Electro-optical modulator and preparation method thereof

Abstract

The invention discloses an electro-optical modulator and a preparation method thereof, and belongs to the technical field of modulators, and the electro-optical modulator comprises a substrate, a waveguide structure, an aluminum oxide protection layer, a multi-layer capacitor structure, a first electrode and a second electrode. The waveguide structure is arranged on the substrate, and the multi-layer capacitor structure is arranged above the waveguide structure from bottom to top; each layer of capacitor structure comprises two pieces of graphene and a dielectric layer, the two pieces of graphene are located on the upper surface and the lower surface of the dielectric layer respectively, and the two pieces of graphene are connected through a first electrode and a second electrode respectively, so that a parallel connection structure of the multiple layers of capacitor structures is achieved, and the larger the number of layers of the capacitor structures is, the larger the light modulation depth is. According to the electro-optical modulator, the modulation depth can be remarkably improved, optical modulation can be better achieved, high-performance indexes such as modulation depth, high speed, broadband and low power consumption are better considered, the electro-optical modulator can be applied to the fields of optical communication, ultrafast laser and optical information processing, and the application range is wider.

Description

Technical Field

[0001] The present invention relates to the technical field of modulators, and in particular to an electro-optical modulator and a preparation method thereof. Background Art

[0002] Electro-optic modulators are key components for generating or modulating high-speed optical signals in photonic integrated systems. The technology of loading modulation voltage onto light waves is called optical modulation technology, and the modulation achieved by electro-optical effect is called electro-optic modulation. Currently, common optical modulators are classified according to optoelectronic materials, including lithium niobate modulators, III-V semiconductor modulators, silicon-based modulators, and organic polymer modulators. These modulators have their own characteristics, but they all have great limitations in specific applications, such as low modulation efficiency, complex electrode structure, and large active area size.

[0003] Graphene is a single layer of carbon atoms in sp 2 Two-dimensional materials densely arranged in a honeycomb structure in a hybrid manner have many unique and excellent properties related to electro-optical modulation applications, such as strong broadband light absorption, ultra-high carrier mobility, excellent thermal conductivity, and adjustable carrier properties.

[0004] At present, graphene-based electro-optical modulation technology is mainly based on a single-layer graphene-dielectric layer-single-layer graphene structure. This structure can take into account high speed, wide band, and low power consumption, but in this structure, only two single-layer graphene sheets interact with light, which limits the modulation depth of the modulator, and thus greatly limits the application of graphene-based electro-optical modulators. Summary of the invention The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes an electro-optic modulator and a preparation method thereof, providing a multi-layer graphene structure, which can better balance high performance indicators such as modulation depth, high speed, wide band, and low power consumption, and has a wider range of applications.

[0005] According to an electro-optic modulator of an embodiment of the first aspect of the present invention, the electro-optic modulator includes a substrate, a waveguide structure, an aluminum oxide protective layer, a multilayer capacitor structure, a first electrode and a second electrode; the waveguide structure is arranged on the upper surface of the substrate; the aluminum oxide protective layer is arranged on the upper surface of the substrate and covers the waveguide structure; the multilayer capacitor structures are arranged in sequence from bottom to top above the waveguide structure, each layer of the capacitor structure includes two graphenes and a dielectric layer, and the two graphenes are respectively arranged on the upper surface and the lower surface of the dielectric layer; the first electrode and the second electrode are respectively arranged on both sides of a plurality of the capacitor structures, one of the graphenes in each of the capacitor structures is electrically connected to the first electrode, and the other graphene is electrically connected to the second electrode.

[0006] The electro-optic modulator according to the embodiment of the present invention has at least the following beneficial effects: The embodiment uses the substrate as the substrate of the electro-optic modulator, sets the waveguide structure on the substrate, and arranges the multilayer capacitor structure from bottom to top above the waveguide structure, and uses an aluminum oxide protective layer to separate the waveguide structure from the multilayer capacitor structure to ensure insulation performance; each layer of the capacitor structure includes two graphenes and a dielectric layer, the two graphenes are respectively located on the upper surface and the lower surface of the dielectric layer, and the two graphenes are respectively connected by a first electrode and a second electrode, thereby realizing a parallel connection structure of the multilayer capacitor structure. The larger the number of layers of the capacitor structure, the greater the light modulation depth. Compared with the single-layer graphene-dielectric layer-single-layer graphene structure, the electro-optic modulator of the embodiment of the present invention can significantly improve the modulation depth, better realize light modulation, and better balance high-performance indicators such as modulation depth, high speed, wide band, and low power consumption. It can be applied to optical communications, ultrafast lasers, optical information processing and other fields, and has a wider range of applications.

[0007] According to some embodiments of the present invention, the number of layers of the capacitor structure is less than or equal to 11 layers.

[0008] According to some embodiments of the present invention, the electro-optic modulator is configured such that when the Fermi level of the graphene is modulated to satisfy |E F |>hv / 2; and switched to the off state when the Fermi level of the graphene is modulated to satisfy |EF|≤hv / 2, wherein h is Planck's constant, v is the frequency of light, and hv is the photon energy.

[0009] According to some embodiments of the present invention, the dielectric layer is an aluminum oxide layer, and the dielectric layers of adjacent capacitor structures are connected to each other.

[0010] According to some embodiments of the present invention, the thickness of the waveguide structure ranges from 50 nm to 500 nm.

[0011] According to some embodiments of the present invention, the electro-optic modulator also includes a supporting layer, which is arranged on both sides of the waveguide structure, the aluminum oxide protective layer is located between the supporting layer and the waveguide structure, and the first electrode, the second electrode and the capacitor structure are respectively located at the upper end of the supporting layer.

[0012] A method for preparing an electro-optic modulator according to a second aspect of the present invention comprises: A sample is obtained by processing the substrate and the waveguide structure; The sample is placed in a magnetron sputtering device and subjected to magnetron sputtering treatment to generate a target substrate having an aluminum oxide protective layer; Prepare graphene by chemical vapor deposition, and transfer the prepared graphene to the target substrate by dry or wet method; Performing magnetron sputtering on the target substrate to generate a dielectric layer on the graphene; Repeating the steps of transferring the prepared graphene to the target substrate by a dry method or a wet method, and performing a magnetron sputtering treatment on the target substrate, to generate a plurality of the graphenes and a plurality of the dielectric layers, and obtaining a target sample, wherein one dielectric layer is disposed between two adjacent graphenes; Electrodes electrically connected to the graphene are respectively generated on both sides of the target sample, so that two adjacent graphenes are connected to different electrodes.

[0013] According to some embodiments of the present invention, the substrate is a glass substrate, and the method of obtaining a sample by processing the substrate and the waveguide structure includes: Cleaning the surfaces of the glass substrate and the waveguide structure with acetone, and applying an auxiliary agent on the surfaces; The glass substrate and the waveguide structure are placed in an oven for heating, the heating temperature ranges from 82° C. to 88° C., and the heating time ranges from 30 min to 35 min.

[0014] According to some embodiments of the present invention, placing the sample into a magnetron sputtering device and performing magnetron sputtering treatment comprises: The sample is placed in a magnetron sputtering device for evacuation and heating, and the vacuum degree is less than or equal to 4×10 - 4 Pa, heating temperature is 300℃, heating time is 10min; An aluminum layer is deposited on the sample, and oxygen and aluminum are introduced for sputtering at the same time. The sputtering time is 50 minutes, and the aluminum oxide protective layer is generated on the surface of the substrate and the waveguide structure.

[0015] According to some embodiments of the present invention, the preparation of graphene by chemical vapor deposition includes: The substrate was electrochemically polished, and the substrate was placed in a quartz tube, purged with argon gas and heated to 600° C. for 10 min; The hydrocarbon precursor methane is introduced into the quartz tube, and heated to 1000° C. for 10 min; During the cooling process, methane gas was continuously introduced until the temperature dropped below 100°C, and then the graphene sample was taken out.

[0016] According to some embodiments of the present invention, before electrodes electrically connected to the graphene are respectively generated on both sides of the target sample, the method further includes: The two side surfaces of the target sample are etched until all edges of the graphene are exposed on the two side surfaces.

[0017] According to some embodiments of the present invention, the step of generating electrodes electrically connected to the graphene on both sides of the target sample comprises: The target sample is placed in a magnetron sputtering device and then evacuated and heated. The vacuum degree is less than or equal to 4×10 -4 Pa, heating temperature is 300℃, heating time is 10min; Gold was introduced for sputtering for 50 minutes. After the sputtering was completed, the resistance and capacitance of the electrodes on both sides of the target sample were detected, and the resistance was greater than 20 MΩ, and the capacitance ranged from 180 fF to 280 fF.

[0018] The method for preparing an electro-optic modulator according to an embodiment of the present invention has at least the following beneficial effects: The sample is obtained by processing the substrate and the waveguide structure, and then the sample is placed in a magnetron sputtering device and subjected to magnetron sputtering treatment to generate a target substrate with an aluminum oxide protective layer; graphene is prepared by chemical vapor deposition, and the prepared graphene is transferred to the target substrate by a dry method or a wet method; the target substrate is subjected to magnetron sputtering treatment to generate a dielectric layer on the graphene, and the above steps are repeated to generate multiple graphenes and multiple dielectric layers to obtain a target sample, and finally electrodes electrically connected to the graphene are generated on both sides of the target sample; the aluminum oxide protective layer is used to form a dielectric layer on the target substrate; the dielectric layer is electrically connected to the target substrate by a magnetron sputtering treatment to generate a dielectric layer on the graphene, and the above steps are repeated to generate multiple graphenes and multiple dielectric layers to obtain a target sample; and electrodes electrically connected to the graphene are generated on both sides of the target sample; the aluminum oxide protective layer is used to form a dielectric layer on the target substrate. The layer separates the waveguide structure from the multilayer capacitor structure to ensure insulation performance; two adjacent graphene layers and a dielectric layer form a capacitor structure, and the multilayer capacitor structure is connected in parallel using electrodes. The electro-optic modulator obtained by the above preparation method has a multilayer capacitor structure. Compared with the single-layer graphene-dielectric layer-single-layer graphene structure, it can significantly improve the modulation depth and better realize light modulation. It can better balance high-performance indicators such as modulation depth, high speed, wide band, and low power consumption, and can be applied to optical communications, ultrafast lasers, optical information processing and other fields, and has a wider range of applications.

[0019] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 is a schematic diagram of the overall structure of an electro-optic modulator according to some embodiments of the present invention; Figure 2 is a graph showing the functional relationship between the number of graphene-aluminum oxide layer structures and light loss in some embodiments of the present invention; Figure 3 is a mode field diagram of an electro-optic modulator in TM mode according to some embodiments of the present invention; Figure 4A diagram of the electric field amplitude generated by the electro-optic modulator along the propagation direction of light in an open circuit state according to some embodiments of the present invention; Figure 5 A diagram showing the electric field amplitude generated by the electro-optic modulator along the propagation direction of light in the off state in some embodiments of the present invention; Figure 6 A flow chart of a method for preparing an electro-optic modulator according to some embodiments of the present invention; Figure 7 A specific example flow chart of a method for preparing an electro-optic modulator according to some embodiments of the present invention.

[0021] Reference numerals: Electro-optic modulator 10; Substrate 100; Waveguide structure 200; Silicon waveguide 210; Aluminum oxide protective layer 300; Capacitor structure 400; graphene 410; dielectric layer 420; A first electrode 510; a second electrode 520; Support layer 600. DETAILED DESCRIPTION

[0022] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0023] In the description of the present invention, it is necessary to understand that the orientation descriptions, such as the front, rear, circumferential, axial, radial and other orientations or positional relationships indicated, are based on the orientations or positional relationships shown in the drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0024] In the description of the present invention, if there is a description of first and second, it is only for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0025] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0026] Reference Figure 1As shown, the electro-optic modulator 10 of the embodiment of the present invention includes a substrate 100, a waveguide structure 200, an aluminum oxide protective layer 300 and a multilayer capacitor structure 400, wherein the waveguide structure 200 is a silicon waveguide 210, the silicon waveguide 210 is arranged on the upper surface of the substrate 100, the aluminum oxide protective layer 300 is arranged on the upper surface of the substrate 100, and the aluminum oxide protective layer 300 covers the silicon waveguide 210. In the embodiment, the silicon waveguide 210 protrudes from the upper surface of the substrate 100, the silicon waveguide 210 is roughly rectangular, and the silicon waveguide 210 has a certain thickness. The aluminum oxide protective layer 300 covers the upper surface and two side surfaces of the silicon waveguide 210, and effectively protects the silicon waveguide 210. The multilayer capacitor structure 400 is arranged in sequence from bottom to top above the silicon waveguide 210, and the aluminum oxide protective layer 300 is located between the bottom capacitor structure 400 and the silicon waveguide 210.

[0027] Each layer of the capacitor structure 400 includes two graphene layers 410 and a dielectric layer 420, wherein one graphene layer 410 is disposed on the upper surface of the dielectric layer 420, and the other graphene layer 410 is disposed on the lower surface of the dielectric layer 420. The electro-optic modulator 10 also includes a first electrode 510 and a second electrode 520, which are disposed on both sides of the plurality of capacitor structures 400, respectively, wherein one graphene layer 410 in each capacitor structure 400 is electrically connected to the first electrode 510, and the other graphene layer 410 is electrically connected to the second electrode 520, so that the multilayer capacitor structure 400 is connected in parallel.

[0028] It can be understood that the substrate 100, as the base of the electro-optic modulator 10, provides a solid foundation for the entire device. The substrate 100 not only carries the structure of the entire device, but also serves as a reference plane for the circuit or optical path to ensure the stability and reliability of the device. In the embodiment, the substrate 100 is specifically made of silicon dioxide (SiO2). The thickness of the silicon dioxide substrate 100 ranges from 0.5μm to 900μm, that is, the thickness of the substrate 100 is at least 0.5μm and does not exceed 900μm. For example, the thickness of the silicon dioxide substrate 100 can be 10μm, 100μm, 500μm, etc. In practical applications, the thickness of the silicon dioxide substrate 100 needs to be selected according to specific application scenarios and requirements. The silicon dioxide substrate 100 has excellent properties such as high temperature stability, optical transparency and mechanical strength. It can withstand high temperature environments, can transmit visible light and ultraviolet rays, and exhibits good refractive index and scattering rate. It is very suitable as a material for making an electro-optic modulator 10.

[0029] The silicon waveguide 210 is a main component of the electro-optic modulator 10, and can effectively confine the optical signal to propagate inside the waveguide. When light is transmitted in the silicon waveguide 210, under the action of the electric field, the distribution of free carriers in the silicon waveguide 210 will change, which can change the phase, intensity and other parameters of the optical signal, thereby realizing optical signal modulation of the electro-optic modulator 10. Specifically, by applying a voltage to the first electrode 510 and the second electrode 520 to form a modulated electric field, the Fermi level of the graphene 410 is regulated, and its absorption coefficient for the transmitted light is changed, thereby realizing switching modulation between the output optical signal 0 and 1.

[0030] Reference Figure 1 As shown, the cross section of the silicon waveguide 210 in the embodiment is rectangular, the silicon waveguide 210 is fixedly arranged on the upper surface of the substrate 100, and the thickness of the silicon waveguide 210 is 50nm to 500nm, that is, the thickness of the silicon waveguide 210 is at least 50nm and does not exceed 500nm. For example, the thickness of the silicon waveguide 210 can be 50nm, 100nm, 300nm, 500nm, etc. In some embodiments, the thickness of the silicon waveguide 210 is preferably in the range of 200nm to 400nm to ensure the effective confinement and transmission efficiency of light in the silicon waveguide 210. It can be understood that when the thickness of the silicon waveguide 210 is less than 50nm, it means that the thickness of the silicon waveguide 210 is too small, and its ability to confine the light field will be weakened, causing the light field to leak more easily to the outside of the waveguide, increasing the transmission loss. When the thickness of the silicon waveguide 210 is greater than 500nm, it means that the thickness of the silicon waveguide 210 is too large, which not only increases the overall size of the electro-optic modulator 10, but also increases the coupling loss. In practical applications, the thickness of the silicon waveguide 210 needs to be selected according to specific application scenarios and requirements.

[0031] It should be noted that, in some embodiments, the silicon waveguide 210 can be replaced by a silicon nitride waveguide 210. The silicon nitride material has the characteristics of high refractive index, wide bandwidth and low loss. The high refractive index of silicon nitride allows the manufacture of a smaller waveguide structure 200, while the low loss characteristic ensures the efficient transmission of optical signals in the waveguide.

[0032] Reference Figure 1 As shown, the aluminum oxide protective layer 300 serves as an isolation layer and has good insulation and thermal stability. The aluminum oxide protective layer 300 is located between the capacitor structure 400 and the silicon waveguide 210, and can provide electrical isolation to prevent current from flowing directly through an unintended path, and can protect the silicon waveguide 210 and the substrate 100.

[0033] In the embodiment, the thickness of the aluminum oxide (Al2O3) protective layer ranges from 20nm to 900nm, and its thickness is at least 20nm, and the thickness does not exceed 900nm. For example, the thickness of the aluminum oxide protective layer 300 can be 50nm, 100nm, 300nm, 500nm, 900nm, etc. In some embodiments, the thickness of the aluminum oxide protective layer 300 is preferably in the range of 200nm to 600nm to ensure stable electrical isolation performance. When the thickness of the aluminum oxide protective layer 300 is less than 20nm, it means that its thickness is too small, and its ability to resist external environmental corrosion will be significantly reduced, reducing the stability and reliability of the electro-optic modulator 10. When the thickness of the aluminum oxide protective layer 300 is greater than 900nm, it means that its thickness is too large. As the thickness of the aluminum oxide protective layer 300 increases, the required material and processing costs will also increase accordingly, and a thicker protective layer will also increase the overall weight and volume, which is not conducive to application scenarios with strict requirements on weight and volume.

[0034] Reference Figure 1 As shown, the multilayer capacitor structure 400 is arranged from top to bottom on the silicon waveguide 210, and the two graphenes 410 in each layer of the capacitor structure 400 are respectively single-layer graphene sheets. By alternately stacking and combining the graphene 410 and the dielectric layer 420, different capacitance values ​​and electric field distributions can be provided as needed. It can be understood that the multilayer capacitor structure 400 generates an electric field by applying a voltage, and then uses the electro-optical effect to change the characteristics of the optical signal in the silicon waveguide 210. The intensity and distribution of the electric field can be controlled by adjusting the number of layers, materials and other parameters of the capacitor structure 400.

[0035] Graphene 410 is a two-dimensional material composed of a single layer of carbon atoms densely arranged in a honeycomb structure in an sp2 hybrid manner. It has many unique and excellent properties related to electro-optical modulation applications, such as strong broadband light absorption, ultra-high carrier mobility, excellent thermal conductivity, and adjustable carrier properties. Specifically, graphene 410 can respond to a wide range of spectra from ultraviolet to far infrared and even terahertz. The ultra-high carrier mobility of graphene 410 enables it to support high-speed photoelectric modulation, which can theoretically reach modulation speeds of GHz or even THz; due to its single-atom-level thickness, no dangling bond interface and ultra-high mechanical strength, graphene 410 is suitable for integration with other nanoscale optoelectronic devices; by changing the carrier concentration of graphene 410 through chemical doping / electrostatic doping, its response parameters to light can be greatly adjusted, thereby achieving dynamic optical modulation; the atomic-level thickness characteristics of graphene 410 also make the modulation process have the characteristics of low energy consumption. Therefore, the electro-optic modulator 10 based on graphene 410 is suitable for the fields of optical communication, ultrafast laser, and optical information processing that require high speed, wide band, and low energy consumption.

[0036] In the related technology, due to the difficulty of modulating multi-layer graphene, the graphene-based electro-optical modulation technology is mainly based on a single-layer graphene-dielectric layer-single-layer graphene structure. This structure can take into account high speed, wide band, and low power consumption. However, in this structure, only two single-layer graphene sheets interact with light, which limits the modulation depth of the modulator, and thus greatly limits the application of graphene-based electro-optical modulators.

[0037] Based on this, refer to Figure 1 As shown, the electro-optic modulator 10 of the embodiment of the present invention has a multilayer capacitor structure 400, each layer of which has a combination structure of a single-layer graphene-aluminum oxide dielectric layer-single-layer graphene. It not only has the excellent characteristics of graphene 410, but also the greater the number of layers of the capacitor structure 400, the greater the light modulation depth. Compared with the single-layer graphene-dielectric layer-single-layer graphene structure in the related art, it can significantly improve the modulation depth, better realize light modulation, and take into account high performance indicators such as modulation depth, high speed, wide band, and low power consumption, and can be applied to optical communications, ultrafast lasers, optical information processing and other fields.

[0038] In the embodiment, the thickness of the graphene 410 in each layer of the capacitor structure 400 is approximately 0.34 nm, and the dielectric layer 420 between the two graphenes 410 is an aluminum oxide layer. Since the aluminum oxide layer has good insulation properties, it can ensure that the two adjacent graphenes 410 are isolated. The two graphenes 410 are conductors and are respectively connected to the first electrode 510 and the second electrode 520. The aluminum oxide layer is the dielectric layer 420, thereby forming the capacitor structure 400.

[0039] It should be noted that, since the adjacent capacitor structures 400 need to be electrically isolated, an aluminum oxide layer is provided on the upper and lower surfaces of each graphene 410, and the dielectric layers 420 of all capacitor structures 400 can be connected to each other to form an integral structure and improve the overall reliability of the electro-optic modulator 10. In addition, the dielectric layer 420 is not limited to the aluminum oxide layer, and other dielectric materials can also replace the aluminum oxide layer, such as hexagonal boron nitride and other materials.

[0040] Reference Figure 1As shown, the electro-optic modulator 10 further includes a support layer 600, the support layer 600 is arranged on both sides of the silicon waveguide 210, the aluminum oxide protective layer 300 is located between the support layer 600 and the silicon waveguide 210, and the first electrode 510, the second electrode 520 and the capacitor structure 400 are respectively located at the upper end of the support layer 600. In the embodiment, the support layer 600 is made of silicon dioxide, wherein the two ends of the bottom capacitor structure 400 are respectively located on the top of the support layer 600 on both sides, and the first electrode 510, the second electrode 520 and the two ends of the capacitor structure 400 can be supported by the support layer 600, thereby improving the structural stability of the electro-optic modulator 10. The specific thickness of the support layer 600 is set according to the installation height requirements of the first electrode 510, the second electrode 520 and the capacitor structure 400.

[0041] In the embodiment, the first electrode 510 and the second electrode 520 are both made of gold material. Gold has the characteristics of high electrical conductivity, stable chemical properties, good ductility and plasticity, etc. The thickness of the first electrode 510 and the second electrode 520 ranges from 20nm to 200nm. The thickness of the first electrode 510 and the second electrode 520 can be the same, or the thickness of the two can be different. For example, the thickness of the first electrode 510 and the second electrode 520 are both 50nm, 100nm, 200nm, etc. In practical applications, the thickness of the first electrode 510 and the second electrode 520 needs to be selected according to the specific application scenario and requirements. It should be noted that since the first electrode 510 and the second electrode 520 need to be connected to the graphene 410 in each layer of the capacitor structure 400, the height of the first electrode 510 and the second electrode 520 is set according to the number of layers of the capacitor structure 400. The more layers of the capacitor structure 400, the greater the height of the first electrode 510 and the second electrode 520. Figure 1 As shown, all the graphenes 410 are arranged sequentially from bottom to top, and are electrically connected to the first electrode 510 and the second electrode 520 in a staggered manner.

[0042] The basic principle of the electro-optic modulator 10 according to the embodiment of the present invention is as follows: A single-layer graphene-aluminum oxide layer-single-layer graphene forms a capacitive structure 400. By applying voltages to the first electrode 510 and the second electrode 520, a modulation electric field is formed. Through this modulation electric field, the Fermi level of the graphene 410 is regulated, its absorption coefficient for the transmitted light is changed, and the switching modulation between the output optical signals 0 and 1 is realized. In the electro-optic modulator 10, by changing the voltage applied to the electrodes, the Fermi level of the graphene 410 can be regulated. When the Fermi level of the graphene 410 is modulated to be greater than half of the photon energy, i.e., |EF|>hv / 2, the graphene 410 itself does not absorb the transmitted light in the silicon waveguide 210. At this time, the electro-optic modulator 10 is in the on state; when the Fermi level of the graphene 410 is modulated to be less than half of the photon energy, i.e., |EF|<hv / 2, the graphene 410 begins to absorb the transmitted light, and the transmitted light is absorbed by the graphene 410 and cannot pass through. At this time, the electro-optic modulator 10 switches to the off state, where h is the Planck constant, v is the frequency of light, and hv is the photon energy. In this way, the electro-optic modulator 10 changes its absorption coefficient for the transmitted light by regulating the Fermi level of the graphene 410, thereby realizing the switching modulation of the output optical signal between 0 and 1.

[0043] The inventor simulated and analyzed the number of layers of the capacitive structure 400 with a single-layer graphene-aluminum oxide layer-single-layer graphene in the electro-optic modulator 10, determined the preferred size of the electro-optic modulator 10 proposed in the embodiment of the present invention, and verified the light modulation ability of the electro-optic modulator 10.

[0044] Refer to Figure 1 As shown, the structure of the electro-optic modulator 10 was drawn in the simulation software, and the optical loss values were obtained by successively simulating by increasing the number of layers of the capacitive structure 400. Refer to Figure 2 As shown, the functional relationship between the number of layers of the single-layer graphene-aluminum oxide layer structure and the optical loss was obtained. Among them, the abscissa represents the number of layers of the single-layer graphene-aluminum oxide layer structure, and the ordinate represents the optical loss value. It can be seen that the optical loss increases with the increase in the number of layers, which means that the larger the number of layers, the greater the optical modulation depth. Therefore, for the electro-optic modulator 10 proposed in the embodiment of the present invention, the more the number of layers of the capacitive structure 400, the better.

[0045] Furthermore, considering that the more the number of layers, the more processing procedures and costs are required. Therefore, the preferred number of layers of the single-layer graphene-aluminum oxide layer in the structure of the electro-optic modulator 10 proposed in the embodiment of the present invention is 22 layers, that is, a capacitive structure 400 of 11 layers of single-layer graphene-aluminum oxide layer-single-layer graphene. It can be seen from Figure 2 that when the number of layers is greater than 22 layers, the influence of the increase in the number of layers on the optical loss becomes smaller and smaller. When the structure of the single-layer graphene-aluminum oxide layer is 22 layers, the electro-optic modulator 10 takes into account both high optical loss and good device size. Reference Figure 3 As shown, the mode field simulation of the electro-optic modulator 10 of the embodiment of the present invention is performed. For the working wavelength of 1.55 μm, in the TM mode, the light field contacts the graphene 410 over a large area, and the interaction intensity between the graphene and the light field is large. Figure 3 It can be seen that the structure of the electro-optic modulator 10 enables the light field to contact with the graphene 410 over a large area, thereby improving the modulation depth of the electro-optic modulator 10 .

[0046] Reference Figure 4 and Figure 5 As shown, the electro-optic modulator 10 of the embodiment of the present invention is respectively in the on state and the off state to perform light transmission simulation. The chemical potential of the graphene 410 in the on state is 0.5596 eV, and the chemical potential of the graphene 410 in the off state is 0.0103 eV, wherein Figure 4 shows the electric field amplitude generated by the electro-optic modulator 10 along the propagation direction when the electro-optic modulator 10 is turned on, Figure 5 The electric field amplitude generated by the electro-optic modulator 10 along the propagation direction when the electro-optic modulator 10 is turned off is shown, so that light modulation can be achieved. Figure 4 and Figure 5 It can be seen that by using the electro-optic modulator 10 of the above embodiment to perform light modulation, a modulation depth of 1 dB / μm can be obtained.

[0047] Reference Figure 6 As shown, the embodiment of the present invention also provides a method for preparing an electro-optic modulator 10, including but not limited to the following steps: In step S100 , a sample is obtained by processing the substrate 100 and the silicon waveguide 210 .

[0048] It can be understood that in the embodiment, a glass substrate is used as the substrate 100, and the glass substrate and the silicon waveguide 210 are pre-processed to obtain a sample. The sample can be understood as a matrix combining the glass substrate and the silicon waveguide 210, wherein the thickness of the glass substrate ranges from 0.5 μm to 900 μm, and the thickness of the silicon waveguide 210 ranges from 50 nm to 500 nm. In actual applications, the thickness of the silicon dioxide substrate 100 and the silicon waveguide 210 is selected according to the specific application scenario and requirements.

[0049] In some embodiments, the specific process of the pre-treatment is step S110, using acetone to clean the surface of the glass substrate and the silicon waveguide 210, and applying an additive on the surface of the glass substrate and the silicon waveguide 210; then the glass substrate and the silicon waveguide 210 are placed in an oven for heating, the heating temperature range is 82° C. to 88° C., and the heating time is 30 min to 35 min. Acetone can effectively remove impurities such as grease, dust, organic pollutants, etc. on the surface of the glass substrate and the silicon waveguide 210, providing a clean, pollution-free substrate for subsequent manufacturing processes.

[0050] The cleaning process can immerse the glass substrate and silicon waveguide 210 in acetone, or wipe or spray with acetone solution to ensure that the surface is thoroughly clean. The additive is used to improve the wettability, adhesion, anti-reflection or other specific properties of the material surface. A layer of additive is evenly coated on the surface of the cleaned glass substrate and silicon waveguide 210. This can be achieved by spin coating, spraying, dipping or brushing. The specific method depends on the characteristics of the additive and the required coating thickness. The glass substrate and silicon waveguide 210 coated with the additive are placed in an oven, and the heating temperature range is set to 82°C to 88°C, and the heating time is 30min to 35min. The selection of this temperature and time range should be based on the specific requirements of the additive to ensure that the additive can be fully cured.

[0051] Step S200 , placing the sample into a magnetron sputtering device and performing magnetron sputtering treatment to generate a target substrate having an aluminum oxide protective layer 300 .

[0052] It can be understood that after the above step S100, a sample of the silicon waveguide 210 combined with the glass substrate is obtained, wherein the silicon waveguide 210 is located on the upper surface of the glass substrate. In step S200, after the sample is subjected to magnetron sputtering, an aluminum oxide protective layer 300 is generated on the surface of the silicon waveguide 210 and the upper surface of the glass substrate, thereby obtaining a target substrate. The aluminum oxide protective layer 300 covers the upper surface and two side surfaces of the silicon waveguide 210, and effectively protects the silicon waveguide 210 and the upper surface of the glass substrate.

[0053] In the embodiment, magnetron sputtering is used to generate an Al2O3 protective layer. Specifically, in step S210, the sample is first placed in a magnetron sputtering device and then vacuumed and heated, wherein the vacuum degree is set to be less than or equal to 4×10-4Pa, the heating temperature is 300°C, and the heating time is 10min; then an aluminum (Al) layer is deposited to enhance the film-base bonding strength, and oxygen (O2) and aluminum (Al) are introduced at the same time to achieve co-sputtering for 50 minutes, thereby generating an Al2O3 protective layer. After sputtering, an XRD diffraction pattern analysis is performed. XRD diffraction is X-ray diffraction, which uses the diffraction phenomenon of X-rays in crystals to obtain the crystal structure information of the material. When X-rays are irradiated onto the crystal, due to the periodic arrangement of atoms or ions inside the crystal, the X-rays will be scattered and interfered to form a specific diffraction pattern. By analyzing these diffraction patterns, information such as the material phase, crystal structure, lattice constant, and unit cell shape can be determined.

[0054] The working principle of magnetron sputtering equipment is based on the sputtering phenomenon and the effect of electromagnetic field. Under the action of electric field, electrons are accelerated to fly to the substrate and collide with argon atoms, causing ionization to produce positive ions and new electrons. New electrons continue to fly to the substrate, while ions are accelerated to fly to the cathode target under the action of electric field, and bombard the target surface with high energy, causing the target material to sputter. The sputtered target atoms or molecules are deposited on the substrate to form a thin film, so that an Al2O3 protective layer can be generated on the surface of the sample.

[0055] Step S300, preparing graphene 410 by chemical vapor deposition, and transferring the prepared graphene 410 to a target substrate by dry method or wet method.

[0056] Dry transfer usually involves spin coating a layer of polymer (such as polymethyl methacrylate, PMMA) on a substrate on which graphene 410 is grown, so that the polymer completely covers the graphene layer. The original substrate is removed by chemical etching or mechanical stripping, leaving behind a polymer-supported graphene layer; the polymer-supported graphene layer is aligned and placed on a target substrate, and then the graphene 410 is brought into close contact with the target substrate by methods such as heat pressing or rolling. Finally, the polymer layer is removed by solvent dissolution or thermal decomposition, leaving behind a pure graphene layer on the target substrate.

[0057] The wet transfer method first spin-coats a layer of polymer on the substrate on which the graphene 410 is grown; uses an appropriate etchant (such as ferric chloride solution for a copper substrate) to etch away the original substrate, leaving the polymer-supported graphene layer floating on the surface of the etching solution; then uses a target substrate (such as a silicon wafer, glass, etc.) to pick up the floating graphene layer, and removes excess etching solution and impurities through appropriate rinsing and drying steps; finally, removes the polymer layer by solvent dissolution or thermal decomposition to complete the transfer of graphene 410.

[0058] The chemical vapor deposition method specifically includes step S310, electrochemically polishing the substrate, placing the substrate in a quartz tube, introducing argon gas and heating to 600°C for 10 minutes; then introducing hydrocarbon precursor methane into the quartz tube, heating to 1000°C for 10 minutes; during the cooling process, continuously introducing methane gas until the temperature reaches 100°C, and then taking out the graphene 410 sample. Finally, the prepared graphene 410 is transferred to the target substrate by a dry method or a wet method.

[0059] Step S400 , performing magnetron sputtering on the target substrate to generate a dielectric layer 420 on the graphene 410 .

[0060] It is understandable that since the dielectric layer 420 is made of aluminum oxide, the Al2O3 layer can be generated by magnetron sputtering. Specifically, step S400 includes step S410, first placing the target substrate into a magnetron sputtering device, then vacuuming and heating the substrate, wherein the vacuum degree is set to be less than or equal to 4×10 -4 Pa, heating temperature is 300℃, heating time is 10min. Then Al layer is deposited, O2 and Al are introduced at the same time to realize co-sputtering for 10min, thereby forming Al2O3 layer.

[0061] Step S500, repeatedly transferring the prepared graphene 410 to a target substrate by a dry method or a wet method, and performing magnetron sputtering treatment on the target substrate, to generate a plurality of graphenes 410 and a plurality of dielectric layers 420, and obtain a target sample, wherein a dielectric layer 420 is arranged between two adjacent graphenes 410.

[0062] Since the capacitor structure 400 has multiple layers, and each layer has a graphene 410 and an aluminum oxide layer, in step S510, the above-mentioned steps S310 and S410 can be repeated multiple times to generate multiple layers of graphene 410 and aluminum oxide layers, and an aluminum oxide layer is arranged between two adjacent graphenes 410 to form a capacitor structure 400.

[0063] Step S600: Generate electrodes electrically connected to the graphene 410 on both sides of the target sample, so that two adjacent graphenes 410 are connected to different electrodes.

[0064] In the embodiment, the first electrode 510 and the second electrode 520 are both made of gold, and the thickness of the first electrode 510 and the second electrode 520 ranges from 20 nm to 200 nm. Since the Al2O3 layer is generated by chemical vapor deposition of the graphene layer and magnetron sputtering, after forming the multi-layer graphene 410 and Al2O3 layer, it is necessary to etch the two sides of the target sample until all the edges of the graphene 410 are exposed on the two sides, and then the first electrode 510 and the second electrode 520 are generated.

[0065] Specifically, electrodes electrically connected to the graphene 410 are generated on both sides of the target sample, including: Step S610: Place the target sample in a magnetron sputtering device and perform vacuuming and heating. The vacuum degree is less than or equal to 4×10 -4 Pa, the heating temperature is 300℃, and the heating time is 10min; then gold (Au) is introduced for sputtering, and the sputtering time is 50min. After sputtering, the resistance and capacitance of the electrodes on both sides of the target sample are detected to ensure the insulation effect of each layer, which meets the requirements of resistance greater than 20MΩ and capacitance range of 180fF to 280fF.

[0066] The electro-optic modulator 10 obtained by the above preparation method has a multilayer capacitor structure 400. Compared with the single-layer graphene-dielectric layer-single-layer graphene structure, it can significantly improve the modulation depth, better realize light modulation, and better balance high-performance indicators such as modulation depth, high speed, wide band, and low power consumption. It can be applied to optical communications, ultrafast lasers, optical information processing and other fields, and has a wider range of applications.

[0067] Of course, the present invention is not limited to the above-mentioned embodiments, and those skilled in the art may make equivalent modifications or substitutions without violating the spirit of the present invention, and these equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. An electro-optic modulator, characterized in that: include: substrate; A waveguide structure is provided on the upper surface of the substrate; an aluminum oxide protective layer, disposed on the upper surface of the substrate and covering the waveguide structure; A multilayer capacitor structure is sequentially arranged above the waveguide structure from bottom to top, each layer of the capacitor structure includes two graphene layers and a dielectric layer, and the two graphene layers are respectively arranged on the upper surface and the lower surface of the dielectric layer; The first electrode and the second electrode are respectively arranged on both sides of the plurality of capacitor structures, and one of the graphenes in each of the capacitor structures is electrically connected to the first electrode, and another of the graphenes is electrically connected to the second electrode.

2. The electro-optic modulator according to claim 1, characterized in that The number of layers of the capacitor structure is less than or equal to 11 layers.

3. The electro-optic modulator according to claim 1, characterized in that The electro-optic modulator is configured such that when the Fermi level of the graphene is modulated to satisfy |E F |>hv / 2; and switched to the off state when the Fermi level of the graphene is modulated to satisfy |EF|≤hv / 2, where h is Planck's constant, v is the frequency of light, and hv is the photon energy.

4. The electro-optic modulator according to claim 1, characterized in that The dielectric layer is an aluminum oxide layer, and the dielectric layers of adjacent capacitor structures are connected to each other.

5. The electro-optic modulator according to claim 1, characterized in that: The thickness of the waveguide structure ranges from 50 nm to 500 nm.

6. The electro-optic modulator according to claim 1, characterized in that: The electro-optic modulator also includes a supporting layer, which is arranged on both sides of the waveguide structure. The aluminum oxide protective layer is located between the supporting layer and the waveguide structure. The first electrode, the second electrode and the capacitor structure are respectively located at the upper end of the supporting layer.

7. A method for preparing an electro-optic modulator, characterized in that: include: A sample is obtained by processing the substrate and the waveguide structure; The sample is placed in a magnetron sputtering device and subjected to magnetron sputtering treatment to generate a target substrate having an aluminum oxide protective layer; Prepare graphene by chemical vapor deposition, and transfer the prepared graphene to the target substrate by dry or wet method; Performing magnetron sputtering on the target substrate to generate a dielectric layer on the graphene; Repeating the steps of transferring the prepared graphene to the target substrate by a dry method or a wet method, and performing a magnetron sputtering treatment on the target substrate, to generate a plurality of the graphenes and a plurality of the dielectric layers, and obtaining a target sample, wherein one dielectric layer is disposed between two adjacent graphenes; Electrodes electrically connected to the graphene are respectively generated on both sides of the target sample, so that two adjacent graphenes are connected to different electrodes.

8. The method for preparing an electro-optic modulator according to claim 7, characterized in that: The substrate is a glass substrate, and the sample is obtained by processing the substrate and the waveguide structure, including: Cleaning the surfaces of the glass substrate and the waveguide structure with acetone, and applying an auxiliary agent on the surfaces; The glass substrate and the waveguide structure are placed in an oven for heating, the heating temperature ranges from 82° C. to 88° C., and the heating time ranges from 30 min to 35 min.

9. The method for preparing an electro-optic modulator according to claim 7, characterized in that: The step of placing the sample into a magnetron sputtering device and then performing a magnetron sputtering treatment comprises: The sample is placed in a magnetron sputtering device for evacuation and heating, and the vacuum degree is less than or equal to 4×10 -4 Pa, heating temperature is 300℃, heating time is 10min; An aluminum layer is deposited on the sample, and oxygen and aluminum are introduced for sputtering at the same time. The sputtering time is 50 minutes, and the aluminum oxide protective layer is generated on the surface of the substrate and the waveguide structure.

10. The method for preparing an electro-optic modulator according to claim 7, characterized in that: The method of preparing graphene by chemical vapor deposition comprises: The substrate was electrochemically polished, and the substrate was placed in a quartz tube, purged with argon gas and heated to 600° C. for 10 min; The hydrocarbon precursor methane is introduced into the quartz tube, and heated to 1000° C. for 10 min; During the cooling process, methane gas was continuously introduced until the temperature dropped below 100°C, and then the graphene sample was taken out.

11. The method for preparing an electro-optic modulator according to claim 7, characterized in that: Before electrodes electrically connected to the graphene are respectively generated on both sides of the target sample, the method further includes: The two side surfaces of the target sample are etched until all edges of the graphene are exposed on the two side surfaces.

12. The method for preparing an electro-optic modulator according to claim 7 or 11, characterized in that: The step of generating electrodes electrically connected to the graphene on both sides of the target sample comprises: The target sample is placed in a magnetron sputtering device and then evacuated and heated. The vacuum degree is less than or equal to 4×10 - 4 Pa, heating temperature is 300℃, heating time is 10min; Gold was introduced for sputtering for 50 minutes. After the sputtering was completed, the resistance and capacitance of the electrodes on both sides of the target sample were detected, and the resistance was greater than 20 MΩ, and the capacitance ranged from 180 fF to 280 fF.

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