Anti-counterfeiting optical element and method for manufacturing the same

Abstract

The application discloses an anti-fake optical element and a preparation method thereof. The anti-fake optical element comprises a plane substrate, and is characterized in that the anti-fake optical element further comprises a surface optical anti-fake layer on the plane substrate; the surface optical anti-fake layer is composed of periodically distributed phase areas; each phase area is composed of a plurality of closely arranged stepped pixel blocks with different heights and the same square bottom surface; and the surface optical anti-fake layer forms an anti-fake pattern under visible light irradiation. The anti-fake optical element has the advantages of low processing cost, strong anti-fake ability, wide application range, clear anti-fake image and the like, and can be applied to the fields of currency, certificates, labels and the like.

Description

Technical Field

[0001] This invention relates to the fields of optical anti-counterfeiting and micro-optics. Specifically, it relates to an anti-counterfeiting optical element and its preparation method. Background Technology

[0002] Anti-counterfeiting technology refers to a series of technical means applied to products, labels, and packaging to identify genuine products, protect consumer rights, prevent infringement, and combat counterfeiting and substandard goods. The emergence of anti-counterfeiting technology is to meet consumers' demands for product quality and safety, while also fulfilling the need to protect intellectual property rights and combat counterfeiting. Globally, the proliferation of counterfeit and substandard products has caused enormous economic losses and social problems. Therefore, anti-counterfeiting technology plays a crucial role in commodity circulation, intellectual property protection, and social governance.

[0003] Image holography is a type of anti-counterfeiting technology. It utilizes special surface structures to transmit or reflect specific anti-counterfeiting patterns when illuminated by a particular beam of light. Existing anti-counterfeiting optical components based on image holography generally utilize diffraction from continuous tilting reflective surfaces (CN112572016B) or metasurface structures (CN107065491B). Continuous reflective surface fabrication requires high precision, is difficult and costly, and is difficult to implement for anti-counterfeiting identification in consumer products. Metasurfaces are divided into geometric phase and resonant phase types. Geometric phase-based metasurfaces are wavelength-insensitive and can operate over a wide wavelength range, but only under circularly polarized light. Resonant phase-based metasurfaces can operate under unpolarized light but are wavelength-sensitive and cannot operate over a wide wavelength range. Furthermore, the microstructure layers of these components require complex coating and etching processes, placing high demands on the substrate material. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides an anti-counterfeiting optical element and its design method, which utilizes phase modulation of an array of tens of millions of stepped pixel blocks within a phase layer to generate a preset anti-counterfeiting pattern. The stepped structure is easily fabricated using nanoimprint technology; it only requires spraying a layer of photoresist onto the surface of the item, followed by molding and peeling.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] On one hand, the present invention provides an anti-counterfeiting optical element, including a planar substrate, characterized in that it further includes a surface optical anti-counterfeiting layer located on the planar substrate; the surface optical anti-counterfeiting layer is composed of periodically distributed phase regions, each phase region being composed of multiple closely arranged stepped pixel blocks of different heights and with the same square bottom surface, so that the surface optical anti-counterfeiting layer forms an anti-counterfeiting pattern under visible light irradiation.

[0007] The planar substrate can be a planar material with a smooth surface, such as plastic film or glass, specifically the surface of product packaging, mobile phone casing, or item label.

[0008] The surface optical anti-counterfeiting layer is composed of periodically arranged step-like phase structures. Within each period, step-like pixel blocks of various heights and with square base shapes are arranged according to a design.

[0009] The stepped structure has a square region in each cycle, with each region closely connected. The cycle and side length are consistent, ranging from 0.5cm×0.5cm to 10cm×10cm. Within each cycle, the side length of the pixel block is 1-10µm, the height is less than 2µm, and the number of pixel blocks is 1000×1000 to 5000×5000.

[0010] The stepped pixel blocks of the surface optical anti-counterfeiting layer can be 2-step, 4-step, or 8-step, with the number of steps N selected according to performance requirements.

[0011] When illuminated by a light source, the optical anti-counterfeiting layer can produce a distinctive anti-counterfeiting pattern, which can be either three-dimensional or two-dimensional.

[0012] The light source required for the optical anti-counterfeiting layer can be a monochromatic laser or a common visible light source, including but not limited to flashlights, mobile phone flashlights, etc.

[0013] Furthermore, the height of the stepped pixel block in a single phase region is calculated as follows:

[0014] S1. Generate a phase matrix with the same number of pixel blocks using random numbers. The modulated reflective surface light field matrix is ​​obtained. ;

[0015] S2. Optical field matrix of the reflecting surface The phase is quantized in N steps, so that continuous phases are quantized according to the interval. Resampling;

[0016] S3. Perform a Fourier transform on the phase-quantized light field to obtain the light field matrix of the imaging surface. ;

[0017] S4. Calculate the light field matrix of the imaging surface. Argument matrix and amplitude matrix And calculate the light intensity of the imaging surface. Uniformity U and efficiency η;

[0018] S5. The complex amplitude matrix of the imaging plane After replacing the amplitude with the anti-counterfeiting pattern matrix P, the inverse Fourier transform is performed to obtain the light field matrix of the reflecting surface. and will The amplitude is replaced using a plane wave matrix;

[0019] S6. Repeat steps S2-S5 until the uniformity U and efficiency η meet the design requirements, and obtain the N-step quantized phase matrix. ;

[0020] S7. Obtain the phase matrix according to the design. Substitute the number of steps N selected in the design into the formula. Obtain the specific step order matrix of the stepped pixel block within a single period. ;

[0021] S8. Calculate the height matrix of the stepped pixel block in a single phase region. The formula is as follows:

[0022] ;

[0023] In the formula, λ is the center wavelength or peak wavelength of the light source used. It is a multiple of the step height, used to suppress dispersion caused by light of non-central wavelengths.

[0024] On the other hand, the present invention also provides a method for preparing an anti-counterfeiting optical element, characterized by comprising the following steps:

[0025] (1) Design processing drawings according to the positional requirements of steps at different depths;

[0026] (2) Using techniques such as electron beam direct writing, laser direct writing, and photolithography, the design drawing files are imported and the designed step shape is made on silicon-based material as a template. The step shape is opposite to the convex and concave direction of the designed step.

[0027] (3) Spray a layer of photosensitive embossing material onto the flat substrate to transfer the pattern of the template;

[0028] (4) The prepared template is brought into contact with the surface coated with the imprinting material, and a certain pressure is applied to transfer the template pattern onto the imprinting material and then cured under ultraviolet light.

[0029] (5) After curing, peel off the template to obtain the anti-counterfeiting optical element.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. This invention uses a random initial phase design, resulting in a large number of designed phases that are difficult to replicate and have good anti-counterfeiting properties.

[0032] 2. It can be directly fabricated using nanoimprint technology without the need for other complex semiconductor processes, resulting in low cost and easy mass production.

[0033] 3. Due to the special multiplication design in the design, no special light source is required to work. The anti-counterfeiting pattern can be clearly observed by simply using common light sources such as mobile phone flashlights or fluorescent lights.

[0034] 4. It has low requirements for flat substrate materials and can be directly applied to the surface of items such as mobile phone cases and outer packaging.

[0035] 5. It does not require complex processes such as thin film deposition and reactive etching, and has the advantages of low cost, fewer types of materials used, and simple process steps.

[0036] 6. Compared to metasurface holographic anti-counterfeiting elements, this anti-counterfeiting optical element, through special phase height adjustment, can reproduce anti-counterfeiting patterns under natural light illumination, and the image reproduction has high clarity and good dispersion suppression effect. Furthermore, this anti-counterfeiting optical element can be directly fabricated on the surface of the item, with low substrate requirements and convenient manufacturing. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the operation of the anti-counterfeiting optical element of the present invention;

[0038] Figure 2 The single-cycle phase distribution and local phase grayscale image of the anti-counterfeiting optical element are designed for Example 1.

[0039] Figure 3 This is a schematic diagram of partial parameters of the optical anti-counterfeiting layer in Example 1, where the side length of the step pixel is P and the height is h.

[0040] Figure 4 This is a scanning electron microscope image of the stepped structure of the optical anti-counterfeiting layer in Example 1.

[0041] Figure 5 The image reproduction result of Example 1 without high dispersion suppression is shown.

[0042] Figure 6 The image reproduction result of Example 1 after high dispersion suppression is shown.

[0043] In the diagram: 1. Light source; 2. Planar substrate; 3. Surface optical anti-counterfeiting layer; 4. Virtual image pattern under reflection conditions of anti-counterfeiting optical elements; 5. Position of human eye. Detailed Implementation

[0044] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] Please see Figure 1 As shown, the anti-counterfeiting optical element of this invention consists of a planar substrate and a surface optical anti-counterfeiting layer. The planar substrate is made of ordinary plastic, and the UV photoresist used in the surface optical anti-counterfeiting layer is MR-UVCur21. The surface optical anti-counterfeiting layer is composed of periodically distributed phase regions. Each phase region consists of multiple closely arranged stepped pixel blocks of different heights with the same square base, allowing the surface optical anti-counterfeiting layer to form an anti-counterfeiting pattern under visible light irradiation. Figure 2 The phase grayscale image of a single phase region in the surface optical anti-counterfeiting layer of Example 1 shows that the number of step pixel blocks within the phase region is 2001×2001, the sampling interval of each step pixel block is 1µm×1µm, and the period is 2cm×2cm. There are four height types for the step pixel blocks, represented by four grayscale levels. Based on the calculation method for the height of the step pixel blocks in a single phase region, the designed phase uniformity is U=78.4%, and the efficiency is η=66.5%.

[0047] Figure 3 This is a partial 3D schematic diagram of the anti-counterfeiting layer of the designed anti-counterfeiting optical element. The bottom side length P of the stepped pixel block is 1µm. Based on the working wavelength of visible light of 550nm, the four heights H of the stepped pixel in this example are 0nm, 350nm, 700nm, and 1050nm, respectively. Each step height corresponds one-to-one with the height matrix of the stepped pixel block in a single phase region.

[0048] Figure 4 The image shows a SEM microscope image of the designed anti-counterfeiting optical element. The processing parameters of the stepped pixel blocks in the anti-counterfeiting layer of the optical element are consistent with the design, and the pixel block structure is clear and the morphology is good, which can meet the requirements.

[0049] Figure 5 The theoretical imaging effect of anti-counterfeiting optical elements without step dispersion suppression under the illumination of a mobile phone flash is shown. Different colors of light will form patterns of different sizes, and the patterns will overlap and invert each other, resulting in reduced image clarity.

[0050] Figure 6 This image shows the anti-counterfeiting optical element designed to withstand illumination from a mobile phone flash. The visible light from the flash is reflected off the element, creating an observable anti-counterfeiting image on its surface. The image was taken using a camera, rather than the human eye, at the same viewing position. The anti-counterfeiting pattern is clearly visible, and chromatic aberration is well suppressed.

[0051] It should be noted that the distance between the observer and the light source and the anti-counterfeiting optical element does not affect the clarity of the anti-counterfeiting pattern, but only the size of the anti-counterfeiting pattern. The closer the light source is, the smaller the pattern is, and the farther the human eye is, the smaller the pattern is.

[0052] The template obtained by this invention is reusable and can be mass-produced through a simple process of gluing, imprinting, curing, and demolding. The process is simple, uses only a single material, and is inexpensive. Furthermore, the template is unique and cannot be copied, therefore it can be used for anti-counterfeiting measures in consumer products.

Claims

1. An anti-counterfeiting optical element, comprising a planar substrate, characterized in that, It also includes a surface optical anti-counterfeiting layer located on the planar substrate; the surface optical anti-counterfeiting layer is composed of periodically distributed phase regions, each phase region is composed of multiple closely arranged stepped pixel blocks of different heights and with the same square bottom surface, so that the surface optical anti-counterfeiting layer forms an anti-counterfeiting pattern under visible light irradiation. The height of the stepped pixel block in the phase region is calculated as follows: S1. Generate a phase matrix with the same number of pixel blocks using random numbers. The modulated reflective surface light field matrix is ​​obtained. ; S2. Optical field matrix of the reflecting surface The phase is quantized in N steps, so that continuous phases are quantized according to the interval. Resampling; S3. Perform a Fourier transform on the phase-quantized light field to obtain the light field matrix of the imaging surface. ; S4. Calculate the light field matrix of the imaging surface. Argument matrix and amplitude matrix And calculate the light intensity of the imaging surface. Uniformity U and efficiency η; S5. The complex amplitude matrix of the imaging plane After replacing the amplitude with the anti-counterfeiting pattern matrix P, the inverse Fourier transform is performed to obtain the light field matrix of the reflecting surface. and will The amplitude is replaced using a plane wave matrix; S6. Repeat steps S2-S5 until the uniformity U and efficiency η meet the design requirements, and obtain the N-step quantized phase matrix. ; S7. Obtain the phase matrix according to the design. Substitute the number of steps N selected in the design into the formula. Obtain the specific step order matrix of the stepped pixel block within a single period. ; S8. Calculate the step height matrix within a single cycle. The formula is as follows: ； In the formula, λ is the center wavelength or peak wavelength of the light source used. It is a multiple of the step height, used to suppress dispersion caused by light of non-central wavelengths.

2. The anti-counterfeiting optical element according to claim 1, characterized in that, The height of the stepped pixel block is a power of 2.

3. The anti-counterfeiting optical element according to claim 1 or 2, characterized in that, The bottom side length of the stepped pixel block is 1um-10um, and the height is less than 2um.

4. The anti-counterfeiting optical element according to claim 1 or 2, characterized in that, Each phase region is between 0.5cm×0.5cm and 10cm×10cm in size and consists of 1000×1000 to 5000×5000 stepped pixel blocks.

5. The anti-counterfeiting optical element according to claim 1 or 2, characterized in that, The planar substrate is a plastic film or glass.

6. The anti-counterfeiting optical element according to claim 1 or 2, characterized in that, The anti-counterfeiting pattern is three-dimensional or two-dimensional, and the light source is a monochromatic laser or a visible light source.

7. A method for manufacturing an anti-counterfeiting optical element as described in any one of claims 1-6, characterized in that, Includes the following steps: Design and fabrication drawings based on the location requirements of steps at different depths; Using techniques such as electron beam direct writing, laser direct writing, and photolithography, the design drawing file is imported and the designed step shape is fabricated on silicon-based material as a template. The step shape has the opposite convex and concave direction to the designed step. A layer of photosensitive embossing material is sprayed onto a flat substrate to transfer the pattern of the template; The prepared template is brought into contact with the surface coated with the imprinting material, and a certain pressure is applied to transfer the template pattern onto the imprinting material, which is then cured under ultraviolet light. After curing, the template is peeled off to obtain the anti-counterfeiting optical element.

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