A preparation method of a nonlinear optical lens based on a plasmonic structure

Abstract

The application provides a method for enhancing nonlinear effect based on a plasmonic structure nonlinear optical lens, a single layer of two-dimensional material is transferred on a designed circular grating, then radial light is introduced in a built experimental light path, and the effect of the prepared nonlinear lens is judged according to CCD imaging and spectrum information. The main experimental method is as follows: a gold film is plated on an etched silicon wafer, a nonlinear lens composed of a circular grating is obtained through ultraviolet photoresist, an atomic layer deposition system (ALD) and a mechanical transfer method, and the effect of the prepared nonlinear lens is judged according to the results of CCD imaging and spectrum information.

Description

Technical Field

[0001] This invention relates to the field of optical lens technology, and in particular to a method for fabricating and testing nonlinear optical lenses based on plasmon structures. Background Technology

[0002] In modern optics, optical lenses, as core components, are widely used in fields such as microscopic imaging, optical communication, and sensing. However, traditional optical lenses face challenges related to diffraction limits, size, and weight, making it difficult to meet the demands for high resolution, dynamic zoom, ultra-thin designs, and beam shaping. Existing conventional Gaussian beams are easy to generate and control, have good beam quality, and are simple to shape. They can be shaped using optical elements such as lenses, gratings, and spatial light modulators to adapt to different application requirements. However, the focusing of Gaussian beams is limited by the diffraction limit, meaning that subwavelength-scale focusing cannot be achieved; in nonlinear media, the nonlinear effects of Gaussian beams are not as significant as those of radially polarized beams. Currently, existing designs achieve nonlinear characteristics through Gaussian beams and plasmonic nanostructures, a relatively mature approach that helps promote the development of nanoscale nonlinear nanophotonic applications.

[0003] Based on the above analysis, the problems and shortcomings of the existing technology are: in the existing technology, few people have utilized the characteristics of radially polarized light to achieve more compact beam focusing to excite the nonlinear characteristics of hybrid plasmonic nanostructures. Summary of the Invention

[0004] This invention provides a research method for nonlinear optical lenses based on plasmonic structures under radial polarization conditions, in order to solve the problem of nonlinear characteristics in existing technologies for achieving more compact beam focusing to excite plasmonic nanostructures.

[0005] To achieve the above objectives, the solution of the present invention is as follows:

[0006] A method for fabricating a nonlinear optical lens based on a plasmonic structure includes the following steps:

[0007] S1: Prepare a circular grating sample;

[0008] S2: Transfer the single layer of WSe2 onto the circular grating prepared in step one to form a nonlinear lens.

[0009] Furthermore, step S1 specifically includes:

[0010] First, a circular grating template was etched onto a substrate using a focused ion beam (FIB). Second, a noble metal film of thickness b was deposited on the etched circular grating template at a specific deposition rate A using thermal evaporation. Then, a transparent glass slide was gently bonded to the fresh noble metal film surface using UV-curable adhesive (Norland Optical Adhesive 61). Afterward, the glass slide and the noble metal film were simultaneously peeled off the silicon wafer using a blade, resulting in an ultra-smooth noble metal film. Because it was previously bonded to the silicon wafer, the noble metal film exhibits a similar flatness to the silicon wafer. Next, an alumina film of a certain thickness was deposited on the surface of the noble metal film using atomic layer deposition (ALD) technology, thus obtaining the circular grating sample.

[0011] Furthermore, the substrate is one of glass, iron plate, steel plate, aluminum plate, silicon wafer, or SiO2 wafer, and the substrate size is 100-1000 mm. 2 .

[0012] Furthermore, the etching cycle is 400nm-800nm, and the etching thickness is 50-80nm.

[0013] Furthermore, the precious metal is one of Au, Ag, and Al, with a deposition rate A of 0.3-0.8 A / s and a thickness b of 150-250 nm.

[0014] Furthermore, step S2 specifically includes:

[0015] First, the torn two-dimensional material was transferred onto a SiO2 / Si substrate; then, a polystyrene solution with a concentration of 0.17 g / ml was spin-coated onto the monolayer WSe2 material at a certain rate. Next, a drop of deionized water was placed on one edge of the SiO2 / Si substrate to peel the composite material off from the SiO2 / Si substrate.

[0016] Next, alignment and transfer were performed using a transfer stage (prcbemini). The circular grating sample prepared in S1 was fixed on the transfer stage, and under microscopic observation, the polystyrene in the aforementioned composite material was aligned and transferred onto the circular gold grating sample. The two-dimensional material covered the center of the circular grating, thus obtaining the sample. Finally, the sample was immersed in an etching solution to dissolve the polystyrene film, obtaining a nonlinear lens.

[0017] Furthermore, the two-dimensional material can be one of WSe2, MoSe2, WS2, MoSe2, graphene, or BN, and the two-dimensional material is a single layer.

[0018] Furthermore, the thickness of the alumina film in step one is 3nm-5nm.

[0019] Furthermore, the polystyrene solution is prepared by dissolving polystyrene with a molecular weight of 260,000 in a toluene solution, wherein the concentration of polystyrene is 0.1 g / ml-0.2 g / ml, and the spin coating rate is 1000-3000 rpm / min.

[0020] Furthermore, the etching solution is a type of dichloromethane or trichloromethane solution.

[0021] A system for experimental testing using vortex beams, the experimental system comprising a 100x objective lens, with a nonlinear lens placed below the 100x objective lens; a first beam splitter, a second beam splitter, and a third beam splitter are sequentially arranged above the 100x objective lens; a WPV10L-780 vortex plate, a polarizer, a second lens, a first lens, and a 780nm laser are sequentially arranged horizontally on the left side of the first beam splitter; a first slit, a first bandpass filter, a third lens, and a spectrometer are sequentially arranged horizontally on the left side of the second beam splitter; a fourth lens, a second bandpass filter, a second slit, a fifth lens, a sixth lens, and a first CCD camera are sequentially arranged horizontally on the right side of the third beam splitter; and a second CCD camera is arranged above the third beam splitter.

[0022] Furthermore, by changing the focal length of the lens assembly, the diameter of the incident beam spot can be adjusted to 5-15 μm, thus achieving control over the spot size.

[0023] The advantages of this invention are:

[0024] 1. Using glass, silicon, SiO2, etc. as substrates, an ultra-smooth gold film with a circular grating can be obtained. The circular grating has advantages such as high sensitivity, anti-interference ability, size and weight. By depositing an aluminum oxide film on the surface of the noble metal film, the transmittance and optical performance of the optical lens are improved. The high polarization sensitivity characteristics of a single-layer two-dimensional material are used to achieve better high-resolution imaging.

[0025] 2. This invention combines radial beams and plasmonic structures to achieve efficient nonlinear optical effects at lower light intensities, thereby enabling the design of high-performance, compact nonlinear optical devices and improving their practical application feasibility. This invention is based on a research method for nonlinear optical lenses with hybrid plasmonic structures under radial polarization conditions. It is simple to operate and allows for qualitative and quantitative analysis using results from CCD imaging and spectral information.

[0026] 3. Introducing radial beams and plasmonic structures can further enhance the performance of optical lenses, such as improving focusing ability, increasing imaging resolution, and enabling multifunctional integration. Plasmonic structures combine the advantages of metallic nanostructures and dielectric materials, significantly improving the performance of optical lenses. Radial beams possess unique focusing characteristics, forming extremely small focal points and extremely high electric field strength after focusing, further enhancing the efficiency of light-matter interaction. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process for fabricating a nonlinear optical lens.

[0028] Figure 2 This is a schematic diagram of the cross-sectional structure of a nonlinear lens.

[0029] Figure 3 This is a schematic diagram of the system structure for experimental testing using a vortex beam. Detailed Implementation

[0030] The present invention will now be described in detail, with examples of these embodiments shown in the accompanying drawings. The invention will be further described in detail below, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0031] Example 1

[0032] A method for fabricating a nonlinear optical lens based on a plasmonic structure includes the following steps:

[0033] S1: Sample for preparing a circular gold grating;

[0034] First, a circular grating template with a period of 700 nm and a thickness of 70 nm was etched on a silicon wafer using a focused ion beam (FIB). Second, a 200 nm gold film was deposited on the etched circular grating template using a thermal evaporation method (model: JSD-400) at a rate of 0.5 A / s. Then, a transparent glass plate was gently bonded to the fresh gold film surface using UV-curable adhesive (Norland Optical Adhesive 61). Afterward, the glass plate and gold film were simultaneously peeled off the silicon wafer using a blade, resulting in an ultra-smooth gold film. Because it was previously bonded to the silicon wafer, the gold film exhibits a similar flatness to the silicon wafer. Next, an atomic layer deposition (ALD) technique was used to deposit a 5 nm thick aluminum oxide film on the gold film surface to improve the transmittance and optical performance of the optical lens, thus obtaining a circular gold grating sample.

[0035] S2: Transfer the monolayer WSe2 onto the gold grating sample prepared in step one to form a nonlinear lens;

[0036] First, the torn monolayer WSe2 material was transferred onto a SiO2 / Si substrate. Then, a 0.17 g / ml PS solution (polystyrene solution) was spin-coated onto the monolayer WSe2 material at a rate of 3000 rpm / min. Next, a drop of deionized water was placed on one edge of the SiO2 / Si substrate. The deionized water reduced the adhesion between the PS / WSe2 film and the SiO2 / Si substrate, allowing the WSe2-PS material to be peeled off. At this point, PS with a monolayer of WSe2 material loaded on its lower surface was obtained.

[0037] Next, alignment and transfer were performed using a transfer stage (PRCBE Mini). The circular gold grating sample was fixed on the transfer stage, and under microscopic observation, the PS was aligned and transferred onto the circular gold grating sample. A monolayer of WSe2 material covered the center of the circular gold grating sample, resulting in a PS-WSe2-Au sample. Finally, the PS-WSe2-Au sample was immersed in a dichloromethane solution to dissolve the PS film, yielding a nonlinear lens.

[0038] Example 2

[0039] A system for experimental testing using a vortex beam, the experimental system comprising a 100x objective lens 18, with a nonlinear lens 17 placed below the 100x objective lens 18; a first beam splitter 6, a second beam splitter 7, and a third beam splitter 11 are sequentially arranged above the nonlinear lens 17; a WPV10L-780 vortex plate 5, a polarizer 4, a second lens 3, a first lens 2, and a 780nm laser 1 are sequentially arranged horizontally on the left side of the first beam splitter 6; a first slit 8, a first bandpass filter 9, a third lens 10, and a spectrometer 19 are sequentially arranged horizontally on the left side of the second beam splitter 7; a fourth lens 12, a second bandpass filter 13, a second slit 14, a fifth lens 15, a sixth lens 16, and a first CCD camera 21 are sequentially arranged horizontally on the right side of the third beam splitter 11; and a second CCD camera 20 is arranged above the third beam splitter 11.

[0040] A 780nm laser 1 emits an incident beam, which is collimated and expanded by a lens combination consisting of a first lens 1 and a second lens 2. The beam size can be controlled by changing the focal length of the lens combination, resulting in a beam diameter of 10µm. The expanded laser beam passes through a polarizer 4 and a WPV10L-780 vortex plate 5 (the expanded laser beam must pass through the center of the WPV10L-780 vortex plate 5). The polarization type is adjusted by changing the fast axis angle of the polarizer 4 and the WPV10L-780 vortex plate 5. When the fast axis directions of the polarizer 4 and the WPV10L-780 vortex plate 5 are parallel, the output is radially polarized light; when the fast axis directions of the polarizer 4 and the WPV10L-780 vortex plate 5 are perpendicular, the output is angularly polarized light. In this embodiment, the fast axis directions of the polarizer 4 and the WPV10L-780 vortex plate 5 are set to be parallel.

[0041] The light emitted by the 780nm laser 1 passes sequentially through the first lens 2, the second lens 3, the polarizer 4, the WPV10L-780 vortex plate 5, and the first beam splitter 6. The reflected light from the beam splitter 6 is incident on the nonlinear lens 17 through the nonlinear lens. The reflected light from the sample passes sequentially through the first beam splitter 6, the second beam splitter 7, and the third beam splitter 11. One output light from the second beam splitter 7 passes sequentially through the first slit 8, the first bandpass filter 9, and the third lens 10 and is incident on the spectrometer 19 to collect the spectral information of the sample. The other output light passes through the third beam splitter 11. One output light from the third beam splitter 11 passes sequentially through the fourth lens 12, the second bandpass filter 13, the second slit 14, the fifth lens 15, and the sixth lens 16 and is incident on the first CCD camera 21 to collect Fourier images. The other light enters the second CCD camera 20 to collect the fundamental and harmonic images.

Claims

1. A method for fabricating a nonlinear optical lens based on a plasmonic structure, characterized in that, Includes the following steps: S1: Sample for preparing a circular gold grating; First, a circular grating template with a period of 700 nm and a thickness of 70 nm was etched on a silicon wafer using a focused ion beam. Second, a 200 nm gold film was deposited on the etched circular grating template at a rate of 0.5 A / s using thermal evaporation. Then, a transparent glass plate was gently adhered to the fresh gold film surface using UV-curable adhesive. Afterward, the glass plate and gold film were simultaneously peeled off the silicon wafer using a blade, resulting in an ultra-smooth gold film. Because it was previously attached to the silicon wafer, the gold film exhibits a similar flatness to the silicon wafer. Next, an aluminum oxide film with a thickness of 5 nm was deposited on the gold film surface using atomic layer deposition (ALD) technology to improve the transmittance and optical performance of the optical lens, thus obtaining a circular gold grating sample. S2: Transfer the monolayer WSe2 onto the gold grating sample prepared in step one to form a nonlinear lens; First, the torn monolayer WSe2 material was transferred onto a SiO2 / Si substrate. Then, a PS solution with a concentration of 0.17 g / ml was spin-coated onto the monolayer WSe2 material at a rate of 3000 rpm / min. Next, a drop of deionized water was placed on one edge of the SiO2 / Si substrate. Under the action of the deionized water, the adhesion between the PS / WSe2 film and SiO2 / Si decreased, and the WSe2-PS material was peeled off from the SiO2 / Si substrate. At this point, PS with a monolayer WSe2 material loaded on the lower surface was obtained. Next, alignment and transfer were performed using a transfer stage; the circular gold grating sample was fixed on the transfer stage, and under the observation of a microscope, the PS was aligned and transferred onto the circular gold grating sample; a single layer of WSe2 material was applied to the center of the circular gold grating sample to obtain a PS-WSe2-Au sample; finally, the PS-WSe2-Au sample was immersed in a dichloromethane solution to dissolve the PS film and obtain a nonlinear lens.

2. A system for experimental testing using a vortex beam, characterized in that, The experimental test system includes a 100x objective lens (18), and a nonlinear lens (17) prepared by the method of claim 1 is placed below the 100x objective lens (18); a first beam splitter (6), a second beam splitter (7) and a third beam splitter (11) are arranged in sequence above the nonlinear lens (17); a WPV10L-780 vortex plate (5), a polarizer (4), a second lens (3), a first lens (2) and a 780nm laser (1) are arranged in sequence on the left side of the first beam splitter (6); a first slit (8), a first bandpass filter (9), a third lens (10) and a spectrometer (19) are arranged in sequence on the left side of the second beam splitter (7); a fourth lens (12), a second bandpass filter (13), a second slit (14), a fifth lens (15), a sixth lens (16) and a first CCD camera (21) are arranged in sequence on the right side of the third beam splitter (11); a second CCD camera (20) is arranged above the third beam splitter (11). A 780nm laser (1) emits an incident beam, which is collimated and expanded by a lens combination of a first lens (2) and a second lens (3). The size of the spot can be controlled by changing the focal length of the lens combination. After the above modulation, the diameter of the spot is 10um. The expanded laser beam passes through a polarizer (4) and a WPV10L-780 vortex plate (5). The expanded laser beam must pass through the center of the WPV10L-780 vortex plate (5). The polarization type is adjusted by adjusting the fast axis angle of the polarizer (4) and the WPV10L-780 vortex plate (5). When the fast axis directions of the polarizer (4) and the WPV10L-780 vortex plate (5) are parallel, the output is radially polarized light. When the fast axis directions of the polarizer (4) and the WPV10L-780 vortex plate (5) are perpendicular, the output is angularly polarized light. The fast axis directions of the polarizer (4) and the WPV10L-780 vortex plate (5) are set to be parallel. The light emitted by the 780nm laser (1) passes sequentially through the first lens (2), the second lens (3), the polarizer (4), the WPV10L-780 vortex plate (5), and the first beam splitter (6). The reflected light from the beam splitter (6) is incident on the nonlinear lens (17) through the nonlinear lens. The reflected light from the sample passes sequentially through the first beam splitter (6), the second beam splitter (7), and the third beam splitter (11) in the optical path. One output light from the second beam splitter (7) passes sequentially through the first slit (8) and the first bandpass filter. The beam splitter (9) and the third lens (10) are incident on the spectrometer (19) to collect the spectral information of the sample; the other output light passes through the third beam splitter (11), and one output light from the third beam splitter (11) passes through the fourth lens (12), the second bandpass filter (13), the second slit (14), the fifth lens (15), and the sixth lens (16) in sequence to be incident on the first CCD camera (21) to collect Fourier images, and the other light enters the second CCD camera (20) to collect the fundamental frequency and harmonic frequency images.

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