CN113607092B - Method and system for measuring small angle of light - Google Patents

Abstract

The invention discloses a method and a system for measuring a small angle of light, which at least includes a telephoto system, a conical lens, an image acquisition system, an image processing system, and the like. The incident light with a small angle passes through the telephoto system to obtain the incident light with a larger angle, and reaches the side surface of the axicon lens through the diaphragm to produce total reflection. The number of total reflections of light with different incident angles in the axicon lens is different, when the total reflection is no longer satisfied. After conditions, it will exit from different positions on the sidewall of the axicon lens, so different incident angles will eventually form different spot images, in which the telephoto system plays the role of angle magnification and enhancement of luminous flux, and the small angle changes are amplified by the telephoto system. Make the spot image change more obvious and improve the angle measurement resolution. The image acquisition system processes the image information after receiving the image, and calculates the real-time light incident angle through the characteristic information of different spot images, such as symmetry axis, centroid position, area and moment of inertia. The invention has the advantages of high angle measurement resolution and simple measurement method.

Description

Method and system for measuring small angle of light

technical field

The invention relates to the field of optical technology, in particular to a method and system for measuring a small angle of light.

Background technique

The measurement of the incident angle of light is widely used in basic research, test measurement, target detection and other fields. The measurement of angle is an important part of geometric measurement technology. Most of the light incident angle measurement systems use optical angle measurement. In recent years, circular grating angle measurement and laser interference angle measurement are commonly used. They have been widely used and have achieved high measurement accuracy. However, there are still some urgent problems. The problems to be solved are, first, a breakthrough in measurement accuracy. Once the measurement accuracy is improved by an order of magnitude, the detection capability of various applications related to the detection of space targets will be greatly improved; second, the manufacturing process is difficult, the structure is complex, and the cost is high. The existing patent publication number CN111256649A uses a single conical lens for angle magnification, and the method of measuring the incident angle of light through the spot image has a simple measurement structure, but the characteristic information of the spot image obtained by this method does not change monotonically. Segmentation processing cannot guarantee consistency in accuracy, and at the same time, the area of the spot image is too large, and the actual implementation process may involve the problem of image stitching.

SUMMARY OF THE INVENTION

The technology of the invention solves the problem: overcomes the deficiencies of the prior art, and provides a method and system for measuring a small angle of light, which has the advantages of high angle measurement resolution and simple measurement.

The principle of the invention: using the telephoto system, the conical lens, the image acquisition system and the image processing system, the incident light is enlarged by the angle of the telephoto system and then enters the large end face of the conical lens through the diaphragm, and realizes total reflection on the side of the conical lens. As the number of total reflections increases, the incident angle of total reflection decreases gradually, and finally emerges from the sidewall of the axicon lens to form a monotonically changing light spot image. The same image processing method is used to process the characteristic information of the light spot image in the entire small-angle measurement range. That is, the corresponding ray incident angle is calculated.

To achieve the above object, the present invention adopts the following technical solutions:

其中

表示锥透镜的半锥角，n是锥透镜材料的折射率，β是望远系统的放大倍率。所述经望远系统后角度放大后入射到锥透镜大端端面的角度区间为

其中

表示锥透镜的半锥角，n是锥透镜材料的折射率。One of the technical solutions of the present invention: a method for measuring a small angle of light. The incident light with a small angle enters from the telephoto system, realizes angle amplification after passing through the telephoto system, and then enters the large end face of the axicon lens to reach the side wall. After several times Total reflection emerges from the sidewall of the axicon lens to form a spot image with regularly changing feature information, and the light incident angle is obtained after image processing on the spot image; the feature information includes the direction of the symmetry axis of the spot image, the position of the centroid, area and moment of inertia. As shown in Figure 4, the small angle interval of the incident light is

in

represents the half cone angle of the axicon, n is the refractive index of the axicon material, and β is the magnification of the telescopic system. The angle range of the incident to the large end face of the axicon lens after the angle is enlarged after the telephoto system is:

in

represents the half cone angle of the axicon, and n is the refractive index of the axicon material.

The light small angle measurement system for realizing the above method includes: a telephoto system, a diaphragm, an axicon, an image acquisition system and an image processing system.

The incident light enters from the telephoto system, passes through the telephoto system, and then enters the large end face of the axicon lens through the diaphragm to reach the side wall, and exits from the side wall of the axicon lens to the image acquisition system to form a spot image with regularly changing characteristic information. It is displayed on the image display system, and the light incident angle can be obtained after processing the spot image by the image processing system.

的小角度光线放大为

的较大角度光线入射到锥透镜，入射光线的微小角度变化经望远系统后会形成明显的角度变化，从而带来光斑图像特征的明显变化，起到集中能量、提高精度的作用；The telescopic system adopts Galileo or Kepler telescopic system, which is placed in front of the diaphragm and coaxial with the diaphragm.

The small-angle ray magnifies to

The larger angle light incident on the axicon lens, the small angle change of the incident light will form a significant angle change after passing through the telephoto system, which will bring about a significant change in the characteristics of the spot image, which plays a role in concentrating energy and improving accuracy;

The diaphragm, in the shape of a circular through hole, with a size smaller than or equal to the diameter of the large port of the axicon, is placed on the surface of the large end of the axicon and is coaxially placed with the axicon;

The parameters of the axicon lens include large port diameter, cone length, cone angle, material refractive index, etc. Axicon lenses with different parameters will form spot images with different characteristic information, which are placed at the rear of the diaphragm and coaxial with the diaphragm. , the large end face of the axicon is placed parallel to the receiving surface of the image acquisition system and the tip of the axicon is close to the receiving surface of the image acquisition system, the incident light is totally reflected in the axicon, and the number of total reflections of the incident light at different angles is different. Under the condition of total reflection, it is emitted from different positions of the side wall of the axicon lens to the image acquisition system to form different spot images. Complete reception, and the characteristic information of the spot image changes regularly;

The image acquisition system has a complete receiving surface, does not lose image information, and can completely receive different spot images formed by incident light rays from different angles after passing through the telephoto system, the diaphragm and the axicon;

The image processing system processes different spot images of the image acquisition system, and calculates corresponding different light incident angles according to the feature information in the different spot images;

The image display system displays the received light spot image;

The image display system is used for displaying the received light spot image.

The regularly changing feature information includes the direction of the symmetry axis, the area, the position of the center of mass, the moment of inertia, and the like.

其中L表示锥透镜的锥长，k表示第k次全反射，α_k为入射光线与锥透镜壁法线方向的夹角，θ₀表示锥透镜的半张角，α表示光线的入射角，n是锥透镜材料的折射率。不同于子午面内的光路轨迹，入射光线在非子午面中的光路轨迹一般是空间螺旋折线，折线可为左旋也可为右旋，当光线入射角度大于某一值时，光线在锥透镜的非子午面会将光线折射到远离中心的位置，例如光线2的传播轨迹，此时光斑图像必然会分裂，分裂后的图像过大，目前实际中存在的图像采集系统难以完整地接收，且光斑分裂后图像将不再是线性规律变化，需提取其他特征信息，同时也需改变图像处理方法，最终必然会造成不同入射光线角度的测量精度不一致的情况，因此分裂后的图像不可取，而本发明只针对小角度测量，对于小角度入射光线，其光斑图像变化呈规律性变化，且光斑面积适中。Figure 2 shows the ray trajectories of light propagating in the meridional and non-meridional planes of the axicon. In the meridional plane of the axicon, such as the propagation trajectory of light 1, the relationship between the height of the light hitting the image acquisition system and the incident angle is expressed as

where L is the cone length of the axicon, k is the k-th total reflection, α _k is the angle between the incident ray and the normal direction of the axicon wall, θ ₀ is the half-opening angle of the axicon, α is the incident angle of the light, n is the refractive index of the axicon material. Different from the optical path trajectory in the meridional plane, the optical path trajectory of the incident light in the non-meridional plane is generally a spatial spiral fold line, and the fold line can be left-handed or right-handed. The non-meridian plane will refract the light to a position away from the center, such as the propagation trajectory of light 2. At this time, the spot image will inevitably be split, and the split image is too large. The current image acquisition system in practice is difficult to receive completely, and the spot is split. After the image will no longer change in a linear law, other feature information needs to be extracted, and the image processing method needs to be changed at the same time, which will inevitably lead to inconsistent measurement accuracy of different incident light angles. Therefore, the split image is not desirable, and the present invention Only for small-angle measurement, for small-angle incident light, the spot image changes regularly, and the spot area is moderate.

Further, the light spot information received by the image acquisition system is processed by the image processing method, and the light incident angle can be obtained by comparing or interpolating with the calibration data.

Further, the spot image with symmetry and regular changes is received by the image acquisition system, and the image features such as centroid position, area, etc. determine the α angle of the light in Figure 3; the direction of the image symmetry axis determines the light in Figure 3. Azimuth β angle.

The advantages of the present invention compared with the prior art are:

的小角度光线，得到的光斑图像特征信息呈单调规律性变化，因此在整个小角度测量范围内采用同一种图像处理方法对光斑图像特征信息进行处理就可以计算得到入射角度，无需对测量角度进行分段处理，且整个小角度测量范围内形成的光斑均能被单个图像采集系统接收面完整接收。本发明具有角度测量分辨率高，同时测量方法简单等优点。(1) The present invention is directed to the angle of incident light rays

Therefore, in the whole small angle measurement range, the same image processing method is used to process the characteristic information of the spot image, and the incident angle can be calculated without the need to measure the angle. Segmented processing, and the light spots formed in the entire small-angle measurement range can be completely received by the receiving surface of a single image acquisition system. The invention has the advantages of high angle measurement resolution and simple measurement method.

(2) In the present invention, both the telephoto system and the axicon lens have an angle magnification effect, and the real-time light incident angle can be obtained by solving the characteristic information of different spot images, such as the direction of the symmetry axis, the position of the centroid, and the area. For the same small angle change, compared with the method of directly using the axicon lens, the angle change will be more severe through the angle magnification of the telephoto system, and then a more obvious and regularly changing light spot image can be obtained through the axicon lens, which can further improve the small angle of light. The measurement accuracy is changed; and the entrance pupil of the telephoto system replaces the diaphragm in the existing patent publication number CN111256649A, which increases the luminous flux of the system, thereby improving the signal-to-noise ratio of the image acquisition system.

Description of drawings

1 is a schematic diagram of a system structure provided by an embodiment of the present invention;

2 is a schematic diagram of the optical path of light propagating in the meridional plane and the non-meridional plane of the axicon lens according to the embodiment of the present invention;

3 is a schematic diagram of an incident angle of light in an embodiment of the present invention;

FIG. 4 is a ray locus diagram of light propagating in the meridional plane of an axicon lens provided by an embodiment of the present invention;

FIG. 5 is a simulation diagram of a spot image formed by light rays with different incident angles on an image acquisition system according to an embodiment of the present invention.

Detailed ways

Embodiments of the present invention provide a method and system for measuring a small angle of light. The system includes a telephoto system, a diaphragm, an axicon, an image acquisition system and an image processing system. The incident light is enlarged by the angle of the telephoto system, and then enters the large end face of the axicon through the diaphragm and reaches the side wall for total reflection. The side wall is emitted to form a spot image. After the image processing system processes the feature information of the spot image, the corresponding light incident angle can be calculated. It will be described in detail below with reference to the accompanying drawings and by way of examples.

Example

As shown in FIGS. 1-2 , a light small angle measurement system of the present invention includes: a telephoto system 2 , a diaphragm 3 , an axicon 4 , an image acquisition system 5 , an image processing system 6 and an image display system 7 . Incident ray 1 is incident on the optical system from the front aperture of the telescopic system, where:

Parameters such as the magnification and size of the telephoto system 2 need to be determined according to the parameters of the axicon 4 and the image acquisition system 5 . If the magnification is too large, the beam energy may be too concentrated, and the formed spot image will be too small, affecting its resolution; if the magnification is too small, the angle magnification effect will not be achieved, and the beam energy will be scattered.

In the specific implementation, it can be designed according to the needs of the system, or an off-the-shelf telescope module can be purchased, and each lens can be arranged coaxially with the axicon 4 during installation. In this embodiment, a Galileo-type telescopic system with a magnification of 5.3 times and a clear aperture size of 11 mm is used, and the light with an incident angle of 0° to 3° is amplified by the telescopic system to an outgoing light of 0° to 15.9° , the slight angle change of the incident light will form a significant angle change after passing through the telephoto system, which will bring about a significant change in the characteristics of the spot image and improve the measurement accuracy of the light angle.

The shape of the diaphragm 3 is circular, and the installation parameters may include its distance from the axicon 4 and the like.

In specific implementation, the diaphragm can be placed close to the end face of the large end of the axicon lens 4, and the size is smaller than or equal to the diameter of the large port of the axicon lens.

Parameters such as the large port diameter, the cone length and the cone angle of the axicon lens 4 need to be determined according to the size parameters of the telephoto system 2 . The installation parameters may include the distance between the telephoto system 2 and the axicon 4 , the distance between the axicon 4 and the receiving surface of the image acquisition system 5 , the angle between the large end face of the axicon 4 and the receiving surface of the image acquisition system 5 , etc.

In specific implementation, the size of the telephoto system 2 and the axicon lens 4 can be set to match, and the two are relatively close, the tip of the axicon lens 4 is placed close to the receiving surface of the image acquisition system 5, and the large end face of the axicon lens 4 is parallel to the image acquisition system. 5 receiving surfaces. In this embodiment, the material of the axicon lens is H-ZBAF21, the diameter of the large port is 10mm, the cone angle is 28.1°, and the spot images formed by the incident light rays from 0° to 3° after passing through the telephoto system, the diaphragm and the axicon lens are all uniform. It can be completely received by the receiving surface of a single image acquisition system, and the characteristic information of the spot image changes regularly.

The image acquisition system 5 is used for receiving the spot image formed by the incident light passing through the optical system.

In the specific implementation, an image acquisition system such as CCD or CMOS can be selected according to the needs of the system.

The image processing system 6 is used to process the characteristic information of the light spot image received by the image acquisition system 5, including the symmetry axis direction, area, and centroid position of the light spot image.

In the specific implementation, the corresponding incident light azimuth information can be calculated by extracting the direction of the symmetry axis of the spot image, and the angle information of the incident light can be calculated by various methods such as the area of the spot image and the position of the centroid, so as to ensure the angle of the incident light. measurement accuracy.

As shown in Figure 3, the spot image with symmetry and regular changes is received through the image acquisition system, and the point where the tip of the cone lens is projected onto the receiving surface of the image acquisition system is used as the origin to establish a coordinate system. Image features such as centroid position, area etc. can determine the inclination angle α angle of the light in Fig. 3; the direction of the image symmetry axis can determine the azimuth angle β angle of the light in Fig. 3.

In this embodiment, the used telephoto system has a magnification of 5.3 times, the cone lens material is H-ZBAF21, the diameter of the large port is 10mm, and the cone angle is 28.1°. The spot image formed by the incident light telescopic system and the axicon lens is shown in Figure 5. In the figure: (a) the incident angle of the light is 0°, (b) the incident angle of the light is 0.2°, and (c) the incident angle of the light is 0.4 °, (d) ray incident angle is 0.6°, (e) ray incident angle is 0.8°, (f) ray incident angle is 1°, (g) ray incident angle is 1.2°, (h) ray incident angle is 1.4 °, (i) ray incident angle is 1.6°, (g) ray incident angle is 1.8°, (k) ray incident angle is 2°, (l) ray incident angle is 2.2°, (m) ray incident angle is 2.4 °, (n) ray incident angle is 2.6°, (o) ray incident angle is 2.8°, (p) ray incident angle is 3°, the magnification of the telephoto system used is 5.3, and the refractive index of the axicon material is 1.72 , the large port diameter is 10mm, and the cone angle is 28.1°.

其中，(i₀,j₀)表示锥透镜中心轴线与成像面的交点，m、n表示图像的像素尺寸，f(i,j)表示在该位置处二值化图像的灰度值，采用转动惯量的方法求解入射角度，得到的测量精度相比现有专利公布号CN111256649A精度提高了32％。The spot image in Figure 5 can be completely received by the receiving surface of the image acquisition system, without the need for image stitching and other processing, which avoids the loss of image information to a certain extent, and the characteristic information of the spot image includes the centroid position, area, etc. in the entire 0°-3° The incident angle of the light changes regularly, and the angle information of the incident light is in a one-to-one correspondence with the characteristic information of the spot image. The point where the tip of the cone lens is projected onto the receiving surface of the image acquisition system is used as the origin to establish a coordinate system, and the spot image is determined. The characteristic information includes the direction of the symmetry axis, the position of the centroid, the area, etc. After image processing, and the calibration data is compared or interpolated, the angle information of the incident light can be obtained. According to the calculation formula of the moment of inertia

Among them, (i ₀ , j ₀ ) represents the intersection of the central axis of the axicon lens and the imaging surface, m and n represent the pixel size of the image, and f(i, j) represents the gray value of the binarized image at this position, using The method of the moment of inertia solves the incident angle, and the obtained measurement accuracy is 32% higher than that of the existing patent publication number CN111256649A.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them. It should be understood by those of ordinary skill in the art that the act of modifying the technical solutions described in the foregoing embodiments or performing equivalent replacement of some or all of the technical features does not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (2)

1. a method for measuring a small angle of light, it is characterized in that: the small angle incident light enters from the telephoto system, realizes angle magnification after the telephoto system, then enters the large end face of the axicon lens to reach the side wall, and exits from the side wall of the axicon lens. , forming a spot image with regularly changing feature information, and performing image processing on the spot image to obtain a light incident angle; The angle of incident to the large end face of the axicon lens after the angle is enlarged after the telescopic system satisfies the condition that total reflection can occur on the side surface of the axicon lens, if

represents the half cone angle of the axicon, n represents the refractive index of the axicon material, when the light is incident from the large end face of the axicon at an angle of α, the refraction angle of the light is α ₀ , and the light reaches the meridian plane of the axicon for the first time The angle between the ray and the normal of the side wall is α ₁ when the axicon is placed in the air

Then when reaching the sidewall on the meridian plane, the condition for total reflection to occur is

The angle interval of the light incident on the large end face of the axicon lens is obtained as

The small angle interval in the small angle incident light is calculated according to the angle interval α of the light incident on the large end face of the axicon, and the small angle interval of the incident light is:

in

represents the half cone angle of the axicon, n is the refractive index of the axicon material, and β is the magnification of the telescopic system. 2. A small-angle measurement system for realizing the method of claim 1, wherein the system comprises: a telephoto system, an axicon, an image acquisition system and an image processing system; In the telephoto system, the diameter of the exit window is larger than the diameter of the large port of the axicon lens, and the small-angle light is enlarged into a large-angle light and incident on the axicon. The role of luminous flux; The axicon lens is emitted from the sidewall of the axicon lens to form a spot image with regularly changing feature information, the large end face of the axicon lens is placed in parallel with the receiving surface of the image acquisition system, and the tip of the axicon lens is close to the receiving surface of the image acquisition system; The image acquisition system receives a spot image with regularly changing feature information; The image processing system processes the light spot images, and calculates corresponding different light incident angles according to feature information in different light spot images.

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