CN116559843A - Laser receiving system and laser radar - Google Patents

Abstract

The application relates to the technical field of optical imaging, in particular to a laser receiving system and a laser radar. The laser receiving system includes: the object side surface to the image side surface along the optical axis direction are sequentially provided with a non-rotationally symmetrical lens group, a rotationally symmetrical lens group and a detector, wherein the non-rotationally symmetrical lens group comprises at least one non-rotationally symmetrical lens; the rotationally symmetric lens group comprises at least one rotationally symmetric lens; the object side or image side of at least one of the non-rotationally symmetric lenses has two-dimensionally distributed diffraction units; the laser receiving system is characterized in that the focal lengths of the laser receiving system in a first direction and a second direction are different, the first direction is any line passing through the optical axis and extending in a plane perpendicular to the optical axis, and the second direction is any line extending in the plane perpendicular to the optical axis and orthogonal to the first direction. The overall length of the laser receiving system is reduced, and the miniaturization of the laser receiving system is facilitated.

Description

Laser receiving system and laser radar

technical field

The present application relates to the technical field of optical imaging, in particular to a laser receiving system and a laser radar.

Background technique

The receiving system in lidar can be divided into proportional receiving system and non-equal receiving system according to the focal length ratio of meridian and sagittal direction; among them, the proportional receiving system means that the focal length of the system meridian and sagittal direction is equal; the non-equal receiving system refers to The focal lengths in the meridional and sagittal directions are not equal. The non-equal receiving system breaks the limitation of the horizontal and vertical focal lengths of the traditional proportional receiving system, so that the focal length in the sagittal direction can be larger than the focal length in the meridian direction, so that the detectors in the lidar receiving system will not be too large under high energy. Overexplosion to increase the dynamic range of the lidar laser receiving system.

However, the total length of the non-equal receiving system in the prior art is relatively long, resulting in a large space occupied by the laser receiving system in the lidar. Therefore, how to realize the miniaturization of the non-equal receiving system has become an urgent problem to be solved.

Contents of the invention

The application provides a laser receiving system and a laser radar. The total length of the laser receiving system is relatively small, so that when the laser receiving system is applied to a laser radar, the space occupied by the laser radar is small, which is conducive to the miniaturization of the laser radar .

In the first aspect, the application provides a laser receiving system, including: a non-rotationally symmetrical lens group, a rotationally symmetric lens group and a detector. The side to the image side is arranged in sequence, wherein the non-rotationally symmetrical lens group may include at least one non-rotationally symmetrical lens, the rotationally symmetrical lens group may include at least one rotationally symmetrical lens, and among the non-rotationally symmetrical lens and a plurality of rotationally symmetrical lenses, at least one The object side or the image side of the lens has two-dimensionally distributed diffraction units, wherein the focal lengths of the laser receiving system in the first direction and the second direction are different, so the laser receiving system is a non-equal receiving system, and the first direction is the transmission Any direction passing through the optical axis and extending in a plane perpendicular to the optical axis, the second direction is a direction extending in a plane perpendicular to the optical axis and perpendicular to the first direction. Specifically, due to the diffraction effect of the light passing through the diffraction unit, the phase modulation is realized, so that the two-dimensionally distributed diffraction unit can correct the aberration of the laser receiving system, thereby reducing the total length of the laser receiving system and realizing the miniaturization of the laser receiving system .

It should be noted that the two-dimensionally distributed diffractive units, that is, the diffractive units are arranged in a plane, and the diffractive units are formed on the object side or image side of at least one of the non-rotationally symmetric lenses and the rotationally symmetric lenses through a micro-nano etching process. . The number of non-rotationally symmetrical lenses can be 2-4, and the number of rotationally symmetrical lenses can be 3-6. Wherein, the object side is the end of the laser receiving system close to the measured object, and the image side is the end of the laser receiving system away from the measured object.

A rotationally symmetric lens refers to a figure that the lens has a center of symmetry and can overlap with the original figure after rotating around the center of symmetry by a certain angle.

In a possible embodiment, in order to realize the miniaturization of the laser receiving system, the laser receiving system can meet the following conditional formula: TTL/EFFL _x ≤ 2.0; where, TTL is the end of the non-rotationally symmetrical lens group away from the detector to the image The length on the optical axis of the side, that is, the length on the optical axis from the end of the non-rotationally symmetrical lens farthest from the detector away from the detector to the side of the image, EFFL _x is the effective focal length of the laser receiving system in the second direction.

In another possible embodiment, in order to realize the miniaturization of the laser receiving system, the laser receiving system can also meet the following conditional formula: |EFFL _x 1/EFFL _x |≥10; wherein, EFFL _x 1 is a non-rotationally symmetric lens The effective focal length of the group in the second direction, EFFL _x is the effective focal length of the laser receiving system in the second direction.

In another possible embodiment, in order to realize the miniaturization of the laser receiving system, the laser receiving system can also meet the following conditional formula: _0.2≤EPDx /EPDy≤5; where, _EPDx is the laser receiving system in the second direction Entrance pupil diameter, EPD _y is the entrance pupil diameter of the laser receiving system in the first direction. In this way, the receiving aperture of the laser receiving system can be made larger, which is beneficial to receive more signals. where the entrance pupil is the effective aperture that confines the incident beam.

In another possible embodiment, in order to increase the field of view that the laser receiving system can receive and improve the field of view of the radar with the laser receiving system, the laser receiving system can also meet the following conditional formula: IH _y /EFFL _y ≥ 0.1; Wherein, IH _y is the effective height of the laser receiving system in the first direction, and EFFL _y is the effective focal length of the laser receiving system in the first direction.

In the above-mentioned embodiments, in order to ensure the miniaturization of the laser receiving system, the period of the diffraction unit may satisfy 500 nm˜20 μm, and the aspect ratio of the diffraction unit may satisfy 1:1˜1:5. The diffraction unit may include a plurality of sub-diffraction units sequentially arranged along the first direction.

From the object side to the image side along the optical axis, the non-rotationally symmetrical lens group includes a first cylindrical lens, a filter and a second cylindrical lens arranged at intervals in sequence; along the optical axis, from the object side to the image side, the rotation is symmetrical The lens group includes a plurality of rotationally symmetrical lenses arranged at intervals, specifically: the rotationally symmetrical lens group includes a first aspheric mirror, a second aspheric mirror and a third aspheric mirror arranged at intervals in sequence; in order to miniaturize the laser receiving system, the diffraction unit can be It is arranged on the object side or image side of at least one of the first cylindrical mirror, the optical filter and the second cylindrical mirror, and/or, the diffraction unit can also be arranged on the first aspheric mirror, the second aspheric mirror and the third The object side or image side of at least one spherical mirror in the aspherical mirrors.

In a possible embodiment, in order to make the laser receiving system a non-equal ratio receiving system, the laser receiving system can also meet the following conditional formula: EFFL _x /EFFL _y ≥ 1.2; where EFFL _x is the laser receiving system in the second The effective focal length of the direction, EFFL _y is the effective focal length of the laser receiving system in the first direction.

In the above embodiment, a diaphragm may further be provided between the non-rotationally symmetrical lens group and the rotationally symmetrical lens group. It should be noted that the aperture can be a square aperture, so that the laser receiving system can receive more signals and improve the ranging capability of the radar with the laser receiving system.

In the above embodiments, the laser receiving system may further include a protective glass, and the protective glass may be disposed between the third aspheric mirror and the detector.

In the above embodiment, the near optical axis of the object side of the first aspheric mirror can be a convex surface, the near optical axis of the image side of the first aspheric mirror can be concave; the near optical axis of the object side of the second aspheric mirror can be concave , the near optical axis of the image side of the second aspheric mirror can be convex, the near optical axis of the object side of the third aspheric mirror can be convex, and the near optical axis of the image side of the third aspheric mirror can be concave.

In the second aspect, the present application also provides a laser radar, including a laser emitting system and the laser receiving system in any technical solution of the above-mentioned first aspect. Since the total length of the laser receiving system is small, it is possible to have the laser receiving system The space occupied by the lidar will be smaller, which is conducive to the miniaturization of the lidar.

Description of drawings

Figure 1a is a schematic structural diagram of a laser receiving system provided in an embodiment of the present application;

Fig. 1b is another structural schematic diagram of the laser receiving system provided by the embodiment of the present application;

FIG. 2 is a schematic structural diagram of the diffraction unit in the laser receiving system provided by the embodiment of the present application;

Fig. 3 is a kind of simulation diagram of the laser receiving system provided by the embodiment of the present application;

Fig. 4a is another structural schematic diagram of the laser receiving system provided by the embodiment of the present application;

Fig. 4b is another structural schematic diagram of the laser receiving system provided by the embodiment of the present application;

Fig. 5 is another simulation diagram of the laser receiving system provided by the embodiment of the present application;

Fig. 6a is another structural schematic diagram of the laser receiving system provided by the embodiment of the present application;

Fig. 6b is another structural schematic diagram of the laser receiving system provided by the embodiment of the present application;

FIG. 7 is another simulation diagram of the laser receiving system provided by the embodiment of the present application.

Reference signs:

1-non-rotational symmetric lens group; 10-first cylindrical lens; 11-filter; 12-second cylindrical lens; 2-rotational symmetric lens group; 20-first aspherical mirror; 21-second aspherical mirror ; 22-the third aspherical mirror; 3-detector; 4-diffraction unit; 40-sub-diffraction unit; 5-diaphragm; 6-protective glass.

Detailed ways

In order to make the purpose, technical solution and advantages of the application clearer, the application will be further described in detail below in conjunction with the accompanying drawings.

When the laser radar is detecting, the laser transmitting system and the laser receiving system of the laser radar work. Among them, the pulse signal or modulated signal emitted by the laser transmitting system is reflected by the measured object and then is reflected by the laser receiving system to complete the distance to the object. to test. Among them, the laser receiving system is usually an important part of the lidar, which can directly affect the energy received by the lidar and the quality of the point cloud, and then affect the ranging capability of the lidar. Since the receiving field of view of the lidar receiving system is fixed, the larger the focal length in the sagittal direction, the larger the size of the spot that the light beam received by the optical receiving system shrinks on the image plane, and the larger the size of the spot, the larger the detector share. The energy is small, so that the detector will not explode under high energy, thereby increasing the dynamic range of the lidar receiving system.

In order to increase the dynamic range of the laser receiving system in the laser radar, the focal length of the laser receiving system in the laser radar in the sagittal direction is generally larger than the focal length in the meridian direction, but this will cause the total length of the laser receiving system in the laser radar to be larger , and the diameter of the first lens in the laser receiving system in the laser radar is relatively large, which leads to a large size of the laser receiving system in the laser radar.

In order to reduce the size of the laser receiving system in the above-mentioned laser radar, the method of increasing the number of lenses in the laser receiving system and using rotating aspheric lenses is usually used in the prior art. However, due to the limitations of system aberrations and other factors, Increasing the number of lenses and using aspherical lenses has a certain limit to the correction of the laser receiving system in the lidar, and increasing the number of lenses and using aspheric lenses will not only increase the cost of the laser receiving system in the lidar, but also increase the laser receiving system in the lidar. The complexity of the system assembly.

Therefore, in order to solve the problem of the large size of the laser receiving system in the laser radar system, the present application provides a new laser receiving system.

The terms used in the following examples are for the purpose of describing particular examples only, and are not intended to limit the application. As used in the specification and appended claims of this application, the singular expressions "a", "an", "said", "above", "the" and "this" are intended to also Expressions such as "one or more" are included unless the context clearly dictates otherwise.

Reference to "one embodiment" or "some embodiments" or the like in this specification means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in other embodiments," etc. in various places in this specification are not necessarily All refer to the same embodiment, but mean "one or more but not all embodiments" unless specifically stated otherwise. The terms "including", "comprising", "having" and variations thereof mean "including but not limited to", unless specifically stated otherwise.

Referring to Fig. 1a, Fig. 1b and Fig. 2, the first direction can be the direction indicated by the solid arrow, the second direction can be the direction indicated by the dotted arrow in the figure, and the first direction can be the meridional direction or the sagittal direction, The second direction may be a direction perpendicular to the first direction (that is, the first direction is a meridional direction and the second direction is a sagittal direction, or the second direction is a meridional direction and the first direction is a sagittal direction). This application provides a laser receiving system, including: non-rotationally symmetrical mirror group 1, rotationally symmetrical mirror group 2 and detector 3, non-rotationally symmetrical mirror group 1, rotationally symmetrical mirror group 2 and detector 3 along the optical axis O The direction is sequentially set between the object side and the image side. Wherein, the non-rotationally symmetric lens group 1 may comprise at least one non-rotationally symmetric lens, and the rotationally symmetric lens group 2 may comprise at least one rotationally symmetric lens. A diffractive unit 4 with a two-dimensional distribution is provided (in FIG. 1a, the diffractive unit 4 is set on one lens in the non-rotationally symmetrical lens group 1 as an example), wherein the focal lengths of the laser receiving system in the first direction and the second direction are different , so that the laser receiving system is a non-equal receiving system; the first direction is any direction that passes through the optical axis O and extends in a plane perpendicular to the optical axis O, and the second direction is perpendicular to the optical axis O extends in a plane and is perpendicular to the first direction. Specifically, the effective focal length of the first direction of the non-rotationally symmetrical lens group 1 is different from the effective focal length of the second direction, which can ensure that the focal lengths of the first direction and the second direction of the laser receiving system are different, so that the laser receiving system is non-rotating. Equivalent receiving system; in addition, the non-rotationally symmetrical lens group 1 and the rotationally symmetrical lens group 2 are independent of each other, so that the laser receiving system can be designed in a modular manner, reducing the difficulty of assembling and testing the laser receiving system. And when the laser receiving system is working, the diffraction effect will occur when the light passes through the diffraction unit to achieve phase modulation, so that the two-dimensionally distributed diffraction unit can correct the aberration of the laser receiving system, thereby reducing the total length of the laser receiving system to achieve laser receiving. System miniaturization.

Wherein, the two-dimensionally distributed diffractive units, that is, the diffractive units are arranged in a plane, and the diffractive units are formed on the object side or image side of at least one of the non-rotationally symmetric lens and the rotationally symmetric lens by micro-nano etching process.

In order to ensure the miniaturization of the laser receiving system, the laser receiving system can meet the following conditions:

TTL/ _EFFLx≤2.0 ; | _EFFLx1 / _EFFLx |≥10;

Among them, TTL is the length of a plurality of non-rotationally symmetrical lenses on the optical axis from the end away from the detector 3 to the side of the image, EFFL _x is the effective focal length of the laser receiving system in the second direction, and EFFL _x 1 is the non-rotationally symmetrical lens group 1 The effective focal length of the receiving laser system in the second direction.

In a possible embodiment, in order to increase the receiving aperture of the laser receiving system and enable the laser receiving system to receive more signals, the laser receiving system can also meet the following conditional formula: 0.2≤EPD _x /EPD _y≤5 ; where , EPD _x is the diameter of the entrance pupil of the laser receiving system in the second direction, EPD _y is the diameter of the entrance pupil of the laser receiving system in the first direction, where the entrance pupil is the effective aperture that limits the incident beam.

In a possible embodiment, the laser receiving system may also meet the following conditional formula: IH _y /EFFL _y ≥ 0.1; wherein, IH _y is the effective height of the laser receiving system in the first direction, which is actually the detection EFFL _y is the effective focal length of the laser receiving system in the first direction. When the laser receiving system meets the conditional expression, the field of view received by the laser receiving system can be improved, thereby improving the field of view of the radar with the laser receiving system.

In a possible embodiment, the laser receiving system can also meet the following conditional formula: EFFL _x /EFFL _y ≥ 1.2; wherein, EFFL _x is the effective focal length of the laser receiving system in the second direction, and EFFL _y is the laser receiving system in The effective focal length in the first direction, so that the laser receiving system is a non-equal receiving system.

In the above-mentioned embodiment, in order to ensure the miniaturization of the laser receiving system, the period of the diffraction unit 4 can meet 500 nm-20 μm, and the aspect ratio of the diffraction unit 4 can meet 1:1-1:5. Specifically, the aspect ratio of the diffraction unit 4 may be 1:1.5, 1:1.8, 1:2.5, 1:3, or 1:4.5. In addition, the diffraction unit 4 may include a plurality of sub-diffraction units 40 arranged along the first direction, the period of the diffraction unit 4 is the distance between the ends of the sub-diffraction units 40, and the aspect ratio of the diffraction unit 4 is the 40 The ratio of the height along the second direction to the width along the first direction.

In the above embodiment, a diaphragm 5 may also be provided between the non-rotationally symmetrical lens group 1 and the rotationally symmetrical lens group 2 . And the aperture 5 can be a square aperture, because the aperture of the square aperture 5 is larger than the aperture of the circular aperture, it can make the laser receiving system receive more signals, and then improve the measurement of the radar with the laser receiving system. distance ability. In addition, the laser receiving system may further include a protective glass 6 , and the protective glass 6 may be disposed between the third aspheric mirror 22 and the detector 3 .

In the above-mentioned embodiments, the non-rotationally symmetrical lens group 1 includes a plurality of non-rotationally symmetrical lenses arranged at intervals, and the non-rotationally symmetrical lenses may specifically be cylindrical lenses, optical filters, etc. It may include a plurality of first cylindrical lenses 10 , optical filters 11 and second cylindrical lenses 12 arranged at intervals in sequence. The rotationally symmetric lens can specifically be an aspheric mirror. As another example, the rotationally symmetric lens group 2 can include a plurality of first aspheric mirrors 20, second aspherical mirrors 21, and third aspherical mirrors 22 arranged at intervals in sequence. The diffraction unit 4 can be provided with On the image side or object side of any one of the first cylindrical lens 10 , the optical filter 11 , the second cylindrical lens 12 , the first aspheric mirror 20 , the second aspheric mirror 21 and the third aspheric mirror 22 . By making the laser receiving system a non-uniform receiving system, the miniaturization of the laser receiving system can also be ensured.

In the above embodiments, the number of non-rotationally symmetrical lenses may be 2-4, and the number of rotationally symmetrical lenses may be 3-6, which is not limited in the present application.

The specific setting position of the diffraction unit 4 is described in detail below:

Example 1

1a and 1b, the laser receiving system in the first embodiment includes a first cylindrical lens 10, a filter 11, a second cylindrical lens 12, an aperture 5, a first non- Spherical mirror 20, second aspheric mirror 21, third aspheric mirror 22, protective glass 6 and detector 3; Wherein, the diffraction unit 4 of two-dimensional distribution can be arranged on the object side of the first cylindrical mirror 10; Specifically, laser receiving The effective focal length of the system in the second direction EFFL _x can be 39mm, the effective focal length of the laser receiving system in the first direction EFFL _y can be 13mm, the effective focal length of the laser receiving system in the first direction and the effective focal length of the laser receiving system in the second direction The ratio of the focal length can be EFFL _y : EFFL _x =1:3; the total length TTL of the laser receiving system can be 60mm, and the ratio of the total length TTL of the laser receiving system to the effective focal length of the laser receiving system in the second direction EFFL _x can be TTL: EFFL _x = 1.49:1; the entrance pupil diameter EPD _y of the laser receiving system in the first direction can be 12.8mm, the entrance pupil diameter EPD _x of the laser receiving system in the second direction can be 8mm, the laser receiving system can be in the first direction The ratio of the entrance pupil diameter EPD _y in one direction to the entrance pupil diameter EPD _x of the laser receiving system in the second direction may be 1:1.6.

From the object side to the image side, the object side of the first cylindrical mirror 10 is R1, the image side is R2, and so on, the object side and the image side of the second cylindrical mirror 12 to the protective glass 6 are R3, R4, R5 respectively , R6, STOP (stop 5), R7, R8, R9, R10, R11, R12, R13 and R14, and the radius of curvature, center thickness, refractive index and Abbe number of each lens can be shown in Table 1, should It is understood that Table 1 is only an illustration, and does not specifically limit the scope of protection of the claims of the present application:

Table 1

The lenses in the rotationally symmetrical lens group 2 in this embodiment are aspheric lenses, and the aspheric lenses can meet the following formula requirements:

Among them, c=1/R, that is, the curvature corresponding to the radius of curvature, r is the distance from any point on the object side or image side of any lens to the optical axis; z represents the sagittal height of the point along the direction of the optical axis, k is the Surface quadratic coefficients; a4, a6, a8, a10, a12, a14, a16, a18, a20, a22 are aspherical coefficients, each data can be referred to as shown in Table 2 below.

Table 2

In this embodiment, the diffraction surface data are as follows, wherein the maximum aspect ratio of the diffraction unit 4 can be about 1:1.39, the diffraction unit 4 can include a plurality of sub-diffraction units 40 arranged along the first direction, and the depth of the diffraction unit 4 is The aspect ratio is the ratio of the height of each sub-diffraction unit 40 along the second direction to the width along the first direction. The diffraction surface of the diffraction unit 4 may conform to the following polynomial:

φ(r)＝(2π/m/λ ₀ )ΣCnr ²ⁿ ;

Wherein, φ(r) is the phase function of the diffraction unit 4, r is the radial distance from the optical axis, and _λ0 is the reference wavelength, that is to say, the diffraction surface is formed by adding the curve of the phase function to the lens surface. The design parameters of the diffractive surface are shown in the following table, where C2-C4 respectively represent the coefficient values of the second-order term and the fourth-order term of the diffractive surface polynomial, and the diffraction order represents the m in the diffractive surface polynomial. Refer to Table 3 for details:

table 3

Reference wavelength λ ₀ 905nm Diffraction order/m 1 C2 -1.792E-3 C4 -1.435E-4

The optical system of this embodiment, the modulation transfer function (mTF through focus, MTF for short) of light on different defocused image planes, refer to Figure 3, wherein, F1～F5 are under different market angles, and the dotted line represents the MTF of the second direction , the solid line represents the MTF in the first direction, the abscissa represents different defocus positions, the unit is mm, and the vertical direction represents the MTF. According to Figure 3, it can be seen that all kinds of aberrations of the laser receiving system are well corrected, that is, when the abscissa is zero, the MTFs in the first direction and the second direction are close to their respective difference limits.

Example 2

4a and 4b, the laser receiving system in the second embodiment includes a first cylindrical lens 10, a filter 11, a second cylindrical lens 12, an aperture 5, a first non- Spherical mirror 20, the second aspheric mirror 21, the third aspheric mirror 22, protective glass 6 and detector 3; Wherein, the diffraction unit 4 of two-dimensional distribution can be arranged on the object side of optical filter 11; Specifically, laser receiving system is in The effective focal length of the second direction EFFL _x can be 39mm, the effective focal length of the laser receiving system in the first direction EFFL _y can be 13mm, the effective focal length of the laser receiving system in the first direction and the effective focal length of the laser receiving system in the second direction The ratio can be EFFL _y : EFFL _x =1:3; the total length TTL of the laser receiving system can be 60 mm, and the ratio of the total length TTL of the laser receiving system to the effective focal length of the laser receiving system in the second direction EFFL _x can be TTL: EFFL _x = 1.49:1; the entrance pupil diameter EPD _y of the laser receiving system in the first direction can be 12.8mm, the entrance pupil diameter EPD _x of the laser receiving system in the second direction can be 8mm, the laser receiving system in the first direction The ratio of the entrance pupil diameter EPD _y to the entrance pupil diameter EPD _x of the laser receiving system in the second direction may be 1:1.6.

From the object side to the image side, the object side of the first cylindrical mirror 10 is R1, the image side is R2, and so on, and the second cylindrical mirror 12 to the protective glass are respectively R3, R4, R5, R6, STOP (stop ), R7, R8, R9, R10, R11, R12, R13 and R14, and the radius of curvature, central thickness, refractive index and Abbe number of each lens can be shown in Table 4, it should be understood that Table 4 is only exemplary Explanation, without any specific limitation on the protection scope of the claims of this application:

Table 4

The lenses in the rotationally symmetrical lens group 2 in this embodiment are aspheric lenses, and the aspheric lenses may conform to the following formula:

Among them, c=1/R, that is, the curvature corresponding to the radius of curvature, r is the distance from any point on the object side or image side of any lens to the optical axis; z represents the sagittal height of the point along the direction of the optical axis, k is the Surface quadratic coefficients; a4, a6, a8, a10, a12, a14, a16, a18, a20, a22 are aspheric coefficients, and the data can be referred to in Table 5 below.

table 5

In this embodiment, the diffraction surface data are as follows. The maximum aspect ratio of the diffraction unit 4 can be about 1:1.56. The diffraction unit 4 can include a plurality of sub-diffraction units 40 arranged along the first direction. The aspect ratio of the diffraction unit 4 is That is, it is the ratio of the height of each sub-diffraction unit 40 along the second direction to the width along the first direction. The diffraction surface of the diffraction unit 4 may conform to the following polynomial:

φ(r)＝(2π/m/λ ₀ )ΣCnr ²ⁿ ;

Wherein, φ(r) is the phase function of the diffraction unit 4, r is the radial distance from the optical axis, and _λ0 is the reference wavelength, that is to say, the diffraction surface is formed by adding the curve of the phase function to the lens surface. The design parameters of the diffractive surface are shown in the table below, where C2-C4 represent the coefficient values of the second-order term and the fourth-order term of the diffractive surface polynomial, respectively, and the diffraction order represents m in the diffractive surface polynomial. Refer to Table 6 for details:

Table 6

Reference wavelength λ ₀ 905nm Diffraction order/m 1 C2 -1.62E-3 C4 -1.37E-4

The optical system of this embodiment, the modulation transfer function (mTF through focus, MTF for short) of light on different defocused image planes, refer to Figure 5, wherein, F1～F5 are under different market angles, and the dotted line represents the MTF of the second direction , the solid line represents the MTF in the first direction, the abscissa represents different defocus positions, the unit is mm, and the vertical direction represents the MTF. According to Fig. 5, it can be seen that all kinds of aberrations of the laser receiving system are well corrected, that is, when the abscissa is zero, the MTFs in the first direction and the second direction are close to their respective difference limits.

Example 3

6a and 6b, the laser receiving system in the third embodiment includes a first cylindrical lens 10, a filter 11, a second cylindrical lens 12, an aperture 5, a first non- Spherical mirror 20, second aspheric mirror 21, third aspheric mirror 22, protective glass 6 and detector 3; wherein, the diffraction unit 4 of two-dimensional distribution can be arranged on the object side of the first aspheric mirror 20; Specifically, the laser receiving system The effective focal length of _EFFLx in the second direction can be 39mm, the effective focal length of the laser receiving system in the first direction EFFLy can be 13mm, the effective focal length of the laser receiving system in the first direction and the effective focal length of the laser receiving system in the second direction The ratio can be EFFL _y : EFFL _x =1:3; the total length TTL of the laser receiving system can be 60 mm, and the ratio of the total length TTL of the laser receiving system to the effective focal length of the laser receiving system in the second direction EFFL _x can be TTL: EFFL _x = 1.49:1; the entrance pupil diameter EPD _y of the laser receiving system in the first direction can be 12.8mm, the entrance pupil diameter EPD _x of the laser receiving system in the second direction can be 8mm, the laser receiving system in the first direction The ratio of the entrance pupil diameter EPD _y to the entrance pupil diameter EPD _x of the laser receiving system in the second direction is 1:1.6.

From the object side to the image side, the object side of the first cylindrical mirror 10 is R1, the image side is R2, and so on, and the second cylindrical mirror 12 to the protective glass are respectively R3, R4, R5, R6, STOP (stop ), R7, R8, R9, R10, R11, R12, R13 and R14, and the radius of curvature, central thickness, refractive index and Abbe number of each lens can be shown in Table 7: It should be understood that Table 7 is only exemplary Explanation, without any specific limitation on the protection scope of the claims of this application:

Table 7

The lenses in the rotationally symmetrical lens group 2 in this embodiment are aspheric lenses, and the aspheric lenses can meet the following formula requirements:

Among them, c=1/R, that is, the curvature corresponding to the radius of curvature, r is the distance from any point on the object side or image side of any lens to the optical axis; z represents the sagittal height of the point along the direction of the optical axis, k is the Surface quadratic coefficients; a4, a6, a8, a10, a12, a14, a16, a18, a20, a22 are aspherical coefficients, and the data can be referred to in Table 8 below.

Table 8

In this embodiment, the diffraction surface data are as follows. The maximum aspect ratio of the diffraction unit 4 can be about 1:1.32. The diffraction unit 4 can include a plurality of sub-diffraction units 40 arranged along the first direction. The aspect ratio of the diffraction unit 4 is That is, it is the ratio of the height of each sub-diffraction unit 40 along the second direction to the width along the first direction. The diffraction surface of the diffraction unit 4 may conform to the following polynomial:

φ(r)＝(2π/m/λ ₀ )ΣCnr ²ⁿ ;

Wherein, φ(r) is the phase function of the diffraction unit 4, r is the radial distance from the optical axis, and _λ0 is the reference wavelength, that is to say, the diffraction surface is formed by adding the curve of the phase function to the lens surface. The design parameters of the diffractive surface are shown in the following table, where C2-C4 respectively represent the coefficient values of the second-order item and the fourth-order item of the diffractive surface polynomial, and the diffraction order represents the m in the diffractive surface polynomial. For details, refer to Table 9:

Table 9

Reference wavelength λ ₀ 905nm Diffraction order/m 1 C2 -1.34E-3 C4 -5.2E-4

The optical system of this embodiment, the modulation transfer function (mTF through focus, MTF for short) of light on different defocused image planes, referring to Figure 7, wherein, F1-F5 are different market angles, and the dotted line represents the MTF of the second direction , the solid line represents the MTF in the first direction, the abscissa represents different defocus positions, the unit is mm, and the vertical direction represents the MTF. According to Fig. 7, it can be seen that all kinds of aberrations of the laser receiving system are well corrected, that is, when the abscissa is zero, the MTFs in the first direction and the second direction are close to their respective difference limits.

The present application also provides a laser radar, including the laser receiving system in any of the above-mentioned technical solutions of the laser transmitting system. Since the total length of the laser receiving system is relatively small, the space occupied by the laser receiving system is relatively small. Conducive to the miniaturization of lidar. The above is only the specific implementation of the application, but the scope of protection of the application is not limited thereto. Anyone familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the application, and should cover Within the protection scope of this application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims (14)

1. A laser receiving system, characterized in that, comprising: a non-rotationally symmetrical lens group, a rotationally symmetrical lens group and a detector arranged sequentially from the object side to the image side along the optical axis direction, wherein: The set of non-rotationally symmetric lenses includes at least one non-rotationally symmetric lens; The set of rotationally symmetric lenses includes at least one rotationally symmetric lens; The object side or the image side of at least one of the non-rotationally symmetric lens and the rotationally symmetric lens has two-dimensionally distributed diffraction units; Wherein, the focal lengths of the laser receiving system in the first direction and the second direction are different, the first direction is any direction passing through the optical axis and extending in a plane perpendicular to the optical axis, and the second The two directions are directions extending in a plane perpendicular to the optical axis and perpendicular to the first direction. 2 . The laser receiving system according to claim 1 , wherein the period of the diffraction unit satisfies 500 nm-20 μm, and the aspect ratio of the diffraction unit satisfies 1:1-1:5. 3. The laser receiving system according to claim 1 or 2, wherein the diffraction unit comprises a plurality of sub-diffraction units arranged in sequence along the first direction. 4. The laser receiving system according to any one of claims 1 to 3, characterized in that, From the object side to the image side along the optical axis, the non-rotationally symmetrical lens group includes a first cylindrical lens, a filter, and a second cylindrical lens arranged at intervals in sequence; From the object side to the image side along the optical axis, the rotationally symmetrical lens group includes a first aspherical mirror, a second aspherical mirror and a third aspherical mirror arranged at intervals in sequence; The diffraction unit is arranged on the object side or image side of at least one of the first cylindrical mirror, the filter and the second cylindrical mirror; and/or, the diffraction unit is arranged on the first An object side or an image side of at least one of an aspheric mirror, the second aspheric mirror and the third aspheric mirror. 5. The laser receiving system according to claim 4, further comprising a protective glass disposed between the third aspheric mirror and the detector. 6. The laser receiving system according to any one of claims 1 to 5, wherein the laser receiving system meets the following conditional formula: TTL/ _EFFLx≤2.0 ; Wherein, the TTL is the length on the optical axis from the end of the non-rotationally symmetrical lens group away from the detector to the image side, and the EFFL _x is the length of the laser receiving system in the second direction effective focal length. 7. The laser receiving system according to any one of claims 1 to 5, wherein the laser receiving system meets the following conditional formula: |EFFL _x 1/EFFL _x |≥10; Wherein, the EFFL _x 1 is the effective focal length of the non-rotationally symmetrical lens group in the first direction, and the EFFL _x is the effective focal length of the laser receiving system in the second direction. 8. The laser receiving system according to any one of claims 1 to 5, wherein the laser receiving system meets the following conditional formula; _EFFLx / _EFFLy≥1.2 ; Wherein, the EFFL _x is the effective focal length of the laser receiving system in the second direction, and the EFFL _y is the effective focal length of the laser receiving system in the first direction. 9. The laser receiving system according to any one of claims 1 to 5, wherein the laser receiving system meets the following conditional formula; _0.2≤EPDx / _EPDy≤5 ; Wherein, the EPD _x is an entrance pupil diameter of the laser receiving system in the second direction, and the EPD _y is an entrance pupil diameter of the laser receiving system in the first direction. 10. The laser receiving system according to any one of claims 1 to 5, characterized in that, the laser receiving system meets the following conditional formula; IH _y /EFFL _y ≥ 0.1; Wherein, the IH _y is the effective height of the laser receiving system in the first direction, and the EFFL _y is the effective focal length of the laser receiving system in the first direction. 11. The laser receiving system according to any one of claims 1-10, characterized in that a diaphragm is further arranged between the non-rotationally symmetrical lens group and the rotationally symmetrical lens group. 12. The laser receiving system according to claim 11, wherein the aperture is a square aperture. 13. The laser receiving system according to any one of claims 1 to 12, wherein the diffraction unit is formed on at least one of the non-rotationally symmetric lens and the rotationally symmetric lens through a micro-nano etching process The object or image side of the lens. 14. A laser radar, characterized by comprising a laser emitting system and a laser receiving system according to any one of claims 1-13.