Zoom super lens system with fixed conjugate distance

Abstract

The utility model provides a variable-focus super lens system with a fixed conjugate distance, and the system sequentially comprises a super lens fixing group which is composed of a single super lens or a plurality of super lens groups with an effective focal length # imgabs0 # from an object point to an image point along an optical axis, and the position of the super lens fixing group is fixed; the super lens zoom group is composed of a single super lens or multiple super lens groups with the effective focal length of # imgabs 1 #, and the position of the super lens zoom group is adjustable in the direction of the optical axis; and the super lens compensation group is composed of a single super lens or a multi-piece super lens group with an effective focal length of # imgabs2, the position of the super lens compensation group is adjustable along the direction of the optical axis and is adjusted along with the position adjustment of the super lens zoom group, and the super lens in the system causes the light direction to change by modulating the light phase. According to the zoom super lens system with the fixed conjugate distance, compact and efficient zoom is realized, and the problem that the zoom range and the imaging quality cannot be considered at the same time is solved.

Description

Technical Field

[0001] The utility model belongs to the technical field of super lenses, and in particular relates to a zoom super lens system with a fixed conjugate distance. Background Art

[0002] Zoom imaging systems are widely used in modern technology, particularly in surveillance, photography, and drone operations, where the importance of zoom functionality is self-evident. However, achieving efficient, high-quality zoom imaging systems currently faces numerous technical challenges. In recent years, metalenses, due to their compact structure and flexible phase control capabilities, have emerged as a key technology for overcoming the limitations of traditional optical components. Metalenses, designed with subwavelength structures, enable precise manipulation of light waves, demonstrating significant potential in applications such as microscopic imaging and light field manipulation.

[0003] Currently, metalens technology has made significant progress in imaging with large fields of view, large apertures, and achromatic aberration. However, these technologies are still mainly limited to fixed-focal-length imaging systems and cannot meet the demand for zoom functions in practical applications. Existing metalens zoom methods usually have the disadvantages of limited zoom range and poor imaging quality. For example, the Alvarez lens achieves zoom by lateral displacement of two metalenses, but its zoom range is limited; the Moiré lens adjusts the focal length by rotating along the optical axis, but due to the limitation of the paraxial approximation, its imaging quality can only achieve the effect of quadratic phase; although the zoom method based on the axial displacement of two metalenses can achieve focal length changes within a certain range, due to the non-constant conjugate distance, the image plane drifts as the focal length changes, and the imaging quality decreases significantly, which seriously affects its feasibility in practical applications. Utility Model Content

[0004] The purpose of the present invention is to solve the shortcomings of the existing technology and provide a zoom metalens system with a fixed conjugate distance that can take into account both zoom range and imaging quality.

[0005] In order to achieve the above-mentioned purpose, the technical solution of the utility model is achieved as follows:

[0006] The utility model provides a fixed conjugate distance zoom metalens system, which comprises the following components in sequence from the object point to the image point along the optical axis:

[0007] The fixed group of super lenses is composed of the effective focal length A single metalens or a multi-metalens group is formed, and the position of the metalens fixed group is fixed;

[0008] The super lens zoom group is composed of the effective focal length The metalens is composed of a single metalens or a multi-metalens group, and the position of the metalens zoom group is adjustable along the optical axis;

[0009] The metalens compensation group is composed of the effective focal length The metalens compensation group is adjustable along the optical axis and is adjusted along with the position of the metalens zoom group;

[0010] The phase distribution of any single metalens in the zoom metalens system satisfies the following conditions:

[0011]

[0012] in, is a non-zero natural number, is the distance from any point on the metalens surface to the center, are all constant coefficients.

[0013] In one embodiment, the zoom metalens system further includes an aperture along the optical axis that moves with the movement of the metalens zoom group, and the aperture is an aperture that transmits light only in the central area.

[0014] In one embodiment, the aperture is one of a fixed-position variable-radius aperture, a position-variable fixed-radius aperture, and a position-variable variable-radius aperture, and the position of the aperture is equivalent to being located at any position between the object point and the image point.

[0015] In one embodiment, a ratio of the effective focal length of the variable focus metalens system to the entrance pupil diameter is greater than or equal to 1.

[0016] In one embodiment, a ratio of the maximum effective focal length to the minimum effective focal length of the variable focus metalens system is greater than or equal to 6.

[0017] In one embodiment, the ratio of the back focus to the total optical length of the zoom metalens system satisfies the following condition:

[0018]

[0019] The back focus (BFL) is the distance from the rear surface of the metalens compensation group to the image point, and the total optical length (TTL) is the distance from the front surface of the metalens fixed group to the image point. The back focus (BFL) changes during zooming, but the total optical length (TTL) is a constant due to the fixed conjugate distance.

[0020] In one embodiment, the effective focal length satisfies the following conditions:

[0021] ,

[0022] .

[0023] In one embodiment, the monolithic metalens includes a transparent substrate and a dielectric microstructure array disposed on a plane of the transparent substrate. The unit structures included in the dielectric microstructure array are divided into at least eight types of unit structures by changes in size and / or shape, and the phase provided by each of the unit structures satisfies uniform or non-uniform sampling in the range of 0 to 2π.

[0024] In one embodiment, an anti-reflection film is coated on the other surface of the transparent substrate.

[0025] In one embodiment, the material of the unit structure is one of Si, GaN, and TiO2, and the material of the transparent substrate is one of SiO2, K9, and BK7.

[0026] Compared with the existing technology, the beneficial effect of the present invention is that, through the three components of the metalens fixed group, the metalens variable magnification group and the metalens compensation group, the advantage of the unchanged conjugate distance in the traditional optical zoom system and the excellent phase modulation capability of the metalens are combined to achieve compact and efficient zooming, and an aperture is introduced to control the entrance pupil diameter of different focal lengths, thereby improving the diffraction limit at the telephoto end, having excellent imaging quality at all focal lengths, and solving the problem that the zoom range and imaging quality cannot be taken into account at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic structural diagram of a zoom metalens system with a fixed conjugate distance according to an embodiment of the present invention when the magnification is 1;

[0028] Figure 2 This is a schematic structural diagram of a zoom metalens system with a fixed conjugate distance according to an embodiment of the present invention when the magnification is 2;

[0029] Figure 3 This is a structural diagram of a fixed conjugate distance zoom metalens system according to an embodiment of the present invention when the magnification is 4;

[0030] Figure 4 This is a schematic structural diagram of a zoom metalens system with a fixed conjugate distance according to an embodiment of the present invention when the magnification is 6;

[0031] Figure 5 This is a curve diagram showing the position changes of the metalens zoom group and the metalens compensation group during the zooming process of the zoom metalens system with a fixed conjugate distance according to one embodiment of the present invention;

[0032] Figure 6 This is a modulation transfer function curve diagram of a zoom metalens system with a fixed conjugate distance according to an embodiment of the present invention when the magnification is 1;

[0033] Figure 7This is a modulation transfer function curve diagram of a zoom metalens system with a fixed conjugate distance according to an embodiment of the present invention when the magnification is 2;

[0034] Figure 8 This is a modulation transfer function curve diagram of a zoom metalens system with a fixed conjugate distance according to an embodiment of the present invention when the magnification is 4;

[0035] Figure 9 This is a modulation transfer function curve diagram of a zoom metalens system with a fixed conjugate distance according to an embodiment of the present invention when the magnification is 6;

[0036] Figure 10 The point spread function of the xy cross section at the focal plane of the zoom metalens system with a fixed conjugate distance according to one embodiment of the present invention when the magnification is 1;

[0037] Figure 11 The point spread function of the xy cross section at the focal plane of the zoom metalens system with a fixed conjugate distance according to one embodiment of the present invention when the magnification is 2;

[0038] Figure 12 The point spread function of the xy cross section at the focal plane of the zoom metalens system with a fixed conjugate distance according to one embodiment of the present invention when the magnification is 4;

[0039] Figure 13 The point spread function of the xy cross section at the focal plane of the zoom metalens system with a fixed conjugate distance according to one embodiment of the present invention when the magnification is 6;

[0040] Figure 14 The xz cross-sectional light field distribution near the focus of a zoom metalens system with a fixed conjugate distance according to an embodiment of the present invention when the magnification is 1;

[0041] Figure 15 The xz cross-sectional light field distribution near the focus of the zoom metalens system with a fixed conjugate distance according to one embodiment of the present invention when the magnification is 2;

[0042] Figure 16 The xz cross-sectional light field distribution near the focus of the zoom metalens system with a fixed conjugate distance according to one embodiment of the present invention when the magnification is 4;

[0043] Figure 17 This is the xz cross-sectional light field distribution near the focus of the zoom metalens system with a fixed conjugate distance according to one embodiment of the present invention when the magnification is 6;

[0044] Figure 18 This is a schematic diagram of another optional aperture position in the zoom metalens system with a fixed conjugate distance of the utility model.

[0045] Explanation of the reference numerals: object point 1, metalens fixing group 2, aperture 3, metalens zoom group 4, metalens compensation group 5, image point 6. DETAILED DESCRIPTION

[0046] like Figure 1 As shown, this embodiment provides a fixed conjugate distance zoom metalens system, which includes, along the optical axis from object point 1 to image point 6, a metalens fixed group 2, which is composed of a single metalens or a multi-metalens group, with an effective focal length of The position of the metalens fixed group 2 is fixed and does not participate in the zoom process. It is used to image the actual object plane in front of the metalens zoom group 4 as the object plane that meets the position required by the metalens zoom group 4. The multi-piece metalens group is composed of multiple single metalens; the aperture 3 is an aperture diaphragm that transmits light only in the central area. It moves with the metalens zoom group 4 to change the entrance pupil diameter (EPD) of different focal lengths, increase the amount of light entering at telephoto, and keep the system with the smallest possible F number when zooming; the metalens zoom group 4 is composed of a single metalens or a multi-piece metalens group, and the effective focal length The position of the super lens zoom group 4 along the optical axis is adjustable. It changes the magnification by changing the object distance and image distance, thereby changing the effective focal length (EFL) of the system. The super lens compensation group 5 is composed of a single super lens or a multi-piece super lens group. The position of the superlens compensation group 5 along the optical axis is adjustable, and its position moves according to the position of the superlens zoom group 4 to ensure that the image plane does not shift and the system conjugate distance remains unchanged during the zoom process.

[0047] The metalens in the system changes the direction of light by modulating the phase of light. The phase distribution of any single metalens satisfies the following conditions:

[0048]

[0049] in, is a non-zero natural number, is the distance from any point on the metalens surface to the center, are all constant coefficients.

[0050] Specifically, the parameters of the zoom metalens system of this embodiment are shown in Table 1:

[0051] Table 1

[0052]

[0053] In this embodiment, the zoom metalens system is designed to have a wavelength of 632.8 nm. The system F number is 1.0 at short focus, and the short focus focal length is 0.7 mm. The system F number is 3.6 at long focus, the design value of the long focus focal length is 4.2 mm, and the zoom ratio (i.e., the ratio of the maximum effective focal length to the minimum effective focal length) is 6. The total optical length TTL of the system is fixed to 7.8 mm during zooming to ensure that the conjugate distance remains unchanged during the zooming process. In order to reserve the distance between the last surface and the sensor, the minimum back focus of the system, i.e., the back focus BFL at short focus, is 2.0 mm. The dielectric microstructure array on the surface of the metalens can provide a phase distribution of , whose phase is described by the polynomial:

[0054]

[0055] in, is the radial coordinate of the metalens, The metalens fixing group 2, the metalens zoom group 4 and the metalens compensation group 5 are each composed of a metalens. See Table 2 for parameters.

[0056] Table 2

[0057]

[0058] See also Figure 1-18 , Figure 1 、 2 Figures 3, 4 are schematic diagrams of the zoom metalens system at magnifications of 1, 2, 4, and 6, respectively, corresponding to focal lengths of 0.7, 1.4, 2.8, and 4.2 mm. The mechanical dimensions of the metalens fixed group 2, metalens zoom group 4, and metalens compensation group 5 are 1 mm in radius. Aperture 3 is an aperture stop located on the front surface of metalens zoom group 4, with a radius of 0.25 mm. Aperture 3 moves with metalens zoom group 4. The metalens substrate is made of SiO2 material with a thickness of 0.6 mm. Adjusting the radius and arrangement of the dielectric microstructure array can produce the desired phase distribution on the metalens surface. The metalens' dielectric microstructure array is an array of dielectric cylindrical layers located on the rear surface of each metalens, toward the image point. The metalens' dielectric cylindrical layer array is made of Si material, with cylindrical unit structures of 378 nm in height arranged with a period of 347 nm. Using cylinders with radii of 48, 56, 59, 61, 63, 64, 67, and 76 nm, which provide phases of 0.39, 1.18, 1.96, 2.75, 3.53, 4.32, 5.11, and 5.90, respectively, the phase distribution is replaced by The components of 0~1 / 4π, 1 / 4π~1 / 2π, 1 / 2π~3 / 4π, 3 / 4π~π, π~5 / 4π, 5 / 4π~3 / 2π, 3 / 2π~7 / 4π, and 7 / 4π~2π are sampled discontinuously from the continuous theoretical phase. The phase distribution is provided according to the dielectric microstructure. The combined effect of the 0.6mm substrate on light propagation, the effective focal lengths of the metalens fixed group 2, the metalens zoom group 4 and the metalens compensation group 5 are mm, mm and mm.

[0059] Figure 5 Figure 3 is a curve diagram of the position change of the metalens zoom group 4 and the metalens compensation group 5 during the zoom process of the zoom metalens system. The position is calculated based on the front surface position of the metalens. Assume that the front surface position of the metalens fixed group 2 is 0. During the zoom process, the metalens compensation group 5 moves with the metalens zoom group 4. When the focal length changes from 0.7 mm to 4.2 mm, the magnification ratio changes from 1x to 6x. The metalens zoom group 4 and the aperture 3 move nonlinearly 1.09 mm away from the metalens fixed group 2, and the metalens compensation group 5 moves 0.79 mm to the opposite position.

[0060] Figure 6 、 7 Figures 8, 9, and 10 are the modulation transfer function (MTF) curves of the zoom metalens system at magnifications of 1, 2, 4, and 6, respectively. These curves depict the contrast of different frequency components after passing through the imaging system. Using 50 lp / mm as a reference standard, the MTFs simulated by ZEMAX in this embodiment are superior to 0.7 across all focal lengths. The short focal length, due to its minimum F-number, exhibits stronger diffraction-limited resolution, with an MTF exceeding 0.95 at 50 lp / mm. The F-number gradually increases at the long focal length, but the presence of the movable aperture increases the entrance pupil diameter at the long focal length, mitigating the increase in F-number and improving diffraction-limited resolution. At a focal length of 4.2 mm, the entrance pupil diameter increases to 1.17 mm, with an F-number of 3.6. At this focal length, the MTF at 250 lp / mm remains above 0.3. This demonstrates that this embodiment exhibits diffraction-limited resolution at all focal lengths.

[0061] Figure 10 、 11, 12, and 13 are the point spread functions of the xy section at the focal plane when the zoom metalens system has a zoom ratio of 1, 2, 4, and 6. This result is obtained by simulation of the angular spectrum theory based on fast Fourier transform, and the object plane is sampled using a 6916×6916 grid. The full width at half maximum (FWHM) of the focused light spot is 0.8μm, 0.99μm, 1.62μm, and 2.33μm, respectively. It can be seen that good focusing effect is achieved at all focal lengths, and there is only light field diffusion caused by diffraction, and no spherical aberration. According to the Airy disk formula, it can be seen that:

[0062]

[0063] Diffraction-limited Airy disk radius and wavelength The system's aperture F-number is related to this. Without a variable-position or -size iris, the entrance pupil diameter (EPD) remains fixed, resulting in a long-focus F-number that is six times that of the short-focus. However, in this embodiment, the entrance pupil diameter increases with focal length, ensuring that the long-focus F-number is only 3.6 times that of the short-focus, improving the diffraction limit at the long focal length. Focusing efficiency can also be calculated based on the xy-section light field distribution. Without considering the transmittance of the metalens itself, focusing efficiency is calculated using the ratio of energy trapped by three times the full width at half maximum (FWHM) to total energy. The results show that focusing efficiency is consistently greater than 70% at all focal lengths, reaching a maximum of 83.47% at the long focal length.

[0064] Figure 14 、 15 Figures 16, 17 show the xz cross-sectional light field distribution near the focal point of the zoom metalens system at zoom ratios of 1, 2, 4, and 6. The figures show the focusing of the light field before and after the focal point, demonstrating ideal focusing across the entire focal range. The telephoto lens exhibits a greater depth of focus, which increases with increasing aperture F-number. Using an adjustable aperture allows for further control of the F-number at the same focal length. The metalens zoom system can be applied to scenarios with varying depth of field requirements.

[0065] Figure 18 is a schematic diagram of another alternative aperture position provided by the present application. The aperture is located 1 mm in front of the fixed group. In this configuration, the aperture is fixed and does not change with focal length. However, the aperture radius is 0.35, 0.43, 0.52, and 0.55 mm at zoom ratios of 1, 2, 4, and 6, respectively. This achieves an effect equivalent to the variable-position, fixed-radius aperture in the aforementioned embodiment. Similarly, the aperture can be designed at different equivalent positions within the system, with the radius selected based on the position.

[0066] The zoom metalens system of this embodiment keeps the image plane from drifting with the focal length. Through the three components of the metalens fixed group, the metalens variable magnification group, and the metalens compensation group, it combines the advantage of the unchanged conjugate distance in the traditional optical zoom system and the excellent phase modulation capability of the metalens, achieving compact and efficient zoom. The aperture is introduced to control the entrance pupil diameter at different focal lengths, improving the diffraction limit at the telephoto end, and having excellent imaging quality at the entire focal length, solving the problem of not being able to strike a balance between zoom range and imaging quality.

[0067] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0068] The one or more embodiments of this application are intended to encompass all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of this application should be included in the scope of protection of this application.

Claims

1. A fixed conjugate distance zoom metalens system, characterized in that: The zoom metalens system comprises, in sequence along the optical axis from the object point (1) to the image point (6): The metalens fixed group (2) is composed of the effective focal length The single-piece metal lens or a multi-piece metal lens group is composed of the metal lens fixed group (2) having a fixed position; The super lens zoom group (4) is composed of the effective focal length The metalens is composed of a single metalens or a multi-metalens group, and the metalens zoom group (4) is positionally adjustable along the optical axis; The super lens compensation group (5) is composed of the effective focal length The metal lens compensation group (5) is adjustable in position along the optical axis and is adjusted along with the position adjustment of the metal lens variable magnification group (4); The phase distribution of any single metalens in the zoom metalens system satisfies the following conditions: in, is a non-zero natural number, is the distance from any point on the metalens surface to the center, are all constant coefficients.

2. The fixed conjugate distance zoom metalens system according to claim 1, wherein: The zoom metalens system further comprises an aperture (3) along the optical axis that moves with the movement of the metalens zoom group (4), and the aperture (3) is an aperture aperture that transmits light only in the central area.

3. The fixed conjugate distance zoom metalens system according to claim 2, wherein: The aperture (3) is one of a fixed-position variable-radius aperture, a position-variable fixed-radius aperture, and a position-variable variable-radius aperture. The position of the aperture (3) is equivalent to being located at any position between the object point (1) and the image point (6).

4. The fixed conjugate distance variable focus metalens system according to any one of claims 1 to 3, wherein: The ratio of the effective focal length of the zoom metalens system to the entrance pupil diameter is greater than or equal to 1.

5. The fixed conjugate distance variable focus metalens system according to any one of claims 1 to 3, wherein: The ratio of the maximum effective focal length to the minimum effective focal length of the zoom metalens system is greater than or equal to 6.

6. The fixed conjugate distance variable focus metalens system according to any one of claims 1 to 3, wherein: The ratio of the back focus to the total optical length of the zoom metalens system satisfies the following conditions: The back focus BFL is the distance from the rear surface of the metalens compensation group (5) to the image point (6), and the total optical length TTL is the distance from the front surface of the metalens fixing group (2) to the image point (6).

7. The fixed conjugate distance variable focus metalens system according to any one of claims 1 to 3, wherein: The effective focal length meets the following conditions: ， 。 8. The fixed conjugate distance variable focus metalens system according to any one of claims 1 to 3, wherein: The monolithic metalens includes a transparent substrate and a dielectric microstructure array disposed on a plane of the transparent substrate. The unit structures included in the dielectric microstructure array are divided into at least eight types of unit structures by changes in size and / or shape, and the phase provided by each unit structure satisfies uniform or non-uniform sampling in the range of 0 to 2π.

9. The fixed conjugate distance variable focus metalens system according to claim 8, wherein: An antireflection film is coated on the other plane of the transparent substrate.

10. The fixed conjugate distance variable focus metalens system according to claim 8, wherein: The material of the unit structure is one of Si, GaN, and TiO2, and the material of the transparent substrate is one of SiO2, K9, and BK7.

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