A micro-nano structure based planar optical element array and a high-efficiency preparation method thereof

Abstract

The present application relates to the technical field of planar optical element, and particularly relates to a planar optical element array based on micro-nano structure and a high-efficiency preparation method thereof.A planar optical element array based on micro-nano structure comprises a substrate, and an array structure is arranged on the substrate, the array structure is composed of a plurality of small-aperture micro-nano structure planar optical element monomers, the array structure is a hexagonal honeycomb array structure, and the micro-nano structure planar optical element monomer is composed of a plurality of groups of concentric circular rings with equal ring width but different heights.Two master plates of monomers are prepared by using high-precision gray-scale lithography technology, a mold is obtained by PDMS mold copying, and then nano-imprinting technology is used to sequentially imprint the two monomers in array order.The preparation method is simple, the manufacturing cost is low, and the replication and manufacturing of small-aperture lenses have high tolerance characteristics;the present application further improves the space utilization rate (K=0.684) of the array structure;and the resolution of the original image can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of planar optical elements, in particular to a planar optical element array based on micro-nano structures and an efficient preparation method thereof. BACKGROUND

[0002] At present, most imaging systems still use traditional refractive lenses to realize phase control of light through light path accumulation, so as to achieve optical functions such as focusing and imaging. However, due to the limitations of imaging principles, medium dispersion, and light wavelength range, the refractive lens has a serious chromatic aberration problem. The achromatic lens group realized through lens cementing, hybridization, and other technologies inevitably leads to a large volume and heavy weight of the imaging system, which is contrary to the development concept of lightweight and miniaturization of modern optical elements.

[0003] With the development of binary optics, planar optical elements based on micro-nano structures bring new hope to break through the above bottleneck. Early Fresnel lenses realize the advantages of planarization, light weight, and low manufacturing cost by compressing the redundant 2π phase of refractive lenses, but their shortcomings are also obvious. Their special structure leads to serious dispersion, making it difficult to achieve true planar imaging. In recent years, relying on the mutual integration of optical and microelectronic processing technologies, Wang Peng and others from the University of Utah designed a planar optical element composed of several concentric circles (each circle has the same width but different heights) through the combination of scalar diffraction theory and optimization algorithm, which realizes the characteristics of planarization and light weight while considering the wide-band achromatic ability. At the same time, gray-scale lithography technology is used to effectively prepare the concentric ring lens. Compared with traditional refractive lenses, the concentric ring lens has obvious advantages (lightweight, integration, wide-band achromatic, etc.), but it also has obvious shortcomings. 1. In terms of the lens itself, there is a certain constraint relationship between the size (lens thickness, lens aperture) and the efficiency of the lens (Xiao Xingjian, Zhu Shining, Li Tao. Design and parameter analysis of wide-band achromatic planar lens [J]. Infrared and Laser Engineering, 2020, 49(9): 53-60). Under the premise of large lens aperture, the thickness of the lens will increase significantly, and the efficiency will be greatly lost. 2. The concentric ring lens is composed of micro-nano structures. Due to the limitations of processing technology, the large aspect ratio and large aperture of the concentric ring lens will have obvious preparation errors, which will further damage the lens efficiency, and the efficiency of the concentric ring lens is lower than the theoretical design value.

[0004] In summary, continuously optimizing the preparation method of the planar optical element array based on micro-nano structures has become the focus of research for researchers in this field. SUMMARY

[0005] The application provides a micro-nano structure plane optical element array and an efficient preparation method thereof, so as to overcome the problems of low lens efficiency and limited processing technology in the prior art.

[0006] To achieve the above object, the technical scheme of the application is as follows: a micro-nano structure plane optical element array, comprising a substrate, wherein an array structure 2 composed of micro-nano structure plane optical elements is arranged on the substrate, the array structure is composed of a plurality of identical first micro-nano structure plane optical element monomers, the first micro-nano structure plane optical element monomer is composed of a plurality of groups of first concentric circular rings with equal ring width but different heights, and the array structure is a hexagonal honeycomb array structure, a plurality of first micro-nano structure plane optical element monomers are arranged at a tangent gap, and a plurality of second micro-nano structure plane optical element monomers with equal focal length but different aperture are arranged at the gap, the second micro-nano structure plane optical element monomer is composed of a plurality of groups of second concentric circular rings with equal ring width but different heights.

[0007] A preparation method of a micro-nano structure plane optical element array, comprising the following steps:

[0008] Step 1: high-precision gray-scale lithography is performed on the designed first micro-nano structure plane optical element monomer and second micro-nano structure plane optical element monomer to manufacture a master piece;

[0009] Step 2: PDMS mold transfer is performed on the master piece of the first micro-nano structure plane optical element monomer and second micro-nano structure plane optical element monomer to obtain a mold;

[0010] Step 3: the master mold of the first micro-nano structure plane optical element monomer and second micro-nano structure plane optical element monomer prepared by the gray-scale lithography manufacturing technology is used for nano-imprint technology replication manufacturing on the substrate, and the first micro-nano structure plane optical element monomer and second micro-nano structure plane optical element monomer are sequentially imprinted in order;

[0011] Step 4: a transfer step is performed on the imprinted pattern, that is, an inductively coupled plasma etching technology of a C4F8, SF6 and O2 mixed gas is used to realize equal-speed etching of photoresist and silicon oxide (concentric circular ring lens material), so as to realize pattern transfer, that is, preparation of the micro-nano structure plane optical element array.

[0012] Compared with the prior art, the application has the following advantages:

[0013] 1.The micro-nano structure planar optical element array structure in the application is composed of a first micro-nano structure planar optical element monomer and a second micro-nano structure planar optical element monomer, the conventional design idea of the circular ring micro-nano structure planar optical element adopts a direct binary search method (DBS) to perform optimization design on the ring height, compared with the design of a large-aperture micro-nano structure planar optical element, the DBS and other optimization algorithms are prone to fall into a local optimal solution between the ring height distribution and the lens efficiency, and the optimization design difficulty is higher than that of a small-aperture micro-nano structure planar optical element, the application replaces the large-aperture micro-nano structure planar optical element with a plurality of small-aperture micro-nano structure planar optical elements to form an array, and the design difficulty is greatly reduced.

[0014] 2.The preparation method is simple, the master version of the two monomers is prepared by using high-precision gray-scale lithography technology, the mold is obtained through PDMS mold turning, and the two monomers are sequentially imprinted in array order by using nano-imprinting technology, the replication process is convenient, the success rate is extremely high, the manufacturing cost of the micro-nano structure planar optical element is greatly reduced, and meanwhile, the replication and manufacturing of the small-aperture lens have high tolerance characteristics.

[0015] 3.The array structure in the application adopts a hexagonal honeycomb arrangement, so that the first micro-nano structure planar optical element monomer has a large filling coefficient (K=0.670) on the substrate, and the second micro-nano structure planar optical element monomer placed outside the gap between the first micro-nano structure planar optical element monomers can further improve the space utilization rate of the array structure (K=0.684).

[0016] 4.The image taken by the micro-nano structure planar optical element array designed in the application can effectively improve the resolution of the original image after image segmentation, merging and recombination and the like. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A plan view of a micro-nano structure planar optical element array provided by the method of the application;

[0018] Figure 2 A sectional view of a micro-nano structure planar optical element array provided by the method of the application;

[0019] Figure 3 A plan view of a first micro-nano structure planar optical element monomer provided by the method of the application;

[0020] Figure 4 A sectional view of a first micro-nano structure planar optical element monomer provided by the method of the application;

[0021] Figure 5 A plan view of a second micro-nano structure planar optical element monomer provided by the method of the application;

[0022] Figure 6 A cross-sectional view of a single micro / nano structure planar optical element provided by the method of the present invention.

[0023] The annotations in the attached figures are explained as follows:

[0024] 1 is the substrate, 2 is the array structure, 3 is the first micro-nano structure planar optical element unit, 4 is the second micro-nano structure planar optical element unit, 5 is the first concentric ring, and 6 is the second concentric ring. Detailed Implementation

[0025] The method of the present invention will now be described with reference to specific embodiments and accompanying drawings.

[0026] This invention provides a planar optical element array based on micro / nano structures. The design concept involves setting an array structure on a substrate, which is composed of multiple small-aperture micro / nano structure planar optical element units. Each micro / nano structure planar optical element unit consists of multiple sets of concentric rings with equal width but different heights. This invention uses high-precision grayscale photolithography to prepare master copies of the two units, obtains a mold through PDMS molding, and then uses nanoimprint lithography to sequentially imprint the two units in array order.

[0027] Example: This invention provides a planar optical element array based on micro / nano structures, comprising a substrate 1, on which an array structure 2 composed of micro / nano planar optical elements is disposed. The array structure 2 is composed of several identical first micro / nano planar optical element units 3, each first micro / nano planar optical element unit 3 consisting of multiple sets of first concentric rings 5 ​​with equal ring width but different heights. The array structure 2 is a hexagonal honeycomb array structure. Second micro / nano planar optical element units 4 with equal focal length but different apertures are respectively disposed at the tangential gaps between the multiple first micro / nano planar optical element units 3. Each second micro / nano planar optical element unit 4 consists of multiple sets of second concentric rings 6 with equal ring width but different heights.

[0028] like Figure 1 As shown, the array structure 2 adopts a hexagonal honeycomb arrangement. The hexagonal honeycomb array structure 2 makes the first micro-nano structure planar optical element 3 have a large filling coefficient (K=0.670) on the substrate 1. The second micro-nano structure planar optical element 4, which is placed outside the gaps between multiple first micro-nano structure planar optical element 3, can further improve the space utilization of the array structure (K=0.684).

[0029] The application provides a high-efficiency preparation method of a micro-nano structure-based planar optical element array, which comprises the following steps: preparing a master of a first micro-nano structure planar optical element monomer 3 and a second micro-nano structure planar optical element monomer 4 by using a high-precision gray-scale lithography technology, obtaining a mold through PDMS mold copying, then sequentially imprinting the first micro-nano structure planar optical element monomer 3 and the second micro-nano structure planar optical element monomer 4 in array order by using a nano-imprinting technology, and finally realizing equal-speed etching of photoresist and silicon dioxide by using an inductively coupled plasma etching technology, so as to realize pattern transfer and complete preparation of the lens array. The specific steps are shown in the following examples.

[0030] Step one, high-precision gray-scale lithography is performed on the designed first micro-nano structure planar optical element monomer 3 and the second micro-nano structure planar optical element monomer 4 to manufacture master pieces of the first micro-nano structure planar optical element monomer 3 and the second micro-nano structure planar optical element monomer 4 respectively.

[0031] Firstly, the working bandwidth and the focal length and other evaluation indexes should be designed as the design target function of the micro-nano structure planar optical element.

[0032] 1) The micro-nano structure planar optical element is designed, the first micro-nano structure planar optical element monomer 3 and the second micro-nano structure planar optical element monomer 4 are respectively composed of N concentric circular rings with equal width d and unequal height h.

[0033] 2) The lens aperture D of the first micro-nano structure planar optical element monomer 3, the maximum lens aperture D m ′ ax (relative to the monomer 3), the length L of the micro-nano structure planar optical element array and the width W of the micro-nano structure planar optical element array are respectively:

[0034] D = 2 = 2;

[0035]

[0036] L = 6Nd;

[0037]

[0038] 3) According to the size relationship between the characteristic size of the micro-nano structure planar optical element monomer and the working wavelength, the height distribution of the output micro-nano structure planar optical element monomer is optimized by combining the scalar diffraction theory and the optimization algorithm, and the array structure 2 composed of the micro-nano structure planar optical element is designed, as shown in Figures 1-2In the embodiment, the micro-nano structure planar optical element includes 7 first micro-nano structure planar optical element monomers 3 and 6 second micro-nano structure planar optical element monomers 4. For specific design parameters, the size of the substrate 1 is 35mm*35mm*2mm; the length L of the micro-nano structure planar optical element array is 30mm, and the width W is 27.32mm; the aperture D of the first micro-nano structure planar optical element monomer 3 is 10mm, and there are 5000 first concentric circular rings 5 with a width d of 1um, and the height distribution h is between 0 and 3um; the aperture D of the second micro-nano structure planar optical element monomer 4 is 1.5mm, and there are 750 second concentric circular rings 6 with a width d of 1um. ′ ′

[0039] Step two, PDMS reverse molding is performed on the master pieces of the first micro-nano structure planar optical element monomer 3 and the second micro-nano structure planar optical element monomer 4 to obtain the mold of the first micro-nano structure planar optical element monomer 3 and the second micro-nano structure planar optical element monomer 4;

[0040] Step three, the master mold of the first micro-nano structure planar optical element monomer 3 and the second micro-nano structure planar optical element monomer 4 prepared according to the gray-scale lithography manufacturing technology is used to perform nano-imprinting technology replication manufacturing on the substrate 1, and the first micro-nano structure planar optical element monomer 3 and the second micro-nano structure planar optical element monomer 4 are sequentially imprinted in a specific order;

[0041] Step four, a transfer step is performed on the imprinted pattern, that is, an inductively coupled plasma etching technology of a mixed gas of C4F8, SF6 and O2 is used to realize equal-speed etching of photoresist and silicon oxide (concentric circular ring lens material), so as to realize pattern transfer, that is, preparation of the micro-nano structure planar optical element array 2.

[0042] The above embodiment is only a relatively optimal technical solution of the present application, and is not regarded as a limitation of the present application. The protection scope of the present application should be the technical solution recited in the claims, including the equivalent replacement solution of the technical features recited in the claims, that is, the equivalent replacement improvement within the scope is also within the protection scope of the present application.​​

Claims

1. A micro-nano structure based planar optical element array, comprising a substrate (1), an array structure (2) of micro-nano structure planar optical elements is arranged on the substrate (1), the array structure (2) is composed of a plurality of identical first micro-nano structure planar optical element monomers (3), the first micro-nano structure planar optical element monomer (3) is composed of a plurality of groups of first concentric circular rings (5) with equal ring width but different heights, characterized in that: The array structure (2) is a hexagonal honeycomb array structure, and a plurality of first micro-nano structure planar optical element monomers (3) are provided with second micro-nano structure planar optical element monomers (4) with equal focal lengths but different apertures at the tangent gaps, respectively, and the second micro-nano structure planar optical element monomers (4) are composed of a plurality of groups of second concentric circular rings (6) with equal ring widths but different heights. ​ 2. The method according to claim 1, wherein, The method comprises the following steps: Step one, high-precision gray-scale lithography is performed on the designed first micro-nano structure planar optical element monomer (3) and the second micro-nano structure planar optical element monomer (4) to manufacture master parts, respectively; Step two, PDMS mold transfer is performed on the master parts of the first micro-nano structure planar optical element monomer (3) and the second micro-nano structure planar optical element monomer (4) to obtain molds, respectively; Step three, the master molds of the first micro-nano structure planar optical element monomer (3) and the second micro-nano structure planar optical element monomer (4) prepared according to the gray-scale lithography manufacturing technology are subjected to nano-imprint technology replication manufacturing on a substrate (1), and the first micro-nano structure planar optical element monomer (3) and the second micro-nano structure planar optical element monomer (4) are sequentially imprinted in order; Step four, a transfer step is performed on the imprinted pattern, that is, an inductively coupled plasma etching technology of a C4F8, SF6, O2 mixed gas is used to realize equal-speed etching of photoresist and silicon oxide, to realize pattern transfer, that is, preparation of a micro-nano structure planar optical element array.

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