Wide-angle optical system

Abstract

This invention belongs to the field of optical imaging technology and discloses a wide-angle optical system. The wide-angle optical system includes a lens and a photoelectric sensor. The lens, along the optical axis, sequentially includes a first lens with negative optical power, a second lens with positive optical power, a third lens with positive optical power, and a fourth lens with negative optical power. At least one lens surface in the lens is a freeform surface used to correct distortion and astigmatism. The system also includes a metasurface element disposed in the optical path for correcting chromatic aberration. This invention can achieve high-quality imaging with ultra-wide-angle, low distortion, and high chromatic aberration correction while simplifying the structure and reducing costs, solving the problems of complex structure, high cost, and difficulty in balancing performance of traditional wide-angle lenses.

Description

Technical Field

[0001] This utility model belongs to the field of optical imaging technology, specifically relating to a wide-angle optical system. Background Technology

[0002] Wide-angle and ultra-wide-angle lenses are widely used in security monitoring, automotive imaging, consumer electronics, and virtual reality. Currently, classic wide-angle lens designs, such as those based on the Cooke three-element or reversed telephoto structures, typically require six or more lenses to achieve a field of view exceeding 180 degrees and simultaneously correct various aberrations such as spherical aberration, coma, astigmatism, field curvature, and distortion. This multi-lens structure not only leads to a bulky and heavy optical system but also significantly increases the complexity and cost of design, assembly, and debugging. Especially for edge distortion and chromatic aberration correction over large field of view, the design freedom of traditional spherical and aspherical lenses is limited, making it difficult to achieve ideal results within a compact structure. This restricts their application in miniaturized and lightweight devices. Utility Model Content

[0003] The present invention aims to at least partially solve the aforementioned technical problems. Therefore, the objective of the present invention is to provide a wide-angle optical system.

[0004] The technical solution adopted in this utility model is as follows:

[0005] To achieve the above objectives, this utility model provides a wide-angle optical system, including a lens and a photoelectric sensor. The lens comprises, arranged sequentially along the optical axis from the object side to the image side: a first lens, which is a negative power lens; a second lens, which is a positive power lens; a third lens, which is a positive power lens; and a fourth lens, which is a negative power lens. The photoelectric sensor is disposed on the image side of the fourth lens. At least one lens surface in the lens is a freeform surface used to correct distortion and astigmatism. Furthermore, the wide-angle optical system also includes a metasurface element disposed in the optical path for correcting chromatic aberration. Through the hybrid design of four lenses and a freeform metasurface structure, unprecedented aberration correction capabilities can be achieved while greatly simplifying the structure and reducing costs.

[0006] In a preferred embodiment, by defining the aperture range of each mirror, the system is made compact and standardized, facilitating mass production. Specifically, the first lens includes a first mirror and a second mirror, the second lens includes a third mirror and a fourth mirror, the third lens includes a fifth mirror and a sixth mirror, and the fourth lens includes a seventh mirror and an eighth mirror; the aperture of the first mirror is 8mm~10mm, the aperture of the second mirror is 4mm~6mm, the aperture of the third mirror is 2mm~4mm, the aperture of the fourth mirror is 2mm~4mm, the aperture of the fifth mirror is 3mm~5mm, the aperture of the sixth mirror is 3mm~5mm, the aperture of the seventh mirror is 3mm~5mm, and the aperture of the eighth mirror is 3mm~5mm.

[0007] In a preferred embodiment, by defining the radius of curvature of each mirror, the optical path deflection is optimized, laying the foundation for achieving an ultra-large field of view of approximately 200°. Specifically, the radius of curvature of the first mirror is 25~35, the radius of curvature of the second mirror is 2.2~2.9, the radius of curvature of the third mirror is 7.5~8.5, the radius of curvature of the fourth mirror is 7.5~8.5, the radius of curvature of the fifth mirror is 5.2~5.8, the radius of curvature of the sixth mirror is 2.2~2.9, the radius of curvature of the seventh mirror is 2.2~2.9, and the eighth mirror is planar.

[0008] In a preferred embodiment, by limiting the thickness of each lens and the inter-lens spacing, the total system length and optical path are precisely controlled, ensuring imaging quality and structural compactness. Specifically, the center thickness of the first lens is 0.5mm~0.8mm, and its sagitta is 1.5mm~2.3mm; the spacing between the second and third mirror surfaces is 5.5mm~7mm, the thickness of the second lens is 3.1mm~4.3mm, the spacing between the fourth and fifth mirror surfaces is 0.05mm~0.9mm, the thickness of the third lens is 2.5mm~3.6mm, and the thickness of the fourth lens is 0.3mm~0.9mm.

[0009] In a preferred embodiment, by defining the refractive index range of each lens and utilizing a high-refractive-index material to enhance the light deflection capability, it is beneficial to achieve system miniaturization. Specifically, the refractive index of the first lens is 1.24~1.8, the refractive index of the second lens is 1.24~1.8, the refractive index of the third lens is 1.28~1.72, and the refractive index of the fourth lens is 1.12~1.86.

[0010] In a preferred embodiment, by limiting the Abbe number of the lens material to greater than 50 and selecting a low dispersion material, the generation of chromatic aberration is fundamentally suppressed.

[0011] In a preferred embodiment, a freeform surface is disposed on the first mirror surface of the first lens facing the object side. This mirror surface is the entry point for capturing rays with the maximum field of view, and placing the freeform surface here can most effectively control the severe distortion and astigmatism introduced by the wide angle.

[0012] In a preferred embodiment, two integration methods for the metasurface element are specified: as a stand-alone flat panel element or directly integrated onto the lens surface, providing a flexible engineering implementation path.

[0013] In a preferred embodiment, the specific physical composition of the metasurface element is defined, namely, a transparent substrate and a subwavelength nanostructure array formed on the transparent substrate and composed of a dielectric material, wherein the subwavelength nanostructure array realizes its optical function.

[0014] The beneficial effects of this utility model are as follows:

[0015] This invention achieves the functionality of a traditional six-element or higher lens using only four lenses combined with a single metasurface element, significantly reducing size, weight, and cost. The introduction of freeform surfaces fundamentally solves the edge distortion and astigmatism problems of ultra-wide-angle lenses; the metasurface element specifically and efficiently corrects chromatic aberration. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the wide-angle optical system according to an embodiment of the present invention.

[0017] Figure 2 This is a flowchart illustrating the imaging method corresponding to the wide-angle optical system of this utility model.

[0018] Figure 3 This is a schematic diagram of the structure of a metasurface element. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings herein can generally be arranged and designed in various different configurations.

[0020] like Figure 1As shown, this utility model provides a wide-angle optical system, which includes, along the optical axis from the object side to the image side, the following components in sequence: a first lens 10, a second lens 20, a third lens 30, a fourth lens 40, a metasurface element 60, and a photoelectric sensor 50. The entire system is encapsulated within a housing (not shown). The system may also include an image processing unit for executing subsequent image correction algorithms.

[0021] The wide-angle optical system primarily employs four lenses. The first lens, 10, has negative optical power and is a concave-convex lens, used to capture light across a wide field of view. The second lens, 20, and the third lens, 30, both have positive optical power and are typically biconvex lenses, used to converge light and correct some aberrations. The fourth lens, 40, has negative optical power and is used to adjust the system's total focal length, working in conjunction with the previous lenses to correct field curvature and astigmatism. This classic anti-telephoto structure (negative-positive-positive-negative) is the foundation for achieving a wide angle.

[0022] The first mirror surface 11 of the first lens 10, facing the object side, is designed as a freeform surface. Unlike traditional spherical surfaces or aspherical surfaces that are only rotationally symmetric, the surface shape of a freeform surface can be described by polynomials such as XY polynomials or Zernike polynomials, and it is asymmetric in both orthogonal directions. This gives designers a great deal of freedom to perform differentiated and refined phase modulation for light rays incident at different field of view angles. Therefore, freeform surfaces can extremely effectively correct the most troublesome barrel distortion and edge astigmatism in ultra-wide-angle lenses, so that straight objects at the edge of the field of view can also be imaged as straight lines and remain sharp.

[0023] This invention also introduces a metasurface element 60. For example... Figure 1 and Figure 3 As shown, in this embodiment, the metasurface element 60 is a separate planar element placed between the fourth lens 40 and the photoelectric sensor 50. It consists of a transparent substrate 61 (such as fused silica) and an array of titanium dioxide (TiO2) nanopillars 62 fabricated on it using semiconductor processes. The size, shape, and arrangement of each nanopillar are precisely designed so that the entire element produces different phase delays for different wavelengths of light (such as red, green, and blue light). Through reverse design, the dispersion generated by the metasurface element 60 can precisely cancel out the axial chromatic aberration and magnification chromatic aberration generated by the four lens array. This avoids the use of expensive ED glass or complex cemented lenses, solving the chromatic aberration problem with a single ultrathin element, and making a significant contribution to the system's thinness and cost control.

[0024] like Figure 2As shown, an imaging method for a wide-angle optical system is described. During optical design (step S701), distortion is controlled to an extremely low level (e.g., <2%) using freeform surfaces, but a simple, predictable low-order residual distortion may still exist. Based on this specific distortion model, a lightweight convolutional neural network (CNN) model is trained (step S702). In practical use, the photoelectric sensor 50 captures the original image (step S703), the image processing unit receives the data (step S704), and calls this pre-trained dedicated model for real-time correction (step S705), ultimately outputting a high-fidelity image with almost no distortion (step S706). Because the model is customized, its computational efficiency is far higher than that of general correction algorithms, and the correction effect is better.

[0025] To more clearly illustrate the beneficial effects of this utility model, the parameters of a specific embodiment are given below, and compared with a conventional design that does not employ the technology of this utility model (based on the utility model patent with publication number CN223092203U).

[0026] Parameter Items Traditional four-piece design This embodiment Remark Field of view (FOV) 180° 200° Benefiting from freeform surface optimization F-number (F / #) 2.8 2.4 Larger aperture, better low-light performance System Length ~20mm ~17mm Metasurface replaces chromatic aberration lens groups, resulting in a more compact design. Maximum distortion >8% (optical) <2% (optical) / <0.5% (after algorithm) Significant advantages of freeform surfaces + cooperative algorithms Longitudinal color difference ~15µm <5µm High-efficiency correction of metasurface elements Lens material Includes 1-2 pieces of high-priced, low-dispersion glass All are ordinary high-refractive-index plastics / glass Metasurface components reduce the requirements for glass materials. Cost Index 1.2 0.8 Simplified structure, common materials, and reduced cost

[0027] In this embodiment, the specific parameters of each lens (such as aperture, radius of curvature, thickness, material, etc.) are selected within the range defined in the content of the utility model. Through optimization by optical design software (such as Zemax or CodeV), excellent imaging performance can be obtained.

[0028] This invention innovatively combines two cutting-edge optical technologies, freeform surfaces and metasurfaces, with a classic four-piece structure, and employs a hardware-algorithm co-design approach. It successfully achieves ultra-wide-angle, high-quality imaging performance in an ultra-compact, low-cost structure, resolving the inherent contradictions of existing technologies and demonstrating significant progressiveness and practical value.

[0029] This utility model is not limited to the above-mentioned optional embodiments. Anyone can derive other forms of products under the guidance of this utility model. However, regardless of any changes made in its shape or structure, any technical solution that falls within the scope of the claims of this utility model shall be protected by this utility model.

Claims

1. A wide-angle optical system characterized by comprising: Includes a lens and a photoelectric sensor (50), the lens comprising components arranged sequentially along the optical axis from the object side to the image side: The first lens (10) is a negative power lens; The second lens (20) is a positive power lens; The third lens (30) is a positive power lens; The fourth lens (40) is a negative power lens; The photoelectric sensor (50) is disposed on the image side of the fourth lens (40); At least one lens surface in the lens is a freeform surface used to correct distortion and astigmatism; The wide-angle optical system also includes a metasurface element (60), which is disposed in the optical path and is used to correct the chromatic aberration of the system.

2. The wide-angle optical system according to claim 1, wherein The first lens (10) includes a first mirror (11) and a second mirror (12), the second lens (20) includes a third mirror (21) and a fourth mirror (22), the third lens (30) includes a fifth mirror (31) and a sixth mirror (32), and the fourth lens (40) includes a seventh mirror (41) and an eighth mirror (42). The aperture of the first mirror (11) is 8mm~10mm, the aperture of the second mirror (12) is 4mm~6mm, the aperture of the third mirror (21) is 2mm~4mm, the aperture of the fourth mirror (22) is 2mm~4mm, the aperture of the fifth mirror (31) is 3mm~5mm, the aperture of the sixth mirror (32) is 3mm~5mm, the aperture of the seventh mirror (41) is 3mm~5mm, and the aperture of the eighth mirror (42) is 3mm~5mm.

3. The wide-angle optical system as described in claim 2, characterized in that, The first mirror (11) has a radius of curvature of 25~35, the second mirror (12) has a radius of curvature of 2.2~2.9, the third mirror (21) has a radius of curvature of 7.5~8.5, the fourth mirror (22) has a radius of curvature of 7.5~8.5, the fifth mirror (31) has a radius of curvature of 5.2~5.8, the sixth mirror (32) has a radius of curvature of 2.2~2.9, the seventh mirror (41) has a radius of curvature of 2.2~2.9, and the eighth mirror (42) is a plane.

4. The wide-angle optical system as described in claim 3, characterized in that, The center thickness of the first lens (10) is 0.5mm~0.8mm, and its sagitta is 1.5mm~2.3mm; the distance between the second mirror (12) and the third mirror (21) is 5.5mm~7mm, the thickness of the second lens (20) is 3.1mm~4.3mm, the distance between the fourth mirror (22) and the fifth mirror (31) is 0.05mm~0.9mm, the thickness of the third lens (30) is 2.5mm~3.6mm, and the thickness of the fourth lens (40) is 0.3mm~0.9mm.

5. The wide-angle optical system as described in claim 1, characterized in that, The first lens (10) has a refractive index of 1.24~1.8, the second lens (20) has a refractive index of 1.24~1.8, the third lens (30) has a refractive index of 1.28~1.72, and the fourth lens (40) has a refractive index of 1.12~1.

86.

6. The wide-angle optical system as described in claim 1, characterized in that, The Abbe number of the first lens (10), the second lens (20), the third lens (30), and the fourth lens (40) is greater than 50.

7. The wide-angle optical system as described in claim 1, characterized in that, The freeform surface is the first mirror surface (11) of the first lens (10) facing the object side.

8. The wide-angle optical system as described in claim 1, characterized in that, The metasurface element (60) is an independent flat plate element disposed between the fourth lens (40) and the photoelectric sensor (50); or, the metasurface element (60) is integrated on the eighth mirror surface (42) of the fourth lens (40).

9. The wide-angle optical system as described in claim 8, characterized in that, The metasurface element (60) includes a transparent substrate and an array of subwavelength nanostructures made of dielectric material formed on the transparent substrate.

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