WO2022257164A1

WO2022257164A1 - Wide-viewing-angle imaging method based on planar lens

Info

Publication number: WO2022257164A1
Application number: PCT/CN2021/100557
Authority: WO
Inventors: 陈绩; 赵云伟; 李涛; 祝世宁
Original assignee: 南京大学
Priority date: 2021-06-08
Filing date: 2021-06-17
Publication date: 2022-12-15
Also published as: CN113484939A

Abstract

A wide-viewing-angle imaging method based on a planar lens, the method comprising: forming a lens array from at least two sub-lenses, and the sub-lenses being planar lenses; and preparing the lens array from a material such as a metasurface, a wide-viewing-angle area being imaged by each sub-lens to obtain a sub-image, focusing parallel light incident at a design angle at a design focus in a focal plane by designing the phase distribution of surfaces of the sub-lenses, and splicing imaging result images of all the sub-lenses in a certain angle range close to the design angle, so as to obtain a full-viewing-angle image of the lens array. Clear imaging by the planar lens at a wide viewing angle can be realized, the number of sub-lenses and a projection function can be designed according to the imaging quality and the viewing angle range requirements, and the method is used for realizing a wide-angle imaging device with a high degree of integration, thereby reducing the size and manufacturing costs of a device, and being easily popularized.

Description

Wide Viewing Angle Imaging Method Based on Plane Lens

technical field

The invention relates to a wide viewing angle imaging method, in particular to a wide viewing angle imaging method based on a plane lens.

Background technique

In the traditional imaging system, a lens group composed of multiple refractive lenses is usually used to eliminate the aberration caused by the light incident at a large angle, so as to realize clear imaging of multiple angles at the same time, but the large curvature incident lens and the subsequent The lens group is bulky, requires high manufacturing precision, and the image in the final imaging result is severely distorted, and the imaging result is more distorted than the real object; another method is to copy the whole or part of a single imaging structural unit into multiple One, to achieve clear imaging of different angles, but it doubles the volume and cost of the entire wide-angle imaging system, and in some cases also requires a curved photodetector, which increases the difficulty of manufacturing. Existing methods are all composed of complex optical systems, making wide-angle imaging devices more and more complex, bulky and expensive, which greatly limits the promotion and application of wide-angle imaging devices.

Contents of the invention

Purpose of the invention: The purpose of the invention is to provide a flat lens array that can realize clear imaging of a wide viewing angle range, reduce equipment volume and manufacturing cost, and facilitate integration.

Technical solution: In the wide viewing angle imaging method based on a plane lens described in the present invention, a lens array is first composed of several sub-lenses, and the sub-lenses are plane lenses; each of the sub-lenses images a wide viewing angle area to obtain a sub-image. A full-view image of the lens array is obtained by splicing images of imaging results of a certain range of angles near the design angle of all the sub-lenses.

The sub-lens is a flat lens, and the phase distribution can be flexibly designed. There are at least two sub-lenses in the lens array, and the same viewing angle range, the more sub-lenses, the higher the imaging quality.

The phase of the sub-lens is composed of a tilt angle phase and a focus phase. The tilt angle phase compensates the phase difference caused by the oblique incidence of the incident light, and the focus phase regulates the focus of the parallel light incident at the design angle at the design focus.

The method of obtaining the full-view image is as follows: add a mask function to the imaging result of each sub-lens to obtain a weighted sub-image, the value of the mask function satisfies the maximum value of 1 at the design focus, and add a mask function to each sub-image The weighted sub-image is obtained, and all weighted sub-images and all mask functions are superimposed and divided to obtain a full-view image.

Beneficial effects: Compared with the prior art, the wide viewing angle imaging method of the present invention realizes clear imaging of wide viewing angles with an ultra-thin, ultra-light lens array that is easily integrated with a planar photoelectric sensor. By designing the phase distribution of the sub-lens surface, the sub-lens The lens receives light incident at different angles in the plane, and by changing the projection function expression of the sub-lens, the imaging position of the sub-lens is changed to increase the design flexibility.

Description of drawings

Fig. 1 is a one-dimensional lens array phase distribution of the present invention;

Fig. 2 is the coordinate regulation of sub-lens of the present invention;

Fig. 3 is the exterior view of the sub-lens whose design angle is 48° in the present invention;

Fig. 4 is the topography diagram of the local structure of the one-dimensional lens array of the present invention;

Fig. 5 is a comparison diagram of focusing at different angles between a traditional hyperbolic phase lens and a one-dimensional lens array of the present invention;

Fig. 6 is a comparison diagram of the modulation transfer function of the traditional hyperbolic phase lens and the one-dimensional lens array of the present invention;

Fig. 7 is the imaging result of the one-dimensional lens array of the present invention;

Fig. 8 is a one-dimensional lens array imaging processing process and results of the present invention;

Fig. 9 is the phase distribution of the two-dimensional lens array of the present invention;

FIG. 10 shows the imaging process and results of the two-dimensional lens array of the present invention.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

Example 1

The imaging method of this program includes the following steps:

(1) Build a lens array

As shown in Figure 1, a one-dimensional lens array of 1*17 arrangement is composed of 17 sub-lenses. The sub-lenses are planar lenses. The sub-lenses in this embodiment are metasurface materials, which can be flexibly designed in practical applications. Lens with phase distribution, such as multi-level diffractive lens, etc. The thickness of the sub-lenses is about 800nm-1200nm, and all the sub-lenses are on the same plane, which is called the lens plane.

As shown in Figure 2, the coordinates of the sub-lens are stipulated. The origin of the coordinate axes is the center of the sub-lens, the xOy plane is the lens plane, the z-axis passes through the center of the sub-lens and is perpendicular to the lens plane, and the xOz plane is the distance between the z-axis and the center of the sub-lens. The plane formed by the incident light, θ is the angle formed by the incident light passing through the center of the sub-lens and the z-axis, that is, the design angle of the sub-lens. The focal plane is the plane parallel to the lens plane through the design focal point. The distance between the focal plane and the lens plane is f. The design focal point of the sub-lens is the point where the parallel light incident along the design angle of the sub-lens focuses on the focal plane. F(θ ) is called the projection function, which is the relative position between the design focus and the lens center in the x direction, and its value can be a negative value. In this embodiment, F(θ)=-fθ, and F(θ) can also be selected in practical applications Other monotonic functions of θ. The design angles θ of the 17 sub-lenses are 0°, ±19°, ±27°, ±33°, ±38°, ±43°, ±48°, ±53° and ±57.5°, respectively.

The phase of each sub-lens consists of a tilt angle phase and a focus phase. The tilt angle phase is used to compensate the phase difference caused by the oblique incidence of parallel light. The focus phase is adjusted to focus the parallel light incident at the design angle at the design focus.

The tilt angle phase φ _t (x, y, θ) of the structural unit at the sub-lens (x, y) satisfies:

The focus phase φ _f (x, y, θ) of the point (x, y) on the sub-lens satisfies:

The total phase of the point (x,y) on the sub-lens satisfies:

In this embodiment, the focal length f of each sub-lens is set to 450 μm; λ is the working wavelength of the sub-lens when imaging.

(2) Preparation of lens array

According to the phase distribution of the one-dimensional lens array designed in step (1), the one-dimensional lens array is prepared by electron beam exposure and dry etching. As shown in Figure 3, the design angle of the sub-lens taken by an optical microscope is 48°. The appearance diagram, as shown in Figure 4, is a part of the structural topography diagram of the one-dimensional lens array taken by an electron microscope.

Use parallel light with incident angles of 0°, 19°, 38° and 57.5° to irradiate the traditional hyperbolic phase lens and the one-dimensional lens array respectively to obtain the focusing situation on the focal plane. The focusing results are shown in Figure 5, where Figure 5 (a) is a focusing diagram of a traditional hyperbolic phase lens, and FIG. 5(b) is a focusing diagram of a one-dimensional lens array. The one-dimensional lens array has a better focusing effect than the traditional hyperbolic phase lens. Calculate the modulation transfer function of the traditional hyperbolic phase lens and the one-dimensional lens array at various incident angles, and the results are shown in Figure 6, where Figure 6(a) is the modulation transfer function of the traditional hyperbolic phase lens, and Figure 6(b) is The modulation function transfer diagram of the one-dimensional lens array, the solid line and the dotted line represent the modulation transfer function in the meridian plane and the sagittal plane respectively. It can be seen from Figure 6 that for the incident light at the same angle, the one-dimensional lens array has a higher resolution rate, so its imaging performance is better than traditional hyperbolic phase lenses.

(3) Imaging result of split lens array

Using the one-dimensional lens array in this embodiment to image the first wide viewing angle object, the imaging result of the one-dimensional lens array is shown in FIG. 7 . The imaging result of the one-dimensional lens array is divided into sub-images of each sub-lens, and the divided sub-images are shown in Fig. 8(a).

(4) Perform image processing on the sub-image to obtain a full-view image

Add a mask function to each sub-image to obtain a weighted sub-image. As shown in Figure 8(b), the size of the mask function is the same as that of a single sub-image, and its value satisfies the maximum value of 1 at the design focus, and the values of other points decrease with the increase of r and are positive numbers, r is the distance in the x-direction from the point to the design focus. Multiply the original image with the same size and the mask function image pixel by pixel to obtain the weighted sub-image, which is shown in Figure 8(c).

Superimpose all weighted sub-images, as shown in Figure 8(d); superimpose all mask functions, as shown in Figure 8(e); divide the superimposed image of the sub-image and the superimposed image of the mask function pixel by pixel to obtain The full-view image, as shown in Fig. 8(f), is the obtained full-view image.

The number of sub-lenses is related to the range of imaging viewing angles and the requirements for imaging quality. The number is at least two. For the same viewing range, the more sub-lenses, the smaller the range of imaging angles each sub-lens is responsible for, and the higher the imaging quality. The final image quality of stitching is also higher.

Comparative example 1

Using a traditional hyperbolic phase lens to image the first wide viewing angle object, the imaging result is shown in Figure 8(g). By comparing Figure 8(f) and Figure 8(g), it can be seen that the one-dimensional lens array of the present invention can image the wide viewing angle object The object forms a clear image, and compared with the traditional hyperbolic phase lens, it can be clearly imaged in a larger field of view.

Example 2

As shown in FIG. 9 , a two-dimensional lens array arranged in 7*7 is composed of 49 sub-lenses, and all the lenses are on the same plane, which is called a lens plane. The coordinates of the sub-lenses are the same as in Example 1, and the design angles of the 49 sub-lenses are respectively 24°, -16°, -8°, 0°, 8°, 16° and 24° in the x and y directions, 49 sub-lenses The design angle θ satisfies

Wherein θ _x is the angle formed by the projection of the sub-lens design angle parallel light in the xOz plane and the z axis, and θ _y is the angle formed by the projection of the sub-metalens design angle light in the yOz plane and the z axis.

In this embodiment, the projection function F(θ)=-ftanθ is taken, the focal length f of each sub-lens is set to 450 μm, and the inclination angle phase of the point (x, y) on the sub-lens is calculated respectively according to formula (1) and formula (2) and focusing phase, the total phase of the sub-lens satisfies:

The method of preparing the lens array, dividing the imaging result of the lens array, and performing image processing on the sub-images to obtain the full-view image is the same as that of Example 1. The imaging result and image processing of the second wide-view object by the two-dimensional lens array are obtained by the full-view image. The results are shown in Fig. 10(a) to (g).

Comparative example 2

Using a traditional hyperbolic phase lens to image the second wide viewing angle object, the imaging result is shown in Figure 10(h). By comparing Figure 10(g) and Figure 10(h), it can be known that the two-dimensional lens array of the present invention can image the wide viewing angle object The object forms a clear image, and compared with the traditional hyperbolic phase lens, it can be clearly imaged in a larger field of view.

Claims

A wide viewing angle imaging method based on a plane lens, characterized in that, a lens array is composed of several sub-lenses, and the sub-lenses are plane lenses; each of the sub-lenses images a wide viewing angle area to obtain a sub-image, and all sub-lenses are A full view image of the lens array is obtained by splicing images of imaging results in a certain angle range around the design angle θ.
The wide viewing angle imaging method based on a plane lens according to claim 1, wherein the phase of the sub-lens is composed of a tilt angle phase and a focus phase, and the tilt angle phase compensates the phase difference generated by oblique incidence of the incident light, The focus phase is adjusted to focus the parallel light incident along the design angle at the design focus.
The wide viewing angle imaging method based on a plane lens according to claim 1, wherein the number of the sub-lenses is at least two.
The wide viewing angle imaging method based on a plane lens according to claim 2, wherein the calculation formula of the oblique phase is:

Where (x, y) is any point on the sub-lens, and λ is the working wavelength of the sub-lens when imaging.
The wide viewing angle imaging method based on a plane lens according to claim 2, wherein the calculation formula of the focus phase is:

Wherein f is the focal length of the sub-lens, and F(θ) is the distance between the vertical projection of the center of the sub-lens on the focal plane and the design focus.
The wide viewing angle imaging method based on a plane lens according to claim 1, wherein the method for obtaining a full viewing angle image is specifically: adding a mask function to each sub-image to obtain a weighted sub-image, all weighted sub-images and all weighted sub-images The mask functions are superimposed and then divided to obtain a full-view image.
The wide viewing angle imaging method based on a plane lens according to claim 6, wherein the mask function achieves a maximum value of 1 at the design focus, and the values of other points decrease with the increase of r and are positive numbers , r is the distance from the point to the design focus.