to light intensity. By using a stable light source and appropriate light intensity adjusting device, constant incident light intensity can be achieved to ensure the comparability of the results of the two-dimensional model and the three-dimensional model. Through these parameters, it can be seen that the modulation depth of the two-dimensional model and the three-dimensional model basically coincides, the modulator has good broadband response, and exhibits excellent modulation performance.

[0049] The present application realizes that the modulation depth of the hybrid plasmonic-like open resonant ring waveguide modulator is 20.46dB / μm, the insertion loss is only 0.28dB / μm, and the quality factor is 73, and the modulation performance is excellent, and has 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 of the number of layers of graphene, modulation depth, insertion loss, area of active device, energy consumption and 3dB bandwidth. It can be seen that the single-layer graphene modulator designed by the present application has great advantages, and these advantages can promote the commercialization process of the hybrid plasmonic-like open resonant ring strip waveguide-based tunable graphene optical modulator.

[0050] These advantages can make the present application applicable in 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, different wavelengths of optical signals are independently modulated to increase the communication capacity. In the field of integrated optics, the present application can be integrated into a photonic integrated circuit to realize small-sized and high-performance optical devices, etc.

Claims

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

2. The hybrid surface plasmon based graphene optical modulator of claim 1, wherein: The width d of the split ring structure is 40-150 nm x The height d of the split ring structure is 40-150 nm y The arm width w of the split ring structure is 5-40 nm.

3. The hybrid surface plasmon based graphene optical modulator of claim 1, wherein: The graphene layer is placed at the position where the light field is the strongest.

4. The hybrid surface plasmon based graphene optical modulator of claim 1, wherein: The graphene layer is replaced by other wide-band Dirac semimetal type two-dimensional materials, and the wide-band Dirac semimetal type two-dimensional materials include transition metal sulfide compounds and black phosphorus.

5. The hybrid surface plasmon based graphene optical modulator of claim 1, wherein: The graphene layer is designed as a single layer, a double layer or a multi-layer.

6. The hybrid surface plasmon based graphene optical modulator of claim 1, wherein: The open-like resonant ring strip waveguide is made of plasmonic materials, and the plasmonic materials include noble metal materials or aluminum.

7. The hybrid surface plasmon based graphene light modulator of claim 1, wherein: The inside of the open-like resonant ring strip waveguide is filled with an insulating dielectric with a relatively low refractive index, and the insulating dielectric includes air and porous silicon dioxide.

8. The hybrid surface plasmon based graphene optical modulator of claim 1, wherein: The dielectric spacer layer is made of aluminum oxide.

9. The hybrid surface plasmon based graphene optical modulator of claim 1, wherein: The gate voltage electrode is made of a gold electrode, the substrate is made of a silver layer, and the bottom electrode is made of a silver electrode.

10. An optical communication chip, characterized by: The chip modulates an optical signal by using the graphene optical modulator based on hybrid surface plasmons according to claim 1.

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