阅读说明：本技术 一种基于超表面的近场双密钥加密方法 (Near-field double-key encryption method based on super surface ) 是由 陈奎先 郑国兴 李子乐 于 2020-12-10 设计创作，主要内容包括：本发明属于信息光学技术领域,公开了一种基于超表面的近场双密钥加密方法,将超表面作为公钥,将入射光的相位分布作为私钥；包括选择入射光的工作波长,优化纳米砖的尺寸参数,使得工作波长下的入射光入射至纳米砖时,纳米砖的交叉偏振转化效率最高、同向偏振转化效率最低；计算获得记录公钥图像的超表面的相位分布信息；确定纳米砖阵列中若干个纳米砖的方向角排布信息并在基底上进行排布,完成公钥的设计；计算获得入射光的相位分布信息,完成私钥的设计。本发明设计的算法简单,设计的自由度更高,安全性极强,且双密钥加密模式更加灵活。(The invention belongs to the technical field of information optics, and discloses a near-field double-key encryption method based on a super surface, which takes the super surface as a public key and takes the phase distribution of incident light as a private key; selecting the working wavelength of incident light, and optimizing the size parameters of the nano brick, so that when the incident light with the working wavelength is incident to the nano brick, the cross polarization conversion efficiency of the nano brick is highest, and the same-direction polarization conversion efficiency of the nano brick is lowest; calculating to obtain the phase distribution information of the super surface of the recorded public key image; determining direction angle arrangement information of a plurality of nano bricks in the nano brick array and arranging on the substrate to complete the design of the public key; and calculating to obtain the phase distribution information of the incident light, and finishing the design of the private key. The algorithm designed by the invention is simple, the design freedom is higher, the safety is extremely strong, and the double-key encryption mode is more flexible.)

1. A near-field double-key encryption method based on a super surface is characterized in that the super surface is used as a public key, and phase distribution of incident light is used as a private key;

the super surface is composed of a substrate and a nano brick array arranged on the substrate, and the nano brick array comprises a plurality of nano bricks which are periodically arranged; the nano brick is of a sub-wavelength size and is of a cuboid structure; the sizes of the nano bricks are consistent, and the direction angles of the nano bricks are different; the two mutually vertical sides of the substrate are respectively an X axis and a Y axis, and the direction angle is the included angle between the long axis of the nano brick and the X axis;

the incident light has uniform intensity, equal amplitude and different phase distribution, and the size of a single phase unit is consistent with the cycle size of the nano brick array;

the near field double-key encryption method based on the super surface comprises the following steps:

step 1, selecting the working wavelength of the incident light, and optimizing the size parameters of the nano brick, so that when the incident light under the working wavelength is incident to the nano brick, the cross polarization conversion efficiency of the nano brick is highest, and the same-direction polarization conversion efficiency of the nano brick is lowest;

step 2, calculating to obtain super-surface phase distribution information for recording the public key image according to the working wavelength and the selected public key image;

step 3, according to the size parameters of the nano bricks and the phase distribution information of the super surface of the recorded public key image, determining the direction angle arrangement information of a plurality of nano bricks in the nano brick array, and arranging the nano bricks on the substrate according to the direction angle arrangement information to complete the design of the public key;

and 4, calculating to obtain the phase distribution information of the incident light according to the phase distribution information of the super surface of the public key image and the selected encryption information, and finishing the design of the private key.

2. The super-surface based near-field dual-key encryption method according to claim 1, wherein the substrate is divided into a plurality of periodic square unit structures with the same size, and one nano-brick is arranged on the working surface of each unit structure;

the size parameters of the nano brick comprise the length of the nano brick, the width of the nano brick, the height of the nano brick and the side length of the unit structure.

3. A super-surface based near-field dual-key encryption method according to claim 1, wherein in the step 2, the phase distribution information of the super-surface recording the public key image is calculated by using the following formula:

wherein the content of the first and second substances,denotes a phase distribution of a super surface on which a public key image is recorded, a (x, y) denotes a complex amplitude distribution of the public key image, and R (x, y) denotes a complex amplitude distribution of reference light used for interference recording.

4. A super-surface based near-field dual-key encryption method according to claim 3, wherein in the step 3, the azimuth angle of the nano-brick is half of the phase size of the corresponding cell in the phase distribution of the super-surface recording the public key image.

5. A super-surface based near-field dual-key encryption method according to claim 1, wherein in step 4, the phase distribution information of the incident light is calculated by using the following formula:

wherein the content of the first and second substances,which represents the phase distribution of the incident light,which represents the phase distribution of the encrypted information,representing the phase distribution of the super-surface where the public key image is recorded.

6. A super-surface based near-field dual-key encryption method according to claim 5, wherein the phase distribution of the encryption information is calculated by using the following formula:

where B (x, y) represents the complex amplitude distribution of the encrypted information, and R (x, y) represents the complex amplitude distribution of the reference light used for the interference recording.

7. A super-surface based near-field dual-key encryption method according to claim 1, wherein the phase delays in the long axis direction and the short axis direction of the nano-bricks are pi and the amplitudes are kept uniform.

8. A super-surface based near-field dual-key encryption method according to claim 1, wherein the number of nano-bricks is the same as the number of pixels of the public key image.

9. The super-surface based near-field dual-key encryption method according to claim 1, wherein the nano-brick is a reflective nano-brick or a transmissive nano-brick; the nano brick is made of a monocrystalline silicon material, and the substrate is made of an aluminum oxide material.

10. The super-surface based near-field dual-key encryption method according to claim 2, wherein the operating wavelength is 633nm, the length of the nano-brick is 225nm, the width of the nano-brick is 110nm, the height of the nano-brick is 230nm, and the side length of the unit structure is 340 nm.

Technical Field

The invention relates to the technical field of information optics, in particular to a near-field double-key encryption method based on a super surface.

Background

Optical encryption technology is a novel encryption means, receives more and more attention due to its unique technical characteristics, and becomes one of the important research contents of modern encryption technology. However, most of the existing near-field encryption technologies are based on the increase of the polarization state, amplitude and number of information channels of light or the encryption by an information transformation method, but the design method of the encryption technology is complicated, and the key is relatively simple, so that the security of the encryption system is low.

For example, the conventional near-field optical encryption technology mostly adopts a polarization multiplexing method to perform encryption recording, and different information channels are formed by using different polarization states, so as to achieve the purpose of encryption. However, the encryption mode is a common single-key encryption mechanism, the information security is at a lower level, and after an illegal user obtains the encrypted data, the encrypted information can be quickly obtained under the condition of having partial prior knowledge.

Disclosure of Invention

The invention provides a near-field double-key encryption method based on a super surface, and solves the problems of complex design mode and low safety of optical encryption in the prior art.

The invention provides a near-field double-key encryption method based on a super surface, which takes the super surface as a public key and takes the phase distribution of incident light as a private key;

the super surface is composed of a substrate and a nano brick array arranged on the substrate, and the nano brick array comprises a plurality of nano bricks which are periodically arranged; the nano brick is of a sub-wavelength size and is of a cuboid structure; the sizes of the nano bricks are consistent, and the direction angles of the nano bricks are different; the two mutually vertical sides of the substrate are respectively an X axis and a Y axis, and the direction angle is the included angle between the long axis of the nano brick and the X axis;

the incident light has uniform intensity, equal amplitude and different phase distribution, and the size of a single phase unit is consistent with the cycle size of the nano brick array;

the near field double-key encryption method based on the super surface comprises the following steps:

step 1, selecting the working wavelength of the incident light, and optimizing the size parameters of the nano brick, so that when the incident light under the working wavelength is incident to the nano brick, the cross polarization conversion efficiency of the nano brick is highest, and the same-direction polarization conversion efficiency of the nano brick is lowest;

step 2, calculating to obtain super-surface phase distribution information for recording the public key image according to the working wavelength and the selected public key image;

step 3, according to the size parameters of the nano bricks and the phase distribution information of the super surface of the recorded public key image, determining the direction angle arrangement information of a plurality of nano bricks in the nano brick array, and arranging the nano bricks on the substrate according to the direction angle arrangement information to complete the design of the public key;

and 4, calculating to obtain the phase distribution information of the incident light according to the phase distribution information of the super surface of the public key image and the selected encryption information, and finishing the design of the private key.

Preferably, the substrate is divided into a plurality of periodic square unit structures with the same size, and one nano brick is arranged on the working surface of each unit structure;

the size parameters of the nano brick comprise the length of the nano brick, the width of the nano brick, the height of the nano brick and the side length of the unit structure.

Preferably, in step 2, the phase distribution information of the super-surface on which the public key image is recorded is calculated by using the following formula:

wherein the content of the first and second substances,denotes a phase distribution of a super surface on which a public key image is recorded, a (x, y) denotes a complex amplitude distribution of the public key image, and R (x, y) denotes a complex amplitude distribution of reference light used for interference recording.

Preferably, in step 3, the azimuth angle of the nano-brick is half of the phase size of the corresponding unit in the phase distribution of the super-surface on which the public key image is recorded.

Preferably, in step 4, the phase distribution information of the incident light is calculated by using the following formula:

wherein the content of the first and second substances,which represents the phase distribution of the incident light,which represents the phase distribution of the encrypted information,representing the phase distribution of the super-surface where the public key image is recorded.

Preferably, the phase distribution of the encrypted information is calculated by using the following formula:

where B (x, y) represents the complex amplitude distribution of the encrypted information, and R (x, y) represents the complex amplitude distribution of the reference light used for the interference recording.

Preferably, the phase delay in the long axis direction and the phase delay in the short axis direction of the nano brick are pi, and the amplitudes are consistent.

Preferably, the number of the nano bricks is the same as the number of pixels of the public key image.

Preferably, the nano brick is a reflective nano brick or a transmissive nano brick; the nano brick is made of a monocrystalline silicon material, and the substrate is made of an aluminum oxide material.

Preferably, the working wavelength is 633nm, the length of the nano brick is 225nm, the width of the nano brick is 110nm, the height of the nano brick is 230nm, and the side length of the unit structure is 340 nm.

One or more technical schemes provided by the invention at least have the following technical effects or advantages:

compared with the traditional near-field polarization encryption technology, the near-field double-key encryption method based on the super surface has the advantages that the design algorithm is simple, the design freedom degree is higher, the safety is extremely high, the double-key encryption mode is more flexible, the method can be widely applied to the fields of information encryption and the like, and the application prospect is wide.

Drawings

Fig. 1 is a schematic structural diagram of a nano-brick unit used in a super-surface-based near-field dual-key encryption method according to an embodiment of the present invention;

fig. 2 is a schematic diagram illustrating polarization conversion efficiency of a nano-brick unit used in a super-surface based near-field dual-key encryption method according to an embodiment of the present invention;

fig. 3 is an initial amplitude distribution and phase distribution diagram of a public key image in a super-surface-based near-field dual-key encryption method according to an embodiment of the present invention;

fig. 4 is an amplitude distribution and a phase distribution diagram of public key image recording in a super-surface-based near-field dual-key encryption method according to an embodiment of the present invention;

fig. 5 is an initial amplitude distribution and phase distribution diagram of the encryption information in the near-field dual-key encryption method based on the super-surface according to the embodiment of the present invention;

fig. 6 is an amplitude distribution and a phase distribution diagram of an encrypted information record in a super-surface-based near-field dual-key encryption method according to an embodiment of the present invention;

fig. 7 is an amplitude distribution and a phase distribution diagram of a private key in a super-surface-based near-field dual-key encryption method according to an embodiment of the present invention;

fig. 8 is a schematic diagram illustrating that a super-surface-based near-field dual-key encryption method according to an embodiment of the present invention only has a public key under the incidence of a working wavelength;

fig. 9 is a schematic diagram illustrating that a super-surface based near-field dual-key encryption method according to an embodiment of the present invention only has a private key when the working wavelength is incident;

fig. 10 is a schematic working diagram of a super-surface based near-field dual-key encryption method under the incidence of a working wavelength according to an embodiment of the present invention.

Wherein, 1-nano brick and 2-unit structure.

Detailed Description

In order to better understand the technical solution, the technical solution will be described in detail with reference to the drawings and the specific embodiments.

As a new optical material, the super surface receives more and more attention with excellent optical performance, and the micro periodic structure of the surface can change the equivalent refractive index of the surface of an object, so that the fine control of light wave parameters is realized. The super-surface processing technology is mature, simple in structure and convenient to copy, and is an excellent choice for realizing a public key in a near-field double-key encryption technology.

The embodiment provides a near-field double-key encryption method based on a super surface, wherein the super surface is used as a public key, and the phase distribution of incident light is used as a private key.

The super surface is composed of a substrate and a nano brick array arranged on the substrate, and the nano brick array comprises a plurality of nano bricks which are periodically arranged; the nano brick is of a sub-wavelength size and is of a cuboid structure; the sizes of the nano bricks are consistent, and the direction angles of the nano bricks are different; the two mutually perpendicular sides of the substrate are respectively an X axis and a Y axis, and the direction angle is an included angle between the long axis of the nano brick and the X axis.

The incident light is uniform in intensity, equal in amplitude and different in phase distribution, and the size of a single phase unit is consistent with the cycle size of the nano brick array.

The near field double-key encryption method based on the super surface comprises the following steps:

step 1, selecting the working wavelength of the incident light, and optimizing the size parameters of the nano brick, so that when the incident light under the working wavelength is incident to the nano brick, the cross polarization conversion efficiency of the nano brick is highest, and the same-direction polarization conversion efficiency of the nano brick is lowest.

Specifically, the substrate is divided into a plurality of periodic square unit structures with the same size, and one nano brick is arranged on the working surface of each unit structure. Referring to fig. 1, one of the nano-bricks 1 and the corresponding unit structure 2 form a nano-brick unit. The length of the nano brick 1 is marked as L, the width of the nano brick is marked as W, the height of the nano brick is marked as H, and the period size (side length) of the unit structure 2 is marked as C. The projection of the nano brick 1 and the center of the unit structure 2 on the XOY plane is superposed. According to the coordinate system adopted by the invention, the length direction and the width direction of the substrate are respectively taken as an X-axis direction and a Y-axis direction, the height direction of the substrate is taken as a Z-axis direction, and an XOY plane is a plane where the upper surface of the substrate is located.

The size parameters of the nano brick comprise the length of the nano brick, the width of the nano brick, the height of the nano brick and the side length of the unit structure. In the nano-brick array, the number of the nano-bricks is equal to the pixel number of the public key, the sizes of all the nano-bricks are the same, and the rotation angle of each nano-brick is determined by the phase distribution of the public key.

The phase delay in the long axis direction and the phase delay in the short axis direction of the nano brick are pi, and the amplitudes are kept consistent. Namely, the amplitude of the nano brick is kept consistent while the phase delay in the long axis direction and the short axis direction is pi by optimally designing the size of the structure dimension of the nano brick. The nano-brick can be equivalent to a miniature half-wave plate. The half-wave plate has a phase control function, when a beam of circularly polarized light passes through the half-wave plate with the alpha dielectric nano-brick at a rotation angle, the circularly polarized light is modulated by the dielectric nano-brick to become circularly polarized light with opposite rotation directions, and a phase delay of +/-2 alpha is added. This is the phase modulation principle of the super-surface in the present invention. The super-surface operates in either transmission or reflection (depending on the particular performance requirements) and is in an operative position at the surface of the super-surface.

The step 1 is equivalent to selecting the working wavelength, and the geometric parameters of the reflective nano-brick are optimized according to the working wavelength and the performance requirement of the half-wave plate. The working wavelength is a visible light band.

The step 1 can be completed by using the existing electromagnetic simulation software platform. When an electromagnetic simulation tool is used for simulation, a beam of circularly polarized light is vertically incident on the surface of the nano brick array, the conversion efficiency of the reflected light of the nano bricks is taken as an optimization object, and a group of geometric parameters with highest cross polarization conversion efficiency and lowest same-direction polarization conversion efficiency are searched. The cross polarization means that left-handed circularly polarized light is converted into right-handed circularly polarized light or right-handed circularly polarized light is converted into left-handed circularly polarized light; the homotropic polarization means that the rotation direction of the left circularly polarized light or the right circularly polarized light is not changed.

For example, the dominant wavelength λ of the visible light band is 633nm, which is the operating wavelength of the near-field dual-key encryption technology. The nano brick is made of a monocrystalline silicon material, and the substrate is made of an aluminum oxide material. The optimized geometric parameters are as follows: l-225 nm, W-110 nm, H-230 nm, C-340 nm. The broadband response and polarization conversion efficiency curve chart of the nano-brick under the geometric parameters is shown in figure 2. The number of the nano-bricks is consistent with the number of the pixels of the public key image, that is, one nano-brick corresponds to one pixel of the public key image, for example, the size of the public key image can be selected to be 500 × 500 pixels.

And 2, calculating to obtain the super-surface phase distribution information of the recorded public key image according to the working wavelength and the selected public key image.

Specifically, the phase distribution information of the super surface recording the public key image is calculated by using the following formula:

wherein the content of the first and second substances,representing the phase distribution of the super-surface on which the public key image is recorded, A (x, y) representing the complex amplitude distribution of the public key image, and R (x, y) representing the reference light for interference recordingA complex amplitude distribution.

The reference light is part of the computer generated hologram and is used only for recording information on the super surface.

The amplitude distribution and the phase distribution corresponding to the public key image are shown in fig. 3.

R (x, y) may be made 1. Wherein a (x, y) is the amplitude distribution of the public key image,is the phase distribution of the public key image. Phase distribution of a super-surface corresponding to a public key image at recordingAs shown in fig. 4.

And 3, determining the direction angle arrangement information of a plurality of nano bricks in the nano brick array according to the size parameters of the nano bricks and the phase distribution information of the super surface of the recorded public key image, and arranging the nano bricks on the substrate according to the direction angle arrangement information to complete the design of the public key.

Specifically, the azimuth angle of the nano-brick is half of the phase size of the corresponding unit in the phase distribution of the super-surface on which the public key image is recorded. And the amplitude distribution is uniform.

And 4, calculating to obtain the phase distribution information of the incident light according to the phase distribution information of the super surface of the public key image and the selected encryption information, and finishing the design of the private key.

Specifically, the phase distribution of the encrypted information is calculated by using the following formula:

wherein the content of the first and second substances,the phase distribution of the encrypted information is represented, B (x, y) represents the complex amplitude distribution of the encrypted information, and R (x, y) represents the complex amplitude distribution of the reference light used for the interference recording.

R (x, y) may be made 1. b (x, y) is the amplitude distribution of the encrypted information,is the phase distribution of the encrypted information. Phase distribution corresponding to public key image during recordingAs shown in fig. 6.

The phase distribution information of the incident light is calculated by adopting the following formula:

and the amplitude distribution of the incident light is uniform as shown in fig. 7.

Wherein the content of the first and second substances,which represents the phase distribution of the incident light,which represents the phase distribution of the encrypted information,representing the phase distribution of the super-surface where the public key image is recorded.

Fig. 8 to 10 are schematic diagrams of the case of respectively having the public key, the private key and the double key at the operating wavelength.

The near-field double-key encryption method based on the super surface provided by the embodiment of the invention at least comprises the following technical effects:

(1) the near-field phase encryption technology has more encryption channels than other parameters such as polarization state and the like, and the degree of freedom of encryption design is higher;

(2) the security of the double encryption technology of the super surface and incident light phase distribution is higher;

(3) the encryption mode of combining the public key and the private key is more flexible;

(4) the phase algorithm in the invention is simple to calculate, does not need multi-step iterative algorithm, and has low requirement on calculation;

(5) the near-field double encryption mode based on the super surface is insensitive to the polarization state of incident light, and encryption information can be obtained by adopting any polarized light for irradiation.

Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to examples, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.