Electro-optical modulator and preparation method of electro-optical modulator

Abstract

The invention provides an electro-optical modulator and a preparation method of the electro-optical modulator. The electro-optical modulator comprises a strip-shaped waveguide, wherein the strip-shaped waveguide comprises a first coupling area used for coupling, straight waveguide areas located on the two sides of the first coupling area respectively, and a gradual change area located between the straight waveguide and the first coupling area; the annular waveguide is in a circular ring shape and comprises a second coupling area used for coupling. Wherein the second coupling region and the first coupling region are respectively an arc section, and the first coupling region and the second coupling region share the same circle center; the graphene film capacitor is located on the surface of the area, except the second coupling area, in the annular waveguide and used for regulating and controlling the coupling state between the strip-shaped waveguide and the annular waveguide. Wherein under the condition that the graphene thin-film capacitor is in a zero bias voltage state, the coupling state between the strip-shaped waveguide and the annular waveguide is in a critical coupling state, so that the modulation efficiency is improved while the size of the device is reduced, and the difficulty of a preparation process is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductors, and in particular to an electro-optic modulator and a method for fabricating the electro-optic modulator. Background Technology

[0002] Electro-optic modulators play a crucial role in cutting-edge fields such as optical communication networks, quantum optics, and high-performance computing systems. Currently widely used silicon-based electro-optic modulators generally suffer from low modulation efficiency due to the weak plasmon dispersion effect and free carrier absorption characteristics of silicon material itself. To achieve sufficient modulation depth, the device size usually needs to reach the millimeter scale.

[0003] To balance high modulation efficiency and small device size, microring resonators are commonly used as the core modulation unit in existing technologies. Compared to millimeter-scale Mach-Zehnder interferometers (MZIs), microring resonators can be reduced to the micrometer scale, significantly enhancing the device's integration potential. However, when the coupling distance between the microring resonator and the straight waveguide is too small, the fabrication difficulty increases significantly. Therefore, how to improve the modulation efficiency of electro-optic modulators, reduce device size, and simultaneously lower the fabrication difficulty has become one of the urgent technical challenges to be addressed.

[0004] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an electro-optic modulator and a method for fabricating the electro-optic modulator, so as to solve the problems in the prior art that the electro-optic modulator cannot simultaneously reduce size, improve modulation efficiency, and reduce fabrication difficulty.

[0006] To achieve the above and other related objectives, the present invention provides an electro-optic modulator, comprising:

[0007] A strip waveguide includes a first coupling region for coupling, straight waveguide regions located on both sides of the first coupling region, and a gradually varying region located between the straight waveguide and the first coupling region;

[0008] A ring-shaped waveguide, in the form of a ring, includes a second coupling region for coupling with the first coupling region; wherein the second coupling region and the first coupling region are each an arc segment, the first coupling region and the second coupling region share a common center, and the radius of the circle in which the first coupling region is located is larger than the radius of the circle in which the second coupling region is located; the spacing between the gradually changing region and the ring waveguide gradually increases or decreases along the direction of light wave propagation;

[0009] A graphene film capacitor is located on the surface of the annular waveguide, excluding the second coupling region, and is used to regulate the coupling state between the strip waveguide and the annular waveguide; wherein, when the graphene film capacitor is at zero bias, the coupling state between the strip waveguide and the annular waveguide is at a critical coupling state.

[0010] In one embodiment, the electro-optic modulator includes: when the graphene film capacitor is at zero bias, controlling the central angles corresponding to the first coupling region and the second coupling region and the coupling spacing between the first coupling region and the second coupling region to make the coupling state between the strip waveguide and the ring waveguide in a critical coupling state.

[0011] In one embodiment, the coupling spacing between the first coupling region and the second coupling region is less than or equal to 300 nanometers.

[0012] In one embodiment, a cladding layer is further included between the graphene thin-film capacitor and the annular waveguide.

[0013] In one embodiment, the graphene film capacitor includes:

[0014] The first graphene film is located in a portion of the cladding surface;

[0015] A second graphene film is located above the first graphene film, with a gap between the first graphene film and the second graphene film, and the first graphene film and the second graphene film are partially overlapped.

[0016] A dielectric layer is located at least between the first graphene film and the second graphene film;

[0017] The first electrode is connected to the first graphene film;

[0018] The second electrode is connected to the second graphene film.

[0019] In one embodiment, the dielectric layer is made of hafnium dioxide, aluminum oxide, hexagonal boron nitride, or calcium fluoride.

[0020] In one embodiment, the spacing between the first graphene film and the second graphene film is 10nm-30nm.

[0021] In one embodiment, the first graphene film includes a first stacking region for stacking with the second graphene film, and a first edge region located on one side of the annular waveguide and connected to the first stacking region. The second graphene film includes a second stacking region stacked with the first stacking region, and a second edge region located on the other side of the annular waveguide and connected to the second stacking region. The first stacking region and the second stacking region are located above the cladding in the annular waveguide, excluding the second coupling region. The first electrode is located at the edge of the first edge region, and the second electrode is located at the edge of the second edge region. A first spacing between the first electrode and the annular waveguide is 1 micrometer to 2 micrometers, and a second spacing between the second electrode and the annular waveguide is 1 micrometer to 2 micrometers. A third distance between the annular waveguide located under the graphene film capacitor and the first boundary of the first stacking region and the second stacking region is equal to a fourth distance between the annular waveguide and the second boundary of the first stacking region and the second stacking region, wherein the third distance and the fourth distance are 0.2 micrometers to 0.4 micrometers.

[0022] In one embodiment, the materials of the first electrode and the second electrode include gold and titanium.

[0023] Secondly, this application provides a method for fabricating an electro-optic modulator, comprising:

[0024] A substrate is provided; the substrate includes a cladding and a strip waveguide and an annular waveguide located within the cladding; wherein, the strip waveguide includes a first coupling region for coupling, straight waveguide regions located on both sides of the first coupling region, and a gradually changing region located between the straight waveguide and the first coupling region; the annular waveguide is circular and includes a second coupling region for coupling with the first coupling region; the second coupling region and the first coupling region are each an arc segment, the first coupling region and the second coupling region share a common center, and the radius of the circle in which the first coupling region is located is larger than the radius of the circle in which the second coupling region is located; the spacing between the gradually changing region and the annular waveguide gradually increases or gradually decreases along the direction of light wave propagation;

[0025] A graphene thin-film capacitor is formed on the cladding surface of the annular waveguide in the region other than the second coupling region; wherein the graphene capacitor is used to regulate the coupling state between the strip waveguide and the annular waveguide; when the graphene thin-film capacitor is at zero bias, the coupling state between the strip waveguide and the annular waveguide is at a critical coupling state.

[0026] The formation of a graphene thin-film capacitor on the cladding surface of the region other than the second coupling region in the annular waveguide includes:

[0027] A first graphene film is formed on the cladding surface of the region in the annular waveguide other than the second coupling region;

[0028] A first electrode is formed on the first graphene film;

[0029] A dielectric layer is formed on the first electrode, the first graphene film, and the substrate;

[0030] A second graphene film is formed on the dielectric layer;

[0031] A second electrode is formed on the second graphene film.

[0032] As described above, the electro-optic modulator and its fabrication method of the present invention have the following beneficial effects:

[0033] The electro-optic modulator and its fabrication method of the present invention include: a strip waveguide, a ring waveguide, and a graphene thin-film capacitor; wherein, the strip waveguide includes a first coupling region for coupling, straight waveguide regions located on both sides of the first coupling region, and a gradually changing region located between the straight waveguide and the first coupling region; the ring waveguide is circular and includes a second coupling region for coupling with the first coupling region; wherein, the second coupling region and the first coupling region are each an arc segment, the first coupling region and the second coupling region share a common center, and the radius of the circle in which the first coupling region is located is larger than the radius of the circle in which the second coupling region is located; the spacing between the gradually changing region and the ring waveguide gradually increases or decreases along the direction of light wave propagation; the graphene thin-film capacitor is located on the surface of the region in the ring waveguide other than the second coupling region, and is used to regulate the coupling state between the strip waveguide and the ring waveguide; wherein, when the graphene thin-film capacitor is at zero bias, the coupling state between the strip waveguide and the ring waveguide is at a critical coupling state. This application achieves a change in coupling state between a strip waveguide and a ring waveguide under zero bias by coupling the strip waveguide and the ring waveguide to a critical coupling state. This allows the graphene film capacitor to achieve a change in coupling state with a small gate voltage change, thereby reducing device size and improving modulation efficiency. Furthermore, since there is a gradually changing region between the straight waveguide and the first coupling region, the mode mismatch problem during coupling can be further improved. Moreover, since the first coupling region and the second coupling region are concentric arcs, the coupling coefficient can be adjusted by controlling the radian of the central angle corresponding to the arc length and the coupling spacing, avoiding the need to reduce the coupling spacing indiscriminately to improve the coupling coefficient and reducing the difficulty of the fabrication process. Attached Figure Description

[0034] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the embodiments of this application and to illustrate the implementation of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application.

[0035] Figure 1 This is a schematic diagram of the structure of an electro-optic modulator provided in one embodiment of this application;

[0036] Figure 2 This is a schematic diagram of the transmission spectrum of an electro-optic modulator with different attenuation factors of a ring waveguide provided in one embodiment of this application;

[0037] Figure 3 This is a schematic diagram illustrating the change in light absorption loss per unit length of graphene film as a function of gate voltage in one embodiment of this application.

[0038] Figure 4 This is a schematic diagram of the structure of a graphene thin film capacitor provided in one embodiment of this application;

[0039] Figure 5 This is a schematic flowchart of a method for fabricating an electro-optic modulator provided in one embodiment of this application;

[0040] Figures 6-13 A schematic diagram of the structure obtained by the fabrication method of the electro-optic modulator provided in one embodiment of this application;

[0041] Figure 14 This is a schematic diagram of the transmission spectrum of an electro-optic modulator under different gate voltages provided in one embodiment of this application. Detailed Implementation

[0042] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0043] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, whole, step, or component, but does not exclude the presence or addition of one or more other features, wholes, steps, or components.

[0044] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0045] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0046] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0047] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0048] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0049] Based on the above, please refer to Figure 1 This application provides an electro-optic modulator, including: a strip waveguide 10, a ring waveguide 20, and a graphene thin film capacitor 30.

[0050] The strip waveguide 10 includes a first coupling region 106 for coupling, straight waveguide regions 102 located on both sides of the first coupling region 106, and a gradually changing region 104 located between the straight waveguide 102 and the first coupling region 106.

[0051] The annular waveguide 20 is circular in shape and includes a second coupling region 202 for coupling with the first coupling region 106. The second coupling region 202 and the first coupling region 106 are each an arc segment, the first coupling region 106 and the second coupling region 202 share the same center, and the radius of the circle in which the first coupling region 106 is located is larger than the radius of the circle in which the second coupling region 202 is located. The spacing between the gradually changing region 104 and the annular waveguide 20 gradually increases or decreases along the direction of light wave propagation.

[0052] The direction of light wave propagation is the direction of light wave propagation in the strip waveguide 10. The spacing between the gradually changing region 104 and the ring waveguide 20 is the spacing between the gradually changing region 104 and the ring waveguide 20 along the radial direction of the ring waveguide 20. Along the direction from the input end to the output end of the strip waveguide 10, the strip waveguide 10 sequentially includes a straight waveguide region 102, a gradually changing region 104, a first coupling region 106, a gradually changing region 104, and a straight waveguide 102 region; wherein, the spacing between the gradually changing region 104 near the input end and the ring waveguide 20 in the radial direction of the ring waveguide 20 gradually decreases, and the spacing between the gradually changing region 104 near the output end and the ring waveguide 20 in the radial direction of the ring waveguide 20 gradually increases. In addition, the spacing between the gradually changing region 104 and the ring waveguide 20 can vary linearly or nonlinearly with the light wave propagation distance, and this application does not impose specific limitations on the structure of the gradually changing region 104.

[0053] The graphene film capacitor 30 is located on the surface of the annular waveguide 20, excluding the second coupling region 202, and is used to regulate the coupling state between the strip waveguide 10 and the annular waveguide 20. When the graphene film capacitor 30 is at zero bias, the coupling state between the strip waveguide 10 and the annular waveguide 20 is at a critical coupling state.

[0054] In the above embodiments, the electro-optic modulator and its fabrication method include: a strip waveguide, a ring waveguide, and a graphene thin-film capacitor; wherein, the strip waveguide includes a first coupling region for coupling, straight waveguide regions located on both sides of the first coupling region, and a gradually changing region located between the straight waveguide and the first coupling region; the ring waveguide is circular and includes a second coupling region for coupling with the first coupling region; wherein, the second coupling region and the first coupling region are each an arc segment, the first coupling region and the second coupling region share the same center, and the radius of the circle in which the first coupling region is located is larger than the radius of the circle in which the second coupling region is located; the spacing between the gradually changing region and the ring waveguide gradually increases or decreases along the direction of light wave propagation; the graphene thin-film capacitor is located on the surface of the region in the ring waveguide other than the second coupling region, and is used to regulate the coupling state between the strip waveguide and the ring waveguide; wherein, when the graphene thin-film capacitor is at zero bias, the coupling state between the strip waveguide and the ring waveguide is at a critical coupling state. This application achieves a change in coupling state between a strip waveguide and a ring waveguide under zero bias by coupling the strip waveguide and the ring waveguide to a critical coupling state. This allows the graphene film capacitor to achieve a change in coupling state with a small gate voltage change, thereby reducing device size and improving modulation efficiency. Furthermore, since there is a gradually changing region between the straight waveguide and the first coupling region, the mode mismatch problem during coupling can be further improved. Moreover, since the first coupling region and the second coupling region are concentric arcs, the coupling coefficient can be adjusted by controlling the radian of the central angle corresponding to the arc length and the coupling spacing, avoiding the need to reduce the coupling spacing indiscriminately to improve the coupling coefficient and reducing the difficulty of the fabrication process.

[0055] In some embodiments, please refer to Figure 1 The electro-optic modulator includes: when the graphene film capacitor 30 is at zero bias, by controlling the central angle B corresponding to the first coupling region 106 and the second coupling region 202 and the coupling distance between the first coupling region 106 and the second coupling region 202, the coupling state between the strip waveguide 10 and the ring waveguide 20 is in a critical coupling state.

[0056] As an example, t is the self-coupling coefficient between strip waveguide 10 and ring waveguide 20, and k is the coupling coefficient between strip waveguide 10 and ring waveguide 20. Ignoring the coupling loss between strip waveguide 10 and ring waveguide 20, t and k satisfy the following relationship: t 2 +k2 =1. The coupling coefficient k between the strip waveguide 10 and the ring waveguide 20 is related to the coupling distance between the first coupling region 106 and the second coupling region 202, and the central angle B corresponding to the first coupling region 106 and the second coupling region 202. That is, the self-coupling coefficient t between the strip waveguide 10 and the ring waveguide 20 can be changed by adjusting the central angle B corresponding to the first coupling region 106 and the second coupling region 202, and the coupling distance between the first coupling region 106 and the second coupling region 202. Furthermore, the formula for calculating the light transmittance T at the output end of the strip waveguide 10 is as follows:

[0057] ;

[0058] Where a is the attenuation factor of the annular waveguide, and ϕ is the phase of the light wave propagating one revolution in the annular waveguide 20; under the condition of resonance (the phase of the light wave propagating one revolution in the annular waveguide 20 is equal to an integer multiple of 2π), the formula for the light transmittance at the output end of the strip waveguide 10 can be simplified to:

[0059] ;

[0060] The critical coupling state is defined as the state where the transmittance of the annular waveguide 20 is close to zero. The annular waveguide attenuation factor 'a' is related to the light transmission loss in the annular waveguide 20, the loss in the coupling region, and the effect of the graphene film capacitance 30. According to... Figure 2 It can be seen that near the critical coupling state, when the waveguide attenuation factor α changes slightly, the light transmittance T at the output end of the strip waveguide 10 changes significantly. Therefore, when the graphene film capacitor 30 is at zero bias, the coupling state between the strip waveguide 10 and the ring waveguide 20 is at a critical coupling state. Please refer to... Figure 3By adjusting the gate voltage of the graphene film capacitor 30, the Fermi level of the graphene film can be modulated, causing a change in the light absorption characteristics of the graphene film capacitor 30 (i.e., a change in the light transmittance of the graphene film capacitor 30). This alters the attenuation factor 'a' of the annular waveguide, thereby changing the light transmittance T at the output of the strip waveguide 10 and improving the modulation efficiency of the electro-optic modulator. Furthermore, according to the formula for calculating the light transmittance T at the output of the strip waveguide 10, when the self-coupling coefficient 't' equals the attenuation factor 'a' of the annular waveguide, the strip waveguide 10 and the annular waveguide 20 in the electro-optic modulator are in a critical coupling state, at which point the light transmittance T at the output of the strip waveguide 10 is zero. In summary, when the graphene film capacitor 30 is at zero bias, the self-coupling coefficient t between the strip waveguide 10 and the ring waveguide 20 can be changed by adjusting the central angle B corresponding to the first coupling region 106 and the second coupling region 202 and the coupling distance between the first coupling region 106 and the second coupling region 202. This makes the self-coupling coefficient t between the strip waveguide 10 and the ring waveguide 20 as close as possible to the waveguide attenuation factor a, so that the coupling state between the strip waveguide 10 and the ring waveguide 20 is in a critical coupling state. Then, by changing the gate voltage of the graphene film capacitor 30, the coupling state between the strip waveguide 10 and the ring waveguide 20 can be changed between undercoupling, critical coupling, and overcoupling, thereby achieving electro-optic modulation with high modulation efficiency.

[0061] In some embodiments, the coupling spacing between the first coupling region and the second coupling region is less than or equal to 300 nanometers.

[0062] As an example, the coupling spacing between the first coupling region and the second coupling region is 10 nanometers, 50 nanometers, 100 nanometers, 150 nanometers, 200 nanometers, 250 nanometers, 300 nanometers, etc.

[0063] In some embodiments, please refer to Figure 4 The graphene thin film capacitor also includes a cladding layer between itself and the ring waveguide.

[0064] As an example, the cladding 204 may be made of materials such as silicon dioxide, silicon oxynitride, and aluminum oxide. The strip waveguide 10 and the ring waveguide 20 may be made of materials such as silicon nitride, lithium niobate, and doped silicon. This application does not impose specific limitations on the materials of the cladding 204, the strip waveguide 10, and the ring waveguide 20.

[0065] In some embodiments, please refer to Figure 4 The height E of the cross-section of the annular waveguide 20 is 0.4 micrometers, and the width D is 0.6 micrometers to 1.4 micrometers.

[0066] The cross-section of the annular waveguide 20 is perpendicular to the direction of light wave propagation within the annular waveguide 20. Figure 4 for Figure 1 The cross-section along the Aa direction. As an example, the width D of the cross-section of the annular waveguide 20 is 0.6 μm, 0.8 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, etc.

[0067] In some embodiments, please refer to Figure 4 The graphene film capacitor includes: a first graphene film 302, a second graphene film 304, a dielectric layer 310, a first electrode 306, and a second electrode 308; wherein, the first graphene film 302 is located in a portion of the surface of the cladding 204; the second graphene film 304 is located above the first graphene film 302, and there is a gap between the first graphene film 302 and the second graphene film 304, and the first graphene film 302 and the second graphene film 304 are partially stacked; the dielectric layer 310 is located at least between the first graphene film 302 and the second graphene film 304; the first electrode 306 is connected to the first graphene film 302; and the second electrode 308 is connected to the second graphene film 304.

[0068] As an example, the first graphene film 302 is located on the surface of the cladding 204 in the region of the annular waveguide 20, excluding the second coupling region.

[0069] In the above embodiments, by making the graphene film capacitor include a first graphene film and a second graphene film, and stacking the first graphene film and the second graphene film, the modulation efficiency can be further improved.

[0070] In some embodiments, the dielectric layer material includes: hafnium dioxide, aluminum oxide, hexagonal boron nitride, and calcium fluoride.

[0071] Preferably, the dielectric layer is made of hafnium dioxide. As a dielectric layer, hafnium dioxide can cause a large change in the Fermi level of graphene when a small voltage is applied, thereby further improving the modulation efficiency.

[0072] In some embodiments, the spacing between the first graphene film and the second graphene film is 10nm-30nm.

[0073] As an example, the spacing between the first graphene film and the second graphene film is 10nm, 15nm, 18nm, 20nm, 22nm, 25nm, 30nm, etc.

[0074] In the above embodiments, by setting the spacing between the first graphene film and the second graphene film to 10nm-30nm, the capacitance of the graphene film capacitor is prevented from being too large, thereby reducing the bandwidth of the electro-optic modulator.

[0075] In some embodiments, please refer to Figure 4The first graphene film 302 includes a first stacking region for stacking with the second graphene film 304, and a first edge region located on one side of the annular waveguide 20 and connected to the first stacking region. The second graphene film 304 includes a second stacking region stacked with the first stacking region, and a second edge region located on the other side of the annular waveguide 20 and connected to the second stacking region. The first stacking region and the second stacking region are located above the cladding 204 in the annular waveguide 20, excluding the second coupling region. The first electrode 306 is located on the first edge region. The second electrode 308 is located at the edge of the second edge region; wherein, the first spacing H between the first electrode 306 and the annular waveguide 20 is 1 micrometer to 2 micrometers, and the second spacing F between the second electrode 308 and the annular waveguide 20 is 1 micrometer to 2 micrometers; the third distance G between the annular waveguide 20 located under the graphene film capacitor and the first boundary of the first and second stacked regions is equal to the fourth distance J between the annular waveguide 20 and the second boundary of the first and second stacked regions, and the third distance G and the fourth distance J are 0.2 micrometers to 0.4 micrometers.

[0076] As an example, the first distance H between the first electrode 306 and the annular waveguide 20 is 1 micrometer, 1.5 micrometer, 2 micrometer, etc., the second distance F between the second electrode 308 and the annular waveguide 20 is 1 micrometer, 1.5 micrometer, 2 micrometer, etc., and the third distance G and the fourth distance J are 0.2 micrometer, 0.3 micrometer, 0.4 micrometer, etc.

[0077] In some embodiments, the materials of the first electrode and the second electrode include gold and titanium.

[0078] This application also provides a method for fabricating an electro-optic modulator; please refer to [reference needed]. Figure 5 ,as well as Figures 6-13 This includes steps S502-S504.

[0079] Step S502: Provide a substrate; the substrate includes a cladding 204 and a strip waveguide and annular waveguide 20 located within the cladding 204; wherein, the strip waveguide includes a first coupling region for coupling, straight waveguide regions located on both sides of the first coupling region, and a gradually changing region located between the straight waveguide and the first coupling region; the annular waveguide 20 is circular and includes a second coupling region for coupling with the first coupling region; the second coupling region and the first coupling region are each an arc segment, the first coupling region and the second coupling region share the same center, and the radius of the circle in which the first coupling region is located is larger than the radius of the circle in which the second coupling region is located; the spacing between the gradually changing region and the annular waveguide 20 gradually increases or gradually decreases along the direction of light wave propagation.

[0080] Step S504: A graphene thin film capacitor is formed on the surface of the cladding 204 in the region other than the second coupling region of the annular waveguide 20; wherein, the graphene capacitor is used to regulate the coupling state between the strip waveguide and the annular waveguide 20; when the graphene thin film capacitor is at zero bias, the coupling state between the strip waveguide and the annular waveguide 20 is at a critical coupling state; wherein, forming the graphene thin film capacitor on the surface of the cladding 204 in the region other than the second coupling region of the annular waveguide 20 includes: forming a first graphene thin film 302 on the surface of the cladding 204 in the region other than the second coupling region of the annular waveguide 20; forming a first electrode 306 on the first graphene thin film 302; forming a dielectric layer 310 on the first electrode 306, the first graphene thin film 302, and the substrate; forming a second graphene thin film 304 on the dielectric layer 310; and forming a second electrode 308 on the second graphene thin film 304.

[0081] As an example, forming a first graphene film 302 on the surface of the cladding 204 in the region other than the second coupling region of the annular waveguide 20 includes: transferring graphene material 301 to the surface of the cladding 204 in the region other than the second coupling region of the annular waveguide 20 using a wet transfer technique, and etching the graphene material 301 using a photolithography process to form the first graphene film 302.

[0082] As an example, forming a first electrode 306 on a first graphene film 302 includes: forming the first electrode 306 on the first graphene film 302 using a photolithography process. Furthermore, the first electrode 306 may include a stack of a titanium layer and a gold layer, where the titanium layer serves as an adhesion layer and the gold layer serves as a conductive layer. The thickness of the titanium layer may include 5nm-15nm, for example, 5nm, 8nm, 10nm, 13nm, 15nm, etc., and the thickness of the gold layer may include 35nm-45nm, for example, 35nm, 40nm, 45nm, etc.

[0083] As an example, forming a dielectric layer 310 on the first electrode 306, the first graphene film 302, and the substrate includes: forming the dielectric layer 310 on the first electrode 306, the first graphene film 302, and the substrate using atomic layer deposition technology.

[0084] As an example, forming a second graphene film 304 on the dielectric layer 310 includes: transferring graphene material onto the dielectric layer using a wet transfer technique, and etching the graphene material using a photolithography process to form the second graphene film 304.

[0085] As an example, forming a second electrode 308 on a second graphene film 304 includes: forming the second electrode 308 on the second graphene film 304 using a photolithography process. Furthermore, the second electrode 308 may include a stack of a titanium layer and a gold layer, where the titanium layer serves as an adhesion layer and the gold layer serves as a conductive layer. The thickness of the titanium layer may include 5nm-15nm, for example, 5nm, 8nm, 10nm, 13nm, 15nm, etc., and the thickness of the gold layer may include 35nm-45nm, for example, 35nm, 40nm, 45nm, etc.

[0086] As an example, after forming the second electrode 308 on the second graphene film 304 in step S504, the method further includes forming an encapsulation layer 312 on the second electrode 308 and the second graphene film 304. The material of the encapsulation layer 312 may include hafnium dioxide. The thickness of the encapsulation layer 312 may include 15nm-25nm, for example, the thickness of the encapsulation layer 312 is 15nm, 20nm, 25nm, etc.

[0087] In summary, the electro-optic modulator and its fabrication method of the present invention include: a strip waveguide, a ring waveguide, and a graphene thin-film capacitor; wherein, the strip waveguide includes a first coupling region for coupling, straight waveguide regions located on both sides of the first coupling region, and a gradually changing region located between the straight waveguide and the first coupling region; the ring waveguide is circular and includes a second coupling region for coupling with the first coupling region; wherein, the second coupling region and the first coupling region are each an arc segment, the first coupling region and the second coupling region share a common center, and the radius of the circle in which the first coupling region is located is larger than the radius of the circle in which the second coupling region is located; the spacing between the gradually changing region and the ring waveguide gradually increases or decreases along the direction of light wave propagation; the graphene thin-film capacitor is located on the surface of the region in the ring waveguide other than the second coupling region, and is used to regulate the coupling state between the strip waveguide and the ring waveguide; wherein, when the graphene thin-film capacitor is at zero bias, the coupling state between the strip waveguide and the ring waveguide is at a critical coupling state. This application achieves the change in coupling state between a strip waveguide and a ring waveguide under zero bias by coupling the strip waveguide and the ring waveguide to a critical coupling state, so that the graphene film capacitor can achieve the change in coupling state with a small gate voltage change. Please refer to [reference needed]. Figure 14 , Figure 14This diagram illustrates the transmission spectra of the electro-optic modulator of this application under different gate voltages. This application improves modulation efficiency while reducing device size. Furthermore, the existence of a gradually varying region between the straight waveguide and the first coupling region further mitigates mode mismatch during coupling. Moreover, the first and second coupling regions are concentric arcs, allowing for adjustment of the coupling coefficient by modifying the radian of the central angle corresponding to the arc length, the coupling spacing, etc., avoiding the need to excessively reduce the coupling spacing to improve the coupling coefficient and reducing the difficulty of fabrication. Therefore, this invention effectively overcomes various shortcomings of the prior art and possesses high industrial applicability.

[0088] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An electro-optic modulator, characterized in that, include: A strip waveguide includes a first coupling region for coupling, straight waveguide regions located on both sides of the first coupling region, and a gradually varying region located between the straight waveguide and the first coupling region; A ring-shaped waveguide, in the form of a ring, includes a second coupling region for coupling with the first coupling region; wherein the second coupling region and the first coupling region are each an arc segment, the first coupling region and the second coupling region share a common center, and the radius of the circle in which the first coupling region is located is larger than the radius of the circle in which the second coupling region is located; the spacing between the gradually changing region and the ring waveguide gradually increases or decreases along the direction of light wave propagation; A graphene film capacitor is located on the surface of the annular waveguide, excluding the second coupling region, and is used to regulate the coupling state between the strip waveguide and the annular waveguide; wherein, when the graphene film capacitor is at zero bias, the coupling state between the strip waveguide and the annular waveguide is at a critical coupling state.

2. The electro-optic modulator according to claim 1, characterized in that, The electro-optic modulator includes: when the graphene film capacitor is at zero bias, controlling the central angles corresponding to the first coupling region and the second coupling region and the coupling distance between the first coupling region and the second coupling region to make the coupling state between the strip waveguide and the ring waveguide in a critical coupling state.

3. The electro-optic modulator according to claim 1, characterized in that, The coupling distance between the first coupling region and the second coupling region is less than or equal to 300 nanometers.

4. The electro-optic modulator according to claim 1, characterized in that, The graphene film capacitor also includes a cladding layer between itself and the annular waveguide.

5. The electro-optic modulator according to claim 4, characterized in that, The graphene film capacitor includes: The first graphene film is located in a portion of the cladding surface; A second graphene film is located above the first graphene film, with a gap between the first graphene film and the second graphene film, and the first graphene film and the second graphene film are partially overlapped. A dielectric layer is located at least between the first graphene film and the second graphene film; The first electrode is connected to the first graphene film; The second electrode is connected to the second graphene film.

6. The electro-optic modulator according to claim 5, characterized in that, The dielectric layer is made of materials including: hafnium dioxide, aluminum oxide, hexagonal boron nitride, and calcium fluoride.

7. The electro-optic modulator according to claim 5, characterized in that, The spacing between the first graphene film and the second graphene film is 10nm-30nm.

8. The electro-optic modulator according to claim 5, characterized in that, The first graphene film includes a first stacking region for stacking with the second graphene film, and a first edge region located on one side of the annular waveguide and connected to the first stacking region. The second graphene film includes a second stacking region stacked with the first stacking region, and a second edge region located on the other side of the annular waveguide and connected to the second stacking region. The first stacking region and the second stacking region are located above the cladding in the annular waveguide, excluding the second coupling region. The first electrode is located at the edge of the first edge region, and the second electrode is located at the edge of the second edge region. A first spacing between the first electrode and the annular waveguide is 1 micrometer to 2 micrometers, and a second spacing between the second electrode and the annular waveguide is 1 micrometer to 2 micrometers. A third distance between the annular waveguide located under the graphene film capacitor and the first boundary of the first stacking region and the second stacking region is equal to a fourth distance between the annular waveguide and the second boundary of the first stacking region and the second stacking region, wherein the third distance and the fourth distance are 0.2 micrometers to 0.4 micrometers.

9. The electro-optic modulator according to claim 5, characterized in that, The materials of the first electrode and the second electrode include gold and titanium.

10. A method for fabricating an electro-optic modulator, characterized in that, include: Provide a base; The substrate includes a cladding and a strip waveguide and an annular waveguide located within the cladding. The strip waveguide includes a first coupling region for coupling, straight waveguide regions located on either side of the first coupling region, and a gradually changing region between the straight waveguide and the first coupling region. The annular waveguide is circular and includes a second coupling region for coupling with the first coupling region. The second coupling region and the first coupling region are each an arc segment, sharing a common center, and the radius of the circle containing the first coupling region is greater than the radius of the circle containing the second coupling region. The spacing between the gradually changing region and the annular waveguide gradually increases or decreases along the direction of light wave propagation. A graphene thin-film capacitor is formed on the cladding surface of the annular waveguide in the region other than the second coupling region; wherein the graphene capacitor is used to regulate the coupling state between the strip waveguide and the annular waveguide; when the graphene thin-film capacitor is at zero bias, the coupling state between the strip waveguide and the annular waveguide is at a critical coupling state. The formation of a graphene thin-film capacitor on the cladding surface of the region other than the second coupling region in the annular waveguide includes: A first graphene film is formed on the cladding surface of the region in the annular waveguide other than the second coupling region; A first electrode is formed on the first graphene film; A dielectric layer is formed on the first electrode, the first graphene film, and the substrate; A second graphene film is formed on the dielectric layer; A second electrode is formed on the second graphene film.

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