Wide-angle super lens for endoscopic imaging system and design method

Abstract

The invention relates to a wide-angle super lens for an endoscopic imaging system and a design method, and the wide-angle super lens comprises at least one lens unit (1); the lens unit (1) comprises a substrate (11) and a micro-nano structure (12) which is arranged on one side of the substrate (11) and is used for modulating an incident light beam; the micro-nano structure (12) comprises a plurality of nano cylinders (121); the transmittance of the nano cylinder (121) is higher than 0.8; the radius r of the nanometer cylinder (121) meets the condition that the radius r of the nanometer cylinder (121) is equal to that of [50 nm, 165 nm] and is equal to that of [185 nm, 200 nm]. The nanocylinders (121) are arranged on the substrate (11) in a phase distribution-based manner. According to the wide-angle super lens, an innovative solution is provided for miniaturization and high-resolution imaging of an endoscope, the microstructure characterization capacity is remarkably improved, and the wide-angle super lens has important clinical application potential.

Description

Technical Field

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

[0002] With the development of minimally invasive techniques, endoscopes face challenges in the coordinated optimization 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 precise imaging requirements in complex anatomical environments.

[0003] The development of modern fiber optic endoscope imaging systems requires the integration of three core features: a wide field of view, sub-cellular resolution, and millimeter-scale miniaturized optical components to meet the precise diagnosis and treatment needs in complex anatomical environments while minimizing the burden caused by invasive detection. Traditional endoscopes rely on multiple sets of refractive lenses to construct the objective lens system, and the inherent contradiction between their physical size and optical performance has long restricted the miniaturization process of the device. Although traditional endoscopes can achieve basic imaging functions, they are prone to image distortion due to spherical aberration and field of view angle limitations, and instantaneous clear vision can only be obtained through repeated balloon occlusion and saline flushing. 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 techniques.

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

[0005] To break through the above limitations, miniaturized lens technology has become a key breakthrough point for innovating endoscope systems. Although traditional gradient refractive index lenses and multi-lens cascading schemes can achieve wide field of view imaging, their inherent limitations significantly restrict clinical applicability: firstly, to achieve a super-hemispherical field of view, 3 - 5 lens units need to be stacked, resulting in system volume expansion and spherical aberration accumulation effects; secondly, the low tolerance for optical axis alignment significantly increases the packaging process complexity. Existing miniaturized optical systems mostly use fisheye lens architectures 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-thin endoscopy.

[0006] Therefore, there is an urgent need for a new lens design scheme 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 for an endoscopic imaging system and a design method thereof.

[0008] To achieve the above-mentioned invention object, the present invention provides a wide-angle superlens for an endoscopic imaging system, comprising: at least one lens unit; The lens unit includes: a substrate, and a micro-nano structure disposed on one side of the substrate for modulating an incident light beam; The micro-nano structure includes a plurality of nano-cylinders; The transmittance of the nano-cylinders is higher than 0.8; The radius of the nano-cylinders r Satisfies: [50nm, 165nm] ∪ [185nm, 200nm]; The nano-cylinders are arranged on the substrate based on a phase distribution manner, and the phase distribution formula is expressed as:

[0009] Wherein, Represents the calculated phase, Represents the diffraction order, Represents the number of polynomial coefficients in the series, Represents the serial number of the polynomial coefficient, Is the coefficient of the i Item, is the normalized radial aperture coordinate, Is the normalized radius of the lens unit, Is the radius of any point on the plane of the lens unit.

[0010] According to one aspect of the present invention, two of the lens units are coaxially arranged; Along the output direction of the incident light, the micro-nano structure of the first lens unit is connected to the substrate of the second lens unit.

[0011] According to one aspect of the present invention, along the output direction of the incident light, the thickness of the substrate of the first lens unit is greater than the thickness of the substrate of the second lens unit; Along the output direction of the incident light, in the phase distribution formula for the nano-cylinders, the diffraction orders Of both the first lens unit and the second lens unit Both satisfy: Both satisfy: Of the first lens unit and the second lens unit, the normalized radii Both satisfy: The coefficient Of the first lens unit is greater than the coefficient Of the second lens unit, and the coefficient Of the first lens unit is less than the coefficient , the coefficient of the first lens unit is greater than the coefficient of the second lens unit , the coefficient of the first lens unit is less than the coefficient of the second lens unit , the coefficient of the first lens unit is greater than the coefficient of the second lens unit .

[0012] According to one aspect of the present invention, in the phase distribution formula for the nanocylinder along the output direction of the incident light, the coefficients of the first lens unit , coefficient , coefficient , coefficient , coefficient respectively satisfy: , , , , ; the coefficients of the second lens unit (1) , coefficient , coefficient , coefficient , coefficient respectively satisfy: , , , , .

[0013] According to one aspect of the present invention, the height of the nanocylinder satisfies:

[0014] wherein, represents the wavelength of the incident light, represents the effective refractive index of the nanocylinder, represents the refractive index of the surrounding medium; the phase modulation of the nanocylinder covers 0 to 2π.

[0015] According to one aspect of the present invention, the substrate is a regular transparent plate; Along the output direction of the incident light, the thickness of the substrate of the first lens unit is 2.3 mm to 2.5 mm, and the thickness of the substrate of the second lens unit is 9.985 μm to 9.990 μm.

[0016] According to one aspect of the present invention, the nanocylinder is an amorphous silicon nanocylinder arranged in a cubic lattice; The substrate is a silica substrate.

[0017] According to one aspect of the present invention, on the substrate, each of the nano-cylinders is arranged based on a corresponding cubic lattice, and the nano-cylinders are coaxially arranged with the cubic lattice. The arrangement period of the cubic lattice for arranging the nano-cylinders is 0.65 μm to 0.75 μm.

[0018] According to one aspect of the present invention, the system aperture of the lens unit is 1.8 mm to 1.9 mm, the working wavelength is 1.5 μm, and the field of view angle is -50° to 50°. The relative illuminance of the lens unit in all fields of view is greater than or equal to 98.89%, and the Strehl Ratio index in each field of view is greater than or equal to 0.995.

[0019] To achieve the above-mentioned invention object, the present invention provides a design method for a wide-angle superlens for the foregoing endoscopic imaging system, including: S1. Set the initial parameters for the wide-angle superlens, where the initial parameters include: incident light wavelength, lens material, entrance pupil diameter, field of view angle, outer dimensions and quantity of the lens unit. S2. Construct the initial configuration of the lens unit, where the lens unit includes: a substrate, and a micro-nano structure disposed on one side of the substrate for modulating the incident light beam, and the micro-nano structure includes a plurality of nano-cylinders. S3. Based on the initial configuration of the lens unit, establish a unit nano-cell for designing the nano-cylinders, where the unit nano-cell includes: a nano-cylinder, a cubic lattice divided based on the substrate, and the nano-cylinder is coaxially arranged with the cubic lattice. S4. Based on the unit nano-cell, determine the diameter scanning range of the nano-cylinders and the arrangement period of the cubic lattice. S5. Set the wavelength of the incident light wave, perform scanning simulation on the nano-cylinders with different heights within the diameter scanning range, and based on the scanning simulation results and the modulation coverage range of the nano-cylinder phase, determine the height, transmittance of the nano-cylinders and the r value range of the radius of the nano-cylinders. S6. Based on the determined value range of the height, transmittance and radius r of the nano-cylinders, match with the phase distribution formula of the nano-cylinders to obtain the positions and sizes of each of the nano-cylinders. S7. Distribute on the substrate based on the positions and sizes of each of the obtained nano-cylinders, and set the thickness of the substrate to construct the lens unit. S8. Repeat steps S3 to S7 based on the number of the lens units in the wide-angle metalens to complete the construction of the wide-angle metalens.

[0020] According to one embodiment of the present invention, the wide-angle metalens of this embodiment can achieve a system aperture of 1.8 mm to 1.9 mm, a field of view range of ±50° at a working wavelength of 1.5 μm, and a relative illuminance of more than 98.89% for all fields of view. The Strehl Ratio index for each field of view remains above 0.995. In addition, the MTF curve of the wide-angle metalens in this embodiment is very close to the diffraction limit under different incident angles, having reliable performance.

[0021] According to one embodiment of the present invention, the wide-angle metalens of this embodiment 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-nano structures between the lens units and the structural design of the nano-cylinders better ensure that its MTF curve is close to the diffraction limit, making it greater than 0.84 at 21 lp / mm.

[0022] According to one embodiment of the present invention, the wide-angle metalens of this embodiment realizes the coordination of correction and focusing based on the optimized design of the doublet metalens architecture. It still maintains a full width at half maximum (FWHM) of 6.212 μm and a low sidelobe intensity of less than 1.74% at the extreme field of view of 50°, significantly superior to the performance degradation trend of traditional spherical lenses.

[0023] According to one embodiment of the present invention, the wide-angle metalens of this embodiment provides an innovative solution for the miniaturization and high-resolution imaging of endoscopes, significantly improving the microstructural characterization ability and having important clinical application potential.

[0024] According to one embodiment of the present invention, the doublet metalens architecture of this embodiment breaks through the field of view-resolution trade-off limitation of traditional refractive lenses through the combination of cascaded correction and focusing, combined with the optimized even polynomial phase distribution and nano-structure parameters. Verified by the finite-difference time-domain method, the array composed of single-crystalline silicon nano-cylinders realizes a phase coverage from 0 to 2π and a transmittance greater than 80%, avoiding resonance loss.

[0025] According to one embodiment of the present invention, the wide-angle metalens of this embodiment not only solves the contradiction between the miniaturization of endoscopes and wide-field imaging, but also provides a new paradigm for subcellular-level resolution imaging in complex environments. With its excellent aberration correction ability, this system is expected to significantly improve the display accuracy of tiny structures while reducing the interference of the surrounding environment. In addition, based on this embodiment, it can be further extended to multi-wavelength achromatic design, combined with the optimization of flexible substrate materials, to promote the application of metalenses in wearable interventional devices and dynamic imaging scenarios, having extremely high application prospects. Brief Description of the Drawings

[0026] Figure 1 Structural diagram of a wide-angle metalens for an endoscopic imaging system according to an embodiment of the present invention; Figure 2 Schematic diagram of the phase distribution of nanocylinders in the micro-nano structure according to an embodiment of the present invention; Figure 3 Radius of any point on the plane of the lens unit according to an embodiment of the present invention and the normalized radius of the lens unit Schematic diagram of the relative position; Figure 4 Structural diagram of the unit nanocell composed of nanocylinders and cubic lattices according to an embodiment of the present invention; Figure 5 Focusing effect diagram of the lens unit in the x-z cross-section for different field angles according to an embodiment of the present invention; Figure 6 Geometric spot diagrams of the lens unit at different field angles according to an embodiment of the present invention, where Figure 6 (a) represents the geometric spot diagram at a field angle of 0°, Figure 6 (b) represents the geometric spot diagram at a field angle of 10°, Figure 6 (c) represents the geometric spot diagram at a field angle of 20°, Figure 6 (d) represents the geometric spot diagram at a field angle of 28°, Figure 6 (e) represents the geometric spot diagram at a field angle of 36°, Figure 6 (f) represents the geometric spot diagram at a field angle of 42°, Figure 6 (g) represents the geometric spot diagram at a field angle of 46°, Figure 6 (h) represents the geometric spot diagram at a field angle of 50°; Figure 7 Diffraction MTF curve diagrams of the lens unit at different field angles according to an embodiment of the present invention; Figure 8 Relative illuminance curve of the lens unit according to an embodiment of the present invention; Figure 9 Phase diagram of the first lens unit along the output direction of the incident light according to an embodiment of the present invention; Figure 10 Phase diagram of the second lens unit along the output direction of the incident light according to an embodiment of the present invention; Figure 11 Phase diagram obtained by simulating the unit nanocell in the scenario of an incident light wavelength of 1.5 μm according to an embodiment of the present invention; Figure 12Transmittance graph obtained by simulating a unit nanocell according to an embodiment of the present invention under the scenario of an incident light wavelength of 1.5 μm; Figure 13 Phase graph obtained by simulating a unit nanocell according to an embodiment of the present invention, where the height of the nanocylinders in the unit nanocell is 1.2 μm and under the scenario of an incident light wavelength of 1.5 μm; Figure 14 Transmittance graph obtained by simulating a unit nanocell according to an embodiment of the present invention, where the height of the nanocylinders in the unit nanocell is 1.2 μm and under the scenario of an incident light wavelength of 1.5 μm. Detailed implementation manners

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] When describing the embodiments of the present invention, the orientation or positional relationships expressed by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" are based on the orientation or positional relationships shown in the relevant drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limitations on the present invention.

[0029] The present invention will be described in detail below in combination with the drawings and specific implementation manners. The implementation manners cannot be described in detail here, but the implementation manners of the present invention are not limited to the following implementation manners.

[0030] As Figure 1 shown, according to an embodiment of the present invention, a wide-angle superlens 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-nano structure 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 both axially opposite side surfaces thereof are planes. Further, the micro-nano structure 12 disposed on one side of the substrate 11 includes a plurality of nanocylinders 121; wherein, the transmittance of the nanocylinders 121 is higher than 0.8; the radius of the nanocylinders 121 r satisfies: [50 nm, 165 nm] ∪ [185 nm, 200 nm]. Further, as Figure 2As shown, the nano-cylinders 121 in the micro-nano structure 12 are arranged on the substrate 11 based on the phase distribution, and the phase distribution formula is expressed as:

[0031] Wherein, represents the calculated phase, represents the diffraction order, represents the number of polynomial coefficients in the series, represents the serial number of the polynomial coefficient, is the coefficient of the i th term, which is the normalized radial aperture coordinate, is the normalized radius of the lens unit 1, is the radius of any point on the plane of the lens unit 1. Refer to Figure 3 .

[0032] Through the above settings, the wide-angle superlens of this solution can fully achieve excellent imaging effects in the near-infrared wide field of view by setting the corresponding lens unit 1. Specifically, through the creatively designed micro-nano structure 12 in the lens unit 1, the present invention can fully meet the requirement of achieving a ±50° field of view coverage at a wavelength of 1.5 μm. At the same time, the relative illuminance 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.

[0033] Through the above settings, the MTF value of the lens unit 1 of this solution is close to the diffraction limit, >0.84 at 21 lp / mm, which fully guarantees the imaging quality of the present invention, provides an innovative solution for the miniaturization and high-resolution imaging of endoscopes, significantly improves the microstructural characterization ability, and has important clinical application potential.

[0034] As Figure 1 shown, according to an embodiment of the present invention, in the wide-angle superlens of the present invention, two lens units 1 are coaxially arranged; wherein, 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. In this embodiment, the micro-nano structure 12 of the first lens unit 1 is connected to the substrate 11 of the second lens unit 1 by abutting or gluing. Thus, through the connected manner, the optimized light beam of the first lens unit 1 can be accurately and reliably transmitted to the second lens unit 1, making the imaging effect of this solution more excellent and fully eliminating the errors on the transmission path.

[0035] As Figure 1As shown, according to an 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-cylinders 121, the diffraction orders of the first lens unit 1 and the second lens unit 1 both satisfy: , the number of polynomial coefficients of the first lens unit 1 and the second lens unit 1 both satisfy: , the normalized radii of the first lens unit 1 and the second lens unit 1 both satisfy: , the coefficient of the first lens unit 1 is greater than the coefficient of the second lens unit 1 , the coefficient of the first lens unit 1 is less than the coefficient of the second lens unit 1 , the coefficient of the first lens unit 1 is greater than the coefficient of the second lens unit 1 , the coefficient of the first lens unit 1 is less than the coefficient of the second lens unit 1 , the coefficient of the first lens unit 1 is greater than the coefficient of the second lens unit 1 .

[0036] Through the above settings, by setting the thicknesses between the substrates 11 of the respective lens units 1 as described above, and based on the above settings of the phase distribution of the nano-cylinders 121, the nano-cylinders 121 of the present invention are made to match their structural characteristics in the distributed positions, so that while the imaging uniformity of each lens unit 1 is better, the imaging performance matching between two adjacent lens units 1 is fully achieved. As a result, it is ensured that the relative illuminance 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.

[0037] According to an embodiment of the present invention, along the output direction of the incident light, in the phase distribution formula for the nano-cylinders 121, the coefficients of the first lens unit 1 , coefficient , coefficient , coefficient , coefficient respectively satisfy: , , , , ; the coefficients of the second lens unit 1 , coefficient , coefficient , coefficient , coefficient respectively satisfy: , , , , .

[0038] Through the above settings, the present invention constitutes a doublet metalens architecture by setting two lens units 1, enabling the present solution to more effectively utilize the near-infrared wide field of view. And by creatively optimizing the phase distribution formula of the nano-cylinders 121 on two adjacent wide-angle metalenses, the micro-nano structures 12 on the two wide-angle metalenses achieve a complementary promotion effect. Specifically, along the output direction of the incident light, the two lens units 1 respectively undertake the wavefront pre-compensation and main focusing functions, enabling the present solution to fully meet the corresponding imaging performance requirements.

[0039] As Figure 4 shown, according to an embodiment of the present invention, the height of the nano-cylinder 121 satisfies:

[0040] wherein, represents the wavelength of the incident light, represents the effective refractive index of the nano-cylinder 121, represents the refractive index of the surrounding medium. In this embodiment, since the opposite ends of the nano-cylinder 121 are respectively in contact with the substrate 11, therefore generally takes the refractive index of the substrate 11.

[0041] In this embodiment, the height of the nano-cylinder 121 is set to be from 0.6 μm to 1.3 μm. Through the above settings, the optimization of the light transmission performance and path of the nano-cylinder 121 is achieved, enabling it to more reliably match the thickness of the corresponding substrate 11, thus fully ensuring the working performance of the present solution.

[0042] As Figure 1 shown, according to an embodiment of the present invention, the substrate 11 is a regular transparent plate body. Among them, along the output direction of the incident light, the thickness of the substrate 11 of the first lens unit 1 is from 2.3 mm to 2.4 mm, and the thickness of the substrate 11 of the second lens unit 1 is from 9.985 μm to 9.990 μm. In this embodiment, the substrate 11 can be made of silica material.

[0043] With the above settings, in this solution, by setting the thickness of the substrate 11 within the above range, the thickness of the substrate 11 can be flexibly set to match the substrate 11 with the nanocylinders 121, so that when the performances presented by different lens units 1 are different, the performances can be mutually matched. Thus, this solution fully meets its service performance and adapts to the corresponding application scenarios, which is more beneficial to ensuring the imaging quality of the present invention.

[0044] In addition, with the above settings, the setting and allocation of the lens units 1 in the wide-angle metalens can be flexibly realized. Especially when multiple lens units 1 are set, the structural matching and imaging quality matching between adjacent lens units 1 are effectively ensured, making the structure and service performance of this solution more excellent.

[0045] According to an embodiment of the present invention, the phase modulation of the nanocylinders 121 covers 0 to 2π.

[0046] With the above settings, the realization of high-quality focusing and imaging in this solution is effectively ensured, providing a reliable guarantee for meeting its high-resolution performance.

[0047] As Figure 4 shown, according to an embodiment of the present invention, the nanocylinders 121 are amorphous silicon nanocylinders arranged in a cubic lattice.

[0048] As Figure 4 shown, according to an embodiment of the present invention, on the substrate 11, each nanocylinder 121 is arranged based on the corresponding cubic lattice, and the nanocylinder 121 is coaxially arranged with the cubic lattice; wherein, the arrangement period of the cubic lattice for arranging the nanocylinders 121 is 0.65 μm to 0.75 μm. In this embodiment, the arrangement period of the cubic lattice is preferably 0.7 μm.

[0049] With the above settings, based on the relatively small set period, the high-order diffraction of the nanocylinders 121 can be effectively suppressed, effectively ensuring the imaging performance of the present invention.

[0050] As Figure 4 shown, according to an embodiment of the present invention, the dimensional variation error of the diameter of the nanocylinders 121 in the direction away from the substrate 11 is within ±10%; thus, the imaging quality and phase coverage range of the nanocylinders 121 are fully ensured.

[0051] As Figure 1As shown, according to an embodiment of the present invention, the system aperture of the lens unit 1 is 1.8 mm to 1.9 mm, the working wavelength is 1.5 μm, and the field of view angle is -50° to 50°; the relative illuminance 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.

[0052] According to an embodiment of the present invention, the present invention provides a design method for the wide-angle superlens for the foregoing endoscopic imaging system, including: S1. Set the initial parameters for the wide-angle superlens, where the initial parameters include: incident light wavelength, lens material, entrance pupil diameter, field of view angle, outer dimensions and quantity of the lens unit 1; S2. Construct the initial configuration of the lens unit 1, where the lens unit 1 includes: a substrate 11, and a micro-nano structure 12 disposed on one side of the substrate 11 for modulating the incident light beam, and the micro-nano structure 12 includes a plurality of nano-cylinders 121; S3. Establish a unit nano-cell for designing the nano-cylinder 121 based on the initial configuration of the lens unit 1, where the unit nano-cell includes: the nano-cylinder 121, a cubic lattice divided based on the substrate 11, and the nano-cylinder 121 is coaxially arranged with the cubic lattice; S4. Determine the diameter scanning range 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 range can be set to 100 nm to 400 nm; the arrangement period of the cubic lattice is set at 0.65 μm to 0.75 μm, preferably 0.7 μm; S5. Set the wavelength of the incident light wave, perform scanning simulation on the nano-cylinders 121 with different heights in the diameter scanning range, and determine the height, transmittance and radius of the nano-cylinder 121 based on the scanning simulation results and the modulation coverage range of the phase of the nano-cylinder 121 r of the value range; in this embodiment, in the step of performing scanning simulation on the nano-cylinders 121 with different heights in the diameter scanning range, the set height range is 0.6 μm to 1.3 μm; S6. Match the determined value range of the height, transmittance and radius r of the nano-cylinder 121 with the phase distribution formula of the nano-cylinder 121 to obtain the positions and sizes of the respective nano-cylinders 121; in this embodiment, the height, transmittance and radius r of the nano-cylinder 121 are realized based on the set distribution law during the process of matching the value range with the phase distribution formula; where the distribution law includes: the nano-cylinder 121 includes a distribution region and a radius rVariation trend; among them, the division rule for the distribution area is as follows: in the direction from the center to the edge of the substrate 11, there are multiple distribution areas for the nano-cylinders 121. Among them, the distribution area at the central position is the first area, and the first area is a planar area. The remaining areas in the direction from the center of the substrate 11 to the edge are annular areas. In this embodiment, the number of annular areas can be correspondingly selected according to the specific design of different lens units 1. For example, it can reach hundreds. Of course, the number of annular areas can also be set to other numbers and adaptively selected based on the phase distribution formula on the lens unit 1, which will not be elaborated here. Through the above-set area distribution, the planar area centered makes the input light have a better transmission effect near the center, while using the annular area near the edge can make the input light more easily and accurately distributed around the central planar area. Thus, based on the combined arrangement of the planar area and the annular area, the lens unit 1 of this solution can fully meet the advantages of wide-angle focusing, high-resolution imaging, and compact structure.

[0053] Furthermore, in the first area, the nano-cylinders 121 are axially symmetrically distributed. Among them, in the first area, there is a central sub-area, and the diameters of the nano-cylinders 121 in the central sub-area are the same. And in the direction from the edge of the central sub-area away from the center to the edge of the first area, the diameters of the remaining nano-cylinders 121 gradually decrease. Based on the above settings, through the further sub-division of the planar area, using nano-cylinders 121 with the same size in the central sub-area can fully meet the requirements that the light transmission in the central position of the first area fully satisfies focusing and is evenly distributed over a large range in the focused area. And outside the central sub-area, using a gradually decreasing diameter can expand the central focused area annularly outward. Thus, this solution fully meets the advantages of wide-angle focusing and high-resolution imaging.

[0054] Furthermore, the edge of the first area can be a regular edge. For example, it can be set as a circle, a polygon, etc., and can be correspondingly set based on the phase distribution of the specific nano-cylinders 121. For example, the edge of the first area can be set as an octagonal edge, and the edge of the central sub-area is rectangular. Among them, the number of nano-cylinders 121 arranged on the four sides (i.e., the long sides) parallel to the central sub-area in the first area is greater than the number of nano-cylinders 121 on the remaining sides (i.e., the short sides). And the diameters of the nano-cylinders 121 on the four sides (i.e., the long sides) parallel to the central sub-area in the first area are different. Among them, in the direction from the center of the long side to both ends, the diameters of the nano-cylinders 121 gradually decrease, and in the direction from the center of the short side to both ends, the diameters of the nano-cylinders 121 gradually decrease.

[0055] In this embodiment, among the multiple annular regions on the substrate 11, in the direction from the center to the edge of the substrate 11, the width of each annular region is gradually reduced, and in the direction from the center to the edge of the substrate 11, the diameter of the nano-cylinders 121 in each annular region is gradually reduced. In this embodiment, in the annular region, the nano-cylinders 121 are axially symmetrically distributed.

[0056] Through the above settings, based on the optimized distribution of the nano-cylinders 121 and combined with the corresponding phase distribution formula, the optimization of the distribution of the nano-cylinders 121 can be achieved, so that the lens unit 1 with the corresponding settings can achieve the optimal optical performance.

[0057] S7. Distribute based on the positions and sizes of the obtained nano-cylinders 121 on the substrate 11, and set the thickness of the substrate 11 to construct the lens unit 1; S8. Repeat steps S3 to S7 based on the number of lens units 1 in the wide-angle superlens to complete the construction of the wide-angle superlens.

[0058] To further illustrate the advantages of the wide-angle superlens of this solution, an example is given.

[0059] In this embodiment, the wide-angle superlens of this solution is realized by adopting the architecture of a doublet superlens. Among them, two lens units 1 are coaxially arranged, and each lens unit 1 uses amorphous silicon circular nano-columns arranged in a cubic lattice as the basic structure of the superlens. Therefore, both of these two lens units 1 have the effect of polarization insensitivity. In this embodiment, the orientations of the micro-nano structures 12 on the two lens units 1 are the same. See Figure 1 , in this embodiment, along the output direction of the incident light, a light-shielding plate with a light-passing hole with an aperture of 0.5 mm can be further arranged in front of the first lens unit 1, which will serve as the entrance for receiving light. Among them, the light-shielding plate and the substrate 11 of the first lens unit 1 can be connected (such as in contact or attached).

[0060] In this embodiment, the substrate 11 of the lens unit 1 is made of silica material, and among them, the diameter of the substrate 11 is 1.83 mm. Along the output direction of the incident light, the thickness of the substrate 11 of the first lens unit 1 is 2.5 mm, and the thickness of the substrate 11 of the second lens unit 1 is 9.989 μm.

[0061] In this embodiment, the micro-nano structure 12 includes multiple nano-cylinders 121, and among them, the nano-cylinders 121 are made of amorphous silicon material.

[0062] 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 shown below.

[0063] Table 1

[0064] Based on the above settings of the phase distribution formula, the phase distribution of the obtained nano-cylinders 121 is simulated by the ray tracing method, and the focusing effects of the wide-angle superlens with the aforementioned double-combination superlens architecture at different field angles are obtained. Among them, the different field angles adopted are: 0°, 10°, 20°, 28°, 36°, 42°, 46°, 50°. See 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. See Figure 6 It can be seen that in the spot diagram of the wide-angle superlens with the aforementioned double-combination superlens architecture, the radius of the Airy disk is 7.147 μm, and the RMS values of the obtained spot radii are 0.508 μm, 0.581 μm, 0.644 μm, 0.993 μm, 0.544 μm, 0.507 μm, 0.758 μm and 0.765 μm respectively. This indicates that all the light rays are within the Airy disk, so the designed lens belongs to a diffraction-limited lens. See Figure 7 It can be seen that in the MTF curves of different fields of the wide-angle superlens with the double-combination superlens architecture, the cut-off frequency of the calculated MTF values is 21 lp / mm. The MTF values at 21 lp / mm for all fields 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. See Figure 8 It can be seen that the relative illuminance (RI) of the wide-angle superlens with the double-combination superlens architecture is higher than 0.9889, which proves that the imaging plane of this wide-angle superlens has good brightness uniformity and ensures the imaging quality of the wide-field endoscope. See Figure 9 , the phase of the designed first lens unit 1 fully satisfies the function of wavefront pre-compensation; see Figure 10 , the phase of the designed second lens unit 1 fully satisfies the function of the main focusing function.

[0065] In this embodiment, the radius of the nano-cylinders 121 rSatisfy: [50nm, 165nm] ∪ [185nm, 200nm]. The arrangement period of the cubic lattice for arranging the nano-cylinders 121 is 0.7μm, and the height of the nano-cylinders 121 is set to 1.2μm. Thus, based on the parameter settings of the nano-cylinders 121 and the period settings of the cubic lattice, simulation is carried out on it using FDTD software under the scenario of an incident light wavelength of 1.5μm, and simulation results can be obtained. See Figures 11 to 14 , it can be seen that the nano-cylinders 121 are in the case of phase modulation covering 0 to 2 . When the radius of the nano-cylinders 121 r satisfies [50nm, 165nm] ∪ [185nm, 200nm], the nano-cylinders 121 fully meet the requirements of phase coverage, and the transmittance is higher than 0.8.

[0066] The above content is only an example of the specific solution of the present invention. For the devices and structures not described in detail therein, it should be understood that general devices and general methods existing in the art are adopted for implementation.

[0067] The above is only one solution of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A wide-angle metalens for an endoscopic imaging system, characterized in that, Comprising: At least one lens unit (1); The lens unit (1) comprises: a substrate (11), and a micro-nano structure (12) disposed on one side of the substrate (11) for modulating an incident light beam; The micro-nano structure (12) comprises a plurality of nano-cylinders (121); The transmittance of the nano-cylinder (121) is higher than 0.8; The radius of the nanocylinder (121) r satisfies: [50 nm, 165 nm] ∪ [185 nm, 200 nm]; The nano-cylinders (121) are arranged on the substrate (11) based on a phase distribution manner, and the phase distribution formula is expressed as: Among them, represents the calculated phase, represents the diffraction order, represents the number of polynomial coefficients in the series, represents the serial number of the polynomial coefficient, is the i coefficient of the item, and is the normalized radial aperture coordinate, is the normalized radius of the lens unit (1), is the radius of any point on the plane of the lens unit (1).

2. The wide-angle metalens for an endoscopic imaging system according to claim 1, wherein There are two lens units (1) arranged coaxially; 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).

3. The wide-angle metalens for an endoscopic imaging system according to claim 2, wherein, 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); In the output direction of the incident light, in the phase distribution formula for the nanocylinder (121), the diffraction orders of the first lens unit (1) and the second lens unit (1) both satisfy: , the number of polynomial coefficients of the first lens unit (1) and the second lens unit (1) both satisfy: , the normalized radii of the first lens unit (1) and the second lens unit (1) both satisfy: , the coefficient of the first lens unit (1) is greater than the coefficient of the second lens unit (1) , the coefficient of the first lens unit (1) is less than the coefficient of the second lens unit (1) , the coefficient of the first lens unit (1) is greater than the coefficient of the second lens unit (1) , the coefficient of the first lens unit (1) is less than the coefficient of the second lens unit (1) , the coefficient of the first lens unit (1) is greater than the coefficient of the second lens unit (1) .

4. The wide-angle metalens for an endoscopic imaging system according to claim 3, wherein In the output direction of the incident light, in the phase distribution formula for the nanocylinder (121), the coefficients of the first lens unit (1) , coefficient , coefficient , coefficient , coefficient respectively satisfy: , , , , ; The coefficients of the second lens unit (1) , coefficient , coefficient , coefficient , coefficient respectively satisfy: , , , , .

5. The wide-angle metalens for an endoscopic imaging system according to claim 4, wherein, The height of the nano-cylinder (121) Satisfies: wherein, represents the wavelength of the incident light, represents the effective refractive index of the nano-cylinder (121), represents the refractive index of the surrounding medium; The phase modulation of the nano-cylinder (121) covers 0 to 2π.

6. The wide-angle metalens for an endoscopic imaging system according to claim 5, wherein The substrate (11) is a regular transparent plate; Along the output direction of the incident light, the thickness of the substrate (11) of the first lens unit (1) is 2.3 mm to 2.5 mm, and the thickness of the substrate (11) of the second lens unit (1) is 9.985 μm to 9.990 μm.

7. The wide-angle metalens for an endoscopic imaging system according to claim 6, wherein The nano-cylinder (121) is an amorphous silicon nano-cylinder arranged in a cubic lattice; The substrate (11) is a silica substrate.

8. The wide-angle metalens for an endoscopic imaging system according to claim 7, wherein On the substrate (11), each nano-cylinder (121) is arranged based on a corresponding cubic lattice, and the nano-cylinder (121) is coaxially arranged with the cubic lattice; The arrangement period of the cubic lattice for arranging the nano-cylinders (121) is 0.65 μm to 0.75 μm.

9. The wide-angle metalens for an endoscopic imaging system according to claim 8, wherein, The system aperture of the lens unit (1) is 1.8 mm to 1.9 mm, the working wavelength is 1.5 μm, and the field of view angle is -50° to 50°; The relative illuminance 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.

10. A design method for a wide-angle superlens for an endoscopic imaging system according to any one of claims 1 to 9, characterized in that, Comprising: S1. Set the initial parameters for a wide-angle superlens, where the initial parameters include: incident light wavelength, lens material, entrance pupil diameter, field of view angle, the external dimensions and quantity of the lens unit (1); S2. Construct the initial configuration of the lens unit (1), where the lens unit (1) comprises: a substrate (11), and a micro-nano structure (12) disposed on one side of the substrate (11) for modulating an incident light beam, and the micro-nano structure (12) comprises a plurality of nano-cylinders (121); S3. Based on the initial configuration of the lens unit (1), establish a unit nano-cell for designing the nano-cylinder (121), where the unit nano-cell comprises: a nano-cylinder (121), a cubic lattice divided based on the substrate (11), and the nano-cylinder (121) is coaxially arranged with the cubic lattice; S4. Based on the unit nano-cell, determine the diameter scanning range of the nano-cylinder (121) and the arrangement period of the cubic lattice; S5. Set the wavelength of the incident light wave, perform a scanning simulation on the nano-cylinders (121) at different heights within 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 phases of the nano-cylinders (121). r The value range of S6. Based on the determined height, transmittance, and radius of the nanocylinder (121) r match the value ranges with the phase distribution formula of the nanocylinder (121) to obtain the positions and sizes of the respective nanocylinders (121); S7. Distribute on the substrate (11) based on the positions and sizes of the obtained respective nano-cylinders (121), and set the thickness of the substrate (11) 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 superlens to complete the construction of the wide-angle superlens.

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