Fractal nanocut paper-based vortex light generator and preparation method thereof

Abstract

The application discloses a fractal nanocut paper-based vortex light generator and a preparation method thereof. The vortex light generator comprises a peripheral fixed part, a central circular plane and a plurality of fractal coiled units. The fractal coiled units connect the central circular plane and the peripheral fixed part. The plurality of fractal coiled units are uniformly distributed around the central circular plane. The fractal coiled units are nanocut paper structures. When the central plane area supported by the fractal coiled units is driven by an external field, the central plane area deforms up and down, and becomes a three-dimensional state after deformation. The vortex light generator can realize small-scale device preparation without preparing a complex large-area structure unit array to support vortex light excitation. The preparation method combines focused ion beam processing and wet etching. After fractal patterning and capillary force deformation, the two-dimensional fractal nanocut paper is deformed into a three-dimensional state, and can be directly used as a vortex light generator.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of three-dimensional micro-nano manufacturing technology, and in particular to a vortex light generator based on fractal nano paper cutting and a preparation method thereof. BACKGROUND

[0002] The field of light field regulation has been increasingly widely concerned by researchers, and in particular, generating orbital angular momentum beams to realize customized vortex light is a very important and meaningful research content. Traditional vortex light generators are not conducive to integration in the new generation of micro-nano optoelectronic systems due to their large size and poor adjustability.

[0003] In addition, with the development of micro-nano optoelectronic devices and systems towards miniaturization and integration, realizing multifunctionality in a small space is the development focus of future micro-nano optoelectronic devices. However, the spatial dimension of traditional optoelectronic devices is fixed after manufacturing, which undoubtedly leads to a single function of the device. Therefore, the preparation of deformable three-dimensional micro-nano optoelectronic devices has become an important way for the development of micro-nano devices towards ultra-miniaturization and functional integration. Among many three-dimensional preparation technologies, 3D printing has received great attention and development, but there are great challenges in using 3D printing to prepare micro-nano optoelectronic devices. At the same time, people have developed some schemes for driving three-dimensional deformation of micro-nano structures using external fields, such as force field and electric field driving. These three-dimensional micro-nano structures have shown unique application value in the optimization of micro-nano optical performance, sensing and regulation.

[0004] However, the three-dimensional micro-nano structures prepared by the above preparation processes are relatively simple, the regulation performance of light field under three-dimensional deformation is low, the regulation function is less, and the customized regulation of light field such as vortex beam excitation cannot be conveniently and efficiently realized, which limits its application scope in the field of micro-nano optoelectronics.

[0005] At present, to realize the customized regulation of light field, designing three-dimensional micro-nano structures of vortex light generators and corresponding convenient preparation processes are urgent problems to be solved. SUMMARY

[0006] Therefore, the present application provides a vortex light generator based on fractal nano paper cutting and a preparation method thereof. The vortex light generator can realize small-scale device preparation without the need to prepare a complex large-area structure unit array to support vortex light excitation. The preparation method combines focused ion beam processing and wet etching, and first performs fractal patterning and then performs capillary force deformation, so that the two-dimensional state fractal nano paper cutting is deformed into a three-dimensional state and can be directly used as a vortex light generator.

[0007] In order to achieve the above object, the technical scheme of the present application is: a vortex light generator based on fractal nanocut paper, comprising a peripheral fixed part, a central circular plane and a plurality of fractal coiled units.

[0008] The fractal coiled units connect the central circular plane and the peripheral fixed part, the plurality of fractal coiled units are uniformly distributed around the central circular plane, and the number of fractal coiled units is even; the fractal coiled unit is a nanocut paper structure, the central plane area supported by the fractal coiled unit deforms up and down when driven by an external field, and becomes a three-dimensional state after deformation.

[0009] A plurality of through holes are formed in the central circular plane.

[0010] After the incident circularly polarized light passes through the vortex light generator, the spin angular momentum of the light is converted into the orbital angular momentum to generate vortex light.

[0011] Preferably, the number of fractal coiled units is 4, 6 or 8.

[0012] Another embodiment of the present application also provides a preparation method of the vortex light generator based on fractal nanocut paper, which is prepared by the following steps for the vortex light generator based on fractal nanocut paper:

[0013] Step 1: take a substrate sample, which is composed of a silicon dioxide substrate and a gold film covered on the substrate, and the surface of the gold film is flat.

[0014] Step 2: design a two-dimensional fractal pattern on the surface of the gold film of the substrate sample according to the vortex light generator; the two-dimensional fractal pattern is a two-dimensional pattern of the vortex light generator before deformation.

[0015] Etch the pre-designed two-dimensional fractal pattern on the substrate sample by using a focused ion beam, and the etching depth reaches the silicon dioxide substrate.

[0016] Step 3: wet etching of the sample in step 2 is carried out by using the prepared hydrofluoric acid solution, which contains the removal of the oxygen-containing layer at a certain depth of the bottom of the gold film and also provides an external driving force for the structure by means of liquid capillary force, so as to obtain the vortex light generator deformed into a three-dimensional state.

[0017] Preferably, a two-dimensional fractal pattern is designed on the surface of the gold film of the substrate sample according to the vortex light generator; the two-dimensional fractal pattern is a two-dimensional pattern of the vortex light generator before deformation. The two-dimensional fractal pattern corresponds to the structural design of the vortex generator, a central reserved area is arranged on the central circular plane, a two-dimensional nanocut paper structure area is arranged on the plurality of fractal coiled units, and a peripheral reserved area is arranged on the peripheral fixed part. The central reserved area is designed with a plurality of through holes. The two-dimensional nanocut paper structure area comprises a plurality of two-dimensional nanocut paper structures arranged around the central reserved area.

[0018] Beneficial effects:

[0019] 1. The fractal nanocut paper based vortex light generator, compared with the existing traditional vortex light generator or two-dimensional super-structured surface vortex light generator, can realize small-scale device preparation and does not need to prepare a complex large-area structure unit array to support vortex light excitation.

[0020] 2. The fractal nanocut paper based vortex light generator, compared with the existing traditional vortex light generator or two-dimensional super-structured surface vortex light generator, can realize small-scale device preparation and does not need to prepare a complex large-area structure unit array to support vortex light excitation. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a fractal nanocut paper based on trampoline inspired design in an embodiment of the present application.

[0022] Figure 2 is a working schematic diagram of a three-dimensional vortex light generator in an embodiment of the present application.

[0023] Figure 3 is a flowchart of preparing a three-dimensional fractal nanocut paper structure by using capillary force in an embodiment of the present application.

[0024] Figure 4 is a scanning electron microscope photograph of the two-dimensional and three-dimensional fractal nanocut paper structures prepared in an embodiment of the present application. From top to bottom, steps ①, ② and ③ of the preparation flow are respectively corresponded to Figure 3

[0025] Figure 5 is a scanning electron microscope photograph of the four and seven structure group vortex light generators prepared in an embodiment of the present application. From left to right, the preparation results of type ABC vortex light generators are respectively shown. Here, type ABC respectively corresponds to four, six and eight equal fractal coiled unit cases.

[0026] Figure 6 is a preliminary verification result based on time domain finite difference simulation in an embodiment of the present application. From top to bottom, the vortex light generation results of type ABC three vortex light generators are respectively corresponded to. Here, type ABC respectively corresponds to four, six and eight equal fractal coiled unit cases. DETAILED DESCRIPTION

[0027] The present application will be described in detail below with reference to the accompanying drawings and embodiments.

[0028] ​According to one embodiment of the present application, a deformable fractal nano-paper-cut is designed to support the generation of vortex beams. Figure 1 A fractal nano-paper-cut inspired by a trampoline is designed, i.e. the surrounding fractal coiled units can be analogized to springs around the trampoline, which can support the central planar region to deform up and down when driven by an external field. Under such a design principle, two-dimensional and three-dimensional fractal nano-paper-cut structures can be obtained.

[0029] The vortex light generator based on the fractal nano-paper-cut includes a peripheral fixed part, a central circular plane, and a plurality of fractal coiled units.

[0030] The fractal coiled units connect the central circular plane and the peripheral fixed part, and the plurality of fractal coiled units are uniformly distributed around the central circular plane. The number of fractal coiled units is even. In the embodiment of the application, the number of fractal coiled units can be 4, 6, or 8.

[0031] The fractal coiled units are nano-paper-cut structures, and the fractal coiled units support the central planar region to deform up and down when driven by an external field, and become three-dimensional after deformation. As shown in Figure 1 An embodiment of a nano-paper-cut structure of the present application is shown. The nano-paper-cut structure in the embodiment of the present application adopts a bending configuration, wherein one end of the nano-paper-cut structure is connected to the central circular plane, and extends outward in a Z or S shape. The outermost ends of all the nano-paper-cut structures can be connected to a peripheral ring to realize the connection between the central circular plane and the peripheral ring. The nano-paper-cut structure can deform into a shape as shown in Figure 2 under the action of an external field.

[0032] A plurality of through holes are formed on the central circular plane.

[0033] The spiral variation morphology and adjustable three-dimensional deformation characteristics of the three-dimensional device can be used to realize Figure 2 The light beam orbital angular momentum excitation is shown. The fractal nano-paper-cut structure is used to realize a vortex light generator. That is, the spin angular momentum of light is converted into orbital angular momentum to generate vortex light after the incident circularly polarized light passes through the generator.

[0034] Figure 3 is a flowchart for preparing a three-dimensional fractal nano-paper-cut structure by using capillary force in one embodiment of the present application. The steps include:

[0035] Step 1: A gold film-silicon dioxide substrate sample is provided, and the surface of the gold film is flat.

[0036] Step 2: The sample is cut by using a focused ion beam, i.e. the step of etching the fractal pattern is etched, to obtain a two-dimensional fractal nano-paper-cut structure etched to the silicon dioxide. The seven through holes etched in the center are used to improve the etching efficiency of the central region in the next wet etching.

[0037] The two-dimensional fractal pattern is a two-dimensional pattern of the vortex light generator without deformation; the two-dimensional fractal pattern corresponds to the structural design of the vortex generator, a central reserved area is arranged on the central circle plane, a two-dimensional nano paper-cut structure area is arranged on the plurality of fractal winding units, and a peripheral reserved area is arranged on the peripheral fixed part; the central reserved area is designed with a plurality of through holes.

[0038] The two-dimensional nano paper-cut structure area includes a plurality of two-dimensional nano paper-cut structures arranged around the central reserved area.

[0039] Step 3: Wet etching of the sample in step 2 with the proportioned hydrofluoric acid solution, which includes removing the oxygen-containing layer at the bottom of the gold film to a certain depth and also using the liquid capillary force to cause "side effects" to the structure, obtaining a three-dimensional fractal nano paper-cut structure deformed downward.

[0040] Example 1

[0041] In this example 1, the method for implementing a fractal nano paper-cut pattern on a gold film-silicon dioxide substrate sample and forming a three-dimensional vortex light generator by wet etching includes the following steps 1 to 2.

[0042] Step 1: Use the capillary force to experimentally prepare a three-dimensional vortex light generator. As shown in Figure 3 .

[0043] Step 1: Provide a gold film-silicon dioxide substrate sample with a thickness of 60 nm and 500 microns, respectively.

[0044] Step 2: Use a 24 pA, 30 kV focused ion beam to etch the fractal pattern designed in step 1 on the above sample, etch to the bottom of the silicon dioxide, the etching seam width is about 100 nm, the center through hole diameter is about 230 nm, and the pattern lateral size is 6 microns. The purpose of the seven through holes in the center etching is to improve the efficiency of the next step of wet etching.

[0045] Step 3: Wet etching of the sample in step 2 with the proportioned hydrofluoric acid solution, which includes removing the oxygen-containing layer at the bottom of the gold film to a certain depth and also using the liquid capillary force to cause "side effects" to the structure, obtaining a three-dimensional vortex light generator deformed downward. According to the above preparation steps, here Figure 4 shows the two-dimensional and three-dimensional vortex light generators prepared in the present application. In addition, after expanding to multiple structures, four and seven structure group vortex light generators prepared are given in Figure 5 .

[0046] Step 2: The working performance of the designed vortex light generator is preliminarily verified by using time-domain finite difference simulation. In the time-domain finite difference numerical simulation software, an infrared waveband circularly polarized Gaussian light beam is incident on the three-dimensional nanometer paper-cut vortex light generator, and the outgoing vortex light beam can be detected on the other side by means of a monitor. Figure 6 From top to bottom are vortex electric field mode and vortex phase generation results of the three vortex light generators of type ABC, and the two characteristics of dark spot at mode center and phase formation vortex state distribution fully prove the generation of the vortex light beam, and the geometric distribution of the vortex light field generated by the devices of type ABC has certain fractal dependence characteristics. Here, the device size is 6 microns, and the detected vortex field size is 3 microns x 3 microns.

[0047] Example 2

[0048] In this embodiment, the three-dimensional vortex light generator is prepared according to the process flow shown in Figure 3 The detailed method for preparing the three-dimensional vortex light generator includes the following steps 1 to 5.

[0049] Step 1: A gold thin film layer with a thickness of 60 nanometers is deposited on a silicon dioxide substrate with a thickness of 500 microns by electron beam evaporation.

[0050] Step 2: A two-dimensional micro-nano structure with a predetermined fractal pattern is etched on the gold film-silicon dioxide substrate sample obtained in step 1 by using a focused ion beam, and the gold film is etched through to the bottom silicon dioxide, as shown in process flow ②. The ion species is Ga + , the ion beam current is 24 pA, the voltage is 30 kV, the etching seam width is about 100 nm, the center through-hole diameter is about 230 nm, and the pattern lateral size is 6 microns.

[0051] Step 3: Hydrofluoric acid and deionized water are mixed in a ratio of 1:4 (for example, 10 mL:40 mL) in a cup to obtain the etching liquid. Note that the measuring cylinder for hydrofluoric acid and the cup for mixing the liquid should be thoroughly dried with nitrogen after cleaning to avoid errors in the concentration of hydrofluoric acid after mixing. The line of sight and the liquid surface should be at the same level when measuring the liquid.

[0052] Step 4: The sample etched in step 2 is clamped and suspended in the etching liquid prepared in step 3, and the etching is started, with a time of 25 minutes.

[0053] Step 5: After the immersion etching of step 4 is completed, the sample is carefully taken out and rinsed with deionized water for two minutes to remove the residual hydrofluoric acid on the surface of the sample, and then the residual liquid on the sample is blown dry by nitrogen or balloon. This process, on the one hand, etches the silicon dioxide at the bottom of the fractal pattern area by hydrofluoric acid to obtain a certain bottom space; on the other hand, the capillary force formed during the drying of the liquid can make the structure sink and deform three-dimensionally, as shown in process flow ③. The etching rate of hydrofluoric acid at a ratio of 1:4 is about 55 nm / min, and the etching depth can be estimated to be 1.375 microns.

[0054] In step 5 above, a plurality of fractal patterns with certain arrangement rules and periods can be formed on the process flow ②, that is, a plurality of structure groups of three-dimensional vortex light generators can be formed after wet etching. Figure 5 Scanning electron microscope photos of four and seven structure group vortex light generators formed on the gold film-silicon dioxide substrate sample. The size of the structure unit here is 5 microns, and the period is 6 microns, which respectively displays the square and hexagonal lattice arrangement of the multi-structure group of the three types of ABC fractal structure units.

[0055] In summary, the above is only a preferred embodiment of the present application, and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A vortex light generator based on fractal nano-paper cutting, characterized in that, It includes an outer fixing part, a central circular plane, and multiple fractal winding units; The fractal winding unit connects the central circular plane to the outer fixing part. Multiple fractal winding units are evenly distributed around the central circular plane, and the number of fractal winding units is even. The fractal winding unit is a nano-paper-cutting structure. When the central plane area supported by the fractal winding unit is driven by an external field, it deforms vertically and becomes three-dimensional. The nano-paper-cutting structure adopts a bending configuration. One end of the nano-paper-cutting structure is connected to the central circular plane and extends outward in a Z or S shape. The outermost ends of all nano-paper-cutting structures are connected to an outer ring to realize the connection between the central circular plane and the outer ring. Multiple through holes are formed on the central circular plane; After incident circularly polarized light passes through the vortex light generator, the spin angular momentum of the light is converted into orbital angular momentum to generate vortex light. The number of fractal winding units is 4, 6, or 8.

2. A method for fabricating a vortex light generator based on fractal nano-paper cutting, characterized in that, The vortex light generator based on fractal nano-paper cutting as described in claim 1 is prepared using the following steps: Step ①: Take a substrate sample, which consists of a silicon dioxide substrate covered with a gold film, and the surface of the gold film is flat. Step 2: A two-dimensional fractal pattern is pre-designed on the gold film surface of the substrate sample according to the vortex light generator; the two-dimensional fractal pattern is the two-dimensional pattern of the vortex light generator when it is not deformed; the two-dimensional fractal pattern corresponds to the structural design of the vortex light generator, with a central reserved area set for the central circular plane, a two-dimensional nano-paper-cutting structure area set for multiple fractal winding units, and an outer reserved area set for the outer fixing part; The central reserved area is designed with multiple through holes; The two-dimensional nano-paper-cutting structure area includes multiple two-dimensional nano-paper-cutting structures arranged around the central reserved area; The pre-designed two-dimensional fractal pattern was etched onto the substrate sample using a focused ion beam, with the etching depth reaching the silicon dioxide substrate. Step 3: Wet etching is performed on the sample from step 2 using a hydrofluoric acid solution of the correct ratio. This process involves removing the oxygen-containing layer at a certain depth at the bottom of the gold film while also using the external field driving force brought by the liquid capillary force to the structure, resulting in a vortex light generator that has been deformed into a three-dimensional state.

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