A wide-angle metalens and design method for endoscopic imaging system

Abstract

The present invention relates to a wide-angle metalens for an endoscopic imaging system and a design method thereof, wherein the wide-angle metalens comprises: at least one lens unit (1); the lens unit (1) comprises: a substrate (11); a micro-nanostructure (12) arranged on one side of the substrate (11) for modulating an incident light beam; the micro-nanostructure (12) comprises a plurality of nano-cylinders (121); the transmittance of the nano-cylinders (121) is higher than 0.8; the radius of the nano-cylinders (121) is greater than 0.8; and the radius of the nano-cylinders (121) is greater than 0.8. r Satisfies: [50nm, 165nm]∪[185nm, 200nm]. The nano-cylinders (121) are arranged on the substrate (11) in a phase distribution manner. The wide-angle super-lens of this solution provides an innovative solution for miniaturization and high-resolution imaging of endoscopes, significantly improves the microstructure characterization capability, and has important clinical application potential.

Description

Technical Field

[0001] The present invention relates to the field of optics, and in particular to a wide-angle metalens for an endoscopic imaging system and a design method thereof. Background Art

[0002] With the development of minimally invasive technology, endoscopes face the challenge of miniaturization, wide field of view, and high resolution in narrow anatomical environments such as the digestive tract and blood vessels. Traditional refractive lens systems are limited by volume expansion, aberration accumulation, and packaging complexity, making it difficult to meet the requirements for precise imaging in complex anatomical environments.

[0003] The development of modern fiber optic endoscope imaging systems needs to integrate three core features: wide field of view, subcellular resolution, and millimeter-level miniaturized optical elements, in order to meet the needs of precise diagnosis and treatment in complex anatomical environments, while minimizing the burden of interventional testing. Traditional endoscopes rely on multiple groups of refractive lenses to construct the objective system. The inherent contradiction between their physical size and optical performance has long restricted the miniaturization process of the instrument. Although traditional endoscopes can achieve basic imaging functions, they are limited by spherical aberration and field of view, which easily lead to image distortion, and require repeated balloon occlusion and saline flushing to obtain an instantaneous clear field of view. Such operations not only prolong the operation time, but may also induce adverse reactions. At the same time, the structural limitations of traditional endoscopes make it difficult to apply them to smaller scenarios, severely restricting the development of minimally invasive technology.

[0004] In recent years, researchers have tried to reduce the size of probes through multimode fiber wavefront shaping technology, but due to the spatiotemporal instability of fiber modal interference, it is difficult to achieve reliable real-time imaging.

[0005] To overcome the above limitations, miniaturized lens technology has become a key breakthrough in the innovation of endoscope systems. Although traditional gradient refractive index lenses and multi-lens cascade solutions can achieve wide-field imaging, their inherent limitations significantly restrict clinical applicability: first, to achieve a super-hemispherical field of view, 3-5 lens units need to be stacked, resulting in system volume expansion and cumulative spherical aberration effects; second, the optical axis alignment tolerance is low, which significantly increases the complexity of the packaging process. Existing micro-optical systems mostly use fisheye lens architecture to achieve wide-angle imaging, but the off-axis astigmatism and curvature radius limitations caused by their curved substrates seriously hinder their integrated application in ultra-fine endoscopy.

[0006] Therefore, a new lens design scheme is urgently needed to meet the development needs of endoscopic imaging systems. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a wide-angle metalens and a design method for an endoscopic imaging system.

[0008] To achieve the above-mentioned object of the invention, the present invention provides a wide-angle metalens for an endoscopic imaging system, comprising: at least one lens unit;

[0009] The lens unit includes: a substrate, a micro-nano structure disposed on one side of the substrate for modulating an incident light beam;

[0010] The micro-nano structure includes a plurality of nano-columns;

[0011] The transmittance of the nano-cylinder is higher than 0.8;

[0012] The radius of the nanocylinder r Satisfies: [50nm,165nm]∪[185nm,200nm];

[0013] The nano-cylinders are arranged on the substrate in a phase distribution manner, and the phase distribution formula is expressed as:

[0014]

[0015] in, represents the calculated phase, represents the diffraction order, represents the number of polynomial coefficients in the series, Indicates the sequence number of the polynomial coefficients, It is i The coefficient of the term is the normalized radial aperture coordinate, is the normalized radius of the lens element, is the radius of any point on the plane of the lens element.

[0016] According to one aspect of the present invention, two lens units are coaxially arranged;

[0017] Along the output direction of the incident light, the micro-nano structure of the first lens unit is connected to the base of the second lens unit.

[0018] According to one aspect of the present invention, along the output direction of the incident light, the thickness of the base of the first lens unit is greater than the thickness of the base of the second lens unit;

[0019] Along the output direction of the incident light, the diffraction orders of the first lens unit and the second lens unit in the phase distribution formula of the nano-cylinder are All meet the following requirements: , the number of polynomial coefficients of the first lens unit and the second lens unit All meet the following requirements: , the normalized radius of the first lens unit and the second lens unit All meet the following requirements: , the coefficient of the first lens unit Greater than the coefficient of the second lens unit , the coefficient of the first lens unit is smaller than the coefficient of the second lens unit , the coefficient of the first lens unit Greater than the coefficient of the second lens unit , the coefficient of the first lens unit is smaller than the coefficient of the second lens unit , the coefficient of the first lens unit Greater than the coefficient of the second lens unit .

[0020] According to one aspect of the present invention, along the output direction of the incident light, in the phase distribution formula for the nano-cylinder, the coefficient of the first lens unit is ,coefficient ,coefficient ,coefficient ,coefficient Satisfy respectively: , , , , ; The coefficient of the second lens unit (1) ,coefficient ,coefficient ,coefficient ,coefficient Satisfy respectively: , , , , .

[0021] According to one aspect of the present invention, the height of the nanocolumns satisfy:

[0022]

[0023] in, represents the wavelength of incident light, represents the effective refractive index of the nanocylinder, represents the refractive index of the surrounding medium;

[0024] The modulation of the phase of the nanocylinder covers 0 to 2π.

[0025] According to one aspect of the present invention, the substrate is a regular transparent plate;

[0026] Along the output direction of the incident light, the thickness of the base of the first lens unit is 2.3 mm to 2.5 mm, and the thickness of the base of the second lens unit is 9.985 μm to 9.990 μm.

[0027] According to one aspect of the present invention, the nano-cylinders are amorphous silicon nano-cylinders arranged in a cubic lattice;

[0028] The substrate is a silicon dioxide substrate.

[0029] According to one aspect of the present invention, each of the nano-cylinders is arranged on the substrate based on a corresponding cubic lattice, and the nano-cylinders are coaxially arranged with the cubic lattice;

[0030] The arrangement period of the cubic lattice used for arranging the nano-columns is 0.65 μm to 0.75 μm.

[0031] According to one aspect of the present invention, the lens unit has a system aperture of 1.8 mm to 1.9 mm, an operating wavelength of 1.5 μm, and a field of view of -50° to 50°;

[0032] The relative illumination of the lens unit in all fields of view is greater than or equal to 98.89%, and the Strehl Ratio index of each field of view is greater than or equal to 0.995.

[0033] To achieve the above-mentioned object of the invention, the present invention provides a design method for the aforementioned wide-angle metalens for an endoscopic imaging system, comprising:

[0034] S1. Setting initial parameters for the wide-angle metalens, wherein the initial parameters include: incident light wavelength, lens material, entrance pupil diameter, field of view angle, dimensions and number of lens units;

[0035] S2. constructing an initial configuration of the lens unit, wherein the lens unit comprises: a substrate, a micro-nanostructure disposed on one side of the substrate for modulating an incident light beam, the micro-nanostructure comprising a plurality of nano-cylinders;

[0036] S3. Establishing a unit nanocell for designing the nanocolumn based on the initial configuration of the lens unit, wherein the unit nanocell includes: a nanocolumn, a cubic lattice divided based on the substrate, and the nanocolumn is coaxially arranged with the cubic lattice;

[0037] S4. Determine the diameter scanning interval of the nano-cylinder and the arrangement period of the cubic lattice based on the unit nano-cell;

[0038] S5. Set the wavelength of the incident light wave, perform scanning simulation on the nano-cylinders of different heights in the diameter scanning range, and determine the height, transmittance and radius of the nano-cylinder based on the scanning simulation results and the modulation coverage range of the nano-cylinder phase. r The value range of

[0039] S6. Based on the determined height, transmittance and radius of the nano-cylinder r The value range of is matched with the phase distribution formula of the nano-cylinder to obtain the position and size of each nano-cylinder;

[0040] S7. distributing the obtained positions and sizes of the respective nano-cylinders on the substrate and setting the thickness of the substrate to construct the lens unit;

[0041] S8. Repeat steps S3 to S7 based on the number of lens units in the wide-angle metalens to complete the construction of the wide-angle metalens.

[0042] According to one solution of the present invention, the wide-angle metalens of this solution can achieve a system aperture of 1.8mm to 1.9mm, an operating wavelength of 1.5μm, a field of view angle range of ±50°, and all fields of view have a relative illumination of more than 98.89%, and the Strehl Ratio index of each field of view is maintained above 0.995. In addition, the MTF curve of the wide-angle metalens in this solution at different incident angles is very close to the diffraction limit, and has reliable performance.

[0043] According to one solution of the present invention, the wide-angle metalens of this solution can be creatively constructed as a near-infrared wide-field metalens based on a doublet metalens architecture. The phase distribution of the optimized cascaded micro-nanostructures and the structural design of the nanocylinders between the lens units more fully ensure that its MTF curve is close to the diffraction limit, making it greater than 0.84 at 21 lp / mm.

[0044] According to one solution of the present invention, the wide-angle metalens of this solution achieves the coordination of correction and focusing based on the optimized design of the doublet metalens architecture, maintaining a full width at half maximum (FWHM) of 6.212μm and a low sidelobe intensity of less than 1.74% at an extreme field of view of 50°, significantly outperforming the performance degradation trend of traditional spherical lenses.

[0045] According to one embodiment of the present invention, the wide-angle metalens of this embodiment provides an innovative solution for miniaturized, high-resolution imaging of endoscopes, significantly improves the microstructure characterization capability, and has important clinical application potential.

[0046] According to one approach of the present invention, a doublet metalens architecture overcomes the field-of-view-resolution trade-off limitations of traditional refractive lenses by combining cascaded correction and focusing with optimized even-order polynomial phase distribution and nanostructure parameters. Finite-difference time-domain analysis demonstrated that an array of single-crystal silicon nanocylinders achieved phase coverage from 0 to 2π and a transmittance greater than 80%, avoiding resonance losses.

[0047] According to one solution of the present invention, the wide-angle super-transparency of the super-lens not only solves the contradiction between endoscope miniaturization and wide-field imaging, but also provides a new paradigm for subcellular resolution imaging in complex environments. With its excellent aberration correction capability, the system is expected to significantly improve the display accuracy of tiny structures while reducing interference from the surrounding environment. In addition, based on this solution, it can be further expanded to multi-wavelength achromatic design, combined with the optimization of flexible substrate materials, to promote the application of super-lenses in wearable interventional devices and dynamic imaging scenarios, which has extremely high application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 1 is a structural diagram of a wide-angle metalens for an endoscopic imaging system according to an embodiment of the present invention;

[0049] Figure 2 Schematic diagram of the phase distribution of nano-cylinders in a micro-nano structure according to one embodiment of the present invention;

[0050] Figure 3 is the radius of any point on the lens unit plane of one embodiment of the present invention Normalized radius of the lens element Schematic diagram of the relative positions of

[0051] Figure 4 A structural diagram of a unit nanocell composed of nanocolumns and cubic lattices according to one embodiment of the present invention;

[0052] Figure 5 This is a diagram showing the focusing effect of a lens unit in an embodiment of the present invention at different field angles in an xz cross section;

[0053] Figure 6 is a geometric point diagram of a lens unit at different field angles according to an embodiment of the present invention, wherein: Figure 6 (a) Geometric spot diagram showing a field of view angle of 0°, Figure 6 (b) shows the geometric spot diagram with a field of view angle of 10°. Figure 6 (c) shows the geometric point diagram with a field of view angle of 20°. Figure 6 (d) shows the geometric point diagram with a field of view angle of 28°. Figure 6 (e) shows the geometric point diagram with a field of view angle of 36°. Figure 6(f) shows the geometric point diagram with a field of view angle of 42°. Figure 6 (g) shows the geometric spot diagram with a field of view angle of 46°. Figure 6 (h) Geometric spot diagram showing a field of view angle of 50°;

[0054] Figure 7 This is a diffraction MTF curve diagram of a lens unit at different field angles according to an embodiment of the present invention;

[0055] Figure 8 is a relative illumination curve of a lens unit according to an embodiment of the present invention;

[0056] Figure 9 is a phase diagram of the first lens unit along the output direction of the incident light in one embodiment of the present invention;

[0057] Figure 10 is a phase diagram of the second lens unit along the output direction of the incident light in one embodiment of the present invention;

[0058] Figure 11 This is a phase diagram obtained by simulating a unit nanocell according to an embodiment of the present invention under a scenario with an incident light wavelength of 1.5 μm;

[0059] Figure 12 This is a transmittance diagram obtained by simulating a unit nanocell according to an embodiment of the present invention under a scenario with an incident light wavelength of 1.5 μm;

[0060] Figure 13 This is a phase diagram obtained by simulation under a scenario where the nanocolumn height in a unit nanocell of one embodiment of the present invention is 1.2 μm and the incident light wavelength is 1.5 μm;

[0061] Figure 14 This is a transmittance graph obtained by simulation under a scenario where the height of the nanocolumns in the unit nanocell of one embodiment of the present invention is 1.2 μm and the incident light wavelength is 1.5 μm. DETAILED DESCRIPTION

[0062] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0063] When describing the embodiments of the present invention, the orientation or positional relationship expressed by the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or positional relationship shown in the relevant drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

[0064] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not limited to the following embodiments.

[0065] like Figure 1 As shown, according to one embodiment of the present invention, a wide-angle metalens for an endoscopic imaging system of the present invention includes: at least one lens unit 1; wherein the lens unit 1 includes: a substrate 11, and a micro-nanostructure 12 disposed on one side of the substrate 11 for modulating an incident light beam; in this embodiment, the substrate 11 is a plate-like structure with a regular shape, and its two axially opposite side surfaces are both flat. Furthermore, the micro-nanostructure 12 disposed on one side of the substrate 11 includes a plurality of nano-cylinders 121; wherein the transmittance of the nano-cylinders 121 is greater than 0.8; the radius of the nano-cylinders 121 is greater than 0.8. r Satisfies: [50nm,165nm]∪[185nm,200nm]. Further, if Figure 2 As shown, the nano-cylinders 121 in the micro-nano structure 12 are arranged on the substrate 11 in a phase distribution manner, and the phase distribution formula is expressed as:

[0066]

[0067] in, represents the calculated phase, represents the diffraction order, represents the number of polynomial coefficients in the series, Indicates the sequence number of the polynomial coefficients, It is i The coefficient of the term is the normalized radial aperture coordinate, is the normalized radius of lens element 1, is the radius of any point on the plane of lens element 1, see Figure 3 .

[0068] Through the above-described configuration, the wide-angle metalens of this embodiment can fully achieve excellent imaging effects in the near-infrared wide field of view by configuring the corresponding lens unit 1. Specifically, the innovatively designed micro-nanostructure 12 in the lens unit 1 enables the present invention to fully meet the requirements of achieving ±50° field of view coverage at a wavelength of 1.5 μm. At the same time, the relative illumination of the lens unit 1 in all fields of view is greater than or equal to 98.89%, and the Strehl Ratio index of each field of view is greater than or equal to 0.995.

[0069] Through the above settings, the MTF value of the lens unit 1 of this solution is close to the diffraction limit, which is greater than 0.84 at 21 lp / mm, fully ensuring the imaging quality of the present invention, providing an innovative solution for miniaturization and high-resolution imaging of endoscopes, significantly improving the microstructure characterization capability, and having important clinical application potential.

[0070] like Figure 1 As shown, according to one embodiment of the present invention, in the wide-angle metalens of the present invention, two lens units 1 are coaxially arranged; wherein, along the output direction of the incident light, the micro-nanostructure 12 of the first lens unit 1 is connected to the substrate 11 of the second lens unit 1. In this embodiment, the micro-nanostructure 12 of the first lens unit 1 and the substrate 11 of the second lens unit 1 are connected by abutting or gluing. Thus, through this connection, the light beam optimized by the first lens unit 1 is accurately and reliably transmitted to the second lens unit 1, making the imaging effect of this solution even better and fully eliminating errors in the transmission path.

[0071] like Figure 1 As shown, according to one embodiment of the present invention, along the output direction of the incident light, the thickness of the substrate 11 of the first lens unit 1 is greater than the thickness of the substrate 11 of the second lens unit 1; further, along the output direction of the incident light, in the phase distribution formula for the nano-cylinder 121, the diffraction orders of the first lens unit 1 and the second lens unit 1 are All meet the following requirements: , the number of polynomial coefficients of the first lens unit 1 and the second lens unit 1 All meet the following requirements: , the normalized radius of the first lens unit 1 and the second lens unit 1 All meet the following requirements: , the coefficient of the first lens unit 1 Greater than the coefficient of the second lens unit 1 , the coefficient of the first lens unit 1 Smaller than the coefficient of the second lens unit 1 , the coefficient of the first lens unit 1 Greater than the coefficient of the second lens unit 1 , the coefficient of the first lens unit 1 Smaller than the coefficient of the second lens unit 1 , the coefficient of the first lens unit 1 Greater than the coefficient of the second lens unit 1 .

[0072] Through the above-mentioned setting, through the above-mentioned setting of the thickness between the substrates 11 of each lens unit 1, and based on the above-mentioned phase distribution setting of the nano-cylinders 121, the nano-cylinders 121 of the present invention are matched with their structural characteristics in terms of distribution position, so that the imaging uniformity of each lens unit 1 is improved, and the imaging performance matching between the two connected lens units 1 is fully achieved, thereby ensuring that the relative illumination value of all fields of view is greater than or equal to 98.89%, achieving high brightness uniformity of the imaging plane, and ensuring the imaging quality of the wide-field endoscope.

[0073] According to one embodiment of the present invention, along the output direction of the incident light, the coefficient of the first lens unit 1 in the phase distribution formula for the nano-cylinder 121 is ,coefficient ,coefficient ,coefficient ,coefficient Satisfy respectively: , , , , ; The coefficient of the second lens unit 1 ,coefficient ,coefficient ,coefficient ,coefficient Satisfy respectively: , , , , .

[0074] Through the above-mentioned arrangement, the present invention forms a double superlens architecture by arranging two lens units 1, so that this solution more effectively utilizes the near-infrared wide field of view, and by creatively optimizing the phase distribution formula of the nanocylinders 121 on the two adjacent wide-angle superlenses, the micro-nanostructures 12 on the two wide-angle superlenses can achieve a complementary promotion effect. Specifically, along the output direction of the incident light, the two lens units 1 respectively assume the wavefront pre-compensation and main focusing functions, so that this solution fully meets the corresponding imaging performance requirements.

[0075] like Figure 4 As shown, according to one embodiment of the present invention, the height of the nanocolumn 121 is satisfy:

[0076]

[0077] in, represents the wavelength of incident light, represents the effective refractive index of the nano-cylinder 121, In this embodiment, since the two opposite ends of the nanocolumn 121 are in contact with the substrate 11, The value of is generally the refractive index of the substrate 11.

[0078] In this embodiment, the height of the nanocolumns 121 is The above setting is set at 0.6 μm to 1.3 μm. The light transmission performance and path of the nano-cylinder 121 are optimized, so that it can more reliably match the thickness of the corresponding substrate 11, thereby fully ensuring the working performance of this solution.

[0079] like Figure 1 As shown, according to one embodiment of the present invention, the substrate 11 is a regular transparent plate. In the output direction of the incident light, the thickness of the substrate 11 of the first lens unit 1 is 2.3 mm to 2.4 mm, and the thickness of the substrate 11 of the second lens unit 1 is 9.985 μm to 9.990 μm. In this embodiment, the substrate 11 can be made of silicon dioxide.

[0080] Through the above-mentioned setting, in this solution, by setting the thickness of the substrate 11 within the above-mentioned range, the thickness of the substrate 11 can be flexibly set to match the substrate 11 with the nano-cylinders 121, thereby achieving mutual matching of performance when there are differences in the performance presented by different lens units 1. As a result, this solution fully meets its performance requirements and adapts to corresponding application scenarios, which is more beneficial to ensuring the imaging quality of the present invention.

[0081] In addition, through the above-mentioned arrangement, the arrangement and distribution of the lens units 1 in the wide-angle metalens can be flexibly realized, especially when multiple lens units 1 are arranged, which effectively ensures the structural matching and imaging quality matching between adjacent lens units 1, making the structure and usage performance of this solution more excellent.

[0082] According to one embodiment of the present invention, the phase modulation of the nano-cylinder 121 covers 0 to 2π.

[0083] Through the above settings, the high-quality focusing and imaging of this solution are effectively guaranteed, providing a reliable guarantee for meeting its high-resolution performance.

[0084] like Figure 4As shown, according to one embodiment of the present invention, the nano-cylinders 121 are amorphous silicon nano-cylinders arranged in a cubic lattice.

[0085] like Figure 4 As shown, according to one embodiment of the present invention, each nano-cylinder 121 is arranged on a substrate 11 based on a corresponding cubic lattice, and the nano-cylinder 121 is arranged coaxially with the cubic lattice; wherein the arrangement period of the cubic lattice used to arrange the nano-cylinders 121 is 0.65μm to 0.75μm. In this embodiment, the arrangement period of the cubic lattice is preferably 0.7μm.

[0086] Through the above arrangement, the high-order diffraction of the nano-cylinders 121 can be effectively suppressed based on the smaller period, thereby effectively ensuring the imaging performance of the present invention.

[0087] like Figure 4 As shown, according to one embodiment of the present invention, the dimensional variation error of the diameter of the nano-cylinder 121 in the direction away from the substrate 11 is within ±10%; thereby, the imaging quality and phase coverage range of the nano-cylinder 121 are fully guaranteed.

[0088] like Figure 1 As shown, according to one embodiment of the present invention, the system aperture of the lens unit 1 is 1.8 mm to 1.9 mm, the operating wavelength is 1.5 μm, and the field of view angle is -50° to 50°; the relative illumination of the lens unit 1 in all fields of view is greater than or equal to 98.89%, and the Strehl Ratio index of each field of view is greater than or equal to 0.995.

[0089] According to one embodiment of the present invention, the present invention provides a design method for the aforementioned wide-angle metalens for an endoscopic imaging system, comprising:

[0090] S1. Setting initial parameters for the wide-angle metalens, wherein the initial parameters include: incident light wavelength, lens material, entrance pupil diameter, field of view angle, dimensions and number of lens units 1;

[0091] S2. Constructing an initial configuration of the lens unit 1, wherein the lens unit 1 includes: a substrate 11, a micro-nanostructure 12 disposed on one side of the substrate 11 for modulating an incident light beam, the micro-nanostructure 12 including a plurality of nano-cylinders 121;

[0092] S3. Establishing a unit nanocell for designing the nanocylinder 121 based on the initial configuration of the lens unit 1, wherein the unit nanocell includes: a nanocylinder 121, a cubic lattice divided based on the substrate 11, and the nanocylinder 121 is coaxially arranged with the cubic lattice;

[0093] S4. Determine the diameter scanning interval of the nano-cylinder 121 and the arrangement period of the cubic lattice based on the unit nano-cell; in this embodiment, the diameter scanning interval can be set to 100nm to 400nm; the arrangement period of the cubic lattice is set to 0.65μm to 0.75μm, preferably 0.7μm;

[0094] S5. Set the wavelength of the incident light wave, perform scanning simulation on the nano-cylinders 121 of different heights in the diameter scanning range, and determine the height, transmittance and radius of the nano-cylinders 121 based on the scanning simulation results and the modulation coverage range of the phase of the nano-cylinders 121 r In this embodiment, in the step of scanning simulation of nano-cylinders 121 of different heights under the diameter scanning interval, the height range is set to 0.6μm to 1.3μm;

[0095] S6. Based on the determined height, transmittance and radius of the nano-cylinder 121 r The value range of is matched with the phase distribution formula of the nano-cylinder 121 to obtain the position and size of each nano-cylinder 121; in this embodiment, the height, transmittance and radius of the nano-cylinder 121 r The value range of is achieved based on the set distribution law in the process of matching based on the phase distribution formula; wherein the distribution law includes: the nano cylinder 121 includes a distribution area and a radius r Changing trend; wherein, the division rule of the distribution area is: in the direction from the center to the edge of the substrate 11, a plurality of distribution areas for the nano-cylinders 121 are set, wherein the distribution area at the center is the first area, and the first area is the surface area, and the remaining areas in the direction from the center to the edge of the substrate 11 are annular areas. In this embodiment, the number of annular areas can be selected according to the specific design of different lens units 1. For example, it can reach hundreds. Of course, the annular areas can also be set to other numbers, and adaptive selection is made based on the phase distribution formula on the lens unit 1, which will not be repeated here. Through the regional distribution set as above, the surface area based on the center makes the input light have a better transmission effect at the position close to the center, and the use of annular areas at the position close to the edge can make the input light easier to accurately distribute around the central surface area. Therefore, the combination of the surface area and the annular area can make the lens unit 1 of this scheme fully meet the advantages of wide-angle focusing, high-resolution imaging and compact structure.

[0096] Furthermore, in the first region, the nano-cylinders 121 are distributed axially symmetrically, wherein the first region has a central sub-region, and the diameters of the nano-cylinders 121 in the central sub-region are uniform. The diameters of the remaining nano-cylinders 121 gradually decrease as they move away from the edge of the central sub-region toward the edge of the first region. Based on this arrangement, by further zoning the opposite regions, the use of uniformly sized nano-cylinders 121 in the central sub-region can fully meet the requirements for light transmission at the center of the first region, fully satisfying the focus while also uniformly distributing the focus area over a wide range. Furthermore, the gradually decreasing diameter outside the central sub-region can expand the central focus area outward in a circular manner, thereby enabling this solution to fully meet the advantages of wide-angle focusing and high-resolution imaging.

[0097] Furthermore, the edge of the first region may be a regular edge, for example, it may be set to a circle, a polygon, etc., and may be set accordingly based on the specific phase distribution of the nanocylinders 121. For example, the edge of the first region may be set to an octagonal edge, while the edge of the central sub-region may be set to a rectangular edge, wherein the number of nanocylinders 121 set on the four sides (i.e., long sides) parallel to the first region and the central sub-region is greater than the number of nanocylinders 121 set on the remaining sides (i.e., short sides), and the diameters of the nanocylinders 121 on the four sides (i.e., long sides) parallel to the first region and the central sub-region are different, wherein the diameter of the nanocylinders 121 gradually decreases in the direction extending from the center of the long side to the two ends, and the diameter of the nanocylinders 121 gradually decreases in the direction extending from the center of the short side to the two ends.

[0098] In this embodiment, the width of each of the multiple annular regions on the substrate 11 gradually decreases from the center to the edge of the substrate 11, and the diameter of the nanocylinders 121 in each annular region gradually decreases from the center to the edge of the substrate 11. In this embodiment, the nanocylinders 121 are arranged in an axisymmetric manner within the annular regions.

[0099] Through the above configuration, based on the optimized distribution of the nano-cylinders 121 and in combination with the corresponding phase distribution formula, the distribution of the nano-cylinders 121 can be optimized, so that the correspondingly configured lens unit 1 can achieve the optimal optical performance.

[0100] S7. Based on the obtained positions and sizes of the respective nano-cylinders 121, the nano-cylinders are distributed on the substrate 11 and the thickness of the substrate 11 is set to construct the lens unit 1;

[0101] S8. Repeat steps S3 to S7 based on the number of lens units 1 in the wide-angle metalens to complete the construction of the wide-angle metalens.

[0102] In order to further illustrate the advantages of the wide-angle metalens of this solution, an example is given to illustrate it.

[0103] In this embodiment, the wide-angle metalens of this solution is implemented using a doublet metalens architecture, wherein two lens units 1 are coaxially arranged. Each lens unit 1 uses amorphous silicon circular nanorods arranged in a cubic lattice as the basic structure of the metalens. Therefore, both lens units 1 have a polarization-insensitive effect. In this embodiment, the orientation of the micro-nanostructures 12 on the two lens units 1 is consistent. Figure 1 In this embodiment, a light shielding plate having a light-transmitting hole with an aperture of 0.5 mm may be further provided in front of the first lens unit 1 along the output direction of the incident light, which will serve as an entrance for receiving light, wherein the light shielding plate and the base 11 of the first lens unit 1 may be connected (e.g., in contact with or attached).

[0104] In this embodiment, the base 11 of the lens unit 1 is made of silicon dioxide, wherein the diameter of the base 11 is 1.83 mm. Along the output direction of the incident light, the thickness of the base 11 of the first lens unit 1 is 2.5 mm, and the thickness of the base 11 of the second lens unit 1 is 9.989 μm.

[0105] In this embodiment, the micro-nano structure 12 includes a plurality of nano-cylinders 121 , wherein the nano-cylinders 121 are made of amorphous silicon.

[0106] In this embodiment, along the output direction of the incident light, the parameter settings in the phase distribution formula of the nano-cylinders 121 on the first lens unit 1 and the parameter settings in the phase distribution formula of the nano-cylinders 121 on the second lens unit 1 are summarized in Table 1.

[0107] Table 1

[0108]

[0109] Based on the above phase distribution formula, the phase distribution of the obtained nano-cylinder 121 is simulated by ray tracing method, and the focusing effect of the wide-angle metalens with different field angles using the aforementioned doublet metalens architecture is obtained. The different field angles used are: 0°, 10°, 20°, 28°, 36°, 42°, 46°, and 50°, respectively. Figure 5 It can be seen that when the incident angle increases from 0° to 50°, the outgoing light maintains a good focusing effect on the focal plane. Figure 6It can be seen that in the spot diagram of the wide-angle metalens using the aforementioned doublet metalens architecture, the radius of the Airy disk is 7.147μm, and the RMS values ​​of the obtained spot radii are 0.508μm, 0.581μm, 0.644μm, 0.993μm, 0.544μm, 0.507μm, 0.758μm, and 0.765μm, respectively. This indicates that all light rays are within the Airy disk, and therefore the designed lens is a diffraction-limited lens. Figure 7 It can be seen that in the MTF curves of different fields of view of the wide-angle metalens using a doublet metalens architecture, the cutoff frequency of the calculated MTF value is 21lp / mm. The MTF values ​​of all fields of view at 21lp / mm are 0.842975, 0.841512, 0.841875, 0.841289, 0.842704, 0.842824, 0.841855 and 0.841605 respectively. The calculated diffraction-limited MTF value is 0.843180, indicating that the designed optical lens has very good imaging quality. Figure 8 It can be seen that the relative illumination (RI) of the wide-angle metalens using the doublet metalens architecture is higher than 0.9889, which proves that the wide-angle metalens imaging plane has good brightness uniformity, ensuring the imaging quality of the wide-field endoscope. Figure 9 , the phase of the designed first lens unit 1 fully satisfies the role of wavefront pre-compensation; see Figure 10 The designed phase of the second lens unit 1 fully satisfies the main focusing function.

[0110] In this embodiment, the radius of the nano-cylinder 121 is r Satisfying: [50nm, 165nm] ∪ [185nm, 200nm], the arrangement period of the cubic lattice used to arrange the nano-cylinders 121 is 0.7μm, and the height of the nano-cylinders 121 is set to 1.2μm. Therefore, based on the parameter settings of the nano-cylinders 121 and the period setting of the cubic lattice, FDTD software is used to simulate it under the scenario of 1.5μm incident light wavelength, and the simulation results can be obtained. Figures 11 to 14 , it can be seen that the phase modulation of nano-cylinder 121 covers 0 to 2 In the case of the radius of the nano-cylinder 121 r When [50nm, 165nm]∪[185nm, 200nm] is satisfied, the nanocylinders 121 fully meet the phase coverage requirement, and the transmittance is higher than 0.8.

[0111] The above contents are merely examples of specific solutions of the present invention. For devices and structures not described in detail, it should be understood that they can be implemented by adopting general devices and methods available in the art.

[0112] The above description is merely one embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A wide-angle metalens for an endoscopic imaging system, characterized in that: include: Two lens units (1) arranged coaxially; The lens unit (1) comprises: a substrate (11), a micro-nanostructure (12) arranged on one side of the substrate (11) and used for modulating an incident light beam; The micro-nano structure (12) includes a plurality of nano-columns (121); The transmittance of the nano-cylinder (121) is higher than 0.8; The radius of the nanocylinder (121) r Satisfies: [50nm,165nm]∪[185nm,200nm]; The nano-cylinders (121) are arranged on the substrate (11) in a phase distribution manner, and the phase distribution formula is expressed as: in, represents the calculated phase, represents the diffraction order, represents the number of polynomial coefficients in the series, Indicates the sequence number of the polynomial coefficients, It is i The coefficient of the term is the normalized radial aperture coordinate, is the normalized radius of the lens element (1), is the radius of any point on the plane of lens element (1); In the direction from the center to the edge of the substrate (11), a plurality of distribution areas for the nano-cylinders (121) are provided, wherein the distribution area at the center is a first area, and the first area is a surface area, and the remaining areas in the direction from the center to the edge of the substrate (11) are annular areas; The first region has a central sub-region, and the diameters of the nano-cylinders (121) in the nano-cylinders (121) are uniform, and the diameters of the remaining nano-cylinders (121) gradually decrease in a direction away from the edge of the central sub-region to the edge of the first region; Along the output direction of the incident light, the micro-nano structure (12) of the first lens unit (1) is connected to the substrate (11) of the second lens unit (1); Along the output direction of the incident light, the thickness of the base (11) of the first lens unit (1) is greater than the thickness of the base (11) of the second lens unit (1); Along the output direction of the incident light, in the phase distribution formula for the nano-cylinder (121), the diffraction orders of the first lens unit (1) and the second lens unit (1) are All meet the following requirements: , the number of polynomial coefficients of the first lens unit (1) and the second lens unit (1) All meet the following requirements: , the normalized radius of the first lens unit (1) and the second lens unit (1) All meet the following requirements: , the coefficient of the first lens unit (1) greater than the coefficient of the second lens unit (1) , the coefficient of the first lens unit (1) is smaller than the coefficient of the second lens unit (1) , the coefficient of the first lens unit (1) greater than the coefficient of the second lens unit (1) , the coefficient of the first lens unit (1) is smaller than the coefficient of the second lens unit (1) , the coefficient of the first lens unit (1) greater than the coefficient of the second lens unit (1) .

2. The wide-angle metalens for an endoscopic imaging system according to claim 1, wherein In the phase distribution formula for the nano-cylinder (121) along the output direction of the incident light, the coefficient of the first lens unit (1) is ,coefficient ,coefficient ,coefficient ,coefficient Satisfy respectively: , , , , ; The coefficient of the second lens unit (1) ,coefficient ,coefficient ,coefficient ,coefficient Satisfy respectively: , , , , .

3. The wide-angle metalens for an endoscopic imaging system according to claim 2, wherein: The height of the nanocolumn (121) satisfy: in, represents the wavelength of incident light, represents the effective refractive index of the nanocylinder (121), represents the refractive index of the surrounding medium; The modulation of the phase of the nanocylinder (121) covers 0 to 2π.

4. The wide-angle metalens for an endoscopic imaging system according to claim 3, wherein The base (11) is a regular transparent plate; Along the output direction of the incident light, the thickness of the base (11) of the first lens unit (1) is 2.3 mm to 2.5 mm, and the thickness of the base (11) of the second lens unit (1) is 9.985 μm to 9.990 μm.

5. The wide-angle metalens for an endoscopic imaging system according to claim 4, wherein: The nano cylinders (121) are amorphous silicon nano cylinders arranged in a cubic lattice; The substrate (11) is a silicon dioxide substrate.

6. The wide-angle metalens for an endoscopic imaging system according to claim 5, wherein: On the substrate (11), each of the nanocolumns (121) is arranged based on a corresponding cubic lattice, and the nanocolumns (121) are coaxially arranged with the cubic lattice; The arrangement period of the cubic lattice used for arranging the nano-columns (121) is 0.65 μm to 0.75 μm.

7. The wide-angle metalens for an endoscopic imaging system according to claim 6, wherein: The lens unit (1) has a system aperture of 1.8 mm to 1.9 mm, an operating wavelength of 1.5 μm, and a field of view of -50° to 50°; The relative illumination of the lens unit (1) in all viewing fields is greater than or equal to 98.89%, and the Strehl Ratio index of each viewing field is greater than or equal to 0.

995.

8. A method for designing a wide-angle metalens for an endoscopic imaging system according to any one of claims 1 to 7, characterized in that: include: S1. Setting initial parameters for the wide-angle metalens, wherein the initial parameters include: incident light wavelength, lens material, entrance pupil diameter, field of view angle, dimensions and number of lens units (1); S2. constructing an initial configuration of the lens unit (1), wherein the lens unit (1) comprises: a substrate (11), a micro-nanostructure (12) disposed on one side of the substrate (11) for modulating an incident light beam, the micro-nanostructure (12) comprising a plurality of nano-cylinders (121); S3. establishing a unit nanocrystal cell for designing the nanocylinder (121) based on the initial configuration of the lens unit (1), wherein the unit nanocrystal cell comprises: a nanocylinder (121), a cubic lattice divided based on the substrate (11), and the nanocylinder (121) is coaxially arranged with the cubic lattice; S4. determining the diameter scanning interval of the nanocolumn (121) and the arrangement period of the cubic lattice based on the unit nanocell; S5. Setting the wavelength of the incident light wave, performing scanning simulation on the nano-cylinders (121) of different heights in the diameter scanning interval, and determining the height, transmittance and radius of the nano-cylinders (121) based on the scanning simulation results and the modulation coverage of the phase of the nano-cylinders (121). r The value range of S6. Based on the determined height, transmittance and radius of the nano-cylinder (121) r The value range of is matched with the phase distribution formula of the nano-cylinder (121) to obtain the position and size of each nano-cylinder (121); S7. Based on the obtained positions and sizes of the respective nano-cylinders (121), the nano-cylinders (121) are distributed on the substrate (11), and the thickness of the substrate (11) is set to construct the lens unit (1); S8. Repeat steps S3 to S7 based on the number of the lens units (1) in the wide-angle metalens to complete the construction of the wide-angle metalens.

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