CN114637176A - Preparation method of Fresnel hologram reproduced by double-dissimilar-image incoherent light - Google Patents
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Abstract
The invention provides a preparation method of a Fresnel hologram reproduced by double-dissimilar incoherent light, which specifically comprises the following steps: firstly, respectively calculating interference holograms of two different object lights and off-axis obliquely incident parallel reference lights in a shorter Fresnel diffraction region; secondly, respectively calculating Fourier transform spectrograms of the two holograms; then, performing band-pass filtering processing on the first frequency spectrogram, reserving the frequency spectrum of the positive first-order diffraction reproduction image only, and performing band-pass filtering processing on the second frequency spectrogram, reserving the frequency spectrum of the negative first-order diffraction reproduction image only; and finally, adding the two filtered frequency spectrograms, and performing inverse Fourier transform calculation to obtain the double-different-image Fresnel hologram. The hologram can be reproduced by using an incoherent light source such as an LED lamp, the reproduced light is two different object images which are respectively positioned at the front side and the rear side of the hologram, and the hologram has obvious floating and sinking scene depth senses, clear imaging, novel and unique visual angle effect, easy identification and suitability for public anti-counterfeiting.
Description
Technical Field
The invention relates to the technical field of anti-counterfeiting, in particular to a preparation method of a Fresnel hologram reproduced by double-dissimilar incoherent light.
Background
With the continuous emergence of new anti-counterfeiting technologies in the world and the increasing demand of the public on anti-counterfeiting level of anti-counterfeiting products, the anti-counterfeiting technologies are continuously extending from the traditional static, single and two-dimensional plane visual effects to the dynamically-changing, three-dimensional and colorful effects.
The image reproduction technology is an effective two-line anti-counterfeiting means, and particularly, when a proper light source is irradiated on the surface of an anti-counterfeiting element, specific image-text information can be observed on a corresponding receiving screen; when the image-text information is directly observed, the image-text information cannot be observed. This image reproduction technique therefore requires certain conditions to be taken to be able to observe the hidden features.
The conventional image reproduction technology generally adopts a diffraction grating, namely, light is diffracted to +/-1 order position through diffraction of a surface micro-relief structure on incident light. The positions of diffraction light spots can be controlled by properly arranging the period and the direction of the diffraction grating, and then a plurality of light spots are combined into pictures and texts with specific meanings. However, due to the diffraction principle, there are ± 1 st order diffraction, and two symmetric patterns generally appear on the left and right of the specular reflection, so that the design of the graphic information is limited. Meanwhile, since the diffraction direction is strictly related to the frequency of the incident light, the light required for the reproduction technology is generally a laser. Whereas when white or daylight illumination is used, the definition of the reproduced pattern is very poor.
Because the white light source is easy to obtain, especially with the popularization of smart phones, the flash lamp is widely used as a white light illumination light source, and even various light sources such as sunlight, a flashlight, a projector light source and the like can be used for illumination of white light reproduction. How to realize clear and unique three-dimensional reproduction of images under the irradiation of white light (such as an LED lamp, an illumination spot lamp and the like on a mobile phone) is a problem to be solved urgently.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a preparation method of a Fresnel hologram reproduced by double-dissimilar-image incoherent light, the hologram can be reproduced by an incoherent light source such as an LED lamp, and the reproduced light is two different object images which are respectively positioned at the front side and the rear side of the hologram, so that the Fresnel hologram has obvious deep floating and sinking scenes, clear imaging, novel and unique visual angle effect, easy identification and suitability for public anti-counterfeiting.
In order to realize the technical scheme, the invention provides a method for preparing a Fresnel hologram reproduced by double-dissimilar incoherent light, which specifically comprises the following steps:
s1, respectively calculating interference holograms of two different object lights and off-axis obliquely incident parallel reference lights in a Fresnel diffraction region in a set range;
s2, respectively calculating Fourier transform spectrograms of the two holograms obtained in the step S1;
s3, performing band-pass filtering processing on the first frequency spectrogram, reserving the frequency spectrum of the positive first-order diffraction reproduction image only, and performing band-pass filtering processing on the second frequency spectrogram, reserving the frequency spectrum of the negative first-order diffraction reproduction image only;
and S4, adding the two filtered spectrograms, and performing inverse Fourier transform calculation to obtain the double dissimilar images Fresnel hologram.
Preferably, the specific calculation process in step S1 is as follows:
s11, drawing two object images Uo1And Uo2Wherein U iso1And Uo2The size range is 2 mm-12 mm;
s12, respectively calculating the Fresnel diffraction light field complex amplitude O of the two object images according to the Fresnel diffraction integral formula1、O2The calculation formulas are respectively as follows:
wherein z isoThe diffraction distance is expressed, and when the complex amplitude of the Fresnel diffraction light field is calculated, the diffraction distance between the object image and the interference hologram is set to be shorterThe Fresnel diffraction area is within the range of 10 mm-30 mm;
s13, setting the reference light R, wherein the expression is as follows:
wherein alpha is1、β1Respectively representing included angles of reference light with an x axis and a y axis, wherein the reference light is off-axis oblique incidence parallel light, and the included angle of the parallel reference light and object light ranges from 5 degrees to 20 degrees;
s14, superposing and summing the complex amplitude of the Fresnel diffraction light field of the object image and the complex amplitude of the oblique incidence parallel reference light, and then calculating the conjugate product of the sum to respectively obtain two high-quality interference holograms II1、II2The calculation process expression is as follows: II1＝(O1+R)(O1+R)*、II2＝(O2+R)(O2+R)*。
Preferably, the object images U of the two object lights in step S11o1、Uo2The size deviation is less than 30%.
Preferably, the object image is one or more of simple patterns, Chinese characters, English letters, characters and numbers with low spatial frequency and few strokes or lines.
Preferably, the object light and the reference light have the same wavelength and are laser wavelengths within a visible light wavelength range of 400nm to 760 nm.
Preferably, the fourier transform spectrograms IIFF of the two holograms in the step S21、IIFF2Calculated by the following formula:
preferably, the bandpass filtering processing procedure in step S3 is as follows:
s31, setting the part of the spectrogram with the normalized intensity larger than 90% to be completely transparent, and blocking the rest part;
s32, calculating to obtain two band-pass filters H1、H2Respectively expressed as:
S33、
the obtained frequency spectrums of the two filtered holograms are as follows: HFF1＝IIFF1·H1、HFF2＝IIFF2·H2。
Preferably, in the step S4, the two bandpassed spectrograms are added, and then inverse fourier transform calculation is performed to obtain the heterodyne fresnel hologram II3The calculation process expression is as follows:
preferably, before the superposition summation is performed on the object diffraction light field and the reference light field in step S14, normalization processing is performed, so that a maximum amplitude ratio of the object diffraction light field to the reference light field is 1: 1.
preferably, the resolution values of the two object images are greater than 10000 dpi.
The preparation method of the Fresnel hologram reproduced by the double-different-image incoherent light has the advantages that:
1) the Fresnel hologram prepared by the method can be reproduced by using incoherent light sources such as an LED lamp, an illumination spot lamp and the like, and the reproduced light is two different object images which are respectively positioned at the front side and the rear side of the hologram, so that the Fresnel hologram has obvious deep floating and sinking scenery senses, clear imaging, novel and unique visual angle effect, easy identification and suitability for public anti-counterfeiting;
2) the first frequency spectrogram is subjected to band-pass filtering, only the frequency spectrum of the positive first-order diffraction reproduced image is reserved, the second frequency spectrogram is subjected to band-pass filtering, only the frequency spectrum of the negative first-order diffraction reproduced image is reserved, only the positive first-order image and the negative first-order image are reserved during diffraction reproduction light, the adverse effects of a zero-order image, low-frequency stray light and the like on the imaging definition of the reproduced image are eliminated, the obtained reproduced image is clear, the obvious upward floating and downward sinking deep sense is realized, the visual angle effect is novel and unique, and eyeballs are attracted;
3) the Fresnel hologram manufactured by the method has the advantages that the diffraction distance is set to be within a shorter Fresnel diffraction area, the coherence requirement of the recorded Fresnel hologram on the reproduced light can be reduced, the incoherent light can also be reproduced, such as an LED lamp and an illumination spot lamp on a mobile phone, and the diffraction distance is shorter, so that the diffraction pattern of an object image is still clearer and the image outline can be distinguished.
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FIG. 1 is a flow chart of the present invention.
Fig. 2 is an interference recording optical path diagram, where firstly is incident object light, secondly is obliquely incident parallel reference light, thirdly is a first object image/second object image, and fourthly is a hologram for interference recording.
FIG. 3 is a diagram of a diffraction-reconstruction optical path, which includes incoherent reconstruction light, positive diffraction-reconstruction image, and negative diffraction-reconstruction image.
Fig. 4 is a first object image in the embodiment.
Fig. 5 is a second object image in the embodiment.
Fig. 6 is a fresnel diffraction light intensity distribution diagram of the first object image in the embodiment.
Fig. 7 is a fresnel diffraction intensity distribution diagram of the second object image in the embodiment.
Fig. 8 is a reproduced image of the first object light without being subjected to the filtering process in the embodiment.
Fig. 9 is a reproduced image of the second light without the filtering process in the embodiment.
Fig. 10 is a filtered bijection fresnel hologram according to an embodiment.
Fig. 11 is a reproduced image of a lenticular fresnel hologram in the embodiment.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by a person skilled in the art without making any inventive step are within the scope of the present invention.
Example (b): a preparation method of a Fresnel hologram reproduced by double-dissimilar incoherent light.
The design calculation of the off-axis fresnel hologram is performed with reference to the interference recording optical path of fig. 2, wherein the first is incident object light, the second is parallel reference light obliquely incident, the third is a first object image/second object image, and the fourth is a hologram recorded by interference.
The first step is to draw two object images, Uo1And Uo2. The size of the two object images is preferably in the range of 2 mm-12 mm; the size deviation is less than 30%, and preferably the two object images are equal in size; the object image is preferably a simple pattern, a Chinese character, an English letter, a character, a number and the like with low spatial frequency and few strokes or lines. In this embodiment, the first object image U is drawno1The second object image U is shown in FIG. 4 as the character "Poleo2The Chinese character "light" as shown in FIG. 5; both object images are equal in size and are set to 5 mm. The resolution of the two object images is preferably greater than 10000 dpi. In this embodiment, the pixels of both object images are 4096, and the resolution is 20808 dpi.
The second step is to respectively calculate the Fresnel diffraction light field complex amplitude O of the two object images according to a Fresnel diffraction integral formula1、O2The calculation formulas are respectively as follows:
wherein z isoRepresents the diffraction distance. When the complex amplitude of the Fresnel diffraction light field is calculated, the diffraction distance between the object image and the interference hologram is set to be in a shorter Fresnel diffraction area, and the preferred range is 10 mm-30 mm; in this embodiment, the diffraction distance is set to 20 mm; because the diffraction distance is set to be within a shorter Fresnel diffraction region, the coherence requirement of the recorded Fresnel hologram on the reproduced light can be reduced, and the incoherent light can also be reproduced, such as an LED lamp and an illumination spot lamp on a mobile phone. The wavelength of the object light can be the standard laser wavelength within the visible light wavelength range of 400nm to 760 nm; in this embodiment, the wavelength of the object light is set to 632.8 nm. The conjugate product of the complex amplitudes of the diffracted light field is the diffracted light intensity distribution; the fresnel diffraction intensity distribution graph of the first object image and the fresnel diffraction intensity distribution graph of the second object image, which are calculated in simulation in this embodiment, are shown in fig. 6 and 7, respectively. Because the diffraction distance is shorter, the diffraction pattern of the object image is still clearer and the image contour can be distinguished.
The third step is to set the reference light R, and the expression is as follows:
wherein alpha is1、β1Respectively representing the included angles of the reference light with the x-axis and the y-axis. The reference light is off-axis oblique incidence parallel light, and the preferred range of the included angle between the parallel reference light and the object light is 5-20 degrees; in this embodiment, the angle between the reference light and the object light is set to 7.8 °, i.e., α1＝90°、β17.8. The reference light and the object light have the same wavelength and are 632.8 nm.
The fourth step is to calculate two interference holograms II separately1、II2. Superposing and summing the complex amplitude of the Fresnel diffraction light field of the object image and the complex amplitude of the oblique incidence parallel reference light, and then calculating the conjugate product of the sum to obtain two interference holograms respectively, wherein the expression of the calculation process is as follows: II1＝(O1+R)(O1+R)*、II2＝(O2+R)(O2+R)*. In order to obtain a high-quality hologram, before superposing and summing an object diffraction light field and a reference light field, normalization processing is carried out, so that the maximum amplitude ratio of the object diffraction light field to the reference light field is 1: 1.
the fifth step is the filtering process of the two holograms. Firstly, Fourier transform calculation is carried out on the two interference holograms to obtain frequency spectrums IIFF of the two holograms1、IIFF2The calculation process expression is as follows:
then, performing band-pass filtering processing on the first frequency spectrogram, and only reserving the frequency spectrum of the positive first-order diffraction reproduction image; and performing band-pass filtering processing on the second frequency spectrum, and reserving the frequency spectrum of the negative first-order diffraction reproduction image. The band-pass filtering is preferably set to allow the parts of the spectrogram with normalized intensity greater than 90% to be completely transparent and the rest to be blocked; the band-pass filtering of the invention is set to be the frequency spectrum transmission with the normalized intensity of more than 95 percent, and the transmission rate of the rest part is 0. Two band-pass filters H1、H2Respectively expressed as:
the frequency spectrums of the two holograms after the filtering treatment are as follows: HFF1＝IIFF1·H1、HFF2＝IIFF2·H2。
The sixth step is to calculate the double different image Fresnel hologram II3. Adding the two frequency spectrums after the band-pass filtering processing, and then proceedingAnd (3) performing inverse Fourier transform calculation to obtain the double different image Fresnel hologram, wherein the expression of the calculation process is as follows:
in this embodiment, the calculated lenticular fresnel hologram is shown in fig. 10.
Referring to fig. 3, diffraction reconstruction images of the fresnel hologram are calculated by simulation using a diffraction reconstruction light path, wherein the hologram is recorded by interference, the incoherent reconstruction light is reflected, the positive-order diffraction reconstruction image is reflected, and the negative-order diffraction reconstruction image is reflected.
When calculating the diffraction reconstruction image of the Fresnel hologram, the reconstruction light C is parallel light, and the expression is as follows:
wherein alpha is2、β2The angles of the reproduction light with respect to the x-axis and the y-axis are shown, respectively. In this embodiment, the reconstruction light is incident perpendicularly to the hologram, i.e., α2＝90°、β290 °; the wavelength of the reproduction light is the same as the wavelengths of the object light and the reference light, and is 632.8nm in this embodiment.
Setting the distance z between the Fresnel hologram and the viewing surfaceiEqual to the above mentioned diffraction distance, in this embodiment 20 mm.
Firstly, simulating and calculating diffraction reproduction images Holo of Fresnel holograms of a first object image and a second object image which are not subjected to filtering processing respectively1、Holo2The calculation process expression is as follows:
in this embodiment, the first fresnel hologram obtained by simulation calculation has a diffraction-reconstructed image as shown in fig. 8. As can be seen from fig. 8, when the hologram is not subjected to the filtering process, the diffracted and reproduced light has a positive first-order image, a negative first-order image, a zero-order image, and low-frequency stray light, and the stray light affects the imaging sharpness of the reproduced image; in fig. 8, the positive primary image is divergent light, and the imaging focal point is at the position of sixty (sixth) shown in fig. 3, and is a virtual image, so that the image looks slightly blurred, and the definition of the positive primary image and the definition of the negative primary image are substantially the same as each other seen by human eyes. Similarly, the diffraction reconstruction image of the second fresnel hologram obtained by simulation calculation is shown in fig. 9, and the light reconstruction situation is the same as that in fig. 8 and is not repeated.
Finally, the diffraction reconstructed image Holo of the double dissimilar image Fresnel hologram is simulated and calculated3The calculation process expression is as follows:
in this embodiment, the diffraction-reconstructed image of the obtained lenticular fresnel hologram is shown in fig. 11. As can be seen from fig. 1, the reproduced light of the double-different-image fresnel hologram is two clear and different diffraction reproduced images, one is a positive-order virtual image "pole" located in front of the hologram, and the visual effect is to have a floating stereoscopic sense of depth; the other is negative first-order real image light which is positioned at the rear side of the hologram, and the visual effect is that the visual effect has sunken three-dimensional scene depth sense; theoretically the visual depth of field is equal to the diffraction distance, in this embodiment ± 20 mm. The visual angle effect is novel and unique, attracts the eyeball.
In the embodiment, the diffraction distance is only 20mm, and the diffraction distance is in a shorter Fresnel diffraction region, so that the requirement on the coherence of the reconstruction light of the double-dissimilar Fresnel hologram can be reduced, and the incoherent light can also be reconstructed, such as an LED lamp, an illumination spot lamp and the like on a mobile phone; simple operation, easy identification and suitability for mass anti-counterfeiting.
The above description is only for the preferred embodiment of the present invention, but the present invention should not be limited to the embodiment and the disclosure of the drawings, and therefore, all equivalent or modifications that do not depart from the spirit of the present invention are intended to fall within the scope of the present invention.
Claims (10)
1. A preparation method of a Fresnel hologram reproduced by double-different-image incoherent light is characterized by comprising the following steps:
s1, respectively calculating interference holograms of two different object lights and off-axis obliquely incident parallel reference lights in a Fresnel diffraction region in a set range;
s2, respectively calculating Fourier transform spectrograms of the two holograms obtained in the step S1;
s3, performing band-pass filtering processing on the first frequency spectrogram, reserving the frequency spectrum of the positive first-order diffraction reproduction image only, and performing band-pass filtering processing on the second frequency spectrogram, reserving the frequency spectrum of the negative first-order diffraction reproduction image only;
and S4, adding the two filtered spectrograms, and performing inverse Fourier transform calculation to obtain the double dissimilar images Fresnel hologram.
2. The method for preparing a fresnel hologram reproduced by using incoherent light with two different images according to claim 1, wherein the specific calculation process in step S1 is as follows:
s11, drawing two object images Uo1And Uo2Wherein U iso1And Uo2The size range is 2 mm-12 mm;
s12, respectively calculating the Fresnel diffraction light field complex amplitude O of the two object images according to the Fresnel diffraction integral formula1、O2The calculation formulas are respectively as follows:
wherein z isoAnd the diffraction distance is expressed, and when the complex amplitude of the Fresnel diffraction light field is calculated, the diffraction distance between the object image and the interference hologram is set to be within a short Fresnel diffraction region and ranges from 10mm to 30 mm.
S13, setting the reference light R, wherein the expression is as follows:
wherein alpha is1、β1Respectively representing the included angles of the reference light with an x axis and a y axis, wherein the reference light is off-axis oblique incidence parallel light, and the included angle range of the parallel reference light and the object light is 5-20 degrees;
s14, superposing and summing the complex amplitude of the Fresnel diffraction light field of the object image and the complex amplitude of the oblique incidence parallel reference light, and then calculating the conjugate product of the sum to respectively obtain two high-quality interference holograms II1、II2The calculation process expression is as follows: II1＝(O1+R)(O1+R)*、II2＝(O2+R)(O2+R)*。
3. The method for producing a heterodiad incoherent light-reconstructed fresnel hologram according to claim 2, characterized in that: the object images U of the two object lights in step S11o1、Uo2The size deviation is less than 30%.
4. The method for producing a heterodiad incoherent light-reconstructed fresnel hologram according to claim 2, characterized in that: the object image is one or more of simple patterns, Chinese characters, English letters, characters and numbers with low spatial frequency and few strokes or lines.
5. The method for producing a heterodiad incoherent light-reconstructed fresnel hologram according to claim 2, characterized in that: the wavelength of the object light is the same as that of the reference light, and the object light is the standard laser wavelength within the visible light wavelength range of 400 nm-760 nm.
6. As claimed in claim 2The preparation method of the Fresnel hologram reproduced by the double-different-image incoherent light is characterized by comprising the following steps of: fourier transform spectrum IIFF of two holograms in the step S21、IIFF2Calculated by the following formula:
7. the method for producing a fresnel hologram reproduced by using incoherent light of two different images according to claim 1 or 6, wherein the bandpass filtering process in step S3 is as follows:
s31, setting the part of the spectrogram with the normalized intensity larger than 90% to be completely transparent, and blocking the rest part;
s32, calculating to obtain two band-pass filters H1、H2Respectively expressed as:
S33、
the obtained frequency spectrums of the two holograms after the filtering treatment are as follows: HFF1＝IIFF1·H1、HFF2＝IIFF2·H2。
8. The method for producing a heterodiad incoherent light-reconstructed fresnel hologram according to claim 1 or 7, characterized in that: in step S4, the two bandpassed spectrograms are added together and the process proceedsObtaining the double different image Fresnel hologram II by the calculation of the line inverse Fourier transform3The calculation process expression is as follows:
9. the method for preparing a fresnel hologram reproduced by using incoherent light with two different images according to claim 2, wherein before the superposition and summation of the object diffraction light field and the reference light field in step S14, normalization is performed to make the maximum amplitude ratio of the two light fields be 1: 1.
10. the method for producing a heterodiad incoherent light-reconstructed fresnel hologram according to claim 2, characterized in that: the resolution values of the two object images are greater than 10000 dpi.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115691299A (en) * | 2022-11-11 | 2023-02-03 | 深圳市深大极光科技有限公司 | Holographic anti-counterfeit label with incoherent light for reproducing multiple depth images and manufacturing method thereof |
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| CN114637176B (en) | 2022-11-01 |
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