Tunable high nonlinear silicon-based graphene multimode slot waveguide and preparation method
By coating the surface of a silicon-based waveguide with a graphene film and an ion gel layer, the optical field effect is enhanced, which solves the problem of insufficient nonlinearity in silicon-based multimode waveguides and enables efficient optical logic operations and multimode optical logic operations.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHONGBEI UNIV
- Filing Date
- 2023-10-27
- Publication Date
- 2026-07-24
AI Technical Summary
Traditional silicon-based multimode waveguides suffer from insufficient nonlinear strength, making it difficult to extend to higher-order modes. Furthermore, the nonlinear efficiency is reduced due to the two-photon absorption effect and free carrier absorption effect of silicon materials, which cannot meet the ever-increasing data processing requirements.
A tunable, highly nonlinear silicon-based graphene multimode slit waveguide structure is employed. By covering the silicon waveguide surface with a graphene film and combining it with an ion gel layer, the high Kerr coefficient and nanoscale thickness of the double electric layer structure of graphene are utilized to enhance the intensity of the optical field. Furthermore, the Fermi level of graphene is modulated by electrodes to reduce transmission loss.
It significantly improves the nonlinear coefficient of the device, shortens the waveguide length, reduces losses, enhances the efficiency of optical logic operations, and achieves high efficiency in high-speed optical logic operations and multimode optical logic operations.
Smart Images
Figure CN117311056B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of silicon-based optoelectronic integrated devices, specifically to a tunable, highly nonlinear silicon-based graphene multimode slit waveguide and its fabrication method. Background Technology
[0002] The more modes a traditional silicon-based multimode waveguide has, the larger the required waveguide width becomes. This leads to an excessively large effective optical field area for lower-order modes, resulting in reduced optical power density and consequently lower nonlinear efficiency. Most importantly, while silicon-based waveguides are excellent nonlinear devices, they are affected by the two-photon absorption effect (TPA) inherent in silicon and the free carrier absorption effect (FCA) generated by TPA, leading to additional absorption losses and further reducing nonlinear efficiency. Therefore, optical logic devices implemented solely using the nonlinearity of silicon-based waveguides cannot meet the demands of ever-increasing data processing volumes.
[0003] Therefore, the insufficient nonlinear strength and difficulty in extending to higher-order modes of silicon-based waveguides in the existing technology limit their application in optical logic devices. Summary of the Invention
[0004] The present invention overcomes the shortcomings of the existing technology, and the technical problem to be solved is: to provide a tunable highly nonlinear silicon-based graphene multimode slit waveguide and its fabrication method.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a tunable high nonlinear silicon-based graphene multimode slit waveguide, comprising a silicon oxide substrate, wherein a plurality of parallel silicon waveguides are disposed on the silicon oxide substrate, the silicon waveguides are strips with rectangular cross-sections, and slit gaps are disposed between them to form multimode slit waveguides, wherein a graphene film extending to the surface of the silicon oxide substrate on both sides is disposed on the surface of the multimode slit waveguide, wherein a first electrode and a second electrode are respectively disposed on the surface of the graphene film on both sides of the multimode slit waveguide, and a third electrode is disposed on the position of the silicon oxide substrate where no graphene film is covered; an ion gel layer is covered on the graphene film, the silicon oxide substrate and each electrode.
[0006] The electrode materials for the first, second, and third electrodes are gold.
[0007] The width of the slit gap is 40–100 nm.
[0008] The width of the silicon waveguide is 200nm to 400nm.
[0009] Furthermore, this invention also provides a method for fabricating a tunable, highly nonlinear silicon-based graphene multimode slit waveguide, comprising the following steps:
[0010] Step 1: Apply photoresist to the silicon surface of the SOI chip and fabricate a slit array structure using electron beam lithography;
[0011] Step 2: Using ICP etching and wet etching processes, the silicon surface is fabricated into a multimode slit waveguide with the same structure as the photoresist.
[0012] Step 3: Prepare a graphene film and transfer it to the multimode slit waveguide surface of the SOI chip, and then pattern the graphene film by ultraviolet lithography or plasma etching.
[0013] Step 4: Fabricate the electrodes and electrode leads;
[0014] Step 5: Spin-coat the top of the SOI chip with ionogel.
[0015] Step two also includes a step of smoothing the inside of the slit.
[0016] In step five, the spin-coating thickness of the ionogel layer is 0.5–2 μm.
[0017] The specific steps for step three are as follows:
[0018] Graphene is grown on copper foil;
[0019] The copper foil with graphene was spin-coated with PMMA adhesive and then baked on a hot plate at 150°C for 20 minutes to increase the hardness of the PMMA adhesive and its adhesion to graphene.
[0020] Place the copper foil coated with PMMA adhesive into a deionized water solution of ferric chloride. After the copper foil is basically removed, use a clean silicon wafer to take it out and transfer it to clean deionized water to soak for 10 to 20 minutes. Then change to clean deionized water and repeat the soaking two to three times until the graphene film sample is clear and transparent.
[0021] The graphene film sample was retrieved using the multimode slit waveguide surface of the SOI chip and then baked on a hot plate at 150°C for 5 minutes.
[0022] The SOI wafer with only graphene adhered is obtained by removing the adhesive using acetone and isopropanol, and then the graphene film is patterned by ultraviolet lithography or plasma etching.
[0023] Compared with the prior art, the present invention has the following advantages:
[0024] 1. The waveguide result of the present invention can confine both TE0 and TE1 mode light in the slit and enhance optical energy, greatly reducing the TPA effect in silicon waveguides, thereby reducing transmission loss;
[0025] 2. The integration of multimode slit waveguide and single-layer graphene in this invention enhances the nonlinear effect: by utilizing the inherent properties of graphene, the optical field located in the graphene is greatly enhanced by the slit, which greatly increases the interaction strength between the highly nonlinear graphene and the optical field, thereby enabling the device as a whole to obtain a huge nonlinear coefficient.
[0026] 3. This invention can simultaneously confine multiple modes to propagate in a narrow slit by adjusting the waveguide width and the slit width, which can solve the problem of excessively large effective optical field area of low-order modes in existing multimode waveguides, resulting in excessively low optical power density.
[0027] 4. This invention utilizes ion gel and graphene to form a double layer with a nanometer-thickness to obtain a supercapacitor-like structure, and then electrostatically modulates the Fermi level structure of graphene, which can solve the problem of complex and difficult process of graphene vertical capacitor structure.
[0028] 5. The significant increase in the nonlinear coefficient of the multimode slit waveguide in this invention enables the entire waveguide structure to achieve the required nonlinear effect strength with a micrometer-level size. Therefore, the overall length of the multimode slit waveguide can be greatly shortened to 500-1000 μm, the overall loss caused by the slit can be greatly reduced, and the overall size of the device can be greatly reduced.
[0029] In summary, this invention provides a tunable, highly nonlinear silicon-based graphene multimode slit waveguide and its fabrication method. The structure integrates graphene and a multimode silicon-based slit waveguide, utilizing the interaction between the high Kerr coefficient graphene and the high power density optical field in the slit to significantly enhance the nonlinear effect intensity of the device. Furthermore, it possesses the ability to extend to higher-order modes. Therefore, the waveguide structure obtained by this invention, as a highly nonlinear device, can realize high-speed optical logic operations based on four-wave mixing effects or more efficient multimode optical logic operations. Attached Figure Description
[0030] Figure 1 A schematic diagram of a tunable, highly nonlinear silicon-based graphene multimode slit waveguide provided in an embodiment of the present invention;
[0031] Figure 2 for Figure 1 A cross-sectional schematic diagram;
[0032] Figure 3 The simulation diagrams show the field strength of the waveguide spacing, where (a) is the field distribution of the slit waveguide mode simulated by Comsol and (b) is the field strength distribution of different slit widths.
[0033] Figure 4 The nonlinear coefficients of the TE0 and TE1 modes vary with waveguide parameters: (a) variation of slit width, with the waveguide width set to 220 nm; (b) variation of waveguide width, with the slit width set to 50 nm.
[0034] In the figure: 1 is a silicon oxide substrate, 2 is a silicon waveguide, 3 is a slit gap, 4 is a graphene film, 5 is the first electrode, 6 is the second electrode, 7 is the third electrode, and 8 is an ion gel layer. Detailed Implementation
[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0036] Example 1
[0037] like Figures 1-2 As shown, Embodiment 1 of the present invention provides a tunable, highly nonlinear silicon-based graphene multimode slit waveguide, comprising a silicon oxide substrate 1, on which a plurality of parallel silicon waveguides 2 are disposed, each silicon waveguide 2 being a rectangular strip with slit gaps 3 forming a multimode slit waveguide. A graphene film 4 extending to the surface of the silicon oxide substrate 1 on both sides is disposed on the surface of the multimode slit waveguide. A first electrode 5 and a second electrode 6 are respectively disposed on the surface of the graphene film 4 on both sides of the multimode slit waveguide. A third electrode 7 is disposed on a position on the silicon oxide substrate 1 where the graphene film 4 is not covered. An ionogel layer 8 is covered above the graphene film 4, the silicon oxide substrate 1, and each electrode. A voltage V is connected between the first electrode 5 and the second electrode 6 via a lead wire. DS The second motor 6 and the third electrode 7 are connected by a lead wire with a voltage V. G .
[0038] Specifically, in this embodiment, the electrode materials of the first electrode 5, the second electrode 6, and the third electrode 7 are gold. For example... Figure 2 As shown, in this embodiment, the width of the graphene film 4 is greater than the width of the multimode slit waveguide, and the length is less than the length of the multimode slit waveguide. It is only distributed in the middle of the multimode slit waveguide, which can reduce the loss.
[0039] Preferably, in this embodiment, the width of the slit gap 3 is 40–100 nm. The width of the silicon waveguide 2 is 200 nm–400 nm. Specifically, in this embodiment, the width of the slit gap 3 is 50 nm, and the waveguide width is 220 nm. The nm-level slit waveguide structure can reduce the structural size to obtain a micrometer-level waveguide structure, and can significantly improve the nonlinear coefficient of the device, thereby improving the multimode optical logic operation conversion efficiency. In this embodiment, the nonlinear enhancement effect of graphene on the silicon waveguide allows the length of the silicon waveguide 2 to be shortened to 500–1000 μm.
[0040] like Figure 3 As shown, (a) is the mode field distribution diagram of the slit waveguide simulated by Comsol; (b) is the field intensity distribution under different slit widths. It can be seen from the figure that in the waveguide of this embodiment, the light field intensity continuously increases as the slit narrows.
[0041] like Figure 4 The figure shows the simulation results of the nonlinear coefficients of the slit and waveguide width variations in this embodiment of the invention. As can be seen from the figure, in the silicon-based graphene multimode slit waveguide of this embodiment, the nonlinear coefficients of both the TE0 and TE1 modes can theoretically reach 10. 6 W -1 m -1 This is on the order of magnitude higher than that of ordinary silicon waveguides, which has a nonlinear coefficient of 200–300 W. -1 m -1 The difference of more than four orders of magnitude demonstrates the enormous nonlinear potential of the silicon-based graphene waveguide proposed in this invention.
[0042] Example 2
[0043] Embodiment 2 of the present invention provides a method for fabricating a tunable, highly nonlinear silicon-based graphene multimode slit waveguide, comprising the following steps:
[0044] Step 1: Apply photoresist to the silicon surface of the SOI chip and fabricate a slit array structure using electron beam lithography;
[0045] Step 2: Using ICP etching and wet etching processes, the silicon surface is fabricated into a multimode slit waveguide with the same structure as the photoresist.
[0046] Step two further includes a smoothing process on the inner side of the slit. Smoothing the waveguide sidewalls through anisotropic wet etching can reduce the loss of the multimode waveguide.
[0047] Step 3: Prepare a graphene film and transfer it to the multimode slit waveguide surface of the SOI chip, and then pattern the graphene film by ultraviolet lithography or plasma etching.
[0048] The specific steps of step three are as follows:
[0049] Growth: Graphene is grown on copper foil;
[0050] Spin-coated PMMA: Spin-coating of the copper foil with graphene is performed, and then the foil is baked on a hot plate at 150°C for 20 minutes to increase the hardness of the PMMA adhesive and its adhesion to the graphene.
[0051] Removing the copper foil: Place the copper foil coated with PMMA adhesive into a deionized water solution of ferric chloride. The sample will float on the surface of the solution. After the copper foil is basically removed, only a thin layer of PMMA adhesive adhering to the graphene remains. Use a clean silicon wafer to remove it and transfer it to clean deionized water for 10 to 20 minutes. Then change to clean deionized water and repeat the soaking two to three times until the graphene film sample is clear and transparent.
[0052] Transfer to SOI wafer: The graphene film sample was retrieved using the multimode slit waveguide surface of the SOI chip, and then baked on a hot plate at 150°C for 5 minutes to completely remove water molecules and increase the adhesion between graphene and the substrate.
[0053] PMMA removal: Acetone and isopropanol are used for photoresist removal to obtain an SOI wafer with only graphene adhering to it. The graphene film is then patterned using UV lithography or plasma etching. Similar to the photoresist removal steps in waveguide fabrication, acetone and isopropanol are used for removal. However, care must be taken not to use ultrasonic vibration cleaning, as this could very likely dislodge the graphene.
[0054] The method for preparing the deionized water solution of ferric chloride is as follows: put an appropriate amount of ferric chloride hexahydrate (FeCl3·6H2O) into a beaker, add an appropriate amount of deionized water, and stir evenly so that the FeCl3·6H2O powder is completely dissolved in the deionized water.
[0055] Step 4: Fabricate the electrodes and electrode leads;
[0056] Step 5: Spin-coat the top of the SOI chip with ionogel.
[0057] In step five, the spin-coating thickness of the ionogel layer is 0.5–2 μm, preferably 1 μm.
[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A tunable, highly nonlinear silicon-based graphene multimode slit waveguide, characterized in that, The system includes a silicon oxide substrate (1), on which a plurality of parallel silicon waveguides (2) are disposed. The silicon waveguides (2) are strips with rectangular cross sections and are separated by slit gaps (3) to form multimode slit waveguides. The surface of the multimode slit waveguides is provided with graphene films (4) that extend to the surface of the silicon oxide substrate (1) on both sides. The surfaces of the graphene films (4) on both sides of the multimode slit waveguides are respectively provided with a first electrode (5) and a second electrode (6). A third electrode (7) is provided on the silicon oxide substrate (1) at a position where the graphene film (4) is not covered. An ion gel layer (8) is covered on the graphene film (4), the silicon oxide substrate (1), and each electrode.
2. The tunable highly nonlinear silicon-based graphene multimode slit waveguide according to claim 1, characterized in that, The electrode material of the first electrode (5), the second electrode (6) and the third electrode (7) is gold.
3. The tunable highly nonlinear silicon-based graphene multimode slit waveguide according to claim 1, characterized in that, The width of the slit gap (3) is 40-100 nm.
4. The tunable highly nonlinear silicon-based graphene multimode slit waveguide according to claim 1, characterized in that, The width of the silicon waveguide (2) is 200nm to 400nm.
5. The method for fabricating a tunable, highly nonlinear silicon-based graphene multimode slit waveguide according to claim 1, characterized in that, Includes the following steps: Step 1: Apply photoresist to the silicon surface of the SOI chip and fabricate a slit array structure using electron beam lithography; Step 2: Using ICP etching and wet etching processes, the silicon surface is fabricated into a multimode slit waveguide with the same structure as the photoresist. Step 3: Prepare a graphene film and transfer it to the multimode slit waveguide surface of the SOI chip, and then pattern the graphene film by ultraviolet lithography or plasma etching. Step 4: Fabricate the individual electrodes and electrode leads; Step 5: Spin-coat the top of the SOI chip with ionogel.
6. The method for fabricating a tunable, highly nonlinear silicon-based graphene multimode slit waveguide according to claim 5, characterized in that, Step two also includes a step of smoothing the inside of the slit.
7. The method for fabricating a tunable, highly nonlinear silicon-based graphene multimode slit waveguide according to claim 5, characterized in that, In step five, the spin-coating thickness of the ionogel layer is 0.5–2 μm.
8. The method for fabricating a tunable, highly nonlinear silicon-based graphene multimode slit waveguide according to claim 5, characterized in that, The specific steps for step three are as follows: Graphene is grown on copper foil; The copper foil with graphene was spin-coated with PMMA adhesive and then baked on a hot plate at 150°C for 20 minutes to increase the hardness of the PMMA adhesive and its adhesion to graphene. Place the copper foil coated with PMMA adhesive into a deionized water solution of ferric chloride. After the copper foil is basically removed, use a clean silicon wafer to take it out and transfer it to clean deionized water to soak for 10 to 20 minutes. Then change to clean deionized water and repeat the soaking two to three times until the graphene film sample is clear and transparent. The graphene film sample was retrieved using the multimode slit waveguide surface of the SOI chip and then baked on a hot plate at 150°C for 5 minutes. The SOI wafer with only graphene adhered is obtained by removing the adhesive using acetone and isopropanol, and then the graphene film is patterned by ultraviolet lithography or plasma etching.