CN114624877A - A Design Method of Large Field of View Diffractive Lenses Working in Infrared Bands - Google Patents

Abstract

The invention discloses a design method of a large-field-of-view diffraction lens working in an infrared band, which is different from the prior method that approximate microstructure height is obtained by a phase inversion or optimization method, but the microstructure is directly calculated, and a self-defined surface type which can be loaded by optical design software is provided, and the self-defined surface type can obtain a sudden change structure which is not contained in the prior optical design software and is similar to a Fresnel lens. The obtained microstructure can be further processed by using a ray tracing method, for example, defocusing is calculated, and data such as PSF (particle swarm optimization) can be further subjected to image analysis, processing and other operations. The invention can directly calculate and simulate the height of the microstructure through the wavelength and the material refractive index required in the optical design, and is suitable for both visible light and infrared bands.

Description

A Design Method of Large Field of View Diffractive Lenses Working in Infrared Bands

technical field

The invention relates to the technical field of optical lenses, in particular to a design method of a diffractive lens with a large field of view working in an infrared band.

Background technique

这里λ为光学系统的工作波长，D为光学系统的口径。由该公式可知，想要分辨率增加，这里的分辨率θ需要减小，这就需要光学系统的口径D不断增大，而口径的增大带来了加工所需精度高、光学系统较复杂以及光学系统重量大等问题。这导致光学系统的轻量化成像受到了限制，特别是对于便携式设备，比如手机相机，以及需要运载火箭进行托运的空间望远镜等应用提出了巨大的挑战。此外，高精度的光学系统带来的是对于透镜的高精度加工技术以及非常严格的公差分配的需要，非常不利于光学系统的量产。With the development of modern optical technology, people have higher and higher requirements for the resolution of optical systems, and according to the resolution formula

Here λ is the working wavelength of the optical system, and D is the aperture of the optical system. It can be seen from this formula that if the resolution is to be increased, the resolution θ here needs to be reduced, which requires the aperture D of the optical system to continuously increase, and the increase of the aperture brings about high processing precision and complex optical system. And the problem of the heavy weight of the optical system. This results in the limitation of lightweight imaging of optical systems, especially for applications such as portable devices, such as mobile phone cameras, and space telescopes that require a launch vehicle to be checked-in. In addition, the high-precision optical system brings the need for high-precision processing technology of the lens and very strict tolerance allocation, which is very unfavorable for the mass production of the optical system.

With the development of semiconductor micro-nano processing and optics, researchers began to use diffractive optical systems as a solution to replace traditional catadioptric/reflective optical systems. The diffractive lens has a strong negative dispersion, so in order to eliminate the dispersion of the diffractive lens, a series of achromatic optical structures, such as refractive/diffractive optical systems, double/multi-layer diffractive elements and Schupmann achromatic optical structures, are designed. However, most of these structures strictly limit the field of view to a small range, and still require the rear optical system for aberration correction. For example, the high precision alignment required for dual/multi-layer diffractive elements also keeps this structure still in the simulation process. These structures limit the application of diffractive lenses in large-field optical systems.

SUMMARY OF THE INVENTION

The present invention provides a method for designing a diffractive lens, so as to solve the problems that the current diffractive optical system achieves the purpose of achromatic, which causes the limited field of view of the optical system and the bloated optical system.

In order to solve the above problems, the present invention provides the following technical solutions:

A method for designing a diffractive lens with a large field of view working in an infrared band, the diffractive lens is composed of annular zones with different microstructures, and the microstructure solving steps include:

Step S1, determine the target wavelength band of the work, and determine the optical material used in the optical design of the wavelength band;

Step S2, determine the aperture and focal length data of the required diffractive lens;

Step S3, according to the working wavelength and the refractive index of the required material, calculate the height of the microstructure; specifically, according to the phase compression formula, calculate the height of each microstructure, and the expression is:

Among them, H _doe is the height of the microstructure, p is the parameter of the height of the microstructure, λ ₀ is the working wavelength of the diffractive lens, and n is the refractive index of the required material;

Step S4, according to the height of the microstructure, determine the maximum radius of each annular zone, and calculate the radius of curvature data of the annular zone, and the expression is:

Among them, H _doe is the height of the microstructure, R _max is the maximum radius of each annulus, c is the radius of curvature of the desired point, and k is the conic coefficient of the desired point;

In step S5, the microstructure data of the diffractive lens is obtained according to the aperture, focal length, microstructure height, and curvature radius of the diffractive lens.

Further, the microstructure height increases with the increase of p, where p is a positive integer greater than 1, and the effect is better when the p value is around 200.

Further, after obtaining the data for each annulus, use the optical design software to load the custom surface and input the data for optimization.

Further, the optical design software obtains the surface shape with abrupt structure by loading the custom surface shape, and the optimization and solution of the surface shape coordinate process includes:

Step S11, determine the front surface of the microstructure, the data on this surface, determine the offset of the end point of the surface relative to the center of the incident surface, and form the microstructure of the front surface of the diffractive lens;

Step S12, determine the radial coordinates of the starting point of the Zth area, and determine the offset relative to the end point of the previous surface;

Step S13, adding the offset of the previous surface at the specified point in S12 to obtain the total offset of the end point of the area;

Step S14, determine the radial coordinates at the given point, determine the area where the given point is located, and calculate the total offset at the given point; wherein, the given point is a non-end point;

Step S15, according to the above data, draw a cross-sectional view of the diffractive lens.

Further, processing is performed using the diffractive lens coordinate data obtained after optimization.

The beneficial effects brought by the technical scheme provided by the present invention:

1. The design principle of the present invention is simple and the efficiency is high.

2. Solve the problem that the current optical design software cannot obtain the abrupt structure similar to the Fresnel lens.

3. It is technical and difficult to imitate.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative effort.

Fig. 1 is the flow chart of the design scheme of the large field of view diffractive lens working in the infrared band provided by the present invention;

Fig. 2 is the custom surface calculation flow chart provided by the present invention;

Fig. 3 is the system dot diagram obtained by optical design software optimization;

4 is a schematic cross-sectional view of a diffractive lens;

Fig. 5 is the actual picture of the diffractive lens obtained by processing.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific examples.

This example provides a method for designing a large field of view diffractive lens working in the infrared band, wherein the large field of view diffractive lens is composed of microstructures with height difference and abrupt structure calculated according to the aspheric surface formula. By combining this method with optical design software, a large field of view diffractive lens with simple principle, convenient processing and excellent performance is designed. Specifically, as shown in Figure 1, the method includes the following steps:

S1, determine the working target wavelength band, and determine the optical material used in the optical design in this wavelength band; wherein, the optical material is a material with easy processing performance within the target working wavelength band; specifically, this implementation is for incident The wavelength band is in the infrared band range of 9-11 μm, and the center wavelength is 9 μm. The optical material used is germanium (refractive index is 4).

S2, determine the required diameter of the diffractive lens, focal length and other data; wherein, the diffractive lens has a diameter of 50mm, a focal length of 74.878mm, an F-number of 4.5, and a field of view angle of 21°.

S3, calculate the height of the microstructure according to the working wavelength and the refractive index of the required material; among them, select p to be 20, and calculate the height of the microstructure, and the expression is:

Among them, H _doe is the height of the microstructure, R _max is the maximum radius of each annulus, c is the radius of curvature of the desired point, and k is the conic coefficient of the desired point.

S4, according to the height of the microstructure, determine the radius of curvature and other data; the expression is:

Among them, H _doe is the height of the microstructure, R _max is the maximum radius of each annulus, c is the radius of curvature of the desired point, and k is the conic coefficient of the desired point.

S5, based on the above data, obtain the microstructure data of the diffractive lens.

Once the data for each annulus is obtained, use the optical design software to load the custom surface and enter the data for optimization. Specifically, in this embodiment, the maximum radius of each annular band is (in mm): 2.5, 5, 7.5, 10, 12, 13.75, 15.3, 16.7, 18, 19.22, 20.37, 21.45 , 22.48, 23.47, 24.42, 25.5, the conic coefficient of each annulus is 0, and the curvature radius of each annulus is (in mm): 229.214, 229.381, 229.650, 229.894, 230.106, 230.276 , 230.431, 230.590, 230.740, 230.917, 231.092, 231.226, 231.414, 231.602, 231.839, 231.975.

In this example, the optical design software is used to optimize the above-mentioned diffractive lens. The flow chart of the custom surface DLL loaded by the optical design software is shown in Figure 2. The simulation results include the vertical incidence and the large-angle incidence in the infrared range. spot distribution. Figure 3 is the system spot diagram of the incident light at various angles after passing through the optical system. The spot diagram shows that under different angles of incidence, the light spot distribution is located in the Airy disk, which belongs to the diffraction limited system, which shows that the diffractive lens is working It has an excellent large field of view function within the band.

Based on the final data obtained, a cross-sectional view of the diffractive lens was drawn, as shown in Figure 4.

Figure 5 shows the final processed diffractive lens, which is processed by diamond turning technology, which has the characteristics of convenient processing and small error.

To sum up, the present invention selects the parameter p according to the wavelength and optical material of the diffractive lens required for focusing, and the microstructure height of the diffractive lens can be determined. The specific parameters of the coordinates. The microstructures used are all quadric surfaces, there is no complex configuration, and the diffractive lens has good tolerance to errors, and can realize the imaging function of a single-piece large-field lens.

Furthermore, it should be noted that, herein, the terms "comprising", "comprising" or any other variation thereof are intended to encompass non-exclusive inclusion, such that a process, method, article or terminal device comprising a series of elements not only includes Those elements, but also other elements not expressly listed or inherent to such process, method, article or terminal equipment. Without further limitation, an element defined by the phrase "comprises a..." does not preclude the presence of additional identical elements in the process, method, article, or terminal device that includes the element.

Finally, it should be noted that the above are the preferred embodiments of the present invention. It should be pointed out that although the preferred embodiments of the present invention have been described, for those skilled in the art, once the basic inventive concept of the present invention is known , without departing from the principles of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the present invention. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the embodiments of the present invention.

Claims (5)

1. a design method of a large field of view diffractive lens working in infrared waveband, is characterized in that, described diffractive lens is made up of the annular zone with different microstructures, and the microstructure solving step comprises: Step S1, determine the target wavelength band of the work, and determine the optical material used in the optical design of the wavelength band; Step S2, determine the aperture and focal length data of the required diffractive lens; Step S3, according to the working wavelength and the refractive index of the required material, calculate the height of the microstructure; specifically, according to the phase compression formula, calculate the height of each microstructure, and the expression is:

Among them, H _doe is the height of the microstructure, p is the parameter of the height of the microstructure, λ ₀ is the working wavelength of the diffractive lens, and n is the refractive index of the required material; Step S4, according to the height of the microstructure, determine the maximum radius of each annular zone, and calculate the radius of curvature data of the annular zone, and the expression is:

Among them, H _doe is the height of the microstructure, R _max is the maximum radius of each annulus, c is the radius of curvature of the desired point, and k is the conic coefficient of the desired point; In step S5, the microstructure data of the diffractive lens is obtained according to the aperture, focal length, microstructure height, and curvature radius of the diffractive lens. 2. The design method of a large field of view diffractive lens working in the infrared waveband as claimed in claim 1, wherein the height of the microstructure increases with the increase of p, where p is a positive integer greater than 1, and p Values around 200 work better. 3. the design method of the large field of view diffractive lens working in the infrared waveband as claimed in claim 1, is characterized in that, after obtaining the data of each annular zone, use optical design software to load self-defined surface, input data to optimize . 4. the design method of the large field of view diffractive lens working in the infrared band as claimed in claim 3, it is characterized in that, the optical design software obtains the surface profile with abrupt structure by loading the custom profile, and carries out the optimization solution The surface coordinate process includes: Step S11, determine the data of the previous surface of the microstructure, determine the offset of the end point of the surface relative to the center of the incident surface, and form the microstructure of the previous surface of the diffractive lens; Step S12, determine the radial coordinates of the starting point of the Zth area, and determine the offset relative to the end point of the previous surface; Step S13, adding the offset of the previous surface at the specified point in S12 to obtain the total offset of the end point of the area; Step S14, determine the radial coordinates at the given point, determine the area where the given point is located, and calculate the total offset at the given point; wherein, the given point is a non-end point; Step S15, according to the above data, draw a cross-sectional view of the diffractive lens. 5 . The method for designing a diffractive lens with a large field of view working in the infrared waveband as claimed in claim 3 , wherein processing is performed using the optimized diffractive lens coordinate data. 6 .

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