A silicon super-structure surface unit and super-structure surface based on Fano resonance

Abstract

The application provides a silicon super-structure surface unit based on Fano resonance and a super-structure surface. The silicon super-structure surface unit based on Fano resonance comprises a unit base and two base protruding ribs. The base protruding ribs are arranged on the side surface of the unit base, and the base protruding ribs extend from the upper surface to the lower surface of the unit base. First base defects are arranged between the two base protruding ribs, and second base defects are arranged on both sides of the two base protruding ribs. The silicon super-structure surface based on Fano resonance comprises a plurality of silicon super-structure surface units based on Fano resonance arranged in an array. Each silicon super-structure surface unit based on Fano resonance is provided with three base defects. The symmetry of the silicon cubic structure is broken by the defects, the weak coupling between the bright and dark modes is induced, the sharp Fano resonance is generated, the large local near-field enhancement is realized, and the two-photon absorption response is greatly enhanced.

Description

Technical Field

[0001] This invention relates to the field of nonlinear optics, and more particularly to a silicon metasurface unit and metasurface based on Fano resonance. Background Technology

[0002] Nonlinear optics, which studies the nonlinear response of media under strongly coherent light and its applications, is an important branch of modern optics. Since the discovery of the second harmonic phenomenon in 1961, marking the formal beginning of research into nonlinear optics, the field has continuously developed and matured. Today, optical nonlinear effects play a crucial role in the realization of modern photonic functional devices, with applications in many areas, including harmonic generation, ultrashort pulse generation, and ultrafast all-optical modulation.

[0003] Two-photon absorption (TPA) is a nonlinear absorption effect involving the simultaneous absorption of two photons during the transition of an electron from its ground state to an excited state in a medium. The concept of two-photon absorption was first proposed in 1931 and further developed in 1961 in CaF₂:Eu₂ 2+ This is the first time it has been observed in a crystalline sample. As an important nonlinear effect, two-photon absorption has wide applications in fields such as three-dimensional microfabrication, fluorescence imaging, and optical storage.

[0004] The optical nonlinearity of materials is inherently weak. To enhance optical nonlinearity, a longer interaction length or a large polarization electric field is typically required to provide high-intensity nonlinear optical interactions. Metasurfaces, due to their advantages of multifunctionality, high integration, and low loss, are being widely developed and applied in various fields. Furthermore, their potential to significantly enhance optical nonlinear responses has been anticipated and confirmed. However, current research on metasurfaces largely focuses on harmonic generation and all-optical modulation, while studies on the two-photon absorption effect of materials are primarily conducted on thin films, and the two-photon absorption effect is not strong. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a silicon metasurface unit based on Fano resonance to eliminate or improve one or more defects present in the prior art.

[0006] One aspect of the present invention provides a silicon metasurface unit based on Fano resonance, the silicon metasurface unit based on Fano resonance comprising a unit matrix and two matrix ribs;

[0007] The substrate ribs are disposed on the side of the unit substrate, and the substrate ribs extend from the upper surface to the lower surface of the unit substrate. A first substrate defect is disposed between two substrate ribs, and a second substrate defect is disposed on both sides of the two substrate ribs.

[0008] Using the above scheme, each silicon metasurface unit based on Fano resonance is provided with three matrix defects. By constructing defects, weak coupling between bright and dark modes is induced, resulting in sharp Fano resonance, achieving large local near-field enhancement, and thus greatly enhancing the two-photon absorption response.

[0009] In some embodiments of the present invention, the cross-sections of the silicon metasurface units based on Fano resonance are all identical within the height range of the substrate ribs.

[0010] In some embodiments of the present invention, within the height range of the substrate ribs, the cross-section of the silicon metasurface unit based on Fano resonance is an axisymmetric shape.

[0011] In some embodiments of the present invention, in the orthographic projection direction of the upper surface of the unit substrate, the side length of the unit substrate at the first substrate defect is greater than the side length of the unit substrate at the second substrate defect.

[0012] In some embodiments of the present invention, the silicon metasurface unit based on Fano resonance further includes a substrate, the substrate being connected to the lower surface of the unit substrate.

[0013] In some embodiments of the present invention, the cross-section of the substrate is square, and in the orthographic projection direction of the upper surface of the unit substrate, the side length of the square substrate is greater than the side length of any side of the unit substrate.

[0014] In some embodiments of the present invention, the substrate is made of silicon dioxide, and the unit matrix and the two matrix ribs are both made of silicon.

[0015] In some embodiments of the present invention, the unit base and the two base ribs are integrally formed.

[0016] In another aspect, the present invention provides a silicon metasurface based on Fano resonance, wherein the silicon metasurface based on Fano resonance comprises an array of multiple silicon metasurface units based on Fano resonance, and the substrates of the multiple silicon metasurface units based on Fano resonance are interconnected or integrally formed.

[0017] In some embodiments of the present invention, the array period of the plurality of said Fano resonance-based silicon metasurface units is 380–1030 nm.

[0018] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows, and will also become apparent in part to those skilled in the art upon studying the text, or may be learned by practice of the invention. The objects and other advantages of the invention will become apparent from the description and the accompanying drawings.

[0019] Those skilled in the art will understand that the objectives and advantages achievable with the present invention are not limited to those specifically described above, and that the above and other objectives achievable with the present invention will become clearer from the following detailed description. Attached Figure Description

[0020] The accompanying drawings, which are provided to further illustrate the invention and form part of this application, are not intended to limit the scope of the invention.

[0021] Figure 1 This is a schematic diagram of the three-dimensional structure of the silicon metasurface unit based on Fano resonance of the present invention;

[0022] Figure 2 This is a top view schematic diagram of the silicon metasurface unit based on Fano resonance of the present invention;

[0023] Figure 3 This is a schematic diagram of another structure of the silicon metasurface unit based on Fano resonance according to the present invention;

[0024] Figure 4 The image shows a simulation result of the silicon metasurface based on Fano resonance according to the present invention.

[0025] Figure 5 This is a schematic diagram of a linear optical path.

[0026] Figure 6 This is a schematic diagram of a nonlinear optical path.

[0027] Figure 7 This is a scanning electron microscope image of the silicon metasurface based on Fano resonance of the present invention;

[0028] Figure 8 The figure shows the experimental results of the silicon metasurface based on Fano resonance in this invention.

[0029] Figure 9 A schematic diagram of a metasurface composed of units with a T-shaped cross-section;

[0030] Figure 10 The image shows a simulation result of a metasurface composed of T-shaped cross-section units.

[0031] Figure 11 This is a schematic diagram of the silicon metasurface based on Fano resonance according to the present invention;

[0032] Figure 12 This is a comparison chart of the results from Comparative Example 2.

[0033] Explanation of reference numerals in the attached figures

[0034] The technical solution of the present invention can be more clearly understood and explained through the above description of the reference numerals in the accompanying drawings and in conjunction with the embodiments of the present invention.

[0035] 1. Unit substrate; 2. Substrate rib; 3. First substrate defect; 4. Second substrate defect; 5. Substrate. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0037] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0038] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0039] It should also be noted that, unless otherwise specified, the term "connection" in this article can refer not only to a direct connection, but also to an indirect connection involving an intermediary.

[0040] In the following description, embodiments of the invention will be illustrated with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar parts, or the same or similar steps.

[0041] To solve the above problems, such as Figure 1 , 2 As shown, the present invention proposes a silicon metasurface unit based on Fano resonance, wherein the silicon metasurface unit based on Fano resonance includes a unit substrate 1 and two substrate ribs 2.

[0042] The substrate rib 2 is disposed on the side of the unit substrate 1. The substrate rib 2 extends from the upper surface to the lower surface of the unit substrate 1. A first substrate defect 3 is disposed between two substrate ribs 2. A second substrate defect 4 is disposed on both sides of the two substrate ribs 2.

[0043] Using the above scheme, each silicon metasurface unit based on Fano resonance is provided with three matrix defects. By constructing defects, the symmetry of the silicon cubic structure is broken, weak coupling between bright and dark modes is induced, sharp Fano resonance is generated, large local near-field enhancement is achieved, and thus the two-photon absorption response is greatly enhanced.

[0044] In the specific implementation process, the base rib 2 is a cuboid, which extends from the upper surface to the lower surface of the unit base 1.

[0045] In the specific implementation process, the unit base 1 is also a cuboid.

[0046] In the specific implementation process, the opposing surfaces of the two substrate ribs 2 and the unit substrate 1 form the first substrate defect 3, and the opposing surfaces of the two substrate ribs 2 and the unit substrate 1 respectively form the second substrate defect 4.

[0047] In some embodiments of the present invention, the cross-sections of the silicon metasurface units based on Fano resonance are all identical within the height range of the substrate rib 2.

[0048] In some embodiments of the present invention, within the height range of the substrate rib 2, the cross-section of the silicon metasurface unit based on Fano resonance is an axisymmetric shape.

[0049] In some embodiments of the present invention, in the orthographic projection direction of the upper surface of the unit substrate 1, the side length of the unit substrate 1 at the first substrate defect 3 is greater than the side length of the unit substrate 1 at the second substrate defect 4. For example... Figure 3 As shown.

[0050] In some embodiments of the present invention, the silicon metasurface unit based on Fano resonance further includes a substrate 5, which is connected to the lower surface of the unit substrate 1.

[0051] In some embodiments of the present invention, the substrate 5 has a square cross-section, and in the orthographic projection direction of the upper surface of the unit base 1, the side length of the square substrate 5 is greater than the side length of any side of the unit base 1.

[0052] In some embodiments of the present invention, the substrate 5 is made of silicon dioxide, and the unit substrate 1 and the two substrate ribs 2 are both made of silicon.

[0053] In some embodiments of the present invention, the unit base 1 and the two base ribs 2 are integrally formed.

[0054] like Figure 11As shown, another aspect of the present invention provides a silicon metasurface based on Fano resonance, wherein the silicon metasurface based on Fano resonance comprises a plurality of silicon metasurface units arranged in an array, and the substrates 5 of the plurality of silicon metasurface units based on Fano resonance are interconnected or integrally formed.

[0055] In some embodiments of the present invention, the array period of the plurality of said Fano resonance-based silicon metasurface units is 380–1030 nm.

[0056] Experimental Example

[0057] like Figure 3 As shown. The array period P of the multiple silicon metasurface units based on Fano resonance is 540 nm, the width of the silicon nanostructure is W = 340 nm, and the height is H = 295 nm. The silicon nanostructure is constructed as shown... Figure 3 The first and second matrix defects are shown, where S1 = 70 nm, S2 = 140 nm, and S3 = 90 nm. We use the finite element method (FEM) numerical simulation to theoretically analyze the designed metasurface.

[0058] When X-ray polarized light is incident normally, the linear transmission spectrum of the metasurface exhibits a distinct asymmetric Fano resonance, achieving a high quality factor Q of 862 at the resonance wavelength of 1034.1 nm. Figure 4 As shown in (a), at the non-resonant wavelength, the ring-shaped electric field lines within the structure are distributed in the XZ plane, manifesting as a magnetic dipole m in the Y direction located in the incident wave plane (XY plane). y For the bright model, see Figure 4 (a) Right inset. At the resonant wavelength, the structure exhibits a ring-shaped electric field distribution in the XY plane, manifested as a magnetic dipole m in the Z direction that is not in the incident wave plane. z For dark stencils, see Figure 4 (a) Left inset. Vertical magnetic dipole m z It cannot be directly excited by normal incident light, but through our design, it can be excited by the transverse magnetic dipole mode m of the bright mode. y Near-field coupling occurs, resulting in a narrow-linewidth Fano resonance. Therefore, we obtain a high-quality factor value in a low-loss dielectric material. Simultaneously, the sharp resonance leads to a large near-field enhancement. Normalizing the near-field enhancement, where E0 is the incident electric field amplitude, E is the near-field amplitude with the metasurface structure, and |E / E0| represents the relative near-field enhancement with the metasurface structure, we obtain the maximum near-field enhancement at the Fano resonance wavelength, with a value of |E / E0| of approximately 56. Figure 4 As shown in (b).

[0059] The linear and nonlinear characterization optical paths based on the Fano resonance silicon metasurface are as follows: Figure 5 and Figure 6 As shown.

[0060] Figure 5 To characterize the optical path linearly, a supercontinuum source outputs broadband coherent light. After the polarizer selects the desired incident polarization direction, the light is focused onto the Fano resonance silicon metasurface sample by lens 1. The transmitted light, after passing through the sample, is reparallelized by lens 2 and then focused and coupled into the spectrometer by lens 3 to obtain the transmission spectrum. By processing the transmission spectra focused on the sample and those passing only through the substrate, linear transmission curves of the metasurface sample at different wavelengths can be obtained.

[0061] Figure 6 The nonlinear characterization optical path is designed. A femtosecond laser (center wavelength 1035 nm, pulse width 122 fs, repetition rate 50.1 MHz) outputs pulsed laser light. An attenuator is used to adjust the incident light power, a half-wave plate is used to tune the polarization state of the incident light, and a 50:50 beam splitter is used for beam splitting and incident light power calibration. 50% of the incident light directly reaches optical power meter 1, and the other 50% is focused onto the metasurface sample before entering optical power meter 2. By recording and processing experimental data under different incident light powers, the nonlinear transmission curve of the metasurface sample can be obtained.

[0062] The designed metasurface was fabricated using standard electron beam lithography, and its scanning electron microscope image is shown below. Figure 7 As shown. Figure 8 (a) shows experimentally measured linear transmission spectra of the metasurface, exhibiting a Fano-like transmission spectral profile with a resonance wavelength around 1035 nm, compared to... Figure 4 The simulation results are similar. Figure 8 (b) shows the nonlinear transmission spectrum under X- and Y-polarized light incidence. As can be seen from the figure, under X-polarized light incidence, the silicon metasurface exhibits significant two-photon absorption when the incident light intensity is low; as the incident light intensity gradually increases, the upper energy levels of the silicon band are gradually filled, preventing further light absorption and leading to TPA saturation. We used a uniform broadening model based on TPA saturation theory to fit the measured experimental data. The fitting results show that the unsaturated TPA coefficient β of the designed silicon metasurface is 173.2 cm / MW, and the TPA saturation intensity I... sat =93MW / cm 2 Compared to other two-dimensional two-photon absorbing materials, such as monolayer MoS2 (β=7.62cm / MW, I0), sat =64.5GW / cm 2Among materials such as perovskite (β = 7-19 cm / MW) and InSe (β = 0.74 cm / MW), our metasurface has a larger β and a lower Ig. sat Typically, β can be two orders of magnitude higher, I sat It can be three orders of magnitude lower. Conversely, when Y-polarized light is incident, the metasurface does not exhibit significant two-photon absorption behavior, which is consistent with... Figure 4 The polarization dependence of the near-field enhancement shown is consistent. This indicates that each silicon metasurface based on Fano resonance in this scheme breaks the symmetry of the silicon cubic structure by constructing defects, inducing weak coupling between bright and dark modes, generating sharp Fano resonance, achieving large local near-field enhancement, and enhancing the two-photon absorption response.

[0063] This patent achieves a significant two-photon absorption response by designing a silicon metasurface with Fano resonance. We obtained a large unsaturated TPA coefficient β through data fitting, and observed obvious TPA saturation at low saturation intensities.

[0064] Comparative Example 1

[0065] For example Figure 9 As shown, a metasurface composed of T-shaped units in cross-section; as Figure 10 The image shows a simulation result of a metasurface composed of T-shaped cross-section units, for comparison. Figure 4 and Figure 10 , Figure 4 neutralization Figure 10 The bright areas represent the electric field, and it is evident that the electric field distributions of the two are significantly different. In the local near-field enhancement induced by the Fano resonance in this scheme, the bright areas exist not only within the metasurface unit region but also in the region surrounded by three defects, with a strong bright display at the central defect. The metasurface composed of T-shaped units is within the unit region, and the brightness at the defect is not obvious. The comparison shows that the local near-field enhancement distribution area of ​​this scheme is large, resulting in a large area integral, which is expected to achieve a significant two-photon absorption response.

[0066] Comparative Example 2

[0067] For example Figure 12 As shown, R is the asymmetry parameter. When R is not 0, meaning the position of defect S3 is offset relative to the center, the metasurface structural unit is not an axisymmetric figure. Defect S3's deviation from the symmetry center is accompanied by a blue shift of the resonance wavelength, an increase in linewidth (i.e., a decrease in Q value), and a decrease in near-field enhancement. The size of defect S1 is adjustable, and S1 may be greater than or equal to S3. Increasing defect S1 is accompanied by a blue shift of the resonance wavelength, a decrease in linewidth (i.e., an increase in Q value), and an increase in near-field enhancement.

[0068] When passing Figure 12Compared with symmetrical metasurface structural units, symmetrical metasurface structural units have higher transmittance and lower losses.

[0069] The idea proposed in this patent to improve optical nonlinear response by utilizing the resonance mechanism of metasurfaces can be widely applied in fields such as nonlinear nanophotonics, neuromorphic photonics, and sensing.

[0070] It should be clarified that the present invention is not limited to the specific configurations and processes described above. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0071] In this invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or in place of features of other embodiments.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Fano resonance based silicon meta-surface unit, characterized in that, The silicon metasurface unit based on Fano resonance includes a unit substrate and two substrate ribs. In the top view of the silicon metasurface unit, the side length of the side connecting the unit substrate and the substrate ribs is the width of the unit substrate. The width of the unit substrate is 340 nm, and the height of the unit substrate is 295 nm. The substrate ribs are disposed on the side of the unit substrate, and the substrate ribs extend from the upper surface to the lower surface of the unit substrate. A first substrate defect is disposed between two substrate ribs, and a second substrate defect is disposed on both sides of the two substrate ribs.

2. The Fano-resonance-based silicon super- surface unit cell of claim 1, wherein, Within the height range of the substrate ribs, the cross-sections of the silicon metasurface units based on Fano resonance all have the same shape.

3. The Fano-resonance-based silicon super- surface unit cell of claim 1, wherein, Within the height range of the substrate ribs, the cross-sections of the silicon metasurface units based on Fano resonance are all axisymmetric.

4. The Fano-resonance-based silicon super- surface unit cell of claim 3, wherein, In the orthographic projection direction of the upper surface of the unit substrate, the side length of the unit substrate at the first substrate defect is greater than the side length of the unit substrate at the second substrate defect.

5. The Fano-resonance based silicon super-structured surface unit cell of any of claims 1-4, wherein, The silicon metasurface unit based on Fano resonance also includes a substrate, which is connected to the lower surface of the unit substrate.

6. The Fano-resonance based silicon super- surface unit cell of claim 5, wherein, The substrate has a square cross-section, and in the orthographic projection direction of the upper surface of the unit substrate, the side length of the square substrate is greater than the side length of any side of the unit substrate.

7. The Fano-resonance-based silicon super- surface unit cell of claim 5, wherein, The substrate is made of silicon dioxide, and the unit matrix and the two matrix ribs are both made of silicon.

8. The Fano-resonance-based silicon super- surface unit cell of claim 1, wherein, The unit matrix and the two matrix ribs are integrally formed.

9. A Fano resonance based silicon super-structure surface characterized in that, The Fano resonance-based silicon metasurface includes an array of multiple Fano resonance-based silicon metasurface units as described in any one of claims 1-8, wherein the substrates of the multiple Fano resonance-based silicon metasurface units are interconnected or integrally formed.

10. The Fano-resonance based silicon super-structure surface of claim 9, wherein, The array period of the multiple silicon metasurface units based on Fano resonance is 380~1030nm.

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