Safety device and method of producing the same

Abstract

A safety device includes at least a first imprinted reflective metal diffraction grating and a second imprinted reflective metal diffraction grating in corresponding regions: wherein, in incident white light, the first diffraction grating exhibits zero-order output in a first region with a substantially uniform grating period, wherein the zero-order output of the first diffraction grating includes different colored first and second sub-outputs parallel and perpendicular to corresponding first and second polarizations of the first diffraction grating; wherein, in incident white light, the second diffraction grating exhibits zero-order output in a second region with a substantially uniform grating period; wherein the zero-order output of the second diffraction grating includes a third and fourth sub-output parallel and perpendicular to corresponding first and second polarizations of the second diffraction grating; wherein the third sub-output differs from the first sub-output, and / or the fourth sub-output differs from the second sub-output; and wherein, for incident white light, the first diffraction grating and the second diffraction grating exhibit substantially the same first-order diffraction efficiency in the first and second regions.

Description

Technical Field

[0001] The present invention relates to a security device for verifying the origin and / or integrity of an object or document, the device being formed as part of the object or document, or the device being applied to the object or document. Background Technology

[0002] Diffraction gratings can be used in security devices to enhance their resistance to duplication. A diffraction grating exhibits at least first-order diffraction output, characterized by colors that change with the viewing angle.

[0003] The safety device further enhances the effect by configuring a diffraction grating, which produces a zero-order output. This zero-order output is significantly different when viewed through different polarization filters, serving as an auxiliary covert diffraction feature that supports the main dominant diffraction features. This is the visible image created by the first-order diffraction output of the diffraction grating. Summary of the Invention

[0004] A safety device comprising at least a first imprinted reflective metal diffraction grating and a second imprinted reflective metal diffraction grating in corresponding regions: wherein, under incident white light, the first diffraction grating exhibits zero-order output in a first region with a substantially uniform grating period, wherein the zero-order output of the first diffraction grating includes different colored first and second sub-outputs parallel and perpendicular to the corresponding first and second polarizations of the first diffraction grating; wherein, under incident white light, the second diffraction grating exhibits zero-order output in a second region with a substantially uniform grating period; wherein the zero-order output of the second diffraction grating includes a third and fourth sub-output parallel and perpendicular to the corresponding first and second polarizations of the second diffraction grating; wherein the third sub-output differs from the first sub-output, and / or the fourth sub-output differs from the second sub-output; and wherein, for incident white light, the first diffraction grating and the second diffraction grating exhibit substantially the same first-order diffraction efficiency in the first and second regions.

[0005] The sum of the first sub-output and the second sub-output can be a colored zero-order output.

[0006] The first and second sub-outputs can differ in terms of the order of their respective output intensities at wavelengths of 420 nm, 530 nm, and 560 nm.

[0007] One of the two sub-outputs can exhibit an output intensity ratio greater than 1.3 between the output intensities at two wavelengths of 420 nm, 530 nm, and 560 nm, and the other of the two sub-outputs can exhibit an output intensity ratio less than 0.8 between the output intensities at the two wavelengths of 420 nm, 530 nm, and 560 nm.

[0008] The first sub-output exhibits an intensity difference of more than 40 points between the output intensities at the two wavelengths of 420 nm, 530 nm, and 560 nm on a 0-255 scale, and the second sub-output also exhibits an intensity difference of more than 40 points between the output intensities at the two wavelengths of 420 nm, 530 nm, and 560 nm on a 0-255 scale.

[0009] The output intensity at the two wavelengths of 420 nm, 530 nm and 560 nm can exhibit a relative oscillation of at least 100 points between the first sub-output and the second sub-output on a 0-255 intensity scale.

[0010] The zero-order output of the second diffraction grating may include different colored third and fourth sub-outputs with corresponding first and second polarizations parallel and perpendicular to the second diffraction grating, respectively; the color of the third sub-output may be different from the color of the first sub-output; and the color of the fourth sub-output may be different from the color of the second sub-output.

[0011] The sum of the third and fourth sub-outputs can have a different color than the sum of the first and second sub-outputs.

[0012] The zero-order output of the first and second diffraction gratings can be different in terms of the order of output intensity at wavelengths of 420 nm, 530 nm, and 560 nm.

[0013] The grating period of the first diffraction grating can be different from that of the second diffraction grating.

[0014] The first diffraction grating may have a substantially uniform aspect ratio in the first region, and the second diffraction grating may have a substantially uniform aspect ratio in the second region, and the first diffraction grating and the second diffraction grating may have the same aspect ratio.

[0015] The safety device may also include a third diffraction grating, wherein, for the corresponding first and second polarizations parallel and perpendicular to the third diffraction grating, in incident white light, the third diffraction grating may present diffraction output and zero-order output in a third region of a substantially uniform grating period, while there is essentially no difference between the fifth and sixth sub-outputs.

[0016] The third diffraction grating exhibits a first-order diffraction efficiency for incident white light in the third region, which is essentially the same as the first-order diffraction efficiency for incident white light in the first and second regions.

[0017] A safety device includes at least a first imprinted reflective metal diffraction grating and a second imprinted reflective metal diffraction grating in corresponding regions; wherein, in incident white light, the first diffraction grating exhibits zero-order output in a first region with a substantially uniform grating period, wherein the zero-order output of the first diffraction grating includes different colored first sub-outputs and second sub-outputs with corresponding first and second polarizations parallel and perpendicular to the first diffraction grating; wherein, in incident white light, the second diffraction grating exhibits zero-order output in a second region with a substantially uniform grating period; wherein the zero-order output of the second diffraction grating includes different colored third and fourth sub-outputs with corresponding first and second polarizations parallel and perpendicular to the second diffraction grating; and wherein the color of the third sub-output is different from the color of the first sub-output; and wherein the color of the fourth sub-output is different from the color of the second sub-output; and wherein the first diffraction grating has a substantially uniform aspect ratio in the first region, and the second diffraction grating has a substantially uniform aspect ratio in the second region, and wherein the first diffraction grating and the second diffraction grating have the same aspect ratio.

[0018] A method for manufacturing a safety device includes: forming at least a first reflective metal diffraction grating and a second reflective metal diffraction grating in corresponding regions through a manufacturing process, the manufacturing process including imprinting one or more grating profiles into a substrate; wherein, in incident white light, the first diffraction grating exhibits zero-order output in a first region with a substantially uniform grating period; wherein the zero-order output of the first diffraction grating includes different colored first and second sub-outputs parallel and perpendicular to corresponding first and second polarizations of the first diffraction grating; wherein, in incident white light, the second diffraction grating exhibits zero-order output in a second region with a substantially uniform grating period; wherein the zero-order output of the second diffraction grating includes a third and fourth sub-output parallel and perpendicular to corresponding first and second polarizations of the second diffraction grating; and wherein the third sub-output differs from the first sub-output, and / or the fourth sub-output differs from the second sub-output; and wherein, in incident white light, the first diffraction grating and the second diffraction grating exhibit substantially the same first-order diffraction efficiency in the first and second regions.

[0019] A method for producing a safety device, the safety device comprising at least a first reflective metal diffraction grating and a second reflective metal diffraction grating in a corresponding region; wherein the method comprises: selecting a set of grating parameters for both the first grating and the second grating, the set of grating parameters achieving substantially the same first-order diffraction efficiency for visible light over a grating period range; and selecting the grating period of the first diffraction grating and the second diffraction grating from the grating period range, taking into account at least the correlation between the overall diffraction efficiency of visible light and the grating period.

[0020] The kit includes the aforementioned safety device and at least one polarizing filter.

[0021] The kit may also include an observer device comprising orthogonal polarizing filters fixed side-by-side.

[0022] The method for testing the authenticity of the above-mentioned safety device includes: observing the safety device sequentially through an orthogonal polarization filter. Attached Figure Description

[0023] Figure 1 The representations of the zero-order and first-order diffraction outputs of the diffraction grating are shown;

[0024] Figure 2 A representation of the zero-order output of two diffraction gratings of a safety device according to an exemplary embodiment is shown;

[0025] Figure 3 The illustration shows a representation of three diffraction gratings with different grating periods and the same aspect ratio in a security device according to an exemplary embodiment;

[0026] Figure 4 The illustration shows representations of some components of a safety device according to an exemplary embodiment;

[0027] Figure 5 and Figure 6 A representation of the manufacturing process of a safety device according to an exemplary embodiment is shown; and

[0028] Figure 7 This illustrates the relationship between the zero-order output intensity of a polarization and the grating period in a production safety device according to an exemplary embodiment.

[0029] Figure 8 An example representation of an alternative stepped shape / contour of a grating according to an exemplary embodiment is shown;

[0030] Figure 9 A representation of another alternative stepped shape / contour example of a grating according to an exemplary embodiment is shown;

[0031] Figure 10 It shows in Figure 8 and Figure 9 In the stepped shape / profile shown, how does the first-order diffraction efficiency change with the number of steps N? Detailed Implementation

[0032] For ease of explanation, the following description is only an example of a security device that defines two diffraction gratings with different grating periods (grating constants), but the technique is equally applicable to the production of security devices that define more diffraction gratings, each with a different grating period. According to some embodiments of the invention, a security device may define diffraction gratings with the same grating period in different regions separated by one or more regions that do not define any diffraction gratings, and / or define one or more diffraction gratings with different grating periods. Multiple diffraction gratings may be arranged into a pattern representing icons or markings familiar to the observer, such as icons or markings associated with the products or documents for which the security device provides certification.

[0033] Figure 1 The diagram shows the representation of the zero-order and 1st-order diffraction outputs of a diffraction grating in response to incident light. In addition to the 1st-order diffraction output, the diffraction grating can also exhibit 2nd-order and higher-order diffraction outputs.

[0034] Figure 2 A representation of a safety device 1 according to an embodiment of the present invention is shown. The safety device 1 defines two reflective metallic diffraction gratings in two corresponding distinct regions 1A and 1B. The two diffraction gratings each present a corresponding single grating period over the entire area of ​​the respective regions 1A and 1B. The grating period of one of the two diffraction gratings differs from that of the other diffraction grating. In this example, one diffraction grating has a period of 500 nanometers, and the other has a period of 600 nanometers. In other embodiments, the safety device may optionally or additionally include diffraction gratings having other periods of less than about 1 micrometer, such as, for example, diffraction gratings having periods in the range of about 300 nanometers to 1100 nanometers, more specifically about 300 nanometers to 750 nanometers.

[0035] The two diffraction gratings are designed to exhibit substantially the same non-zero first-order diffraction efficiency for the same incident light in the visible spectrum, thereby providing a clear first-order visible diffraction image (composed of the first-order diffraction outputs of the gratings) whose color varies with the viewing angle.

[0036] Figure 2 The zero-order output of two diffraction gratings in response to incident white light is shown. The zero-order output is shown as the relative intensity of the output intensity on a linear 0-255 scale at short (S), medium (M), and long (L) wavelengths of 420 nm, 530 nm, and 560 nm. These three wavelengths are the peak absorption wavelengths of three different types of cone cells in the human eye. Figure 2The following are shown: (a) the zero-order output of the diffraction grating when viewed through a 90-degree polarizer (S-polarization filter) that selectively transmits light polarized at 90 degrees to the direction of the grating fringes; (b) the zero-order output of the diffraction grating when viewed through a 0-degree polarizer (P-polarization filter) that selectively transmits light polarized at 0 degrees to the direction of the grating fringes; and (c) the sum of (a) and (b), as observed by an observer without any intermediate polarizer (polarization filter).

[0037] For each diffraction grating, the grating parameters are chosen such that there is a clear contrast between the zero-order outputs of different polarizations. For each of the two diffraction gratings, the zero-order color observed by an observer through the polarization filter is significantly different between the S and P polarization filters. There are variations in the order of output intensity at the L, M, and S wavelengths between the two zero-order sub-outputs (P sub-output and S sub-output). For diffraction grating 1A, the order of output intensity (from highest to lowest) is LMS for S polarization and SML for P polarization. For diffraction grating 1B, the order of output intensity (from highest to lowest) is LSM for S polarization and LMS for P polarization.

[0038] The significant swing in relative intensity between the output intensities at at least two of the three LMS wavelengths enhances the striking contrast between the two polarizations. For diffraction grating 1A, the intensity ratio between the output intensities at the L and S wavelengths is approximately 2.2 (203 / 93) for S polarization and approximately 0.6 (133 / 215) for P polarization; and the variation in the intensity ratio between the two polarizations is approximately 1.6. For diffraction grating 1B, the intensity ratio between the output intensities at the M and S wavelengths is approximately 0.7 (114 / 157) for S polarization and approximately 1.7 (192 / 112) for P polarization; and the variation in the intensity ratio is approximately 1.0. The greater variation in the intensity ratio between the output intensities at two of the three LMS wavelengths provides a more significant color contrast between the two polarizations.

[0039] The significant variation in output intensity at least two of the three LMS wavelengths between two polarizations can be represented in terms of points on a linear 0-255 scale. For diffraction grating 1A, for S-polarization, the output intensity at the L wavelength is 110 points greater than that at the S wavelength, but for P-polarization, the output intensity at the L wavelength is 82 points less than that at the S wavelength. This is the overall swing of the output intensity at the L and S wavelengths over the two polarizations, which is 82 + 110 = 192 points. Similarly, for diffraction grating 1B, for S-polarization, the output intensity at the M wavelength is 43 points less than that at the S wavelength, but for P-polarization, the output intensity at the M wavelength is 80 points greater than that at the S wavelength. This is the overall swing of the output intensity at the M and S wavelengths over the two polarizations, which is 43 + 80 = 123 points. This greater variation in the overall swing of the output intensity at least two of the three LMS wavelengths between two polarizations can provide a more significant color contrast between the two polarizations.

[0040] If, for each S and P polarization, the order of the output intensity at the LMS wavelength is different between the zero-order outputs of the first and second diffraction gratings, the perception of color changes between the two polarizations is enhanced. When observed through an S polarizer, the intensity levels (from high to low) of diffraction grating 1A are LMS, and the intensity levels (from high to low) of diffraction grating 1B are LSM. Similarly, when observed through a P polarizer, the intensity levels (from high to low) of diffraction grating 1A are SML, and the intensity levels (from high to low) of diffraction grating 1B are LMS.

[0041] According to an exemplary embodiment, the two diffraction gratings 1A and 1B have the same aspect ratio, and the aspect ratio is uniform over the entire region of each diffraction grating 1A and 1B. (Reference) Figure 3 The aspect ratio is defined as the ratio of the stripe width W to the depth D. The stripe width W is equal to half the period P; therefore, the aspect ratio is also defined as the ratio of half a period (P / 2) to the depth D. Figure 3 The diagram illustrates the use of two or more diffraction gratings with correspondingly different grating periods P but the same aspect ratio, as an example of three diffraction gratings with different grating periods. Figure 3 In the example shown, the aspect ratio of all three diffraction gratings is approximately 1. The magnitude of the aspect ratio can be confirmed in the final security device using atomic force microscopy (AFM) or scanning electron microscopy (SEM).

[0042] According to one exemplary embodiment, the security device additionally includes at least one area (such as...) Figure 2At least one diffraction grating (enclosing the boundaries of two diffraction grating regions 1A and 1B) exhibits first-order and higher-order diffraction outputs, but its zero-order output is substantially uncorrelated with polarization. The order of the output intensity at the LMS wavelength is the same for both S-polarization and P-polarization, and / or the intensity at the LMS wavelength does not substantially change between S-polarization and P-polarization. Including one or more such diffraction gratings can further enhance the anti-copying capability of the security device.

[0043] Safety device 1 may form part of the product or documentation for which it is certified. Alternatively, the safety device may be manufactured as a label for post-manufacturing application on the product or documentation. Figure 4 An example of such a label is shown. At the heart of the label is a substrate 18 having an upper metallized surface that defines one or more diffraction gratings of the type described above. This upper surface is coated with a polymer material to define a transparent outer coating 4. An adhesive 6 is disposed on the reverse (underside) of the substrate 18, and a peelable release liner 8 protects the underside of the adhesive 6.

[0044] Figure 5 and Figure 6 The illustration shows a method according to an exemplary embodiment, which, after selecting the grating parameters of the diffraction grating, produces a safety device defining two diffraction gratings as described above.

[0045] According to this exemplary embodiment, the technique for selecting grating parameters to achieve the desired effect includes: (i) determining a set of grating parameters (such as aspect ratio, etc.) that produce substantially the same first-order diffraction efficiency for the same incident light in the visible spectrum, but producing a significant overall diffraction efficiency difference between P-polarization and S-polarization (for light in the visible spectrum) in a grating period range of less than 1 micrometer, such as, for example, about 300 nm to 750 nm; and (ii) for this set of grating parameters, plotting a graph of the zero-order output intensity versus grating period for each of the L, M, and S wavelengths of the aforementioned white light in both P and S polarizations; and (iii) selecting one or more corresponding grating periods for one or more corresponding diffraction gratings of the security device that produce a significant zero-order color contrast between S and P polarizations. The selection of grating constants can be achieved by incorporating these graphs into physical optics design software, such as virtual lab fusion software available from LightTrans GmbH, to generate a virtual representation of the zero-order sub-output without having to produce a physical prototype.

[0046] Figure 7Examples of graphs showing the zero-order output intensity versus grating period for S-polarization (polarization where the electric field vector is perpendicular to the direction of the grating groove extension) at each of the L, M, and S wavelengths of the aforementioned white light are shown. For P-polarization (polarization where the electric field vector is parallel to the direction of the grating groove extension), the zero-order output intensity has a smaller correlation with the grating period and fluctuates much less than that of S-polarization.

[0047] The intensity of the zeroth-order output of a wavelength in the visible spectrum represents the overall diffraction efficiency of the grating at that wavelength in the visible spectrum. The zeroth-order output color of incident white light observed by an observer is a stable subtractive color. When a grating in white light is observed through a polarizer, the observed zeroth-order color is the total incident visible light of that polarization minus the portion of incident visible light that forms the first-order and higher-order diffraction outputs.

[0048] According to this exemplary embodiment, achieving substantially identical first-order diffraction efficiencies for two or more diffraction gratings involves using the same aspect ratio (e.g., about 1:1 or higher) for both diffraction gratings and the entire region across each grating (i.e., the entire region across each region of uniform grating period). The presence of polarization-dependent zero-order color effects is not apparent from the first-order diffraction outputs of the two gratings. In other words, designing the two gratings to have substantially identical first-order diffraction efficiencies for the visible spectrum conceals the presence of polarization-dependent zero-order color effects. The concealment of polarization-dependent zero-order color effects further enhances the security functionality of the security device. The polarization-dependent zero-order color effect becomes an evidentiary detail, only observable by sequentially observing the zero-order output through a pair of orthogonal polarization filters, or by observing the grating in polarized incident light (such as light emitted by a liquid crystal display (LCD) device). The aforementioned technique includes a prototyping step that seamlessly integrates secondary concealed diffraction features into the design of the diffraction grating for which a clear first-order diffraction pattern is a primary diffraction feature.

[0049] refer to Figure 5 The outlines of two diffraction gratings are created on the upper surface of an electron beam (e-beam) sensitive resist 10 (e.g., a positive resist) using an electron beam writing technique. This technique includes individual electron beam exposure of the resist elements and development of the resulting solubility pattern using a suitable developer. As described above, in this example, each diffraction grating is designed to have uniform parameters (grating period, etc.) over the entire corresponding area occupied by the diffraction grating.

[0050] A high-gaussian point electron beam is used to expose resist 10. Each fringe of each diffraction grating is divided into a two-dimensional grid of elements, each element having a size equal to that of a single electron beam exposure. The duration of exposure of each element to the electron beam is calculated based on (i) the desired fringe depth and (ii) a nonlinear relationship between the electron beam exposure time and the depth at which the electron beam reduces the positron beam resist solubility. The calculation of the exposure time for each element also includes proximity correction, which takes into account the proximity effect, by which the electron beam exposure of one element contributes some exposure to directly adjacent elements and, to a lesser extent, to more distant elements (according to a Monte Carlo distribution). The exposure time of the elements is calculated to compensate for this contribution, thereby obtaining the correct fringe depth.

[0051] In this example, the stripes and periodicity are configured to be precisely divided into integer numbers of grid elements. By avoiding overlapping areas in the exposed grid, this increases the accuracy of obtaining the profile in the resist, which could otherwise result in areas of varying depths. Some examples of the lateral dimensions of each grid element are 10 nm, 25 nm, and 50 nm.

[0052] When some or all of the diffraction gratings are blazed gratings or contour gratings, a technique for exposing electron beam resist according to an exemplary embodiment includes treating the volume of the positron beam resist to be removed as a series of horizontal layers to be exposed sequentially. This series of exposures, when added together, yields the desired fringe profile. The technique includes calculating proximity correction by calculating a Monte Carlo distribution of cumulative exposures of varying intensities. One advantage of this incremental exposure technique is that any single error has only a small effect on the cumulative exposures required to give a precise depth, and it can self-correct in the case of multiple exposures.

[0053] The upper surface is electroplated to form a metal (e.g., nickel) layer 12 on the upper surface of the patterned resist, and then the nickel layer 12 is stripped from the resist 10. The nickel replicas 12 of the resist 10 are then used to manufacture intermediate masters, and these intermediate masters are used to generate one or more imprinting pads 16.

[0054] refer to Figure 6 The embossed pad 16 is mechanically pressed into the surface of the substrate 18 (such as a plastic or paper substrate) to replicate the outlines defining the diffraction gratings 1A and 1B on the surface of the substrate 18. A thin metal (e.g., aluminum) layer 20 is formed in situ on the embossed surface of the substrate 18 by a vapor deposition process.

[0055] The above detailed description uses a grating example with a square wave profile, but the grating can have other profile shapes. For a grating profile where the fringe depth varies along the fringe width, the aspect ratio is defined as the ratio of the fringe width to the maximum fringe depth; as mentioned above, in the example above, the aspect ratio is approximately 1 or higher. Figure 8 and Figure 9 An example of an optional stepped profile for a grating is shown.

[0056] For a stepped-phase grating, the Fourier series coefficients of the grating are given by the following equation, where d, N, and M are... Figure 9 The parameters are shown.

[0057]

[0058] From this formula, the following coefficients can be derived:

[0059]

[0060] The relative efficiency of each diffraction order can be expressed as:

[0061]

[0062] Figure 10 This illustrates how the first-order diffraction efficiency depends on the phase quantization level (N). In this example, the first-order diffraction efficiency is approximately 40% for N=2 (binary phase grating), approximately 68% for N=3, and reaches over 91% for N=6 and higher.

[0063] Apart from any modifications explicitly mentioned above, it will be apparent to those skilled in the art that various other modifications can be made to the described embodiments within the scope of this invention.

[0064] It should be noted that each individual feature, and any combination of two or more such features, is described separately herein. To a certain extent, such features or combinations can be implemented based on the present specification as a whole, according to common general knowledge of those skilled in the art, regardless of whether such features or combinations solve any problem disclosed herein, and without limiting the scope of the claims. It should also be noted that aspects of the invention can consist of any such individual features or combinations of features.

Claims

1. A safety device, comprising: A first diffraction grating and a second diffraction grating, wherein the first diffraction grating and the second diffraction grating are imprinted reflective metal diffraction gratings in corresponding areas of the security device: In the incident white light, the first diffraction grating presents a zero-order output in a first region of a substantially uniform grating period, wherein the zero-order output of the first diffraction grating includes different colored first sub-outputs and second sub-outputs that are parallel to and perpendicular to the corresponding first polarization and second polarization of the first diffraction grating. In the incident white light, the second diffraction grating exhibits a zero-order output in a second region with a substantially uniform grating period; wherein the zero-order output of the second diffraction grating includes a third sub-output and a fourth sub-output parallel to and perpendicular to the corresponding first and second polarizations of the second diffraction grating; wherein the third sub-output differs from the first sub-output, and / or the fourth sub-output differs from the second sub-output; and For incident white light, the first diffraction grating and the second diffraction grating exhibit substantially the same first-order diffraction efficiency in the first region and the second region, thereby providing a first-order visible diffraction image.

2. The safety device according to claim 1, wherein, The sum of the first sub-output and the second sub-output is a colored zero-order output.

3. The safety device according to claim 1, wherein, The first sub-output and the second sub-output are different in terms of the order of their respective output intensities at wavelengths of 420 nm, 530 nm and 560 nm.

4. The safety device according to claim 3, wherein, One of the first sub-outputs and the second sub-output exhibits an output intensity ratio greater than 1.3 between the output intensities at two wavelengths of 420 nm, 530 nm, and 560 nm, and the other of the two sub-outputs exhibits an output intensity ratio less than 0.8 between the output intensities at the two wavelengths of 420 nm, 530 nm, and 560 nm.

5. The safety device according to claim 4, wherein, The first sub-output exhibits an intensity difference of more than 40 points between the output intensities at the two wavelengths of 420 nm, 530 nm, and 560 nm on a 0-255 scale, and the second sub-output also exhibits an intensity difference of more than 40 points between the output intensities at the two wavelengths of 420 nm, 530 nm, and 560 nm on a 0-255 scale.

6. The safety device according to claim 5, wherein, The output intensity at the two wavelengths of 420 nm, 530 nm and 560 nm exhibits a relative oscillation of at least 100 points between the first sub-output and the second sub-output on a 0-255 intensity scale.

7. The safety device according to claim 1, wherein, The zero-order output of the second diffraction grating includes a different colored third sub-output and a fourth sub-output, which are parallel to and perpendicular to the corresponding first and second polarizations of the second diffraction grating; and wherein the color of the third sub-output is different from the color of the first sub-output; and wherein the color of the fourth sub-output is different from the color of the second sub-output.

8. The safety device according to claim 7, wherein, The sum of the third sub-output and the fourth sub-output has a different color than the sum of the first sub-output and the second sub-output.

9. The safety device according to claim 7 or 8, wherein, The zero-order outputs of the first and second diffraction gratings are different in terms of the order of output intensity at wavelengths of 420 nm, 530 nm, and 560 nm.

10. The safety device according to claim 1, wherein, The grating period of the first diffraction grating is different from the grating period of the second diffraction grating.

11. The safety device according to claim 1, wherein, The first diffraction grating has a substantially uniform aspect ratio in the first region, and the second diffraction grating has a substantially uniform aspect ratio in the second region, wherein the first diffraction grating and the second diffraction grating have the same aspect ratio.

12. The safety device according to claim 1, further comprising a third diffraction grating, wherein, For the corresponding first and second polarizations parallel and perpendicular to the third diffraction grating, in incident white light, the third diffraction grating exhibits diffraction output and zero-order output in a third region of a substantially uniform grating period, while there is essentially no difference between the fifth and sixth sub-outputs.

13. The safety device according to claim 12, wherein, The third diffraction grating exhibits a first-order diffraction efficiency for incident white light in the third region, which is substantially the same as the first-order diffraction efficiency for incident white light in the first and second regions.

14. A safety device, comprising: A first diffraction grating and a second diffraction grating, wherein the first diffraction grating and the second diffraction grating are imprinted reflective metal diffraction gratings in corresponding areas of the safety device; In the incident white light, the first diffraction grating presents a zero-order output in a first region of a substantially uniform grating period, wherein the zero-order output of the first diffraction grating includes different colored first sub-outputs and second sub-outputs that are parallel to and perpendicular to the corresponding first polarization and second polarization of the first diffraction grating. In the incident white light, the second diffraction grating exhibits a zero-order output in a second region with a substantially uniform grating period; wherein the zero-order output of the second diffraction grating includes different colored third and fourth sub-outputs with corresponding first and second polarizations parallel and perpendicular to the second diffraction grating, respectively; and wherein the color of the third sub-output is different from the color of the first sub-output; and wherein the color of the fourth sub-output is different from the color of the second output; and The first diffraction grating has a substantially uniform aspect ratio in the first region, and the second diffraction grating has a substantially uniform aspect ratio in the second region, wherein the first diffraction grating and the second diffraction grating have the same aspect ratio, thereby providing a first-order visible diffraction image.

15. A method for producing a safety device, comprising: A first diffraction grating and a second diffraction grating are formed, wherein the first diffraction grating and the second diffraction grating are reflective metal diffraction gratings formed in corresponding areas of the safety device by a manufacturing process, the manufacturing process including imprinting one or more grating profiles into a substrate; In the incident white light, the first diffraction grating exhibits a zero-order output in a first region of a substantially uniform grating period; wherein the zero-order output of the first diffraction grating includes different colored first sub-outputs and second sub-outputs that are parallel to and perpendicular to the corresponding first polarization and second polarization of the first diffraction grating. In the incident white light, the second diffraction grating exhibits a zero-order output in a second region with a substantially uniform grating period; wherein the zero-order output of the second diffraction grating includes a third sub-output and a fourth sub-output parallel to and perpendicular to the corresponding first and second polarizations of the second diffraction grating; and wherein the third sub-output differs from the first sub-output, and / or the fourth sub-output differs from the second sub-output; and In the incident white light, the first diffraction grating and the second diffraction grating exhibit substantially the same first-order diffraction efficiency in the first region and the second region, thereby providing a first-order visible diffraction image.

16. A method for manufacturing a safety device, the safety device comprising a first diffraction grating and a second diffraction grating, wherein, The first diffraction grating and the second diffraction grating are reflective metal diffraction gratings in corresponding regions of the safety device; wherein, the method includes: A set of grating parameters is selected for both the first and second diffraction gratings. This set of grating parameters achieves essentially the same first-order diffraction efficiency for visible light over the grating period range, thereby providing a first-order visible diffraction image; and The grating periods of the first and second diffraction gratings are selected from the range of grating periods by taking into account at least the correlation between the overall diffraction efficiency of visible light and the grating period.

17. A kit comprising a safety device according to any one of claims 1 to 14, and at least one polarizing filter.

18. The kit of claim 17, further comprising an observer device including orthogonal polarizing filters fixed side-by-side.

19. A method for testing the authenticity of a safety device according to any one of claims 1 to 14, comprising: The safety device is observed sequentially through an orthogonal polarization filter.

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