A design method of a refractive-diffractive hybrid lens and a lens

Abstract

The present invention provides a design method of a refractive-diffractive hybrid lens and a lens, according to the main wavelength λ a , sub-wavelength λ b , lens material, determine the refractive index n of the wavelength in the lens a and n b ; Then calculate the optical path modulation of the lens δOPL; According to n a and n b Calculate and distribute the refractive optical path modulation δOPL of the lens r and diffraction path length modulation δOPL d ; According to δOPL r and the center thickness d of the lens, calculate the approximate surface shape of the optical surface; according to the actual optical path of the parallel light to the back focus, fine-tune the approximate surface shape until the actual optical path of each light ray of the incident parallel light is equal; according to δOPL d , calculate the approximate structure of the diffraction microstructure; according to the actual optical path of the incident parallel light to the back focus, fine-tune the diffraction microstructure until the difference in the actual optical path of each light of the incident parallel light is the main wavelength λ a The structure and parameters of the lens to be designed are determined, and the design of the refractive-diffractive hybrid lens is completed. The lens obtained by this method has higher precision, better achromatic effect, and shorter design time.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile lighting, and in particular to a design method of a refractive-diffractive hybrid lens and a lens. Background Art

[0002] The lens is the core component of the high and low beam module. It has the function of deflecting light and projecting the low beam baffle image to the front of the car. The cost, weight and optical effect of the lens are the key concerns of the high and low beam module. Glass lenses have low dispersion and excellent heat resistance, but they are difficult to process, costly and heavy; plastic lenses have the advantages of light weight, low cost and easy processing, but commonly used plastic materials have their own defects. For example, polymethyl methacrylate (PMMA) has low dispersion, but its heat resistance cannot meet the requirements of automotive headlights; polycarbonate (PC) has excellent heat resistance, but large dispersion, which will cause the low beam cutoff line to turn blue or yellow.

[0003] The refractive-diffractive hybrid lens is an ideal solution. This technology sets a diffractive microstructure on the surface of a traditional lens, decomposes the refractive power of the lens into refractive power and diffractive power, and uses the negative dispersion characteristics of the diffractive lens to offset the lens chromatic aberration introduced by the material. The single-lens high and low beam module adopts a refractive-diffractive hybrid lens to ensure a sharp cutoff line and weaken the color of the cutoff line; the pixel headlight module adopts a refractive-diffractive hybrid lens, which can omit the achromatic lens, thereby reducing the number of lenses, module weight and cost. The processing of the glass-based refractive-diffractive hybrid lens is cumbersome and has no advantages in terms of process and cost; thanks to the development of single-point diamond turning technology and injection molding process precision, as long as a diffractive microstructure is added to the mold core of the plastic lens, the refractive-diffractive hybrid lens of the plastic substrate can be mass-produced.

[0004] In terms of design methods, although Zemax's BINARY2 surface module can be used for the design and simulation of refractive diffractive lenses, its optimization process for high-order aberrations is extremely cumbersome, and it only performs phase modulation design on the diffraction part, and cannot generate 3D data of the diffraction microstructure, which is not conducive to subsequent processing. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in order to overcome the deficiencies in the prior art, the present invention provides a refractive-diffractive hybrid lens design method and lens, which can overcome the chromatic aberration introduced by the material, converge the incident parallel light of different wavelengths to the rear focus, and ensure that the near-beam cutoff line is sharp and has no dispersion. The design method of the present invention can be based on a given lens material, a given lens size, and the main and secondary wavelengths of the light λ a and λ b , lens center thickness d and lens focal length f, calculate the lens surface shape, and the output lens surface shape can be directly used for processing.

[0006] The technical solution adopted by the present invention to solve its technical problems is: a method for designing a refractive-diffractive hybrid lens, wherein parallel light is incident from one side of the lens and converges on the other side of the lens after being refracted and diffracted by the lens, the side of the lens on which the parallel light is incident is called the first optical surface, and the other side is called the second optical surface, the point where the light converges is called the back focus, and the surface shape of the first optical surface is recorded as z1, and the surface shape of the second optical surface is recorded as z2; the first optical surface and the second optical surface intersect with the optical axis respectively, and the distance between the two intersection points is the central thickness d of the lens; the distance between the back focus and the second optical surface is f, and one of the first optical surface and the second optical surface has a diffraction microstructure.

[0007] In order to simplify the design and reduce the processing and testing costs, one of the lens surface types z1 and z2 is a preset value. For ease of description, it is assumed that z2 is a preset value and the diffractive microstructure is only located on the first optical surface.

[0008] The parallel light parallel to the optical axis and incident on the first optical surface is composed of two or more monochromatic lights or polychromatic lights, and converges to the rear focus after passing through the first optical surface and the second optical surface in sequence.

[0009] The design methodology includes the following steps:

[0010] Step 1: Based on the selected dominant wavelength λ a and the secondary wavelength λ b And the material of the lens determines the main wavelength λ a The refractive index n in the lens a and the secondary wavelength λ b The refractive index n in the lens b , assuming λ a >λ b , then for commonly used lens materials (K9 glass, PMMA, PC, etc.), n a <n b .

[0011] Step 2: Calculate the optical path modulation δOPL of the lens based on the distance f between the rear focus and the second optical surface.

[0012] The refractive-diffractive hybrid lens of the present invention converges parallel light to the rear focus of the lens. According to Fermat's principle, for any light within the lens aperture, if the incident light is parallel to the optical axis, the optical path from the light to the rear focus is equal and constant, and the optical path of the light is expressed as:

[0013] OPL(r)=C (1)

[0014] Where C is a constant; r is the distance from any point on the lens surface to the optical axis, and r∈[0,R], R is the clear radius of the refractive-diffractive hybrid lens, and formula (1) is used to describe plane waves.

[0015] The optical path from the lens surface to the back focus is:

[0016]

[0017] Since the radius of light passing through the center of the lens is r = 0, the optical path of the light passing through the center of the lens is as follows according to formula (2):

[0018] L(0)=f(3)

[0019] Then, taking this light as the reference, the optical path modulation δOPL of the refractive-diffractive hybrid lens is:

[0020]

[0021] Where L(r) represents the distance from the point r on the optical axis to the rear focus of the lens; n 空气 represents the refractive index of air, n 空气 =1.

[0022] Step 3: According to the main wavelength λ a The refractive index n a and the secondary wavelength λ b The refractive index n b , calculate and distribute the refractive optical path modulation of the lens δOPL r and diffraction path length modulation δOPL d .

[0023] Based on the difference in refractive index between the refractive material and air, the lens uses the change in thickness of the lens to create an optical path difference and deflect the light. Therefore, for a thin lens, the relationship between its thickness gradient, refractive index and optical path modulation is:

[0024] δOPL r =δt×(n-1) (5)

[0025] Among them, δOPL r is the refractive optical path modulation, δt is the thickness difference of the lens in the optical axis (z-axis) direction, and n is the refractive index of the lens.

[0026] For light of different wavelengths a and b, the amount of modulation introduced by the lens is related to the refractive index of the material for the two wavelengths:

[0027]

[0028] Among them, δOPL ra is the refraction path length modulation of light a, δOPL rb is the refraction path modulation of light b, n a is the refractive index of light ray a in the lens, n b is the refractive index of light ray b in the lens.

[0029] Take the wavelength of light a as the main wavelength λ a , then the refraction path modulation of light b is related to the main wavelength λ a Deviation ΔOPL r for:

[0030]

[0031] The diffraction device uses the diffraction microstructure to produce phase modulation, thereby realizing optical path modulation. Therefore, the diffraction optical path modulation amount δOPL d The relationship with the phase modulation amount φ is:

[0032] δOPL d =φ×λ (8)

[0033] Take the wavelength of light a as the main wavelength λ a , the wavelength of light b is the secondary wavelength λ b , then the diffraction path modulation of light b is related to the main wavelength λ a Deviation ΔOPL d for:

[0034]

[0035] Among them, δOPL da is the diffraction path length modulation of light a, δOPL db is the diffraction path modulation of light ray b, λ a is the wavelength of light a, λ b is the wavelength of light b.

[0036] Since the total optical path modulation of the lens is the sum of the refraction optical path modulation and the diffraction optical path modulation, the optical path modulation for light a is:

[0037]

[0038] Due to the refraction optical path modulation δOPL ra and diffraction path length modulation δOPL da is directly proportional, that is:

[0039]

[0040] Due to λ a , b and n a 、n b are all given values ​​in advance. Therefore, according to formula (10) and formula (11), the refractive optical path modulation amount δOPL of the lens on light a can be solved. ra and diffraction path length modulation δOPL da .

[0041] When the refraction path modulation δOPL of light a is determined ra and diffraction path length modulation δOPL da Then, according to formula (6) and formula (9), the refractive optical path modulation amount δOPL of the optical path modulation amount of light b can be determined: rb and diffraction path length modulation δOPL db , thus calculating the total refractive optical path modulation of the lens δOPL r and the total diffraction path length modulation δOPL d :

[0042] δOPL r =δOPL ra +δOPL rb (12)

[0043] δOPL d =δOPL da +δOPL db (13)

[0044] According to the above formula, the refractive optical path modulation of the lens is realized as follows: r and diffraction path length modulation δOPL d calculation and allocation.

[0045] Step 4: Based on the refraction optical path modulation δOPL r and the lens center thickness d, calculate the approximate surface shapes of the first optical surface and the second optical surface, which are surface shape z1 and surface shape z2 respectively.

[0046] In order to simplify the design and reduce the detection workload, usually one of the first optical surface and the second optical surface has a surface parameter that is a predetermined spherical surface. In the present invention, the second optical surface is a predetermined spherical surface.

[0047] The wall thickness t of the lens and the refractive optical path modulation δOPL ra Related, that is The first lens surface shape z1 and the second lens surface shape z2 are related to the wall thickness t, that is:

[0048] z1≈z2-t (14)

[0049] Substituting t into formula (14), we get:

[0050]

[0051] According to formula (15), δOPL ra The approximate expression of the first optical surface is directly obtained.

[0052] If both surfaces are free-form surfaces, other limiting conditions need to be given in advance to determine z1 and z2.

[0053] Step 5: According to the actual optical path from the incident parallel light to the rear focus, the approximate surface shapes z1 and z2 of the lens calculated in step 4 are precisely adjusted until the actual optical paths of the incident parallel light rays are equal. At this time, the precise surface shapes of the first optical surface and the adjusted first optical surface are obtained, which are surface shape z′1 and surface shape z′2, respectively.

[0054] Step 5 mainly includes two processes: (1) calculating the actual optical path; and (2) accurately adjusting the surface shape. These two processes are described in detail below.

[0055] (1) Calculate the actual optical path:

[0056] After obtaining the approximate expression of the first optical surface, the calculation method of the actual optical path is as follows: establish a lens coordinate system, with the optical axis direction as the z direction, the direction perpendicular to the optical axis as the r direction, and the intersection of the first optical surface and the optical axis as the origin O. The parallel light intersects the first optical surface at the first intersection point P1, is refracted and diffracted by the first optical surface, is deflected, intersects the second optical surface at the second intersection point P2, and is refracted by the second optical surface to reach the rear focus P f .

[0057] Calculate the coordinates of the first intersection point P1; according to the first intersection point P1, the back focus P f , approximate surface shape z2 and optical medium refractive index n, use Fermat's principle to obtain the coordinates of the second intersection point P2, so that the first intersection point P1, the second intersection point P2 and the rear focus P of the lens f The optical path between them is the shortest, and the coordinate of the rear focus is P f (f+d,0), then the first intersection point P1 to the back focus P f The optical path length of the light is expressed by the equation:

[0058]

[0059] Among them, the size of r depends on the distance between P1 or P2 and the optical axis. At this time, from the incident surface O of the parallel light to the back focus P f The total optical path of the light is:

[0060]

[0061] The O plane refers to the plane passing through the origin O and perpendicular to the optical axis.

[0062] Transform the distance between parallel light and the optical axis and calculate all optical paths.

[0063] In formula (17), OPL(r) must be a constant to ensure that the incident parallel light converges at the rear focus of the lens. However, δOPLra The formula of z1 approximates the lens as a thin lens and ignores the influence of the direction of the light inside the lens on the light path. Therefore, the optical path from the light incident through the O plane and parallel to the optical axis to the rear focus is not a constant, and z1 needs to be fine-tuned.

[0064] (2) Precisely adjust the surface shape:

[0065] Taking the optical path of the light propagating along the optical axis as the reference, that is, r = 0, the optical path fine-tuning amount is:

[0066] ΔδOPL ra =OPL(r)-OPL(0) (18)

[0067] Let Δz1 be the fine adjustment amount of the first optical surface, ΔδOPL ra is the optical path length δOPL ra The fine-tuning amount of the optical path is written as follows:

[0068] ΔδOPL ra =Δz1(1-n a ) (19)

[0069] Wherein, Δz1 is the fine adjustment amount of the approximate surface shape z1 of the first optical surface, and Δz1=z′1-z1, z′1 is the precise surface shape of the first optical surface after fine adjustment; δOPL ra is the optical path length δOPL ra The fine-tuning amount, and ΔδOPL ra =δOPL′ ra -δOPL ra , δOPL′ ra is the optical path after fine-tuning.

[0070] The fine adjustment of the lens approximate surface shape z1 is determined by the actual optical path deviation ΔδOPL ra , refractive index n a The direction angle cosθ of the light after passing through the first optical surface is calculated, and the fine adjustment amount of the approximate surface shape z1 of the first optical surface is expressed as:

[0071]

[0072] Substituting formula (20) into the formula Δz1=z′1-z1, the precise surface shape z′1 of the adjusted first optical surface is expressed as:

[0073]

[0074] The adjusted surface shape is obtained according to formula (21).

[0075] In step 5, the face shape is precisely adjusted at least once. When the face shape is fine-tuned twice or more times, the face shape after the last adjustment is used as the approximate face shape, and OPL(r) is recalculated according to step 5 using the fine-tuned face shape z1′. The face shape z1 is fine-tuned twice or more times to ultimately ensure that OPL(r) is a constant.

[0076] Since the design effect is achieved, it is sufficient to set the diffraction microstructure at one of z1 and z2 and make fine adjustments. Fine-tuning both surfaces at the same time will not improve the optical effect of the lens, but will only increase the design complexity and processing / testing costs.

[0077] Step 6: According to the diffraction path modulation δOPL d , approximate calculation of the diffraction microstructure.

[0078] The diffraction microstructure of the refractive-diffractive hybrid lens is manifested as tiny steps on the refractive-diffractive surface, that is, the diffraction microstructure is a tiny step. According to the principle of binary optics, the step height is changed to change the optical path difference to an integer multiple of the wavelength. The modulation performance of the diffraction microstructure on the light remains unchanged. Therefore, the modulation amount of the diffraction microstructure on the optical path depends on the decimal part of the diffraction modulation amount, which is expressed by the formula:

[0079] δOPL stepa =mod(δOPL da ,mλ a ) (twenty two)

[0080] Among them, mod is the remainder function, m is a positive integer, and generally m=1.

[0081] The step height refers to formula (22). If the diffractive microstructure is located on the first optical surface, then:

[0082]

[0083] If the diffractive microstructure is located on the second optical surface, then:

[0084]

[0085] Among them, z step Represents the approximate structure of the diffraction microstructure.

[0086] ΔδOPL ra is a continuous value, while ΔδOPL stepa It is calculated by formula (22), where the remainder function in formula (22) is stepa Steps were introduced.

[0087] Step 7: According to the actual optical path from the parallel light to the back focus, fine-tune the step height of the diffraction microstructure until the difference in the actual optical path of each light is the main wavelength λ aAn integer multiple of .

[0088] If the diffraction microstructure is located on the first optical surface, for the convenience of expression, after adding the diffraction microstructure, the optical path calculation formula (17) is transformed as follows:

[0089]

[0090] Among them, the int function is an integer function. When the diffraction provides positive refractive power, the function is rounded up, otherwise the function is rounded down.

[0091] If the diffractive microstructure is located on the second optical surface, for the convenience of expression, after adding the diffractive microstructure, the optical path calculation formula (17) is transformed as follows:

[0092]

[0093] At this time, the coordinates of P2 in the formula are (r,z2+z step ).

[0094] In formula (26), the second optical surface can be a spherical surface or other surface shapes.

[0095] Since the compensation term int(δOPL is added to the above two deformation formulas d / λ a )*λ a , so the goal of fine tuning is still to adjust OPL(r) to a constant. The fine tuning formula refers to formula (18) and formula (21), and the diffraction path fine adjustment amount is:

[0096] ΔδOPL da =OPL(r)-OPL(0) (27)

[0097] If the diffractive microstructure is located on the first optical surface, the diffractive microstructure after fine-tuning is:

[0098]

[0099] If the diffractive microstructure is located on the second optical surface, the diffractive microstructure after fine-tuning is:

[0100]

[0101] Using the fine-tuned z step Recalculating OPL(r) can give z step Perform secondary or multiple fine-tuning to ensure that OPL(r) is constant, that is, the optical path of the fine-tuned light meets the following conditions: mod(OPL-C,λ a )=m, C is a constant, and m is a non-negative integer.

[0102] Step 8: Based on the precise surface shapes z′1 and z′2 of the first optical surface and the second optical surface obtained in step 5, and the precise structure z′ of the diffraction microstructure obtained in step 7, step ′, determine the structure and parameters of the lens to be designed, and complete the design of the refractive-diffractive hybrid lens.

[0103] A refractive-diffractive hybrid lens, the surface parameters of which are generated by the above-mentioned design method.

[0104] The present invention has the following beneficial effects: it is not limited to the parameter restrictions of the existing design software on the refractive diffraction hybrid surface, and a rotationally symmetric or non-rotationally symmetric optical surface with higher degrees of freedom can be obtained, and point cloud data that can be used for mechanical processing can be directly output. The lens obtained by this method has higher precision, more outstanding achromatic effect, and shorter design time. For different wavelengths, materials, and appearance requirements, the initial parameters in the program can be modified, so the program can be reused. In this article, a PC material, single spherical lens is used as an example for explanation. BRIEF DESCRIPTION OF THE DRAWINGS

[0105] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0106] Figure 1 It is a schematic diagram of focusing of the refractive-diffractive hybrid lens of the present invention.

[0107] Figure 2 It is a schematic diagram of the optical path of an ideal lens.

[0108] Figure 3 It is a curve diagram of the distribution optical path modulation amount.

[0109] Figure 4 This is a schematic diagram of the optical path calculation of an actual lens.

[0110] Figure 5 It is the r-OPL curve during the process of fine-tuning the first optical surface.

[0111] Figure 6 It is to fine-tune the r-z1 and r-z2 curves of the first optical surface.

[0112] Figure 7 It is a schematic diagram of the overall optical surface with a diffraction structure.

[0113] Figure 8 This is a partial enlarged image of the optical surface with a diffraction structure.

[0114] Fig. 9 This is a comparison chart of the cutoff lines of refractive lenses / refractive-diffractive hybrid lenses.

[0115] In the figure: 1. first optical surface, 2. second optical surface, 3. optical axis, 4. back focus of lens, 5. diffraction microstructure, 6. parallel light. DETAILED DESCRIPTION

[0116] The present invention will now be described in detail with reference to the accompanying drawings. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner, and therefore only shows the components related to the present invention.

[0117] like Figure 1 and Figure 2 As shown, the parallel light 6 is parallel to the optical axis 3, and the light passes through the refractive-diffractive hybrid lens and converges to the lens back focus 4. For the convenience of description, in this example, the refractive-diffractive hybrid lens is set as a rotationally symmetric lens, the optical axis direction is the z direction, the direction perpendicular to the optical axis is the r direction, the intersection of the first optical surface 1 and the optical axis 3 is the origin O, and the rotationally symmetric lens surface with the optical axis as the symmetry axis can be represented by r, z1, z2 and z step Description: If the diffractive microstructure is located on the first optical surface 1, then the first optical surface 1 (including the diffractive microstructure) is z1+z step , if the diffractive microstructure is located on the second optical surface 2, then the second optical surface 2 (including the diffractive microstructure) is z2+z step , r∈[0,R]. The center thickness of the lens is d=z2(0)-z1(0); assuming the back focal length of the lens is f, the coordinates of the back focal point of the lens are P f (f+d,0).

[0118] The initial design conditions are as follows: the center thickness of the lens is d = 15 mm, the back focal length is f = 34 mm, the lens radius is R = 27 mm, and the lens material is polycarbonate (PC). The diffraction microstructure is set on the first optical surface 1, and the second optical surface 2 is a spherical surface with a curvature radius of radius2 = -100 mm.

[0119] Step 1: Design the dominant wavelength λ a =580nm, design sub-wavelength λ b =480nm. According to the optical properties of PC materials at room temperature, the lens has a a The refractive index n a is 1.5862, for the secondary wavelength λ b The refractive index n b It is 1.6006.

[0120] Step 2: Based on the initial conditions, calculate the optical path modulation of the lens: parallel light 6 is incident perpendicular to the lens, and the optical path of each light ray is calculated starting from the plane passing through the origin O and perpendicular to the optical axis. Figure 2 As shown, the lens is regarded as an ideal lens without thickness. The parallel light 6 is modulated by the lens and converges to the rear focus of the lens. According to Fermat's principle, the optical path of each parallel light to the rear focus is equal:

[0121] OPL(r)=OPL(0)=34mm

[0122] Then from formula (4):

[0123]

[0124] Step 3: Calculate the refraction path modulation and diffraction path modulation according to formula (10) and formula (11).

[0125] set up Then formula (11) is written as:

[0126] A λ ×δOPL da +A n ×δOPL ra =0

[0127] Formula (10) is written as:

[0128]

[0129] Solve the two equations together to get δOPL da and δOPL ra ,like Figure 3 shown.

[0130] Step 4: Based on the refraction optical path modulation δOPL r , lens center thickness d and given second optical surface parameters, the surface shape z1 of the first optical surface is approximately calculated.

[0131] According to the example setting, the radius of curvature of the second optical surface is radius2 = -100mm, the aspheric coefficient k2 = 0, and the surface shape expression is as follows:

[0132]

[0133] δOPL calculated from step 3 ra , the surface shape of the first optical surface can be calculated:

[0134]

[0135] Here, the angle change of the light after passing through the first optical surface is ignored, and it is assumed that the light inside the first optical surface is still parallel to the optical axis, so the obtained z1 is an approximate value.

[0136] Step 5: Based on the actual optical path from the parallel light 6 to the rear focus 4, fine-tune the lens surface until the actual optical path of each light is equal.

[0137] like Figure 4As shown, the intersection point of the light with the first optical surface 1 is P1, and the intersection point with the second optical surface 2 is P2. The optical path consists of three segments: the optical path from the O plane to the first plane L1=z1, the optical path from the first intersection point to the second intersection point The optical path between the second intersection point and the rear focus of the lens Among them, the first intersection point depends on the distance r between the incident light and the optical axis, written as (z1(r),r), and P2 depends on the Fermat principle: P2 is located on the second optical surface {(z2,r)} and the optical path Take the minimum. In this example, the diffraction microstructure is located on the first optical surface, and the diffraction modulation amount has nothing to do with the P2 coordinate, so P2 needs to satisfy Take the minimum.

[0138] According to formula (17) and formula (18), z1 can be finally determined through multiple iterations. In this embodiment, the number of iterations is 5. During the iteration process, the OPL of each parallel incident light beam changes as follows: Figure 5 As shown in the figure, the changes of the first optical surface during the iteration are as follows: Figure 6 As shown, the first optical surface and the second optical surface determined after 5 iterations are as follows Figure 7 shown.

[0139] Step 6: According to the diffraction path modulation δOPL da , approximate calculation of the diffraction microstructure 5.

[0140] As calculated in step 3, the diffraction path length modulation δOPL da It is a negative value, with a maximum value of 0 at r = 0 and a minimum value of -0.9947 mm at r = 27. According to the principle of binary optics, assuming m = 1, we can obtain δOPL step , and use the following formula to calculate the diffraction step height of the first optical surface:

[0141]

[0142] The maximum height of the step is |λ a / (1-n a )|=0.989μm.

[0143] Step 7: According to the actual optical path from the parallel light to the back focus, fine-tune the step height of the diffraction microstructure until the difference in the actual optical path of each light is the main wavelength λ a An integer multiple of .

[0144] Since the optical path modulation δOPL da To avoid a sudden change in the diffraction microstructure near r = 0, the rounding calculation of formula (25) is rounded up, and the diffraction microstructure is calculated and fine-tuned to ensure that OPL (r) is a constant. The calculation process is similar to step 5. The optical surface after optimization is as follows Figure 7 and Figure 8 As shown, Figure 7 It is an overview of the first optical surface surf1, the second optical surface surf2, and the focal plane image. Figure 8 It is a partial enlarged view of the first optical surface surf1 (with diffractive microstructure).

[0145] In order to verify the accuracy of the design in this paper, the calculated optical surface and diffraction path modulation are fitted into the parameters of the BINARY2 surface and input into the ZEMAX software for simulation. Fig. 9 In contrast, the use of the refractive-diffractive hybrid lens in this article can significantly optimize the blurring and bluing phenomenon of the low beam cutoff line.

[0146] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the scope of the present invention through the above description. The technical scope of this invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for designing a refractive-diffractive hybrid lens, characterized in that: Parallel light is incident from one side of the lens, and converges on the other side of the lens after being refracted and diffracted by the lens. The side of the lens where the parallel light is incident is called the first optical surface, and the other side is called the second optical surface. The point where the light converges is called the back focus, and the surface shape of the first optical surface is recorded as z1, and the surface shape of the second optical surface is recorded as z2; the first optical surface and the second optical surface intersect with the optical axis respectively, and the distance between the two intersection points is the center thickness d of the lens; The distance between the back focus and the second optical surface is f, and one of the first optical surface and the second optical surface has a diffractive microstructure; The design methodology includes the following steps: Step 1: Based on the selected dominant wavelength λ a and the secondary wavelength λ b And the material of the lens determines the main wavelength λ a The refractive index n in the lens a and the secondary wavelength λ b The refractive index n in the lens b ; Step 2: Calculate the optical path modulation δOPL of the lens according to the distance f between the rear focus and the second optical surface; Step 3: According to the main wavelength λ a The refractive index n a and the secondary wavelength λ b The refractive index n b , calculate and distribute the refractive optical path modulation of the lens δOPL r and diffraction path length modulation δOPL d ; Step 4: Based on the refraction optical path modulation δOPL r and the lens center thickness d, calculate the approximate surface shapes of the first optical surface and the second optical surface, which are surface shape z1 and surface shape z2 respectively; Step 5: According to the actual optical path from the incident parallel light to the back focus, the approximate surface shapes z1 and z2 of the lens calculated in step 4 are precisely adjusted until the actual optical paths of the incident parallel light rays are equal. At this time, the precise surface shapes of the first optical surface and the second optical surface after adjustment are obtained, which are surface shapes z′1 and z′2 respectively; Step 6: According to the diffraction path modulation δOPL d , calculate the approximate structure of the diffraction microstructure; Step 7: According to the actual optical path of the incident parallel light to the back focus, the approximate structure of the diffraction microstructure in step 6 is precisely adjusted until the difference in the actual optical path of each light ray of the incident parallel light is the main wavelength λ a Integer multiples of , the precise structure z of the diffraction microstructure is obtained. step ′; Step 8: Based on the precise surface shapes z′1 and z′2 of the first optical surface and the second optical surface obtained in step 5, and the precise structure z′ of the diffraction microstructure obtained in step 7, step ′, determine the structure and parameters of the lens to be designed, and complete the design of the refractive-diffractive hybrid lens.

2. The method for designing a refractive-diffractive hybrid lens according to claim 1, wherein: Calculating the optical path modulation amount δOPL of the lens in step 2 specifically includes the following steps: Parallel light can converge to the rear focus of the lens through a refractive-diffractive hybrid lens. Therefore, according to Fermat's principle, for any light within the lens aperture, when the incident light is parallel to the optical axis, the optical path from the light to the rear focus is equal and constant. The incident light path is expressed as: OPL(r)=C (1) Where C is a constant; r is the distance from any point on the lens surface to the optical axis, and r∈[0,R], R is the light transmission radius of the refractive-diffractive hybrid lens; The optical path from the lens surface to the back focus is: Since the radius of light passing through the center of the lens is r = 0, the optical path of the light passing through the center of the lens is as follows according to formula (2): L(0)=f(3) Then, taking this light as the reference, the optical path modulation δOPL of the refractive-diffractive hybrid lens is: Where L(r) represents the distance from the point r on the optical axis to the rear focus of the lens; n 空气 Represents the refractive index of air.

3. The method for designing a refractive-diffractive hybrid lens according to claim 2, wherein: In step 3, the refractive optical path modulation of the lens is calculated and allocated as δOPL r and diffraction path length modulation δOPL d The specific steps include: Based on the difference in refractive index between the refractive material and air, the lens uses the change in thickness of the lens to create an optical path difference and deflect the light. Therefore, for a thin lens, the relationship between its thickness gradient, refractive index and refractive optical path modulation is: δOPLr=δt×(n-1) (5) Among them, δOPL r is the refractive optical path modulation, δt is the thickness difference of the lens in the direction of the optical axis, and n is the refractive index of the lens; For light of different wavelengths a and b, the amount of modulation introduced by the lens is related to the refractive index of the material for the two wavelengths: Among them, δOPL ra is the refraction path length modulation of light a, δOPL rb is the refraction path modulation of light b, n a is the refractive index of light ray a in the lens, n b is the refractive index of light ray b in the lens; Take the wavelength of light a as the main wavelength λ a , then the refraction path modulation of light b is related to the main wavelength λ a Deviation ΔOPL r for: The diffractive lens uses the diffractive microstructure to generate phase modulation, thereby achieving optical path modulation. Therefore, the diffraction optical path modulation amount δOPL d The relationship with the phase modulation amount φ is: δOPLd=φ×λ (8) Take the wavelength of light a as the main wavelength λ a , the wavelength of light b is the secondary wavelength λ b , then the diffraction path modulation of light b is related to the main wavelength λ a Deviation ΔOPL d for: Among them, δOPL da is the diffraction path length modulation of light a, δOPL db is the diffraction path modulation of light ray b, λ a is the wavelength of light a, λ b is the wavelength of light b; Since the total optical path modulation of the lens is the sum of the refraction optical path modulation and the diffraction optical path modulation, the optical path modulation for light a is: Due to the refraction optical path modulation δOPL ra and diffraction path length modulation δOPL da is proportional to each other, that is: Due to λ a , b and n a 、n b are all given values ​​in advance. Therefore, according to formula (10) and formula (11), the refractive optical path modulation amount δOPL of the lens on light a can be solved. ra and diffraction path length modulation δOPL da ; When the refraction path modulation δOPL of light a is determined ra and diffraction path length modulation δOPL da Then, the refraction path modulation δOPL of light b is calculated according to formula (6) and formula (9): rb and diffraction path length modulation δOPL db , thus calculating the total refractive optical path modulation of the lens δOPL r and the total diffraction path length modulation δOPL d : δOPL r =δOPL ra +δOPL rb (12) δOPL d =δOPL da +δOPL db (13) According to formula (12) and formula (13), the refractive optical path modulation of the lens δOPL is realized r and diffraction path length modulation δOPL d calculation and allocation.

4. The method for designing a refractive-diffractive hybrid lens according to claim 3, wherein: Calculating the initial surface shapes of the surface shape z1 of the first optical surface and the surface shape z2 of the second optical surface in step 4 specifically includes the following steps: The wall thickness t of the lens and the refractive optical path modulation δOPL ra Related, that is The surface shape z1 of the first optical surface and the surface shape z2 of the second optical surface are related to the wall thickness t, that is: z1≈z2-t (14) Substituting t into formula (14), we get: The second optical surface is a predetermined spherical surface.

5. The method for designing a refractive-diffractive hybrid lens according to claim 4, wherein: The calculation of the actual optical path from the incident parallel light to the back focus in step 5 includes the following steps: A lens coordinate system is established, with the optical axis direction as the z direction, the direction perpendicular to the optical axis as the r direction, and the intersection of the first optical surface and the optical axis as the origin O. The parallel light intersects the first optical surface at the first intersection point P1, is refracted and diffracted by the first optical surface, is deflected, intersects the second optical surface at the second intersection point P2, and is refracted by the second optical surface to reach the rear focus P f ; According to the position of the parallel light and the approximate surface shape z1 in the lens coordinate system, the coordinates of the first intersection point P1 are calculated; according to the first intersection point P1, the back focus P f , approximate surface shape z2 and optical medium refractive index n, use Fermat's principle to obtain the coordinates of the second intersection point P2, so that the first intersection point P1, the second intersection point P2 and the rear focus P of the lens f The optical path between them is the shortest, and the coordinate of the rear focus is P f (f+d,0), then the first intersection point P1 to the back focus P f The optical path length of the light is expressed by the equation: Among them, the size of r depends on the distance between P1 or P2 and the optical axis. At this time, from the parallel light incident surface O plane to the back focus P f The total optical path of the light is: Among them, O plane refers to the plane passing through the origin O and perpendicular to the optical axis; Transform the distance between parallel light and the optical axis and calculate all optical paths.

6. The method for designing a refractive-diffractive hybrid lens according to claim 5, wherein: In step 5, the lens approximate surface shapes z1 and z2 are precisely adjusted. The fine-tuning amount needs to be calculated first. The calculation of the fine-tuning amount includes the following steps: Taking the optical path of the light propagating along the optical axis as the reference, that is, r = 0, the optical path fine-tuning amount is: ΔδOPL ra =OPL(r)-OPL(0) (18) Let Δz1 be the fine adjustment amount of the first optical surface, ΔδOPL ra is the optical path length δOPL ra The fine-tuning amount of the optical path is written as follows: ΔδOPL ra =Δz1(1-n a ) (19) Wherein, Δz1 is the fine adjustment amount of the approximate surface shape z1 of the first optical surface, and Δz1=z′1-z1, z′1 is the precise surface shape of the first optical surface after fine adjustment; ΔδOPL ra is the optical path length δOPL ra The fine-tuning amount, and ΔδOPL ra =δOPL′ ra -δOPL ra , δOPL ra is the optical path after fine-tuning; The fine adjustment of the lens approximate surface shape z1 is determined by the actual optical path deviation ΔδOPL ra , refractive index n a The direction angle cosθ of the light after passing through the first optical surface is calculated, and the fine adjustment amount of the approximate surface shape z1 of the first optical surface is expressed as: Substituting formula (20) into the formula Δz1=z′1-z1, the precise surface shape z′1 of the adjusted first optical surface is expressed as: The adjusted surface shape is obtained according to formula (21).

7. The method for designing a refractive-diffractive hybrid lens according to claim 6, wherein: In step 5, the face shape is precisely adjusted at least once. When the face shape is fine-tuned twice or more times, the face shape after the last adjustment is used as the approximate face shape, and OPL (r) is recalculated according to step 5 using the fine-tuned face shape. The face shape is fine-tuned twice or more times to ultimately ensure that OPL (r) is a constant.

8. The method for designing a refractive-diffractive hybrid lens according to claim 6, wherein: Calculating the approximate structure of the diffraction microstructure in step 6 includes the following steps: The diffraction microstructure of the refractive-diffractive hybrid lens is manifested as tiny steps on the refractive-diffractive surface. According to the principle of binary optics, the height of the steps is changed to change the optical path difference to an integer multiple of the wavelength. The modulation performance of the diffraction microstructure on the light remains unchanged. Therefore, the modulation amount of the diffraction microstructure on the optical path depends on the fractional part of the diffraction modulation amount, which can be expressed by the formula: δOPL stepa =mod(δOPL da ,mλ a ) (22) Wherein, mod is the remainder function, m is a positive integer, generally m=1; The step height refers to formula (22). If the diffractive microstructure is located on the first optical surface, then: If the diffractive microstructure is located on the second optical surface, then: Among them, z step Represents the approximate structure of the diffraction microstructure.

9. The method for designing a refractive-diffractive hybrid lens according to claim 8, wherein: The precise adjustment of the approximate structure of the diffraction microstructure in step 7 includes the following steps: When the diffractive microstructure is located on the first optical surface, after adding the diffractive microstructure, the optical path calculation formula (17) is transformed as follows: Among them, the int function is an integer function. When the diffraction provides positive refractive power, the function is rounded up, otherwise the function is rounded down; When the diffractive microstructure is located on the second optical surface, after adding the diffractive microstructure, the optical path calculation formula (17) is transformed as follows: At this time, the coordinates of P2 in the formula are (r,z2+z step ); Since the compensation term int(δOPL is added to the above two deformation formulas d / λ a )*λa, so the goal of fine tuning is still to adjust OPL(r) to a constant. The fine tuning formula refers to formula (18) and formula (21), and the diffraction path fine-tuning amount is: ΔδOPL da =OPL(r)-OPL(0) (27) When the diffraction microstructure is located on the first optical surface, the diffraction microstructure after fine-tuning is: When the diffraction microstructure is located on the second optical surface, the diffraction microstructure after fine-tuning is: Using the fine-tuned z step Recalculate OPL(r) for z step Perform secondary or multiple fine-tuning to ensure that OPL(r) is constant, that is, the optical path of the fine-tuned light meets the following conditions: mod(OPL-C,λ a )=m, C is a constant, and m is a non-negative integer.

10. A refractive-diffractive hybrid lens, characterized in that: The surface parameters of the lens are generated by the design method described in any one of claims 1-9.

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