Nonlinear waveguide

Abstract

The invention belongs to the field of nonlinear optical devices, and particularly discloses a nonlinear waveguide. The nonlinear waveguide comprises a sub-wavelength grating waveguide and a two-dimensional material, wherein the two-dimensional material is located on the surface of the sub-wavelength grating waveguide. According to the technical scheme, the evanescent field of the waveguide is enhanced through the sub-wavelength grating structure, then the two-dimensional material with the high nonlinear effect is integrated in the evanescent field area, the two-dimensional material and the evanescent field generate stronger interaction, then the nonlinear effect is further enhanced, and compared with the mode that the surface of a common waveguide is directly combined with the two-dimensional material, the non-linear effect is further enhanced. The nonlinear waveguide provided by the invention has a higher nonlinear effect.

Description

Technical Field

[0001] This application belongs to the field of nonlinear optical device technology, and more specifically, relates to a nonlinear waveguide. Background Technology

[0002] Optical integrated devices based on nonlinear optical effects have shown great application potential, such as on-chip Raman amplification and lasers, wavelength conversion, optical logic gates, optical frequency comb generation, and quantum entanglement. While existing nonlinear optical devices have wide applications in many fields, their nonlinear effects are generally low.

[0003] In 2020, David J. Moss et al. published a paper introducing the integration of two-dimensional materials on microring resonators to improve the nonlinearity of devices, specifically by depositing two-dimensional graphene oxide material on a silicon nitride microring resonator. According to the calculations in the paper, after depositing a single layer of graphene oxide, the nonlinear coefficient of the device was approximately [value missing]. After laying down the double-layer graphene material, the nonlinear coefficient of the device is approximately 27.6. Without the deposition of two-dimensional material, the nonlinear coefficient of the device is only about [value missing]. It is evident that laying down two-dimensional materials can enhance the nonlinear effect of the microring resonator. However, the nonlinear effect remains very limited even with this method. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, this application provides a nonlinear waveguide, which aims to solve the technical problem of low nonlinear effect of existing nonlinear waveguides.

[0005] To achieve the above objectives, in a first aspect, this application provides a nonlinear waveguide, comprising a subwavelength grating waveguide and a two-dimensional material, wherein the two-dimensional material is located on the surface of the subwavelength grating waveguide.

[0006] Preferably, the two-dimensional material is located on the upper surface of the subwavelength grating waveguide.

[0007] Preferably, the two-dimensional material is located on the side surface between the individual grating grids in the subwavelength grating waveguide.

[0008] Preferably, the two-dimensional material is attached to the side surfaces between the individual grating grids by growth.

[0009] Preferably, the duty cycle of the subwavelength grating waveguide is not greater than 0.9.

[0010] Preferably, the core layer of the subwavelength grating waveguide has an equivalent refractive index greater than the cladding refractive index.

[0011] Preferably, the core layer of the subwavelength grating waveguide is made of silicon.

[0012] Preferably, the core layer of the subwavelength grating waveguide is made of aluminum gallium arsenide.

[0013] Preferably, the core layer of the subwavelength grating waveguide is made of lithium niobate.

[0014] Preferably, the thickness of the two-dimensional material is no more than 40 nanometers.

[0015] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: (1) In this application, a stronger evanescent field is obtained by utilizing the structural characteristics of the subwavelength grating waveguide. Then, a two-dimensional material with a high nonlinear effect is integrated in the evanescent field region. The two-dimensional material and the evanescent field generate a stronger interaction, which further enhances the nonlinear effect. Compared with the direct bonding of two-dimensional material to the surface of ordinary strip waveguide, the nonlinear waveguide of this application has a higher nonlinear effect. (2) In this application, two-dimensional material is placed on the side surface between each grating grid in the subwavelength grating waveguide. Here, the two-dimensional material can interact with a stronger and more concentrated evanescent field, thereby greatly improving the conversion efficiency of nonlinear effects.

[0016] (3) In this application, the structure of the two-dimensional material can be customized as needed. Through research, it was found that by setting the duty cycle of the subwavelength grating waveguide to 0.9, the nonlinear effect of the waveguide device can be further improved without affecting the original function of the device. (4) In this application, by selecting materials with better nonlinear effects, such as aluminum gallium arsenide or lithium niobate, to make the core layer of the subwavelength grating waveguide, the overall nonlinear effect of the device can be further improved. (5) Increasing the thickness of two-dimensional materials can further enhance the nonlinear effect, but increasing the thickness will also increase the waveguide loss. This application has found a balance point for the thickness of two-dimensional materials through research. At this balance point, only a small amount of loss is needed to further enhance the nonlinear effect. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a two-dimensional material located on the upper surface of a subwavelength grating waveguide, as provided in an embodiment of this application.

[0018] Figure 2 This is a schematic diagram of the structure of a two-dimensional material located on the side surface of a subwavelength grating waveguide, as provided in an embodiment of this application.

[0019] Figure 3 This is a graph showing the relationship between the thickness of a two-dimensional material and the nonlinear coefficient provided in the embodiments of this application.

[0020] Figure 4 This is a graph showing the relationship between the thickness of a two-dimensional material and its loss, provided in an embodiment of this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] The embodiments of this application are described below with reference to the accompanying drawings.

[0023] Example 1: like Figure 1 The figure shows a nonlinear waveguide provided in Embodiment 1 of this application, which includes a subwavelength grating waveguide and a two-dimensional material. The subwavelength grating waveguide includes a core layer and a lower cladding layer. In the figure, the core layer includes multiple grating grids, which are arranged at certain intervals according to a duty cycle. In this embodiment, the duty cycle is 0.9. The core layer is made of silicon, and the lower cladding layer is made of silicon dioxide. In this embodiment, the two-dimensional material is located on the upper surface of the subwavelength grating waveguide.

[0024] Based on the structural characteristics of subwavelength grating waveguides, the transmitted light is no longer tightly bound, but is distributed extensively in the air gap. This means that the light field intensity (i.e., evanescent field) in the air gap region is greatly enhanced. By utilizing the structural characteristics of subwavelength grating waveguides to obtain a stronger evanescent field, and then integrating two-dimensional materials with high nonlinear effects in the evanescent field region, the two-dimensional materials and the evanescent field generate stronger interactions, thereby further enhancing the nonlinear effect. Compared with directly bonding two-dimensional materials to the surface of ordinary waveguides, the embodiments of this application have higher nonlinear effects.

[0025] Its preparation process is as follows: (1) Select an SOI wafer with an appropriate silicon layer thickness and a buried silicon dioxide layer and use a standard cleaning process to remove contaminants from the wafer surface; (2) Spin-coating photoresist onto the surface of the SOI wafer; (3) The designed subwavelength grating waveguide device pattern is transferred onto the photoresist using an electron beam lithography machine; (4) Place the exposed wafer into the developing solution to form a mask pattern; (5) Transfer the photoresist mask pattern into the silicon layer using plasma etching; (6) Use chemical solvents to remove residual photoresist; (7) Transfer two-dimensional material onto the subwavelength grating waveguide.

[0026] The nonlinear waveguide described in this embodiment can be prepared by following the above steps.

[0027] Example 2: like Figure 2 As shown, this is a nonlinear waveguide provided in Embodiment 2 of this application, which includes a subwavelength grating waveguide and a two-dimensional material. The structure of the subwavelength grating waveguide is basically the same as that of the subwavelength grating waveguide in Embodiment 1, and the duty cycle is selected as 0.6. The core layer is made of silicon, aluminum gallium arsenide, or lithium niobate.

[0028] As shown in the figure, in this embodiment, the two-dimensional material is located on the side surface between each grating grid. Because the evanescent field on the side surface between each grating grid is stronger and more concentrated, the nonlinear waveguide structure provided in this embodiment has better nonlinear effects.

[0029] In this embodiment, the two-dimensional material is grown onto the side surfaces between the various grating grids. Specific growth methods include chemical vapor deposition, liquid phase exfoliation, epitaxial growth, or molecular beam epitaxy. The appropriate growth method can be selected based on the specific material and process requirements.

[0030] Example 3: The advantages of the nonlinear waveguide of this application are now illustrated through a comparative embodiment: Comparative Example 1 uses a strip waveguide with a width of 500 nm, a height of 220 nm, and a core layer of Si. The surface is not covered with two-dimensional material.

[0031] Based on the results of numerical simulation, the nonlinear coefficient of Comparative Example 1 is [not specified] near a wavelength of 1550 nm. Approximately .

[0032] Comparative Example 2 uses a strip waveguide with a width of 500 nm, a height of 220 nm, and a core layer of Si. Two-dimensional gallium selenide (GaSe) is used to cover the upper surface of the strip waveguide with a thickness of 10 nm.

[0033] Based on the results of numerical simulation, the nonlinear coefficients of Comparative Example 2 are [not specified] near a wavelength of 1550 nm. Approximately .

[0034] Comparative Example 3 uses a subwavelength grating waveguide with a width of 500 nm, a height of 220 nm, and a core material of Si. The subwavelength grating waveguide has a period of 300 nm and a duty cycle of 0.7. Two-dimensional gallium selenide (GaSe) is used to cover the upper surface of the subwavelength grating waveguide with a thickness of 10 nm.

[0035] Based on the results of numerical simulation, the nonlinear coefficient of the nonlinear waveguide in Comparative Example 1 is [value missing] near a wavelength of 1550 nm. Approximately .

[0036] As can be seen from Comparative Examples 1 and 2 in this embodiment 3, integrating two-dimensional materials on a strip waveguide can reduce nonlinear effects from... Upgraded to .

[0037] As can be seen from Comparative Examples 2 and 3, replacing the strip waveguide with a subwavelength grating waveguide of the same size can reduce nonlinear effects. Upgraded to .

[0038] It is evident that the nonlinear effect of subwavelength grating waveguide integrated two-dimensional materials is greatly improved compared to that of ordinary strip waveguide integrated two-dimensional materials.

[0039] GaSe was chosen as the two-dimensional material because it has extremely high third-order polarizability, resulting in very high third-order nonlinear effects. Since the two-dimensional material is very thinly deposited on the waveguide surface, its deposition has little impact on the distribution of the mode field within the waveguide.

[0040] The modes propagating in subwavelength grating waveguides have a stronger evanescent field. Therefore, the two-dimensional material covering the surface of the subwavelength grating waveguide can interact more strongly with the evanescent field than the two-dimensional material covering the surface of a regular waveguide, thereby enhancing the nonlinear effect of the waveguide.

[0041] Example 4: Increasing the thickness of a two-dimensional material can further enhance the nonlinear effect, but it also increases waveguide loss. This embodiment discloses the balance point of the two-dimensional material thickness: In this embodiment, the subwavelength grating waveguide has a width of 600 nm, a height of 220 nm, a grating period of 300 nm, a duty cycle of 0.6, and operates at a wavelength of 1550 nm. The thickness of the two-dimensional material laid on the subwavelength grating waveguide was scanned, and the relationship between the waveguide's nonlinear coefficient and the thickness of the two-dimensional GaSe material is as follows: Figure 3 As shown, the nonlinear coefficient of the subwavelength grating waveguide exhibits a positive correlation with the thickness of the two-dimensional material. Furthermore, even a mere 10 nm two-dimensional GaSe can produce a nonlinear coefficient on the order of 10⁴, significantly higher than that of a typical Si waveguide (approximately...). It is two orders of magnitude higher.

[0042] However, the thicker the two-dimensional material, the greater the loss after laying it. Figure 4 The loss at the interface between the mode field of the subwavelength grating waveguide without two-dimensional material and the mode field with two-dimensional material of different thicknesses is caused by mode field mismatch. The two lines in the figure represent the cases where the edge of the two-dimensional material is located in the silicon region and the air region of the subwavelength grating waveguide, respectively.

[0043] When the thickness of the two-dimensional material is less than or equal to 40 nm, the loss in both cases is less than 0.3 dB. The loss of the strip silicon waveguide in the air cladding is approximately 0.3 dB / mm, and considering only the mode mismatch caused by the two-dimensional material, it would result in a loss of approximately 1 mm of silicon waveguide. Since this simulation does not account for the additional scattering loss of modes between waveguides with and without two-dimensional material due to uneven edges of the two-dimensional material, the actual loss would be greater than this result. Considering all the above factors, including the influence of nonlinear coefficients and waveguide loss, it is not recommended that the thickness of the two-dimensional material exceed 40 nm. Exceeding 40 nm will lead to significant loss.

[0044] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0045] The terms "first" and "second," etc., used in the specification and claims of this application are used to distinguish different objects, not to describe a specific order of objects. For example, "first response message" and "second response message," etc., are used to distinguish different response messages, not to describe a specific order of response messages.

[0046] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0047] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0048] Furthermore, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0049] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. "Fixed connection" refers to a connection where the relative positional relationship remains unchanged after connection. "Rotary connection" refers to a connection where the components can rotate relative to each other after connection. "Sliding connection" refers to a connection where the components can slide relative to each other after connection. The directional terms mentioned in the embodiments of this application, such as "top," "bottom," "inner," "outer," "left," and "right," are only for reference to the directions in the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of this application, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0050] Furthermore, the mathematical concepts mentioned in the embodiments of this application, such as symmetry, equality, parallelism, and perpendicularity, are limitations specific to the current technological level, rather than absolute and strict mathematical definitions. Slight deviations are permissible; approximations of symmetry, equality, parallelism, and perpendicularity are all acceptable. For example, "A and B are parallel" means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. "A and B are perpendicular" means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0051] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A nonlinear waveguide, characterized in that, It includes a subwavelength grating waveguide and a two-dimensional material, wherein the two-dimensional material is located on the surface of the subwavelength grating waveguide.

2. The nonlinear waveguide according to claim 1, characterized in that, The two-dimensional material is located on the upper surface of the subwavelength grating waveguide.

3. The nonlinear waveguide according to claim 1, characterized in that, The two-dimensional material is located on the side surface between the individual grating grids in the subwavelength grating waveguide.

4. The nonlinear waveguide according to claim 3, characterized in that, The two-dimensional material is attached to the side surfaces between the individual grating grids by growth.

5. The nonlinear waveguide according to claim 1, characterized in that, The duty cycle of the subwavelength grating waveguide is no greater than 0.

9.

6. The nonlinear waveguide according to claim 1, characterized in that, The core layer of the subwavelength grating waveguide has an equivalent refractive index greater than that of the cladding.

7. The nonlinear waveguide according to claim 1, characterized in that, The core layer of the subwavelength grating waveguide is made of silicon.

8. The nonlinear waveguide according to claim 1, characterized in that, The core layer of the subwavelength grating waveguide is made of aluminum gallium arsenide.

9. The nonlinear waveguide according to claim 1, characterized in that, The core layer of the subwavelength grating waveguide is made of lithium niobate.

10. The nonlinear waveguide according to claim 1, characterized in that, The thickness of the two-dimensional material is no more than 40 nanometers.

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