CN116559843A

CN116559843A - Laser receiving system and laser radar

Info

Publication number: CN116559843A
Application number: CN202210104875.0A
Authority: CN
Inventors: 徐运强; 周勇; 李鑫; 王晓芳
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2022-01-28
Filing date: 2022-01-28
Publication date: 2023-08-08

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

Background

The receiving system in the laser radar can be divided into an equal ratio receiving system and an unequal ratio receiving system according to the focal length ratio of meridian and sagittal directions; wherein, the equal ratio receiving system means that the meridian and the sagittal focal length of the system are equal; the anisometric receiving system refers to the fact that meridian and sagittal focal lengths are unequal. The anisometric receiving system breaks the limit that the transverse and longitudinal focal lengths of the traditional anisometric receiving system are consistent, so that the focal length in the sagittal direction can be larger than the focal length in the meridian direction, and further the detector in the laser radar receiving system is not over-exploded under high energy, so that the dynamic range of the laser radar receiving system is increased.

However, since the total length of the anisometric receiving system in the prior art is long, the laser radar has a large space occupied by the laser receiving system, and therefore, how to miniaturize the anisometric receiving system is a problem to be solved.

Disclosure of Invention

The application provides a laser receiving system and laser radar, this laser receiving system's overall length is less to make when laser receiving system is applied to in the laser radar, the space that the laser radar occupy is less, is favorable to the miniaturization of laser radar.

In a first aspect, there is provided a laser light receiving system comprising: the optical system comprises an asymmetric lens group, a rotational symmetric lens group and a detector, wherein the asymmetric lens group, the rotational symmetric lens group and the detector are sequentially arranged from an object side surface to an image side surface along the optical axis direction, the asymmetric lens group can comprise at least one asymmetric lens, the rotational symmetric lens group can comprise at least one rotationally symmetric lens, the object side surface or the image side surface of at least one lens in the asymmetric lens and the plurality of rotationally symmetric lenses is provided with diffraction units distributed in two dimensions, and the focal lengths of a laser receiving system in a first direction and a second direction are different, so that the laser receiving system is an anisometric receiving system, the first direction is any direction which passes through the optical axis and extends in a plane perpendicular to the optical axis, and the second direction is a direction which extends in the plane perpendicular to the optical axis and is orthogonal to the first direction. Specifically, as the light passes through the diffraction unit to generate diffraction effect, the phase modulation is realized, so that the diffraction unit with two-dimensional distribution can correct the aberration of the laser receiving system, and the total length of the laser receiving system is reduced, thereby realizing the miniaturization of the laser receiving system.

The diffraction units distributed in two dimensions, i.e., diffraction units, are disposed in a plane, and the diffraction units are formed on an object side surface or an image side surface of at least one of the non-rotationally symmetrical lens and the rotationally symmetrical lens by a micro-nano etching process. The number of the non-rotationally symmetrical lenses can be 2-4, and the number of the rotationally symmetrical lenses can be 3-6. The object side surface is one end of the laser receiving system, which is close to the object to be measured, and the image side surface is one end of the laser receiving system, which is far away from the object to be measured.

The rotationally symmetrical lens is a graph which has a symmetrical center and can be overlapped with the original graph after rotating around the symmetrical center by a certain angle.

In one possible embodiment, to achieve miniaturization of the laser receiving system, the laser receiving system may conform to the following conditional expression: TTL/EFFL _x Less than or equal to 2.0; wherein TTL is the length of the non-rotationally symmetrical lens group on the optical axis from the end far from the detector to the image side, i.e. the length of the non-rotationally symmetrical lens furthest from the detector on the optical axis from the end far from the detector to the image side, EFFL _x Is the effective focal length of the laser receiving system in the second direction.

In another possible embodiment, in order to achieve miniaturization of the laser receiving system, the laser receiving system may further conform to the following conditional expression: EFFL (electronic file format) _x 1/EFFL _x The I is more than or equal to 10; wherein EFFL is _x 1 is the effective focal length of the non-rotationally symmetric lens group in the second direction, EFFL _x Is the effective focal length of the laser receiving system in the second direction.

In still another possible embodiment, in order to achieve miniaturization of the laser receiving system, the laser receiving system may further conform to the following conditional expression: EPD of 0.2 +. _x EPDy is less than or equal to 5; wherein EPD is _x For the entrance pupil diameter of the laser receiving system in the second direction, EPD _y Is the entrance pupil diameter of the laser receiving system in the first direction. Thus, the receiving caliber of the laser receiving system can be larger, and more signals can be received advantageously. Wherein the entrance pupil isLimiting the effective aperture of the incident beam.

In still another possible embodiment, in order to increase the angle of view that the laser receiving system can receive, the laser receiving system may further conform to the following conditional expression; IH (IH) _y /EFFL _y More than or equal to 0.1; wherein IH _y For the effective height of the laser receiving system in the first direction, EFFL _y Is the effective focal length of the laser receiving system in the first direction.

In the above-described embodiment, in order to ensure miniaturization of the laser receiving system, the period of the diffraction unit may satisfy 500nm to 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 disposed sequentially in the first direction.

The non-rotationally symmetrical lens group comprises a first cylindrical lens, an optical filter and a second cylindrical lens which are sequentially arranged at intervals along the optical axis direction from the object side surface to the image side surface; the rotationally symmetrical lens group comprises a plurality of rotationally symmetrical lenses which are arranged at intervals along the optical axis direction from the object side surface to the image side surface, and specifically comprises: the rotationally symmetrical lens group comprises a first aspheric mirror, a second aspheric mirror and a third aspheric mirror which are sequentially arranged at intervals; in order to miniaturize the laser light receiving system, the diffraction unit may be provided on the object side surface or the image side surface of at least one of the first cylindrical mirror, the optical filter, and the second cylindrical mirror, and/or the diffraction unit may be provided on the object side surface or the image side surface of at least one of the first aspherical mirror, the second aspherical mirror, and the third aspherical mirror.

In one possible embodiment, in order to make the laser receiving system an anisometric receiving system, the laser receiving system may also conform to the following conditional expression; EFFL (electronic file format) _x /EFFL _y Not less than 1.2; wherein EFFL is _x EFFL is the effective focal length of the laser receiving system in the second direction _y Is the effective focal length of the laser receiving system in the first direction.

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

In the above embodiment, the laser receiving system may further include a cover glass, and the cover glass may be disposed between the third aspherical mirror and the detector.

In the above embodiment, the object-side paraxial region of the first aspherical mirror may be convex, and the image-side paraxial region of the first aspherical mirror may be concave; the object-side paraxial region of the second aspherical mirror may be concave, the image-side paraxial region of the second aspherical mirror may be convex, the object-side paraxial region of the third aspherical mirror may be convex, and the image-side paraxial region of the third aspherical mirror may be concave.

In a second aspect, the present application further provides a laser radar, including a laser emission system and a laser receiving system in any one of the above first aspects, where the total length of the laser receiving system is smaller, so that the space occupied by the laser radar with the laser receiving system is smaller, which is beneficial to miniaturization of the laser radar.

Drawings

Fig. 1a is a schematic structural diagram of a laser receiving system according to an embodiment of the present application;

fig. 1b is a schematic structural diagram of a laser receiving system according to an embodiment of the present application;

fig. 2 is a schematic structural diagram of a diffraction unit in the laser receiving system according to the embodiment of the present application;

fig. 3 is a simulation diagram of a laser receiving system according to an embodiment of the present application;

fig. 4a is a schematic structural diagram of a laser receiving system according to an embodiment of the present application;

fig. 4b is a schematic structural diagram of a laser receiving system according to an embodiment of the present disclosure;

fig. 5 is a further simulation diagram of the laser receiving system provided in the embodiment of the present application;

fig. 6a is a schematic structural diagram of a laser receiving system according to an embodiment of the present disclosure;

fig. 6b is a schematic structural diagram of a laser receiving system according to an embodiment of the present disclosure;

fig. 7 is a simulation diagram of a laser receiving system according to an embodiment of the present application.

Reference numerals:

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

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the present application more apparent, the present application will be described in further detail with reference to the accompanying drawings.

When the laser radar detects, the laser emission system and the laser receiving system of the laser radar work, wherein a pulse signal or a modulated signal emitted by the laser emission system is reflected by a detected object and then is detected by the laser receiving system, so that the distance of the object is detected. The laser receiving system is generally used as an important component of the laser radar, and can directly influence the energy received by the laser radar and the quality of point cloud, so as to influence the ranging capability of the laser radar. Because the receiving view angle of the laser radar receiving system is fixed, the larger the focal length in the sagittal direction is, the larger the light spot size formed by the light beam received by the optical receiving system on the image surface is, and the larger the light spot size is, the smaller the energy allocated by the detector is, and the detector is not over-exploded under high energy, so that the dynamic range of the laser radar receiving system is increased.

In order to increase the dynamic range of the laser receiving system in the laser radar, the focal length in the sagittal direction of the laser receiving system in the laser radar is generally larger than the focal length in the meridional direction, however, this results in that the total length of the laser receiving system in the laser radar is larger, and the caliber of the first lens in the laser receiving system in the laser radar is larger, thereby resulting in that the size of the laser receiving system in the laser radar is larger.

In order to reduce the size of the laser receiving system in the laser radar, the number of lenses in the laser receiving system is generally increased and a rotating aspheric lens is used in the prior art, however, due to the limitation of factors such as system aberration, there is a limit to increasing the number of lenses and correcting the laser receiving system in the laser radar by using the aspheric lens, and increasing the lenses and using the aspheric lens not only increases the cost of the laser receiving system in the laser radar, but also increases the complexity of assembling the laser receiving system in the laser radar.

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

The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the specification and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include, for example, "one or more" such forms of expression, unless the context clearly indicates to the contrary.

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

Referring to fig. 1a, 1b and 2, the first direction may be a direction indicated by a solid arrow, the second direction may be a direction indicated by a dotted arrow in the drawing, and the first direction may be a meridian direction or a sagittal direction, and the second direction may be a direction perpendicular to the first direction (i.e., the first direction is a meridian direction, the second direction is a sagittal direction, or the second direction is a meridian direction, the first direction is a sagittal direction). The application provides a laser receiving system, which comprises: the non-rotationally symmetrical lens group 1, the rotationally symmetrical lens group 2 and the detector 3 are sequentially arranged between the object side surface and the image side surface along the optical axis O direction. Wherein the non-rotationally symmetric lens group 1 may include at least one non-rotationally symmetric lens, the rotationally symmetric lens group 2 may include at least one rotationally symmetric lens, and in the non-rotationally symmetric lens and the rotationally symmetric lens, an object side surface or an image side surface of the at least one lens is provided with two-dimensional distributed diffraction units 4 (in fig. 1a, taking the diffraction units 4 as an example provided on one lens in the non-rotationally symmetric lens group 1), wherein 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 an arbitrary direction passing through the optical axis O and extending in a plane perpendicular to the optical axis O, and the second direction is a direction extending in a plane perpendicular to the optical axis O and orthogonal to the first direction. Specifically, the effective focal length of the non-rotationally symmetrical lens group 1 in the first direction is different from the effective focal length of the non-rotationally symmetrical lens group in the second direction, so that the focal lengths of the laser receiving system in the first direction and the laser receiving system in the second direction are different, and the laser receiving system is a non-equal ratio receiving system; in addition, the non-rotationally symmetrical lens group 1 and the rotationally symmetrical lens group 2 are mutually independent, so that the laser receiving system can be in a modularized design, and the difficulty in assembling and testing the laser receiving system is reduced. When the laser receiving system works, light can generate diffraction effect through the diffraction units to realize phase modulation, so that the diffraction units distributed in two dimensions can correct the aberration of the laser receiving system, and further the total length of the laser receiving system is reduced, and the miniaturization of the laser receiving system is realized.

The diffraction units are arranged in a plane, and the diffraction units are formed on the object side surface or the image side surface of at least one of the non-rotationally symmetrical lens and the rotationally symmetrical lens through a micro-nano etching process.

In order to ensure miniaturization of the laser receiving system, the laser receiving system may conform to the following conditional expression:

TTL/EFFL _x ≤2.0；|EFFL _x 1/EFFL _x |≥10；

wherein TTL is the length of the multiple non-rotationally symmetrical lenses on the optical axis from one end of the detector 3 to the image side, EFFL _x EFFL is the effective focal length of the laser receiving system in the second direction _x 1 is the effective focal length of the non-rotationally symmetric lens group 1 in the second direction of the laser receiving system.

In one possible embodiment, in order to increase the receiving caliber of the laser receiving system, so that the laser receiving system can receive more signals, the laser receiving system may further meet the following conditional expression: EPD of 0.2 +. _x /EPD _y Less than or equal to 5; wherein EPD is _x For the entrance pupil diameter of the laser receiving system in the second direction, EPD _y Is the entrance pupil diameter of the laser receiving system in the first direction, wherein the entrance pupil is the effective aperture that limits the incident beam.

In one possible embodiment, the laser receiving system may further satisfy the following conditional expression: IH (IH) _y /EFFL _y More than or equal to 0.1; wherein IH _y For the effective height of the laser receiving system in the first direction, which is actually the height above the detector 3, 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 angle of view received by the laser receiving system can be improved, and the field of view of the radar with the laser receiving system is further improved.

In one possible embodiment, the laser receiving system may also conform to the following conditional expression; EFFL (electronic file format) _x /EFFL _y Not less than 1.2; wherein EFFL is _x EFFL is the effective focal length of the laser receiving system in the second direction _y The effective focal length of the laser receiving system in the first direction is set so that the laser receiving system is an anisometric receiving system.

In the above-described embodiment, in order to ensure miniaturization of the laser light receiving system, the period of the diffraction unit 4 may expire to be 500nm to 20 μm, and the aspect ratio of the diffraction unit 4 may satisfy 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, etc. In addition, the diffraction unit 4 may include a plurality of sub-diffraction units 40 disposed 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 ratio of the height of each sub-diffraction unit 40 along the second direction to the width along the first direction.

In the above embodiment, the 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, and as the aperture of the square aperture 5 is larger than that of the circular aperture, the laser receiving system can receive more signals, so that the range finding capability of the radar with the laser receiving system is improved. In addition, the laser light receiving system may further include a cover glass 6, and the cover glass 6 may be disposed between the third aspherical mirror 22 and the detector 3.

In the above-described embodiment, the non-rotationally symmetrical lens group 1 includes a plurality of non-rotationally symmetrical lenses disposed at intervals, and the non-rotationally symmetrical lenses may be cylindrical lenses, optical filters, or the like, and the non-rotationally symmetrical lens group 1 may include a plurality of first cylindrical lenses 10, optical filters 11, and second cylindrical lenses 12 disposed at intervals in order, for example. The rotationally symmetric lens may specifically be an aspherical lens, and further exemplary, the rotationally symmetric lens group 2 may include a plurality of first, second and third aspherical lenses 20, 21 and 22 sequentially disposed at intervals, and the diffraction unit 4 may be disposed at an image side or an object side of any one of the first cylindrical lens 10, the optical filter 11, the second cylindrical lens 12, the first, second and third aspherical lenses 20, 21 and 22. So that the laser receiving system is an unequal ratio receiving system, and the miniaturization of the laser receiving system can be ensured.

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

The specific arrangement of the diffraction unit 4 will be described in detail below:

example 1

Referring to fig. 1a and 1b, the laser light receiving system in the first embodiment includes, in order from the object side to the image side, a first cylindrical mirror 10, an optical filter 11, a second cylindrical mirror 12, a diaphragm 5, a first aspherical mirror 20, a second aspherical mirror 21, a third aspherical mirror 22, a cover glass 6, and a detector 3; wherein the two-dimensionally distributed diffraction units 4 may be disposed at the object side of the first cylindrical mirror 10; specifically, the laser receiving system is in the second direction EFFL _x The effective focal length of (a) may be 39mm, the laser receiving system may be EFFL in a first direction _y The effective focal length of the laser receiving system in the first direction may be 13mm and the ratio of the effective focal length of the laser receiving system in the second direction may be EFFL _y ：EFFL _x =1:3; the total length TTL of the laser receiving system can be 60mm, and the total length TTL of the laser receiving system and the EFFL of the laser receiving system in the second direction _x The ratio of the effective focal lengths of (2) may be TTL: EFFL (electronic file format) _x =1.49:1; entrance pupil diameter EPD of laser receiving system in first direction _y May be 12.8mm, the entrance pupil diameter EPD of the laser receiving system in the second direction _x May be 8mm, the entrance pupil diameter EPD of the laser receiving system in the first direction _y Entrance pupil diameter EPD in a second direction with a laser receiving system _x May be 1:1.6.

From the object side surface to the image side surface, the object side surface of the first cylindrical lens 10 is R1, the image side surface is R2, and so on, the object side surface and the image side surface of the second cylindrical lens 12 to the protective glass 6 are R3, R4, R5, R6, STOP (diaphragm 5), R7, R8, R9, R10, R11, R12, R13, and R14, respectively, and the radius of curvature, center thickness, refractive index, and abbe number of each lens can be as shown in table 1, and it should be understood that table 1 is merely an exemplary illustration, and the scope of the claims of the present application is not specifically limited:

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:

wherein c=1/R, namely, the curvature corresponding to the curvature radius, and R is the distance from any point on the object side surface or the image side surface of any lens to the optical axis; z represents the sagittal height of the point along the optical axis, and k is the quadric surface coefficient of the surface; a4, a6, a8, a10, a12, a14, a16, a18, a20, a22 are aspherical coefficients, and each data can be referred to as table 2 below.

TABLE 2

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

φ(r)＝(2π/m/λ ₀ )ΣCnr ²ⁿ ；

wherein φ (r) is the phase function of the diffraction element 4, r is the radial distance from the optical axis, λ ₀ Is the reference wavelength, that is, the diffraction plane is formed as a curve of the lens surface plus a phase function. The design parameters of the diffraction surface are shown in the following table, wherein C2-C4 respectively represent the 2 nd order and 4 th order of the diffraction surface polynomialCoefficient values, diffraction orders represent m in the diffraction plane polynomial, refer specifically to table 3:

TABLE 3 Table 3

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

In the optical system of this embodiment, the modulation transfer function (mTF through focus, abbreviated as MTF) of light on different defocus image planes is shown in fig. 3, where F1 to F5 are different market angles, the dashed line represents the MTF in the second direction, the solid line represents the MTF in the first direction, the abscissa represents different defocus positions in mm, and the longitudinal direction represents the MTF. As can be seen from fig. 3, various aberrations of the laser receiving system are well corrected, i.e. when the abscissa is zero, the MTFs of the first and second directions are both close to the respective difference limits.

Example 2

Referring to fig. 4a and 4b, the laser light receiving system in the second embodiment includes, in order from the object side to the image side, a first cylindrical mirror 10, an optical filter 11, a second cylindrical mirror 12, a diaphragm 5, a first aspherical mirror 20, a second aspherical mirror 21, a third aspherical mirror 22, a cover glass 6, and a detector 3; wherein the two-dimensionally distributed diffraction units 4 may be disposed at the object side of the optical filter 11; specifically, the laser is connectedReceiving system in second direction EFFL _x The effective focal length of (a) may be 39mm, the laser receiving system may be EFFL in a first direction _y The effective focal length of the laser receiving system in the first direction may be 13mm and the ratio of the effective focal length of the laser receiving system in the second direction may be EFFL _y ：EFFL _x =1:3; the total length TTL of the laser receiving system can be 60mm, and the total length TTL of the laser receiving system and the EFFL of the laser receiving system in the second direction _x The ratio of the effective focal lengths of (2) may be TTL: EFFL (electronic file format) _x =1.49:1; entrance pupil diameter EPD of laser receiving system in first direction _y May be 12.8mm, the entrance pupil diameter EPD of the laser receiving system in the second direction _x May be 8mm, the entrance pupil diameter EPD of the laser receiving system in the first direction _y Entrance pupil diameter EPD in a second direction with a laser receiving system _x May be 1:1.6.

From the object side to the image side, the object side of the first cylindrical lens 10 is R1, the image side is R2, and so on, the second cylindrical lens 12 to the protective glass are R3, R4, R5, R6, STOP (diaphragm), R7, R8, R9, R10, R11, R12, R13, and R14, respectively, and the radius of curvature, center thickness, refractive index, and abbe number of each lens can be as shown in table 4, and it should be understood that table 4 is only an exemplary illustration, and the scope of the claims of the present application is not specifically limited:

TABLE 4 Table 4

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

wherein c=1/R, namely, the curvature corresponding to the curvature radius, and R is the distance from any point on the object side surface or the image side surface of any lens to the optical axis; z represents the sagittal height of the point along the optical axis, and k is the quadric surface coefficient of the surface; a4, a6, a8, a10, a12, a14, a16, a18, a20, a22 are aspherical coefficients, and each data can be referred to as table 5 below.

TABLE 5

In this embodiment, the diffraction surface data is as follows, and the maximum aspect ratio of the diffraction unit 4 may be about 1:1.56 the diffraction element 4 may comprise a plurality of sub-diffraction elements 40 arranged in a first direction, the aspect ratio of the diffraction element 4 being the ratio of the height of each sub-diffraction element 40 in the second direction to the width in the first direction. The diffraction surface of the diffraction unit 4 may conform to the polynomial:

φ(r)＝(2π/m/λ ₀ )ΣCnr ²ⁿ ；

wherein φ (r) is the phase function of the diffraction element 4, r is the radial distance from the optical axis, λ ₀ Is the reference wavelength, that is, the diffraction plane is formed as a curve of the lens surface plus a phase function. The diffraction surface design parameters are shown in the following table, wherein C2-C4 represent the 2 nd order and 4 th order coefficient values of the diffraction surface polynomial, respectively, and the diffraction order represents m in the diffraction surface polynomial, and refer to table 6 specifically:

TABLE 6

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

In the optical system of this embodiment, the modulation transfer function (mTF through focus, abbreviated as MTF) of light on different defocus image planes is shown in fig. 5, where F1 to F5 are different market angles, the dashed line represents the MTF in the second direction, the solid line represents the MTF in the first direction, the abscissa represents different defocus positions in mm, and the longitudinal direction represents the MTF. As can be seen from fig. 5, various aberrations of the laser receiving system are well corrected, i.e. when the abscissa is zero, the MTFs of the first and second directions are both close to the respective difference limits.

Example 3

Referring to fig. 6a and 6b, the laser light receiving system in the third embodiment includes, in order from the object side to the image side, a first cylindrical mirror 10, an optical filter 11, a second cylindrical mirror 12, a diaphragm 5, a first aspherical mirror 20, a second aspherical mirror 21, a third aspherical mirror 22, a cover glass 6, and a detector 3; wherein the two-dimensionally distributed diffraction units 4 may be disposed at the object side of the first aspherical mirror 20; specifically, the laser receiving system is in the second direction EFFL _x The effective focal length of the laser receiving system in the first direction EFFLy may be 39mm, and the ratio of the effective focal length of the laser receiving system in the first direction to the effective focal length of the laser receiving system in the second direction may be EFFL _y ：EFFL _x =1:3; the total length TTL of the laser receiving system can be 60mm, and the total length TTL of the laser receiving system and the EFFL of the laser receiving system in the second direction _x The ratio of the effective focal lengths of (2) may be TTL: EFFL (electronic file format) _x =1.49:1; entrance pupil diameter EPD of laser receiving system in first direction _y May be 12.8mm, the entrance pupil diameter EPD of the laser receiving system in the second direction _x May be 8mm, the entrance pupil of the laser receiving system in the first directionDiameter EPD _y Entrance pupil diameter EPD in a second direction with a laser receiving system _x The ratio of (2) is 1:1.6.

From the object side to the image side, the object side of the first cylindrical lens 10 is R1, the image side is R2, and so on, the second cylindrical lens 12 to the cover glass are R3, R4, R5, R6, STOP (diaphragm), R7, R8, R9, R10, R11, R12, R13, and R14, respectively, and the radius of curvature, center thickness, refractive index, and abbe number of each lens can be as shown in table 7: it is to be understood that table 7 is merely exemplary and is not intended to limit the scope of the claims of the present application in any way:

TABLE 7

wherein c=1/R, namely, the curvature corresponding to the curvature radius, and R is the distance from any point on the object side surface or the image side surface of any lens to the optical axis; z represents the sagittal height of the point along the optical axis, and k is the quadric surface coefficient of the surface; a4, a6, a8, a10, a12, a14, a16, a18, a20, a22 are aspherical coefficients, and each data can be referred to as table 8 below.

TABLE 8

In this embodiment, the diffraction surface data is as follows, the maximum aspect ratio of the diffraction unit 4 may be about 1:1.32, the diffraction unit 4 may include a plurality of sub-diffraction units 40 disposed along the first direction, and the aspect ratio of the diffraction unit 4 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 polynomial:

φ(r)＝(2π/m/λ ₀ )ΣCnr ²ⁿ ；

wherein φ (r) is the phase function of the diffraction element 4, r is the radial distance from the optical axis, λ ₀ Is the reference wavelength, that is, the diffraction plane is formed as a curve of the lens surface plus a phase function. The diffraction surface design parameters are shown in the following table, wherein C2-C4 represent the 2 nd order and 4 th order coefficient values of the diffraction surface polynomial, respectively, and the diffraction order represents m in the diffraction surface polynomial, and refer to table 9 specifically:

TABLE 9

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

In the optical system of this embodiment, the modulation transfer function (mTF through focus, abbreviated as MTF) of light on different defocus image planes is shown in fig. 7, where F1 to F5 are different market angles, the dashed line represents the MTF in the second direction, the solid line represents the MTF in the first direction, the abscissa represents different defocus positions in mm, and the longitudinal direction represents the MTF. As can be seen from fig. 7, various aberrations of the laser receiving system are well corrected, i.e. when the abscissa is zero, the MTFs of the first and second directions are both close to the respective difference limits.

The application also provides a laser radar, including the laser receiving system among the above-mentioned arbitrary technical scheme of laser emission system, because the overall length of laser receiving system is less to make the space that the laser radar who has this laser receiving system occupy less, be favorable to the miniaturization of laser radar. The foregoing is merely specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think about changes or substitutions within the technical scope of the present application, and the changes or substitutions are intended to be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A laser light receiving system, comprising: the optical axis direction is from object side to image side set gradually non-rotational symmetry lens group, rotational symmetry lens group and detector, wherein:

the non-rotationally symmetric lens group includes at least one non-rotationally symmetric 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 rotationally symmetric lenses has two-dimensionally distributed diffraction units;

the laser receiving system is characterized in that the focal length of the laser receiving system is different in a first direction and a second direction, the first direction is any direction passing through the optical axis and extending in a plane perpendicular to the optical axis, and the second direction is a direction extending in the plane perpendicular to the optical axis and orthogonal to the first direction.

2. The laser light receiving system according to claim 1, wherein a period of the diffraction unit satisfies 500nm to 20 μm, and an aspect ratio of the diffraction unit satisfies 1: 1-1:5.

3. The laser light receiving system according to claim 1 or 2, wherein the diffraction unit includes a plurality of sub-diffraction units arranged in order along the first direction.

4. A laser light receiving system according to any one of claims 1 to 3, wherein,

the non-rotationally symmetrical lens group comprises a first cylindrical lens, an optical filter and a second cylindrical lens which are sequentially arranged at intervals along the optical axis direction from the object side surface to the image side surface;

the rotationally symmetrical lens group comprises a first aspheric mirror, a second aspheric mirror and a third aspheric mirror which are sequentially arranged at intervals along the optical axis direction from the object side surface to the image side surface;

the diffraction unit is arranged on the object side surface or the image side surface of at least one of the first cylindrical mirror, the optical filter and the second cylindrical mirror; and/or the diffraction unit is arranged on the object side surface or the image side surface of at least one of the first aspheric mirror, the second aspheric mirror and the third aspheric mirror.

5. The laser light receiving system according to claim 4, further comprising a cover glass disposed between the third aspherical mirror and the detector.

6. The laser light receiving system according to any one of claims 1 to 5, wherein the laser light receiving system conforms to the following conditional expression:

TTL/EFFL _x ≤2.0；

wherein the TTL is the length of the end of the non-rotationally symmetrical lens group away from the detector to the image side surface on the optical axis, the EFFL _x An effective focal length of the laser receiving system in the second direction.

7. The laser light receiving system according to any one of claims 1 to 5, wherein the laser light receiving system conforms to the following conditional expression:

|EFFL _x 1/EFFL _x |≥10；

wherein the EFFL _x 1 is the effective focal length of the non-rotationally symmetric lens group in the first direction, the EFFL _x An effective focal length of the laser receiving system in the second direction.

8. The laser light receiving system according to any one of claims 1 to 5, wherein the laser light receiving system conforms to the following conditional expression;

EFFL _x /EFFL _y ≥1.2；

wherein the EFFL _x For an effective focal length of the laser receiving system in the second direction, the EFFL _y An effective focal length of the laser receiving system in the first direction.

9. The laser light receiving system according to any one of claims 1 to 5, wherein the laser light receiving system conforms to the following conditional expression;

0.2≤EPD _x /EPD _y ≤5；

wherein the EPD is _x For the entrance pupil diameter of the laser receiving system in the second direction, the EPD _y Is the entrance pupil diameter of the laser receiving system in the first direction.

10. The laser light receiving system according to any one of claims 1 to 5, wherein the laser light receiving system conforms to the following conditional expression;

IH _y /EFFL _y ≥0.1；

wherein the IH _y For the effective height of the laser receiving system in the first direction, the EFFL _y An effective focal length of the laser receiving system in the first direction.

11. The laser light receiving system according to any one of claims 1 to 10, wherein a diaphragm is further provided between the non-rotationally symmetrical lens group and the rotationally symmetrical lens group.

12. The laser light receiving system according to claim 11, wherein the diaphragm is a square diaphragm.

13. The laser light receiving system according to any one of claims 1 to 12, wherein the diffraction unit is formed on an object side surface or an image side surface of at least one of the non-rotationally symmetrical lens and the rotationally symmetrical lens by a micro-nano etching process.

14. A lidar comprising a laser emitting system and a laser receiving system according to any of claims 1 to 13.