Optical system and imaging device

Abstract

The optical system comprises a first lens group, a second lens group and an image sensor which are sequentially arranged from an object side to an image side, the first lens group comprises a field angle increasing part and a polarization conversion part which are sequentially arranged from the object side to the image side, the field angle is increased by the first lens group, and the polarization conversion part is used for polarization conversion. The light rays are emitted at different angles according to the polarization characteristics, so that polarization state images are respectively formed in different specific areas of the image sensor; the second lens group is used for focusing the polarization state image in each specific area. The optical system solves the problems that a metasurface lens is sensitive to response to a large incident angle and imaging is not ideal enough, the field angle is increased by arranging the field angle increasing part, hardware parameters of the optical system are limited, imaging on an image sensor is maximized finally, meanwhile, overlapping and crossing of polarization images are reduced, and the imaging quality is improved. The optical system has good optical performance, and is suitable for various high-performance polarization imaging applications.

Description

Technical Field

[0001] The utility model relates to an optical system, in particular to an imaging device with the optical system. Background Art

[0002] Polarization imaging technology can obtain the spatial distribution information and physical and chemical information of the target object. Compared with traditional intensity imaging, polarization imaging can provide richer information, so it has important application value in many fields, such as face recognition, material analysis, biomedical imaging, etc. However, traditional polarization imaging technology has problems such as large size, heavy weight, poor consistency and stability, which limits its application in consumer electronic products.

[0003] Metasurface optical components are considered an important platform for developing the next generation of highly integrated polarization imaging systems due to their small size, multifunctionality, and easy integration. Metasurface optical components can realize novel applications such as ultra-thin plane lenses and multifunctional vector holography. By regulating structures such as nanocolumns, different forms of polarization state modulation such as circular polarization, elliptically polarized light, and linear polarization can be achieved. However, when realizing polarization imaging, metasurfaces often face challenges in parameters such as polarization extinction ratio and imaging effective signal-to-noise ratio. Especially in the case of large field of view, the sensitivity of metasurfaces to large incident angles may affect the polarization extinction ratio and imaging efficiency, and it is also necessary to ensure that sub-images of different polarization states have sufficient number of pixels and clarity.

[0004] Therefore, although the combination of polarization imaging technology and metasurface optical elements has great potential in theory, it still faces many challenges in practical applications. Utility Model Content

[0005] In order to solve at least one of the many challenges of combining polarization imaging technology and metasurface in the prior art, the purpose of the present utility model is to provide an optical system with a large field of view and high imaging quality, and an imaging device having the optical system.

[0006] To achieve the above-mentioned purpose of the utility model, an embodiment of the utility model provides an optical system, comprising a first lens group, a second lens group and an image sensor arranged in sequence from the object side to the image side, the first lens group comprises a field angle increasing portion and a polarization conversion portion arranged in sequence from the object side to the image side, the polarization conversion portion comprises a plurality of polarization-sensitive sub-wavelength primitives, the field angle increasing portion increases the field angle, and the polarization conversion portion emits light at different angles according to polarization characteristics, so as to form polarization state images in different specific areas of the image sensor respectively;

[0007] The second lens group is used to focus the polarization state image in each of the specific areas;

[0008] The optical system satisfies:

[0009] f*tanθ grating >0.5,

[0010] IMGH>3.0,

[0011] FOV image >3*θ grating ,

[0012] Wherein, f is the effective focal length of the optical system, θ grating is the diffraction angle of the central field of view light in the optical system after passing through the first lens group, IMGH is the target surface size of the image sensor, FOV image is the angular field of view of the image sensor.

[0013] As a further improvement of the present invention, the number of the specific areas is 4, the 4 specific areas are distributed in two rows and two columns, and the 4 specific areas do not overlap each other.

[0014] As a further improvement of the present invention, at least two of the specific areas are substantially tangent to each other, and each of the specific areas is substantially tangent to an imaging edge of the image sensor.

[0015] As a further improvement of the present invention, the combined focal length f1 of the first lens group and the combined focal length f2 of the second lens group satisfy:

[0016] 50 <f1 / f2<90。

[0017] As a further improvement of the present invention, the optical system further includes an aperture stop disposed between the first lens group and the second lens group, and a distance d between the first lens group and the aperture stop satisfies:

[0018] 0.05 <d<0.8;

[0019] The optical system includes a plurality of metalenses, and the plurality of metalenses all satisfy:

[0020] 20<|Δφ / R M |<430,

[0021] Wherein, Δφ is the maximum phase difference provided by the metalens at a single wavelength, R M is the optical effective radius of the metalens.

[0022] As a further improvement of the present invention, the first lens group includes a first super lens, and the polarization conversion unit includes the multiple polarization-sensitive sub-wavelength elements on one surface of the first super lens.

[0023] As a further improvement of the present invention, the superlens also includes a second superlens, the second lens group includes a plurality of focusing refracting lenses, the first superlens is arranged between the second superlens and the plurality of focusing refracting lenses, the field of view angle increasing portion also includes a plurality of non-polarization-sensitive sub-wavelength elements arranged on one surface of the first superlens close to the object side and at least one surface of the second superlens, and the plurality of focusing refracting lenses are used for focusing imaging.

[0024] As a further improvement of the present utility model, the first lens group also includes a plurality of refractive lenses, the second lens group includes a plurality of focusing refractive lenses, the first superlens is arranged between the plurality of refractive lenses and the plurality of focusing refractive lenses, the field of view angle increasing portion also includes the plurality of refractive lenses, and the plurality of focusing refractive lenses are used for focusing imaging.

[0025] As a further improvement of the present invention, the superlens also includes a second superlens and several focusing superlenses in the second lens group, the first superlens is arranged between the second superlens and the several focusing superlenses, the field of view angle increasing unit also includes a plurality of non-polarization-sensitive sub-wavelength elements arranged on one surface of the first superlens close to the object side and at least one surface of the second superlens, and the several focusing superlenses are used for focusing imaging.

[0026] To achieve one of the above purposes of the utility model, an embodiment of the utility model provides an imaging device, which includes the above optical system.

[0027] Compared with the prior art, the utility model has the following beneficial effects: the optical system solves the problem that the metasurface lens is sensitive to large incident angles and the imaging is not ideal. The field of view angle is increased by the field of view angle increasing part, so that the incident angle to the polarization conversion part is reduced, the efficiency of polarization conversion is improved, and thus the extinction ratio is improved. By limiting the hardware parameters of the optical system, the final imaging on the image sensor is maximized while reducing the overlap and intersection of polarization images, that is, the image can be presented more clearly. The light-collecting ability of the large field of view angle and the imaging of pixels of a sufficient number and size make the effective signal energy higher. The optical system has good optical performance and is suitable for various high-performance polarization imaging applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of imaging on the image sensor of the utility model;

[0029] Figure 2 It is a schematic structural diagram of the optical system of the first embodiment of the utility model;

[0030] Figure 3is a graph showing the variation of the resolution of the optical system at each incident angle with the spatial frequency in the first embodiment of the utility model;

[0031] Figure 4 is a graph showing the relative illumination of the optical system of the first embodiment of the utility model changing with the height of the field of view;

[0032] Figure 5 It is a structural schematic diagram of an optical system of a second embodiment of the utility model;

[0033] Figure 6 is a graph showing the variation of the resolution of the optical system at each incident angle with the spatial frequency according to the second embodiment of the utility model;

[0034] Figure 7 is a graph showing the change in relative illumination of the optical system of the second embodiment of the utility model with the height of the field of view;

[0035] Figure 8 It is a structural schematic diagram of an optical system of a third embodiment of the utility model;

[0036] Fig. 9 is a graph showing the variation of the resolution at each incident angle with the spatial frequency of the optical system of the third embodiment of the utility model;

[0037] Fig.10 is a graph showing the relative illumination of the optical system of the third embodiment of the utility model changing with the height of the field of view;

[0038] Among them, 100, a first lens group; 110, a first super lens; 120, a second super lens; 130, a refractive lens; 200, a second lens group; 210, a focusing refractive lens; 220, a focusing super lens; 300, an image sensor; and 400, an aperture stop. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below in conjunction with the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional changes made by a person skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0040] It should be understood that the terms used herein, such as "upper", "above", "lower", "below", etc., indicating spatial relative positions, are used for the purpose of convenience to describe the relationship of one unit or feature relative to another unit or feature as shown in the drawings. The terms of spatial relative positions may be intended to include different orientations of the device in use or operation other than the orientation shown in the drawings.

[0041] An embodiment of the utility model provides an optical system with a large field of view and high imaging quality, and an imaging device having the optical system.

[0042] The imaging device and optical system can meet many applications in consumer electronic products such as face recognition and material analysis. The optical system of this embodiment can complete these tasks, with a field of view of more than 80° and presenting multiple sub-images in different polarization states, specifically 4 polarization state images. Moreover, the 4 polarization state images can be presented on the target surface to the maximum extent without overlapping each other. Larger and clearer polarization state images are conducive to subsequent computational analysis of neural networks. In addition, the total length of the optical system is within 4 mm, with the characteristics of small size and excellent imaging.

[0043] An imaging device of this embodiment includes an optical system, which includes a first lens group 100, a second lens group 200 and an image sensor 300 arranged in sequence from the object side to the image side. The first lens group 100 includes a field angle increasing portion and a polarization conversion portion arranged in sequence from the object side to the image side, the polarization conversion portion includes a plurality of polarization-sensitive sub-wavelength primitives, the field angle increasing portion increases the field angle, and the polarization conversion portion emits light at different angles according to polarization characteristics to form polarization state images in different specific areas of the image sensor 300; the second lens group 200 is used to focus the polarization state images in each specific area. The image sensor 300 is used to capture the polarization state images focused by the second lens group 200.

[0044] The optical system meets the following requirements:

[0045] f*tanθ grating >0.5, (Formula 1)

[0046] IMGH>3.0, (Formula 2)

[0047] FOV image >3*θ grating , (Formula 3)

[0048] Where f is the effective focal length of the optical system, θ grating is the diffraction angle of the central field light in the optical system after passing through the first lens group 100, IMGH is the target surface size of the image sensor 300, FOV image is the field of view angle range of the image sensor 300.

[0049] By controlling formulas 1, 2, and 3, the four polarization state images presented on the image sensor 300 can be shifted to a suitable position, that is, a state that does not cross each other and is maximized on the image sensor 300, such as Figure 1As shown. Specifically, by using Formula 1 and Formula 3, the polarization grating of the first lens group 100 and the focal length of the entire optical system can be designed in coordination, so that each polarization state image is offset to the optimal range, ensuring that multiple polarization state images do not overlap each other and the area is maximized, and also avoiding the problem of insufficient utilization of the image sensor area by the polarization image due to the grating diffraction angle being too small or too large. By using Formula 2, the diagonal size of the target surface size of the image sensor 300 is made larger than 3.0 mm, which can ensure that the system has a sufficiently large image surface and pixel number, so that the polarization state image pixel reaches at least 50w or more. By using Formula 3, it is possible to avoid the problem that the grating diffraction angle is too small, the polarization state image pixel is too far from the edge, resulting in an area too small and insufficient number of pixels, or the polarization state image overflows the edge of the image sensor 300 due to the grating diffraction angle being too large.

[0050] The first lens group 100 includes a first superlens 110, and the polarization conversion unit includes the plurality of polarization-sensitive sub-wavelength primitives on one side of the first superlens 110. The polarization-sensitive primitives may be in a shape that is not completely symmetrical in all directions, such as a square or a triangle, and nanopillars such as square pillars may be controlled to realize different polarization states, such as circular polarization, elliptically polarized light, and linear polarization.

[0051] The polarization state images are imaged in multiple specific areas of the image sensor 300, and these specific areas correspond to multiple different polarization state images. In this embodiment, the multiple specific areas are four imaging circles, and the size of the imaging circles is maximized without interfering with each other and exceeding the sensor range. Figure 1 As shown, the four specific areas are distributed in two rows and two columns, and the four specific areas do not overlap. These areas are distributed in two rows and two columns to ensure that each polarization state image has enough space for imaging and does not interfere with each other. In addition, by adjusting the elementary structure and arrangement of the polarization conversion unit, after the light passes through the first lens group 100, it is irradiated to the corresponding area of ​​the image sensor 300 according to its polarization state.

[0052] By designing the optical system and optimizing the parameters, the effective distribution of the four polarization state images on the image sensor 300 is achieved, which is suitable for high-precision polarization imaging applications.

[0053] Further, at least two specific regions are substantially tangent to each other, and each specific region is substantially tangent to an imaging edge of the image sensor 300. This configuration can maximize the use of the area of ​​the image sensor 300, ensuring that each polarization state image has enough space for imaging.

[0054] In order to make the distribution of specific areas on the image sensor 300 meet the tangency requirement, the first metalens 110 in the first lens group 100 needs to be further designed and adjusted. Lights of four different polarization states will be irradiated onto four specific areas of the image sensor 300 respectively, and the focusing ability of the second lens group 200 is also required, that is, the effective focal length f and the diffraction angle θ in the above formula 3 are grating , so that at least two regions are tangent at the edge. By precisely controlling the elementary structure and arrangement of the first metalens 110 and the parameters of the second lens group 200, precise illumination of light can be achieved, so that at least two polarization state images are substantially tangent at the edge of the image sensor 300, and finally the correct position and clear imaging of the polarization state images on the image sensor 300 are ensured.

[0055] Furthermore, the combined focal length f1 of the first lens group 100 and the combined focal length f2 of the second lens group 200 satisfy:

[0056] 50 <f1 / f2<90;

[0057] By constraining the ratio of f1 / f2 , the optical system can be imaged on multiple specific areas of the image sensor 300 after sequentially passing through the first lens group 100 and the second lens group 200 at a specific large incident angle.

[0058] In addition, the optical system further includes an aperture stop 400 disposed between the first lens group 100 and the second lens group 200, and a distance d between the first lens group 100 and the aperture stop 400 satisfies:

[0059] 0.05 <d<0.8。

[0060] The distance d affects the assembly process between the first lens group 100 and the second lens group 200, the total optical length of the optical system, and the vignetting size of each field light beam after passing through the aperture stop 400 after being emitted from the first metalens 110. The setting range of the distance d ensures the optical performance while realizing the compact layout of the system. The specific value of the distance d needs to be optimized according to the actual application and performance requirements of the system. Specifically, if d is around 0.05 mm, the first lens group 100 and the second lens group 200 are assembled with the same lens barrel structure to minimize the total optical length, which is beneficial to the miniaturization of the module size, and the vignetting after passing through the aperture stop 400 after emitting from the first super lens 110 is relatively minimal, and the light energy transmission loss is smaller; if d is around 0.7-0.8 mm, the first lens group 100 and the second lens group 200 are mostly assembled with two lens barrels and then assembled by dispensing, the total length of the optical system will be larger than the former, and the vignetting of the external field light beam after emitting through the first super lens 110 will increase. The increase in vignetting can be reduced by reducing the aperture of the first super lens 110 of the super structure, avoiding the risk of very uneven brightness in the upper and lower areas of the polarization state image.

[0061] Furthermore, the optical system includes a plurality of metalenses, and the plurality of metalenses all satisfy:

[0062] 20<|Δφ / R M |<430,

[0063] Where Δφ is the maximum phase difference provided by the metalens at a single wavelength, R M is the optical effective radius of the metalens. In addition to the first metalens, the metalens provided in the optical system may also include the second metalens in the following embodiments 1 and 3, and the plurality of focusing metalens in embodiment 3, that is, all metalens in the optical system of this embodiment meet the requirements of the formula.

[0064] Under a single wavelength, the phases provided by different positions of the first superlens 110 are generally different. By constraining the relationship between the maximum phase difference of the first superlens 110 and the optical effective radius of the optical system through this condition, the first superlens 110 has a better phase matching effect, realizes effective modulation of polarized light, and ensures clear imaging of polarization state images, so as to give full play to the optical performance of the first superlens 110. M The limitations also limit the parameters of the elementary structure, size and arrangement of the first metalens 110 to achieve the expected phase modulation effect.

[0065] By precisely controlling the phase difference and optical effective radius of the first superlens 110, effective modulation of polarized light and clear imaging effects are achieved, which is suitable for application scenarios with high requirements for polarization modulation accuracy.

[0066] The following three embodiments are used to illustrate the above parameters and different situations of the optical system.

[0067] Example 1

[0068] In this embodiment, Figure 2 As shown, the superlens also includes a second superlens 120, the second lens group 200 includes a plurality of focusing refracting lenses 210, the first superlens 110 is arranged between the second superlens 120 and the plurality of focusing refracting lenses 210, the field of view increasing portion also includes a plurality of non-polarization-sensitive sub-wavelength primitives arranged on a surface of the first superlens 110 close to the object side and at least one surface of the second superlens 120, the light incident angle on the object side of the second superlens 120 is greater than the light exit angle on the image side, and the plurality of focusing refracting lenses 210 are used for focusing imaging. Figure 2 The number of the medium focusing refractive lenses 210 is set to three in the figure.

[0069] The specific parameters of the optical system provided in Example 1 are shown in Table 1-1, and the parameters of each lens in the optical system, such as the surface type, curvature, lens thickness, material, cone coefficient and other parameters are shown in Table 1-2. Among them, OBJ is the object side, S1 and S2 are the object side surface and image side surface of the second super lens 120, S3 and S4 are the object side surface and image side surface of the first super lens 110, wherein the image side surface of the second super lens 120 includes a nanostructure layer, and the object side surface and image side surface of the first super lens 110 both include a nanostructure layer. STO is the aperture stop 400, S5-S10 are the object side surface and image side surface of the three focusing and refractive lenses 210, respectively, S11-S12 are the object side surface and image side surface of the color filter, and S13 is the image side. The three focusing and refractive lenses 210 all use aspheric surfaces, and AI are the coefficients of the 4th, 6th, and 20th order terms of the aspheric surfaces, respectively. The expression used for the aspheric surface is In the formula, z is the surface vector height parallel to the optical axis of the optical system, c is the center point curvature of the aspheric surface (1 / R), k is the quadratic surface constant (cone coefficient), A~I correspond to high-order coefficients respectively, and the specific coefficient values ​​are shown in Table 1-3.

[0070] In this embodiment, the constraint f*tan(θ grating)=0.86, through the coordinated design of the first super lens 110 and the focal length of the imaging system, the center of the polarization state image is offset to a relatively optimal position, ensuring that the four polarization state images do not overlap and the occupied area is maximized, and controlling f1 / f2=82.8, constraining this ratio so that the edge field of view light beam passes through the first lens group 100 and hits the second lens group 200 to focus and image to the specified position of the image sensor 300, so that the imaging circles of the four polarization state images do not interfere with each other, and do not overflow the sensor boundary. And control d=0.05, that is, all lenses of the optical system are assembled in the same lens barrel to ensure the miniaturization of the optical system. Limit FOV image =3.5*θ grating , so that the light beam diffracted by the first super lens 110 is focused to a reasonable position by the image sensor 300, while ensuring that the field of view angle can cover the maximum angle of the first super lens 110. Constraint |Δφ / R M |=410, by controlling the ratio between the maximum phase difference and the optical effective radius of the first superlens 110, the 2π phase period borne by the first superlens 110 within a unit length is made to conform to the matching effect of the micro-nano structure on its target phase, so that the optical performance of the first superlens 110 can be more fully exerted.

[0071] Figure 3 A curve diagram showing the resolution of the optical system of this embodiment at various incident angles as a function of spatial frequency is shown, wherein the horizontal axis is the spatial frequency, in units of line pairs / mm; the vertical axis is the resolution value, in a range of 0-1.0, Figure 3 In the above example, the maximum incident angle is divided into 10 equal parts to obtain multiple incident angles. The larger the incident angle, the lower the resolution. Figure 3 The lower the curve is on the same horizontal axis, the larger the incident angle is.

[0072] Figure 4 The graph of the relative illumination of the optical system of this embodiment as a function of the height of the field of view is shown. The horizontal axis in the graph can be the field of view height or the normalized field of view height, i.e., the maximum angle is 1, and the horizontal axis ranges from 0 to 1.0; the vertical axis is the value of the relative illumination, ranging from 0 to 100%. The far right side of the graph represents the relative illumination of the edge field of view, and the relative illumination of this embodiment is 45%, which can meet the requirements.

[0073] Table 1-1

[0074] Parameter Type Numeric Working band 940nm F-number 2.4 Field of view 83° System length 4mm

[0075] Table 1-2

[0076] Face number Surface type Radius of curvature thickness Material Cone coefficient OBJ Spherical endless endless S1 Spherical endless 0.5 1.465,65.77 S2 Metasurface endless 0.35 S3 Metasurface endless 0.5 1.465,65.77 S4 Metasurface endless 0.05 STO Spherical endless 0.018 S5 Aspheric 2.548 0.279 1.67,19.4 30.766 S6 Aspheric -2.142 0.259 4.053 S7 Aspheric -1.493 0.539 1.54,56 5.274 S8 Aspheric -4.873 0.216 31.028 S9 Aspheric 0.761 0.454 1.67,19.4 -0.485 S10 Aspheric 0.779 0.379 -1.77 S11 Spherical endless 0.21 1.517,64.16 S12 Spherical endless 0.235 S13 Spherical endless

[0077] Table 1-3

[0078] Face number A B C D E F G H I S5 -7.862E-01 8.497E-01 -2.193E+02 7.473E+03 -1.453E+05 1.674E+06 -1.136E+07 4.195E+07 -6.503E+07 S6 -7.039E-01 -2.094E+00 8.305E+01 -2.023E+03 2.817E+04 -2.373E+05 1.198E+06 -3.336E+06 3.936E+06 S7 -4.794E-01 9.942E+00 -1.389E+02 1.487E+03 -9.622E+03 3.984E+04 -1.032E+05 1.514E+05 -9.505E+04 S8 -1.461E+00 -1.000E+01 3.094E+02 -3.185E+03 1.822E+04 -6.192E+04 1.242E+05 -1.355E+05 6.189E+04 S9 -1.869E+00 3.120E+00 -1.212E+01 4.368E+01 -1.046E+02 1.582E+02 -1.464E+02 7.571E+01 -1.674E+01 S10 -5.425E-01 -9.438E-01 5.239E+00 -1.085E+01 1.310E+01 -9.864E+00 4.564E+00 -1.190E+00 1.343E-01

[0079] Example 2

[0080] In this embodiment, Figure 5 As shown, the first lens group 100 further includes a plurality of refractive lenses 130, the second lens group 200 includes a plurality of focusing refractive lenses 210, the first metalens 110 is disposed between the plurality of refractive lenses 130 and the plurality of focusing refractive lenses 210, the field of view angle increasing portion further includes a plurality of refractive lenses 130, the light incident angles on the object side of the plurality of refractive lenses 130 are greater than the light exit angles on the image side, and the plurality of focusing refractive lenses 210 are used for focusing imaging. Figure 5 Three middle refractive lenses 130 are provided, and three focusing refractive lenses 210 are also provided.

[0081] The specific parameters of the optical system provided in Example 2 are shown in Table 2-1, and the parameters of each lens in the optical system, such as the surface type, curvature, lens thickness, material, cone coefficient and other parameters are shown in Table 2-2. Among them, OBJ is the object side, S1~S6 are the object side and image side of the three refractive lenses 130 respectively, S7 and S8 are the object side and image side of the first super lens 110, and the image side of the first super lens 110 includes a nanostructure layer. STO is the aperture stop 400, S9-S14 are the object side and image side of the three focusing refractive lenses 210 respectively, S15-S16 are the object side and image side of the color filter, and S17 is the image side. The three refractive lenses 130 and the three focusing refractive lenses 210 all use aspheric surfaces, and AG are the coefficients of the 4th, 6th to 16th order terms of the aspheric surfaces respectively. The expression used for the aspheric surface is In the formula, z is the surface vector height parallel to the optical axis of the optical system, c is the center point curvature of the aspheric surface (1 / R), k is the quadratic surface constant (cone coefficient), A~I correspond to high-order coefficients respectively, and the specific coefficient values ​​are shown in Table 1-3.

[0082] In this embodiment, the constraint f*tan(θ grating )=0.84, through the coordinated design of the first super lens 110 and the focal length of the imaging system, the center of the polarization state image is offset to a relatively optimal position, ensuring that the four polarization state images do not overlap and the occupied area is maximized, and controlling f1 / f2=54.5, constraining this ratio so that the edge field of view light beam passes through the first lens group 100 and hits the second lens group 200 to focus and image to the specified position of the image sensor 300, so that the imaging circles of the four polarization state images do not interfere with each other, and do not overflow the sensor boundary. And control d=0.07, that is, all lenses of the optical system are assembled in the same lens barrel to ensure the miniaturization of the optical system. Limit FOV image =3.24*θgrating , so that the light beam diffracted by the first super lens 110 is focused to a reasonable position by the image sensor 300, while ensuring that the field of view angle can cover the maximum angle of the first super lens 110. Constraint |Δφ / R M |=420, by controlling the ratio between the maximum phase difference and the optical effective radius of the first superlens 110, the 2π phase period borne by the first superlens 110 within a unit length is made to conform to the matching effect of the micro-nano structure on its target phase, thereby giving full play to the optical performance of the first superlens 110.

[0083] Figure 6 A curve diagram showing the resolution of the optical system of this embodiment at various incident angles as a function of spatial frequency is shown, wherein the horizontal axis is the spatial frequency, in units of line pairs / mm; the vertical axis is the resolution value, in a range of 0-1.0, Figure 6 In the above example, the maximum incident angle is divided into 10 equal parts to obtain multiple incident angles. The larger the incident angle, the lower the resolution. Figure 6 The lower the curve is on the same horizontal axis, the larger the incident angle is.

[0084] Figure 7 A curve chart showing the relative illumination of the optical system of this embodiment as a function of the field of view height is shown. In the figure, the horizontal axis can be the field of view height or the normalized field of view height, that is, the maximum angle is 1, and the horizontal axis ranges from 0 to 1.0; the vertical axis is the relative illumination value, ranging from 0 to 100%. Figure 7 The far right side of the figure represents the relative illumination of the edge field of view. The relative illumination of this embodiment is 38%, which can meet the requirements.

[0085] Table 2-1

[0086] Parameter Type Numeric Working band 940nm F-number 2.45 Field of view 80° System length 5.2mm

[0087] Table 2-2

[0088]

[0089]

[0090] Table 2-3

[0091] Face number A B C D E F G S1 7.627E-01 -3.237E+01 4.577E+02 -3.745E+03 1.961E+04 -6.609E+04 1.377E+05 S2 -1.374E+00 8.563E+00 -1.521E+03 4.713E+04 -7.375E+05 6.722E+06 -3.615E+07 S3 -2.563E+00 6.152E+01 -2.466E+03 7.602E+04 -1.375E+06 1.491E+07 -9.689E+07 S4 -1.346E+00 7.152E+01 -2.466E+03 7.646E+04 -1.291E+06 1.263E+07 -7.359E+07 S5 -4.097E-01 1.888E+01 -3.711E+02 1.658E+04 -2.935E+05 2.680E+06 -1.381E+07 S6 -5.909E-01 2.662E-01 -3.538E+01 8.546E+02 -1.014E+04 6.779E+04 -2.583E+05 S9 -7.862E-01 8.497E-01 -2.193E+02 7.473E+03 -1.453E+05 1.674E+06 -1.136E+07 S10 -7.039E-01 -2.094E+00 8.305E+01 -2.023E+03 2.817E+04 -2.373E+05 1.198E+06 S11 -4.794E-01 9.942E+00 -1.389E+02 1.487E+03 -9.622E+03 3.984E+04 -1.032E+05 S12 -1.461E+00 -1.000E+01 3.094E+02 -3.185E+03 1.822E+04 -6.192E+04 1.242E+05 S13 -1.869E+00 3.120E+00 -1.212E+01 4.368E+01 -1.046E+02 1.582E+02 -1.464E+02 S14 -5.425E-01 -9.438E-01 5.239E+00 -1.085E+01 1.310E+01 -9.864E+00 4.564E+00

[0092] Example 3

[0093] In this embodiment, Figure 8As shown, the superlens also includes a second superlens 120 and a plurality of focusing superlenses 220 in the second lens group 200, the first superlens 110 is arranged between the second superlens 120 and the plurality of focusing superlenses 220, the field of view angle increasing portion also includes a plurality of non-polarization-sensitive sub-wavelength primitives arranged on a surface of the first superlens close to the object side and at least one surface of the second superlens 120, the light incident angle on the object side of the second superlens 120 is greater than the light exit angle on the image side, and the plurality of focusing superlenses 220 are used for focusing imaging. Figure 8 The number of the middle focusing refractive lens 210 is one.

[0094] The specific parameters of the optical system provided in Example 3 are shown in Table 3-1, and the parameters of each lens in the optical system, such as the surface type, curvature, lens thickness, material and other parameters are shown in Table 3-2. Among them, OBJ is the object side, S1~S4 are the object side and image side of the second super lens 120 and the first super lens 110 respectively, the image side of the second super lens 120 includes a nanostructure layer, and the object side and image side of the first super lens 110 both include a nanostructure layer. STO is the aperture stop 400, S8-S9 are the object side and image side of the focusing super lens 220 respectively, S10-S11 are the object side and image side of the color filter, and S12 is the image side.

[0095] In this embodiment, the constraint f*tan(θ grating )=0.96, through the coordinated design of the first super lens 110 and the focal length of the imaging system, the center of the polarization state image is offset to a relatively optimal position, ensuring that the four polarization state images do not overlap and the occupied area is maximized, and controlling f1 / f2=66.7, constraining this ratio so that the edge field of view light beam passes through the first lens group 100 and hits the second lens group 200 to focus and image to the specified position of the image sensor 300, so that the imaging circles of the four polarization state images do not interfere with each other and do not overflow the sensor boundary. And control d=0.05, that is, all lenses of the optical system are assembled in the same lens barrel to ensure the miniaturization of the optical system. Limit FOV image =3.32*θ grating , so that the light beam diffracted by the first super lens 110 is focused to a reasonable position by the image sensor 300, while ensuring that the field of view angle can cover the maximum angle of the first super lens 110. Constraint |Δφ / R M |=400, by controlling the ratio between the maximum phase difference and the optical effective radius of the first superlens 110, the 2π phase period borne by the first superlens 110 within a unit length is made to conform to the matching effect of the micro-nano structure on its target phase, thereby giving full play to the optical performance of the first superlens 110.

[0096] Fig. 9A curve diagram showing the resolution of the optical system of this embodiment at various incident angles as a function of spatial frequency is shown, wherein the horizontal axis is the spatial frequency, in units of line pairs / mm; the vertical axis is the resolution value, in a range of 0-1.0, Fig. 9 In the above example, the maximum incident angle is divided into 10 equal parts to obtain multiple incident angles. The larger the incident angle, the lower the resolution. Fig. 9 The lower the curve is on the same horizontal axis, the larger the incident angle is.

[0097] Fig.10 A curve chart showing the relative illumination of the optical system of this embodiment as a function of the field of view height is shown. In the figure, the horizontal axis can be the field of view height or the normalized field of view height, that is, the maximum angle is 1, and the horizontal axis ranges from 0 to 1.0; the vertical axis is the relative illumination value, ranging from 0 to 100%. Fig.10 The far right side of the figure represents the relative illumination of the edge field of view. The relative illumination of this embodiment is 98%, which can meet the requirements.

[0098] Table 3-1

[0099] Parameter Type Numeric Working band 940nm F-number 3.1 Field of view 78° System length 5.25mm

[0100] Table 3-2

[0101] Face number Surface type Radius of curvature thickness Material OBJ Spherical endless endless S1 Spherical endless 0.5 1.465,65.77 S2 Metasurface endless 0.35 S3 Metasurface endless 0.5 1.465,65.77 S4 Metasurface endless 0.05 STO Spherical endless 1.299 S8 Metasurface endless 0.625 1.465,65.77 S9 Spherical endless 0.1 S10 Spherical endless 0.21 1.523,54.52 S11 Spherical endless 1.616 S12 Spherical endless

[0102] Compared with the commonly used technology, this embodiment has the following beneficial effects:

[0103] This optical system solves the problem that the metasurface lens is sensitive to large incident angles and the imaging is not ideal. The field of view angle is increased by providing a field of view angle increasing unit, so that the incident angle to the polarization conversion unit is reduced, the efficiency of polarization conversion is improved, and thus the extinction ratio is improved. By limiting the hardware parameters of the optical system, the final imaging on the image sensor 300 is maximized while reducing the overlap and intersection of polarization images, that is, the image can be presented more clearly. The light-collecting capability of a large field of view angle and imaging with a sufficient number and size of pixels make the effective signal energy higher. This optical system has good optical performance and is suitable for various high-performance polarization imaging applications.

[0104] It should be understood that although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0105] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the utility model. They are not intended to limit the protection scope of the utility model. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the utility model should be included in the protection scope of the utility model.

Claims

1. An optical system, characterized in that: The invention comprises a first lens group, a second lens group and an image sensor which are sequentially arranged from the object side to the image side, wherein the first lens group comprises a field angle increasing portion and a polarization conversion portion which are sequentially arranged from the object side to the image side, wherein the polarization conversion portion comprises a plurality of polarization-sensitive sub-wavelength primitives, the field angle increasing portion increases the field angle, and the polarization conversion portion emits light at different angles according to the polarization characteristics, so as to form polarization state images in different specific areas of the image sensor respectively; The second lens group is used to focus the polarization state image in each of the specific areas; The optical system satisfies: f*ck grating >0.5, IMGH>3.0, FOV image >3*θ grating , Wherein, f is the effective focal length of the optical system, θ grating is the diffraction angle of the central field of view light in the optical system after passing through the first lens group, IMGH is the target surface size of the image sensor, FOV image is the angular field of view of the image sensor.

2. The optical system according to claim 1, characterized in that The number of the specific areas is 4, the 4 specific areas are distributed in two rows and two columns, and the 4 specific areas do not overlap with each other.

3. The optical system according to claim 2, characterized in that At least two of the specific areas are substantially tangent to each other, and each of the specific areas is substantially tangent to an imaging edge of the image sensor.

4. The optical system according to claim 1, characterized in that The combined focal length f1 of the first lens group and the combined focal length f2 of the second lens group satisfy: 50 <f1 / f2<90。 5. The optical system according to claim 1, characterized in that The optical system further includes an aperture stop disposed between the first lens group and the second lens group, and a distance d between the first lens group and the aperture stop satisfies: 0.05<d<0.8。 6. The optical system according to claim 1, characterized in that The optical system includes a plurality of metalenses, and the plurality of metalenses all satisfy: 20<|Δφ / R M |<430, Wherein, Δφ is the maximum phase difference provided by the metalens at a single wavelength, R M is the optical effective radius of the metalens; The superlens includes a first superlens, and the polarization conversion unit includes the plurality of polarization-sensitive sub-wavelength elements on one surface of the first superlens.

7. The optical system according to claim 6, characterized in that The superlens also includes a second superlens, the second lens group includes a plurality of focusing refracting lenses, the first superlens is arranged between the second superlens and the plurality of focusing refracting lenses, the field of view angle increasing portion also includes a plurality of non-polarization-sensitive sub-wavelength elements arranged on one surface of the first superlens close to the object side and at least one surface of the second superlens, and the plurality of focusing refracting lenses are used for focusing imaging.

8. The optical system according to claim 6, characterized in that The first lens group also includes a plurality of refractive lenses, the second lens group includes a plurality of focusing refractive lenses, the first superlens is arranged between the plurality of refractive lenses and the plurality of focusing refractive lenses, the field of view angle increasing portion also includes the plurality of refractive lenses, and the plurality of focusing refractive lenses are used for focusing imaging.

9. The optical system according to claim 6, characterized in that The superlens also includes a second superlens and several focusing superlenses in the second lens group, the first superlens is arranged between the second superlens and the several focusing superlenses, the field of view angle increasing unit also includes a plurality of non-polarization-sensitive sub-wavelength elements arranged on one surface of the first superlens close to the object side and at least one surface of the second superlens, and the several focusing superlenses are used for focusing imaging.

10. An imaging device, characterized in that: The imaging device comprises the optical system as claimed in any one of claims 1-9.

Images