Underwater visible near-infrared image square telecentric imaging system

Abstract

This invention relates to an underwater visible and near-infrared image-side telecentric imaging system. Its optical system includes two spherical refractive lenses and one planar superlens, with all optical elements having a coaxial structure. The arrangement, in order of light incidence, is: a negative lens bent towards the light incidence direction, a positive lens facing away from the light incidence direction, and the planar superlens. The system's aperture stop is located on the front surface of the negative lens. This invention utilizes a combination of positive and negative lenses and a superlens to achieve aberration correction and balance. Designed with an image-side telecentric structure, this invention can serve as a telescope system for visible and near-infrared imaging spectrometers, and can also be used independently as a visible and near-infrared imaging lens. The system features a relatively large aperture, excellent imaging quality, and a compact, small structure.

Description

Technical Field

[0001] This utility model relates to an underwater visible and near-infrared telecentric imaging system, belonging to the field of optical design technology. Background Technology

[0002] Compared to land-based imaging, underwater imaging faces more severe technical challenges. The strong absorption and scattering of light by water significantly impacts image quality, a bottleneck that urgently needs to be overcome. To meet the unique requirements of underwater optical imaging, imaging systems are developing towards lightweight and miniaturization. Notably, in low-light environments, infrared imaging systems exhibit significant advantages over traditional visible light systems. Therefore, developing miniaturized underwater imaging systems that combine visible and near-infrared wavelengths is of significant practical importance.

[0003] Prior to this invention, Chinese invention patent CN118938450A provided an underwater visible-near-infrared image-side telecentric imaging system, whose optical elements included four spherical lenses and two aspherical lenses. This lens employed aspherical technology during its design process to correct and balance some aberrations, ultimately resulting in an image-side telecentric lens with a large relative aperture, miniaturization, and lightweight design. However, its six-element structure increased the complexity of the system design and resulted in poor imaging performance. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a compact underwater visible and near-infrared telecentric imaging system with high imaging quality.

[0005] The technical solution adopted to achieve the purpose of this invention is to provide an underwater visible and near-infrared telecentric imaging system. Its optical elements are coaxial and include, in order of light incident direction, a negative lens that bends towards the light incident direction, a positive lens that faces away from the light incident direction, and a planar superlens. The aperture stop of the system is set at the front surface of the negative lens.

[0006] The front and rear surfaces of the negative lens are standard spherical surfaces with radii of curvature R and R, respectively. 11 and R 12 The condition -21.42mm≤R is satisfied. 11 ≤-21.38mm, -94.10mm≤R 12 ≤-93.50mm; the light transmission apertures of the front and rear surfaces are 7.370mm and 7.608mm respectively; the thickness of the negative lens ranges from 0.89 to 1.12mm;

[0007] The front and rear surfaces of the positive lens are standard spherical surfaces with radii of curvature R and R, respectively. 21 and R 22 The condition 18.89mm≤R is met.21 ≤18.92mm, 47.79mm≤R 22 ≤47.89mm; the light transmission apertures of the front and rear surfaces are 8.778mm and 9.628mm respectively; the thickness of the positive lens ranges from 4.50 to 4.91mm;

[0008] The planar superlens has a center thickness ranging from 18.31 to 18.33 mm, and light-transmitting apertures of 10.542 mm and 8.654 mm on its front and rear surfaces, respectively. Corresponding to different wavelengths, the phase distribution polynomials of the front and rear surfaces are... As shown in equation (I):

[0009] (I)

[0010] Where M is the diffraction order of the planar superlens surface, and N is the number of polynomial coefficients. It is a power series of x and y. Let be the coefficients of each term in the polynomial, representing the coefficient of the i-th term in the phase distribution polynomial for wavelength j; the coefficients of each term in the phase distribution polynomial on the front surface of the planar superlens range from -150 to 20 ≤ A. 11 ≤-15000, 535≤A 21 ≤549, 24≤A 31 ≤38, -10890≤A 12 ≤-10875, 384≤A 22 ≤395, 12≤A 32 ≤24, -8545≤A 13 ≤-8535,300≤A 23 ≤310, 9≤A 33 ≤18, -7031≤A 14 ≤-7023, 246≤A 24 ≤253, 7≤A 34 ≤14, -5973≤A 15 ≤-5969, 209≤A 25 ≤214, 7≤A 35 ≤12; The coefficients of each term in the polynomial of the phase distribution on the back surface of the planar superlens range from -10 to 125 ≤ A. 11 ≤-10090, 1834≤A 21 ≤1863, 168≤A 31 ≤198, -7765≤A 12 ≤-7725, 1315≤A 22 ≤1340, 80≤A 32 ≤105, -6230≤A 13≤-6200, 1020≤A 23 ≤1045, 60≤A 33 ≤80, -5190≤A 14 ≤-5165, 840≤A 24 ≤860, 45≤A 34 ≤62, -4445≤A 15 ≤-4423, 712≤A 25 ≤728, 36≤A 35 ≤52.

[0011] The present invention describes an underwater visible-near-infrared telecentric imaging system, wherein the center-to-center distance between adjacent surfaces of the negative lens and the positive lens ranges from 0.92 to 1.11 mm; the center-to-center distance between adjacent surfaces of the positive lens and the planar superlens ranges from 0.61 to 0.79 mm; and the distance between the center of the light-emitting surface of the planar superlens and the image plane ranges from 1.705 to 1.715 mm.

[0012] The front and rear surfaces of the planar superlens are subwavelength-scale titanium dioxide nanopillar unit structures; the cross-section of the nanopillar is a square with a side length of 50-170 nm, and the height of the nanopillar is 560 nm; the lattice constant of the unit structure nanopillar is 255 nm.

[0013] This invention provides an underwater visible-near-infrared image-side telecentric imaging system, wherein the angle between the principal ray of the outgoing beam and the normal to the image plane in each field of view is less than 1.92°. The overall dimensions of the imaging system are φ10.6×32.5mm.

[0014] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0015] 1. The image-side telecentric imaging system provided by this utility model consists of only three lenses, two of which are designed with standard spherical surfaces. The system is a coaxial structure, which reduces the difficulty and cost of lens processing and also has the advantage of small size, thus having practical application value.

[0016] 2. The image-side telecentric imaging system provided by this utility model adopts a planar superlens, which improves the residual aberrations of the positive and negative lens groups and enhances the aberration correction capability of the system.

[0017] 3. The image-side telecentric imaging system provided by this utility model, through the reasonable selection of materials for the positive and negative lens groups and a superlens, increases the numerical aperture of the system while achieving aberration correction and balance, thus significantly improving the system's light-gathering ability and imaging quality. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the imaging system provided in an embodiment of the present invention;

[0019] In the diagram, 1. Object plane; 2. Negative lens; 3. Positive lens; 4. Planar superlens; 5. Image plane;

[0020] Figure 2 Phase distribution diagrams of the front and rear surfaces of the planar superlens provided for embodiments of this utility model;

[0021] Figure 3 This is a ray tracing point diagram of the imaging system provided in this embodiment of the present invention;

[0022] Figure 4 This is a graph of the MTF (Mean Transfer Function) of the imaging system provided in this embodiment of the present invention. Detailed Implementation

[0023] The specific implementation schemes of this utility model will be further described below with reference to the accompanying drawings and embodiments. Example 1

[0024] This embodiment provides an underwater visible and near-infrared telecentric imaging system. Its optical elements consist only of positive and negative lens groups and a planar superlens. The spectral range is 400nm to 1000nm, the focal length is 12mm, the F number is 1.67, and the field of view is 32°.

[0025] See appendix Figure 1 This is a schematic diagram of the image-side telecentric imaging system provided in this embodiment. Each optical element has a coaxial structure. According to the direction of light incidence, the optical elements are, in sequence, a negative lens 2 that bends towards the direction of light incidence, a positive lens 3 that faces away from the direction of light incidence, and a planar superlens 4. The aperture stop of the system is set at the front surface of the negative lens. When the image-side telecentric system images an object at infinity, the incident light beam emitted from the object surface 1 passes through the negative lens 2 and the positive lens 3 in sequence. After the spherical aberration is corrected by the positive and negative lens group, the light beam disperses and converges at the image surface 5 through the planar superlens 4 to form an image.

[0026] The parameters of each optical element in this embodiment are shown in Table 1.

[0027] Table 1:

[0028]

[0029] The imaging system provided by the technical solution of this embodiment has an optical system with a total length of only 32.43 mm.

[0030] The planar superlens provided in this embodiment has phase distribution polynomials on its front and rear surfaces corresponding to different wavelengths. As shown in the following polynomial:

[0031] ,

[0032] Where the diffraction order of the planar superlens surface is M, and N is the number of polynomial coefficients, the polynomial... It is a normalized power series of x and y, and the aperture diameters of the front and rear surfaces are 10.542 mm and 8.654 mm, respectively. denoted as coefficients of the polynomial, representing the coefficient of the i-th term of the phase distribution polynomial for wavelength j. See Tables 2 and 3 for the coefficient values ​​of the front and rear surfaces of the planar superlens in this embodiment.

[0033] Table 2:

[0034]

[0035] Table 3:

[0036]

[0037] See appendix Figure 2 This is a phase distribution diagram of the front and rear surfaces of the planar superlens provided in this embodiment at a wavelength of 400nm. (a) shows the phase distribution of the front surface, and (b) shows the phase distribution of the rear surface.

[0038] In this embodiment, the front and rear surfaces of the planar superlens are subwavelength-scale titanium dioxide nanopillar unit structures. The nanopillars have square cross-sections with side lengths D ranging from 50 nm to 170 nm and heights h of 560 nm. The lattice constant of the unit structure nanopillars is p = 255 nm. Since the phase distribution on the surface of the planar superlens differs at different wavelengths, this embodiment employs a dispersive unit structure with a square cross-section. By selecting different square side lengths D, a planar dispersive superlens is constructed to achieve phase response to different wavelengths.

[0039] See appendix Figure 3 It is a ray tracing dot plot of light passing through the imaging system provided in this embodiment. In the figure, the root mean square radius of the dot plots corresponding to the five wavelengths of 400nm, 550nm, 700nm, 850nm and 1000nm is less than 0.64μm, and the geometric radius of the dot plots is less than 1.49μm.

[0040] See appendix Figure 4 This refers to the MTF curves of the imaging system provided in this embodiment, corresponding to the image planes of each field of view. Figure 3It can be seen that at the image plane, when the cutoff frequency is 120 lp / mm, the MTF values ​​of each field of view at wavelengths of 400nm (a), 550nm (b), 700nm (c), 850nm (d) and 1000nm (e) are all greater than 0.7, which are close to the diffraction limit. The curves are relatively smooth, indicating that the lens imaging is clear and uniform, and the system has good imaging quality in the entire wavelength range and field of view.

[0041] The underwater visible and near-infrared telecentric imaging system provided by this invention consists of only two spherical lenses and one superlens. The system undergoes rigorous aberration correction and features a large numerical aperture, excellent imaging quality, and high light energy utilization. Furthermore, its simple and compact structure makes it easy to manufacture and assemble, and it has broad application prospects.

Claims

1. An underwater visible-near-infrared telecentric imaging system, characterized in that: The optical elements of the imaging system are coaxial, and in order of light incident direction, they include a negative lens (2) that bends towards the light incident direction, a positive lens (3) that faces away from the light incident direction, and a planar superlens (4); the aperture stop of the system is set on the front surface of the negative lens. The front and rear surfaces of the negative lens (2) are standard spherical surfaces with radii of curvature R and R, respectively. 11 and R 12 The condition -21.42mm≤R is satisfied. 11 ≤-21.38mm, -94.10mm≤R 12 ≤-93.50mm; the light transmission apertures of the front and rear surfaces are 7.370mm and 7.608mm respectively; the thickness of the negative lens ranges from 0.89 to 1.12mm; The front and rear surfaces of the positive lens (3) are standard spherical surfaces with radii of curvature R and R, respectively. 21 and R 22 The condition 18.89mm≤R is met. 21 ≤18.92mm, 47.79mm≤R 22 ≤47.89mm; the light transmission apertures of the front and rear surfaces are 8.778mm and 9.628mm respectively; the thickness of the positive lens ranges from 4.50 to 4.91mm; The planar superlens (4) has a center thickness ranging from 18.31 to 18.33 mm, and the apertures of the front and rear surfaces are 10.542 mm and 8.654 mm, respectively. Corresponding to different wavelengths, the phase distribution polynomials of the front and rear surfaces are... As shown in equation (I): （I） Where M is the diffraction order of the planar superlens surface, and N is the number of polynomial coefficients. It is a power series of x and y. Let be the coefficients of each term in the polynomial, representing the coefficient of the i-th term in the phase distribution polynomial for wavelength j; the coefficients of each term in the phase distribution polynomial on the front surface of the planar superlens range from -150 to 20 ≤ A. 11 ≤-15000, 535≤A 21 ≤549, 24≤A 31 ≤38, -10890≤A 12 ≤-10875, 384≤A 22 ≤395, 12≤A 32 ≤24, -8545≤A 13 ≤-8535, 300≤A 23 ≤310, 9≤A 33 ≤18, -7031≤A 14 ≤-7023, 246≤A 24 ≤253, 7≤A 34 ≤14, -5973≤A 15 ≤-5969, 209≤A 25 ≤214, 7≤A 35 ≤12; The coefficients of each term in the polynomial of the phase distribution on the back surface of the planar superlens range from -10 to 125 ≤ A. 11 ≤-10090, 1834≤A 21 ≤1863, 168≤A 31 ≤198, -7765≤A 12 ≤-7725, 1315≤A 22 ≤1340, 80≤A 32 ≤105, -6230≤A 13 ≤-6200, 1020≤A 23 ≤1045, 60≤A 33 ≤80, -5190≤A 14 ≤-5165, 840≤A 24 ≤860, 45≤A 34 ≤62, -4445≤A 15 ≤-4423, 712≤A 25 ≤728,36≤A 35 ≤52.

2. The underwater visible-near-infrared telecentric imaging system according to claim 1, characterized in that: The center distance between adjacent surfaces of the negative lens (2) and the positive lens (3) ranges from 0.92 to 1.11 mm; the center distance between adjacent surfaces of the positive lens (3) and the planar superlens (4) ranges from 0.61 to 0.79 mm; the distance between the center of the light exit surface of the planar superlens (4) and the image plane (5) ranges from 1.705 to 1.715 mm.

3. The underwater visible-near-infrared telecentric imaging system according to claim 1, characterized in that: The front and rear surfaces of the planar superlens are subwavelength-scale titanium dioxide nanopillar unit structures; the cross-section of the nanopillar is a square with a side length of 50-170 nm, and the height of the nanopillar is 560 nm; the lattice constant of the unit structure nanopillar is 255 nm.

4. The underwater visible-near-infrared telecentric imaging system according to claim 1, characterized in that: The angle between the principal ray of the outgoing beam and the normal to the image plane in each field of view is less than 1.92°.

5. The underwater visible-near-infrared telecentric imaging system according to claim 1, characterized in that: The underwater visible near-infrared telecentric imaging system has external dimensions of φ10.6×32.5mm.

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