阅读说明：本技术 消除零级光的振幅型超表面计算全息片的设计方法 (Design method of amplitude type super surface computer hologram for eliminating zero-order light ) 是由 李子乐 郑国兴 邓娟 单欣 李仲阳 于 2019-11-22 设计创作，主要内容包括：本发明公开了一种消除零级光的振幅型超表面计算全息片的设计方法。通过构建新的振幅分布函数,借助于超表面纳米砖的振幅调控特性消除了振幅型计算全息零级像,以获得清晰,无零级,具有较高成像质量的再现像。本发明可应用于高端防伪、图像显示等领域。(The invention discloses a design method of an amplitude type super-surface computer hologram for eliminating zero-order light. By constructing a new amplitude distribution function, the amplitude type calculation holographic zero-order image is eliminated by virtue of the amplitude regulation and control characteristic of the super-surface nano brick, so that a clear, zero-order-free and high-imaging-quality reproduced image is obtained. The invention can be applied to the fields of high-end anti-counterfeiting, image display and the like.)

1. A design method of amplitude type super surface computer hologram for eliminating zero-order light is characterized in that: the method comprises the following steps:

1) obtaining original amplitude distribution f (x, y) on the computed hologram according to a target image of a far field and an optimization algorithm; the far field holographic image amplitude distribution is:

2) constructing a new amplitude distribution function

when u-v-0, F1(0, 0) -F (0, 0) -a₀0; therefore, the far-field hologram of f' is the zero-order-eliminated far-field hologram of f (x, y); according to the above formula

3) constructing a nano brick unit structure, and optimizing to obtain the structural parameters of the nano brick unit structure; the nano brick unit structure comprises a substrate and a nano brick arranged on the working surface of the substrate, wherein the nano brick and the working surface form a nano brick structure unit; setting the directions of two edges parallel to the working surface of the substrate as an x axis and a y axis respectively to establish an xoy coordinate system, wherein the surface of the nano brick parallel to the working surface is provided with a long axis L and a short axis W, and the steering angle theta of the nano brick is the included angle between the long axis L of the nano brick and the x axis direction; the structural parameters of the nano brick structural unit comprise a long axis L, a short axis W and a height H of the nano brick and the size of the side length C of the working face; the nano brick unit structure is any anisotropic structure, namely a long axis L is not equal to a short axis W:

4) calculating to obtain a turning angle theta value of the nano bricks in each unit structure in the super-surface structure array according to the new amplitude distribution f' (x, y) based on the unit structure parameters of the nano bricks, and finally arranging the turning angle theta values of the nano bricks corresponding to each position obtained by calculation on each unit structure in the super-surface structure array, so as to obtain the super surface material capable of eliminating zero-order far-field amplitude type holography;

5) a polarizer and an analyzer are arranged in a light path, the polarizer is arranged in front of the super-surface structure and used for generating linear polarized light, and the analyzer is arranged behind the super-surface structure and used for unifying the polarization direction of emergent light; when the polarizer is vertical to the analyzer, amplitude calculation holographic patterns of zero elimination level can be formed in a far field; the amplitude type calculation hologram designed based on the super-surface polarizer in the amplitude calculation hologram pattern can eliminate a zero-order image; the amplitude type calculation hologram designed based on the super-surface half-wave plate in the amplitude calculation hologram pattern can eliminate a zero-order image and has higher diffraction efficiency.

2. The design method of amplitude type super surface computer hologram for eliminating zero order light according to claim 1, wherein:

if the nano brick unit structure is a nano brick half-wave plate, the structural parameters of the nano brick half-wave plate can be optimized according to the following method: the method comprises the steps of scanning a nano brick structure unit under a working wavelength by taking the optimization target of vertically incidence of circularly polarized light with the working wavelength to the nano brick structure unit, wherein the cross polarization efficiency of emergent light is not lower than 80% and the same-direction polarization efficiency of the emergent light is not higher than 5%, and obtaining the structural parameters of the nano brick structure unit required by the target through electromagnetic simulation optimization;

if the nano-brick unit structure is a nano-brick polarizer, the structural parameters of the nano-brick polarizer can be optimized according to the following method: the method comprises the steps of scanning a nano brick unit structure under a working wavelength by taking the linear polarized light with the polarization direction along the long axis of the nano brick as an optimization target, reflecting the linear polarized light with the polarization direction along the short axis of the nano brick, and transmitting the linear polarized light with the polarization direction along the short axis of the nano brick as an optimization target, and obtaining the structural parameters of the nano brick unit structure required by the target through electromagnetic simulation optimization.

3. Use of a method of designing a zero order light-annihilating amplitude-type super-surface computer hologram according to claim 1 or 2 for designing a super-surface material.

Technical Field

The invention relates to the technical field of micro-nano optics and image display, in particular to a design method of an amplitude type super-surface computer-generated hologram for eliminating zero-order light.

Background

The common photography is based on the principle of geometric optical imaging, the intensity of light wave is recorded, the space object is imaged on a plane, and the three-dimensional information of the object is lost due to the loss of the phase of the light wave. The optical holography records the light wave emitted by an object in the form of interference fringes by utilizing the interference principle, and because the amplitude and phase information of the object light wave are stored in the recording medium, a three-dimensional image which is lifelike to the original object can be formed. However, the conventional hologram has strong zero-order light, which greatly affects the imaging quality of the reproduced image and interferes with the observation of the reproduced image.

Disclosure of Invention

The invention aims to provide a design method of an amplitude type super-surface computer generated hologram for eliminating zero-order light.

In order to achieve the above object, a first aspect of the present invention provides a method for designing an amplitude-type super-surface hologram for eliminating zero-order light, comprising: the method comprises the following steps:

(1) principle for eliminating amplitude type calculation holographic zero-order image

First, the original amplitude distribution f (x, y) on the computed hologram is obtained from the far-field target image and an optimization algorithm, such as the GS algorithm. The amplitude distribution of the far-field holographic image is then:

as can be seen from the above formula (1), the zero-order image of the far-field hologram is:

combine (1) to (2) if

The far field holographic image distribution of f' is then:

when u-v-0, F1(0, 0) -F (0, 0) -a₀0; therefore, the far-field hologram of f' is the zero-order-eliminated far-field hologram of f (x, y); according to the above principle, according to the formulaA new amplitude distribution f' (x, y) on the hologram can be recalculated; since the range of f' (x, y) is (-1, 1). Therefore, to eliminate the zero order also requires finding a medium that can record negative amplitudes.

(2) Super-surface amplitude regulation principle

Assuming a nano brick Jones matrix of

The rotation angle is theta, the incident light is linearly polarized light, and the Jones matrix is

The emergent light Jones vector after passing through the nano brick is as follows:

simplifying to obtain:

for equation (5), when the polarization analysis direction is α₂When the analyzer analyzes the deviation, the Jones matrix of the emergent light is as follows:

the transmitted light intensity at this time is:

when the polarization direction of the polarizer is vertical to that of the analyzer, the transmitted light intensity is:

the amplitude of the emergent light is:

if the nano brick is a polarizer, then a is 0, B is 1 or a is 1, B is 0, then the rotation angle range of the nano brick polarizer is [0 °,180 ° ]]In that [ -1/2,1/2 ] can be realized]Continuous amplitude modulation of the range. If the nano-brick is a half-wave plate, A is 1, B is-1, and the rotation angle range of the nano-brick polarizer is [0 DEG, 180 DEG ]]In, can realize [ -1,1 [ ]]Continuous amplitude control of the range when the nanobelt is a polarizer, the emergent intensity of the transmitted light is 1/4sin (2 theta-2 α)₁) When the nano-brick is a half-wave plate, the emergent light intensity of the transmitted light is sin (2 theta-2 α)₁) Therefore, compared with the zero-eliminating level calculation holographic plate designed based on the nano-brick polarizer, the zero-eliminating level calculation holographic plate designed based on the nano-brick half-wave plate has higher diffraction efficiency.

(3) Nano brick structure parameter optimization

The nano brick unit structure comprises a substrate and a nano brick arranged on the substrate, wherein the interface of the substrate and the nano brick is a working surface. The nano-brick and the substrate form a nano-brick structural unit. Setting the directions of two edges parallel to the working surface as an x axis and a y axis respectively to establish an xoy coordinate system, wherein the surface of the nano brick parallel to the working surface is provided with a long axis L and a short axis W, and the steering angle theta of the nano brick is the included angle between the long axis L of the nano brick and the x axis direction;

the nano brick unit structure can be any anisotropic structure. If the nano brick is a polarizer, the method for optimizing the unit structure parameters of the nano brick polarizer comprises the following steps: the method comprises the steps of scanning a nano brick polarizer unit structure under a working wavelength by taking the linear polarized light with the polarization direction along the long axis of a nano brick as a reflection target and the linear polarized light with the polarization direction along the short axis of the nano brick as a transmission target or the linear polarized light with the polarization direction along the long axis of the nano brick as a transmission target and the linear polarized light with the polarization direction along the short axis of the nano brick as a reflection target, and obtaining the structural parameters of the nano brick unit structure required by the target through electromagnetic simulation optimization.

If the nano brick is used as a half-wave plate, the method for optimizing the unit structure parameters of the half-wave plate of the nano brick comprises the following steps: the method comprises the steps of scanning a nano brick structure unit under a working wavelength by taking the optimization target of vertically incidence of circularly polarized light with the working wavelength to the nano brick structure unit, wherein the cross polarization efficiency of emergent light is not lower than 80% and the same-direction polarization efficiency of the emergent light is not higher than 5%, and obtaining the structural parameters of the nano brick structure unit required by the target through electromagnetic simulation optimization;

based on the principle, the amplitude type calculation holographic zero-order image elimination design based on the super surface material can be realized according to the following steps:

(1) firstly, according to a far-field target image and an optimization algorithm, obtaining an original amplitude distribution f (x, y) on a computed hologram.

(2) According to the principle of eliminating amplitude type calculation holographic zero-order image, a new amplitude distribution f' (x, y) on the holographic plate is designed.

(3) And finally, distributing the steering angle theta values of the nano bricks corresponding to the positions obtained by calculation on each structural unit in the super-surface structure array, so as to obtain the super-surface material capable of eliminating zero-order far-field amplitude type holography.

(4) The polarizer and the analyzer are arranged in the light path, the polarizer is arranged in front of the super-surface structure and used for generating linear polarization light, and the analyzer is arranged behind the super-surface structure and used for unifying the polarization direction of emergent light. When the polarizer is perpendicular to the direction of the analyzer, an amplitude calculation holographic image of zeroth elimination order can be formed in a far field.

The invention also provides an application of the amplitude type calculation holographic zero-order image elimination method based on the metamaterial in designing the metamaterial.

Compared with the prior art, the invention at least has the following advantages and beneficial effects:

1) the amplitude calculation holographic zero-order image elimination method based on the super surface material can effectively eliminate the zero order of the reproduced holographic image, improve the diffraction efficiency and improve the image quality of the holographic image. Therefore, the method has very wide application prospect;

2) the sizes of the nano brick structure units are all sub-wavelength levels, so the super surface designed by the invention has small volume, light weight and high integration, and is suitable for the development of miniaturization in the future.

3) The amplitude calculation holographic zero-order image elimination method based on the super surface material not only can be suitable for Fresnel holographic design but also is suitable for Fourier holographic design.

4) The method for eliminating the amplitude calculation holographic zero-order image based on the super surface material can be used for eliminating any anisotropic structure of a super surface unit structure. And is therefore insensitive to manufacturing errors.

5) The zero order can be well eliminated by utilizing the super-surface half-wave plate structure to design amplitude type calculation hologram. The zero order can be eliminated and the diffraction efficiency can be improved by designing the amplitude type computer generated hologram by utilizing the super-surface half-wave plate structure. Compared with the holographic plate designed based on the super-surface polarizer structure, the diffraction efficiency of the holographic plate can be 4 times higher.

6) The amplitude type calculation hologram designed by the method can realize zero-order image elimination in a broadband wavelength range, and the image contrast is unchanged.

Drawings

FIG. 1 is a schematic diagram illustrating the effect of the super-surface structure array according to the present invention;

FIG. 2 is a schematic structural view of a super-surface structure unit according to the present invention;

FIG. 3 is a scanning result graph of the transmittance and reflectance of the nano-brick polarizer according to the wavelength variation in the present invention;

FIG. 4 is a far field target holographic image 1 of the present invention;

FIG. 5 is a holographic image based on a nano polarizer design without eliminating the zero order image;

FIG. 6 is a holographic image based on the design of nano-brick polarizer to eliminate the zero-order image.

FIG. 7 is a graph of the scanning results of the transmittance of the half-wave plate of the nano-brick according to the wavelength variation;

FIG. 8 is a far field target holographic image 2 of the present invention;

FIG. 9 is a holographic image without zero order image elimination based on nanometer half-wave plate design in the present invention;

FIG. 10 is a holographic image based on a nanometer half-wave plate design to eliminate a zero-order image in the present invention.

Detailed Description

The invention is described in further detail below with reference to specific figures and specific embodiments.