CN111273261A - Coaxial transmitting and receiving laser radar based on off-axis incidence - Google Patents
Coaxial transmitting and receiving laser radar based on off-axis incidence Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/491—Details of non-pulse systems
- G01S7/4911—Transmitters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/491—Details of non-pulse systems
- G01S7/4912—Receivers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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Abstract
The invention discloses a coaxial transmitting and receiving laser radar based on off-axis incidence, which comprises a laser light source, a laser receiving unit and a laser receiving unit, wherein the laser light source is used for transmitting laser beams; a collimating unit for generating a collimated beam; the emission component is positioned in the emission light path and is used for enabling the collimated light beams to be incident into the projection unit; the polarization conversion unit is used for changing the polarization state of the light beam emitted from the polarization beam splitting unit, and the light beam with the changed polarization state enters the projection unit again; the reflector is used for changing the propagation direction angle of the linearly polarized light; the receiving component is positioned in the receiving light path and receives photons returned by the projection unit; the polarization conversion unit is used for changing the polarization state of the photons returned by the projection unit, the focusing unit converges the photons received by the receiving light path to the receiving end detector, and the optical filter filters interference photons in the photons returned by the projection unit; the projection unit is a micro-reflector driven based on MEMS or motor or other electronic modes; the invention provides a laser radar which is simple in structure, high in receiving efficiency and larger in scanning field of view.
Description
Technical Field
The invention relates to the technical field of laser radars, in particular to a coaxial transmitting and receiving laser radar based on off-axis incidence.
Background
In recent years, with the development of various new technologies such as artificial intelligence, internet of things, 5G technology and the like, the gradual breakthrough of material technology and the like, the development of laser radars suitable for various applications such as automatic driving, three-dimensional mapping, security monitoring and the like is trendy. The laser radar is provided with intelligent eyes for sensing application of various artificial intelligence to various surrounding environments by virtue of high resolution, excellent anti-interference capability and all-weather continuous work; and then, the automatic driving of L3 and above is really realized in the field of automatic driving by matching with a logic control algorithm, the laser radar is a visual sensor which can perfectly replace human eyes on the way of helping the robot to intelligently walk, and in the field of security monitoring, the all-weather work is not influenced by the intensity of external light because the high-resolution laser radar uses laser for active detection, so that the laser radar is the most ideal detection equipment for replacing the existing monitoring camera.
However, in the existing coaxial technical solution, the laser radar scans the field of view in a mechanical rotation manner, the scanning field of view is limited, and the scanning field of view is not easily expanded by other manners. Meanwhile, the mechanical rotation rate is low, the image resolution is reduced, the limitation of the reflecting mirror is caused, and the receiving efficiency is low.
Disclosure of Invention
The present invention is directed to an off-axis incidence-based on-axis transmitting and receiving lidar, so as to solve the problems mentioned in the background art.
In order to achieve the purpose, the invention provides the following technical scheme: an off-axis incidence based on-axis transmit and receive lidar comprising: the laser device comprises a laser light source, a collimation unit, a transmitting assembly, a receiving assembly and a projection unit;
the laser light source is used for emitting laser beams;
the laser light source can be a semiconductor laser, a laser diode, a solid laser or a gas laser and is used for actively emitting laser beams;
the collimation unit is used for collimating the light beam emitted by the laser light source, reducing the divergence angle of the laser light beam and generating a collimated light beam;
the emission component is positioned in the emission light path and is used for enabling the collimated light beams to be incident into the projection unit; the transmitting assembly comprises a polarization beam splitting unit, a polarization conversion unit and a reflector; the polarization conversion unit is used for changing the polarization state of the light beam emitted from the polarization beam splitting unit, and the light beam with the changed polarization state enters the projection unit again; the reflector is used for changing the propagation direction angle of the linearly polarized light;
the receiving component is positioned in the receiving light path and used for receiving the photons returned by the projection unit; the receiving assembly comprises a polarization conversion unit, a polarization beam splitting unit, an optical filter, a focusing unit and a receiving end detector; the polarization conversion unit is used for changing the polarization state of the photons returned by the projection unit, the polarization beam splitting unit selects different exit ports according to the polarization state conversion state of the returned photons by the polarization conversion unit, the focusing unit converges the photons received by the receiving light path to the receiving end detector, and the optical filter filters interference photons in the photons returned by the projection unit to eliminate the influence of other wavelength noises;
the projection unit is a micro reflector driven based on MEMS or motor or other electronic modes; the polarization conversion unit is used for projecting the polarized light after passing through the polarization conversion unit in the horizontal direction and the vertical direction at certain scanning angles respectively, and receiving photons returned by diffuse reflection of the projected photons after passing through a distant object.
Further, the polarization beam splitting unit includes: the device comprises a first polarization light splitting unit, a second polarization light splitting unit and a third polarization light splitting unit, wherein the first polarization light splitting unit is arranged at the output end of a collimation unit and is used for splitting a collimated light beam into two linearly polarized light beams with orthogonal polarization states, and the two linearly polarized light beams respectively form a first emission light path and a second emission light path; the first emission light path and the second emission light path are projected to the second polarization light splitting unit and the third polarization light splitting unit respectively; the second polarization light splitting unit and the third polarization light splitting unit are provided with polarization conversion units along the emitting direction of the emitting light path.
Further, the polarization conversion unit comprises a first polarization conversion unit and a second polarization conversion unit, the second polarization conversion unit is arranged behind the third polarization splitting unit, and the first polarization conversion unit is arranged behind the second polarization splitting unit; the polarization conversion unit is used for converting the linearly polarized light after passing through the polarization light splitting unit into circularly polarized light or elliptically polarized light in the emitting light path; the polarization conversion unit is used for converting the photons returned by the projection unit from circularly polarized light or elliptically polarized light into linearly polarized light in the receiving optical path; the polarization conversion unit is a quarter-wave plate and is a birefringent crystal sheet with a certain thickness.
Further, the optical filter includes: the focusing unit comprises a first optical filter and a second optical filter, and comprises: the receiving end detector comprises a first focusing unit and a second focusing unit, and comprises: a first receiving light path detector and a second receiving light path detector; the receiving optical path includes: the first optical filter can be positioned among the first polarization conversion unit, the second polarization splitting unit, the first focusing unit, the first receiving light path detector and the projection unit of the first receiving light path; and the second optical filter can be positioned among the second polarization conversion unit, the third polarization light splitting unit, the second focusing unit, the second receiving light path detector and the projection unit of the second receiving light path.
Further, the system also comprises an auxiliary system, wherein the auxiliary system comprises: the auxiliary reflector is provided with a small hole for light beams of the compensation light source to pass through, the auxiliary reflector receives photons returned by the compensation light source reflected by the optical filter and reflects the received photons to the auxiliary focusing unit, and the image sensor is used for acquiring the photons converged by the auxiliary focusing unit.
Further, the auxiliary system is located in the emission light path, and the emission light path includes: a first emission light path and a second emission light path; the auxiliary system may be located in the first emission light path and the second emission light path, or may be located in the first emission light path or the second emission light path.
Furthermore, the polarization beam splitting unit is a polarization beam splitting prism, or a coated polarization beam splitting sheet, or an optical crystal capable of generating o light and e light.
Further, the mirror is located in an emission optical path, and the emission optical path includes: a first emission light path and a second emission light path; the reflector is positioned in the first emission light path and/or the second emission light path and is used for changing the light transmission direction of the first emission light path and/or the second emission light path to form off-axis double-beam incidence or multi-beam incidence.
Furthermore, the optical power of the compensation light source can be automatically and dynamically adjusted along with the intensity of the outside light illumination.
Furthermore, when the number of the laser light sources is one, one laser beam is divided into two beams by a beam splitter or a coupler, each beam assembly comprises a collimation unit, an emission assembly and a receiving assembly, after the two beams of light pass through the emission assembly, the first emission light path and the second emission light path of each beam of light can be incident to the same projection unit or two or more projection units, and the modes of the beams of light incident to the projection units can be freely combined; when the number of the laser light sources is two or more, the number of the light beams incident to the projection unit is two to four times of the number of the light sources, the number of the projection unit can be one or more, and the light beams and the projection unit can be freely combined to realize the field angle expansion; and 360-degree omnibearing coverage detection is realized.
Compared with the prior art, the technical scheme of the invention has the following advantages: the off-axis incidence-based coaxial transmitting and receiving laser radar provided by the embodiment of the invention can realize incidence of two beams or a plurality of beams, on one hand, the scanning view field angle of the projection unit can be expanded, and the range of a wider angle can be detected, on the other hand, all photons reflected back to the projection unit are received by polarization, and the polarization light splitting unit and the polarization conversion unit can not absorb light energy, so that the receiving efficiency of the photons is improved, and more distant object information can be detected; the auxiliary system emits light beams with different wavelengths from the laser light source, the power of the compensation light source is dynamically adjusted according to the external light intensity, and the functions of calibration, video fusion and the like with higher precision are realized.
Drawings
Fig. 1 is a schematic structural diagram of a laser radar according to a first embodiment of the present invention;
FIG. 2 is a schematic diagram of a polarization beam splitter unit with a polarization beam splitter prism according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a polarization beam splitter unit according to an embodiment of the present invention, illustrating interference light noise by taking a polarization beam splitter prism as an example;
FIG. 4 is a schematic diagram of a polarization beam splitter unit with a Wollaston prism according to an embodiment of the present invention;
fig. 5 is a schematic diagram illustrating polarization conversion of a P-end polarization splitting unit in a laser radar structure according to an embodiment of the present invention;
fig. 6 is a schematic diagram illustrating polarization conversion of an S-end polarization splitting unit in a laser radar structure according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a scanning sequence of a projection unit in a lidar architecture according to an embodiment of the present invention;
fig. 8 is a schematic view of an optical path of a focusing unit in a laser radar structure according to a first embodiment of the present invention;
fig. 9 is a schematic side view in the X direction of two off-axis incident beams in a laser radar structure according to an embodiment of the present invention;
fig. 10 is a schematic view of a distribution of scanning fields in a cross section of two off-axis incident beams in a laser radar structure according to an embodiment of the present invention;
FIG. 11 is a schematic view of a laser radar structure according to an embodiment of the present invention scanning a field of view with four off-axis incident light beams;
fig. 12 is a schematic structural diagram of a laser radar according to a second embodiment of the present invention;
fig. 13 is a schematic diagram of a transmitting and receiving structure of a lidar assistance system according to a second embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only and do not represent the only embodiments.
It should be noted that the terms "first," "second," and the like in the description and claims of this application and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Example one
In one embodiment, an off-axis incidence based on-axis transmitting and receiving lidar is provided, as shown in fig. 1. The laser radar comprises a laser light source 10, a collimation unit 20, a first polarization beam splitting unit 301, a second polarization beam splitting unit 302, a third polarization beam splitting unit 303, a first polarization conversion unit 401, a second polarization conversion unit 402, a reflector 50, a first optical filter 601, a second optical filter 602, a first focusing unit 801, a second focusing unit 802, a first receiving optical path receiving end detector 701, a second receiving optical path receiving end detector 702 and a projection unit 90; the laser light source 10 emits a laser beam; the collimation unit 20 is used for collimating the laser beam and reducing the divergence angle of the beam, so that the laser beam can be projected for a longer distance;
the first polarization beam splitting unit 301 is located in the light path of the emitting component, and splits collimated laser into two linearly polarized light beams with polarization states perpendicular to each other, the polarization state of the first emitting light path light beam is P light parallel to the paper surface direction, and enters the second polarization beam splitting unit 302 after being transmitted along the incident light direction, and the polarization state of the second emitting light path light beam is S light perpendicular to the paper surface and is reflected upwards, and enters the third polarization beam splitting unit 303 after being reflected by the reflector 50;
after the P light passes through the second polarization splitting unit 302, the polarization state and the propagation direction remain unchanged, the second polarization splitting unit 302 is connected with the first polarization conversion unit 401 by optical cement or gluing, and can be separately placed, which is explained in the embodiment by the optical cement or gluing connection manner, and the P light passes through the first polarization conversion unit 401, and the polarization state is converted into left-handed or right-handed circularly polarized light, and is incident to the projection unit 90; after the S light passes through the third polarization light splitting unit 303, the polarization state remains unchanged, the propagation direction is reflected by the bonding surface of the third polarization light splitting unit 303 and then enters the second polarization conversion unit 402, the second polarization conversion unit 402 and the third polarization light splitting unit 303 are fixed by means of optical cement or bonding, and can also be placed separately, which is explained in the embodiment of optical cement or bonding, the S light passes through the second polarization conversion unit 402, and then the polarization state is converted into right-handed or left-handed circularly polarized light, which is incident to the projection unit 90; after the first emission light path beam and the second emission light path beam are simultaneously incident to the projection unit 90, scanning fields are respectively formed in the horizontal direction and the vertical direction and projected to a distant object. The projection unit 90 is a MEMS galvanometer, a mechanical rotating mirror or a rotating prism, and is not limited herein. The polarization beam splitting unit can be a polarization beam splitter or a polarization beam splitter prism.
Fig. 2 is a schematic structural diagram of a polarization beam splitter unit according to an embodiment of the present invention, where the polarization beam splitter unit includes a first right-angle prism 3011 and a second right-angle prism 3012, a polarization beam splitter film 3013 is plated on an inclined surface of the first right-angle prism 3011, and is glued with an inclined surface of the second right-angle prism 3012, and antireflection films are plated on right-angle sides of the first right-angle prism 3011 and the second right-angle prism 3012. The input light is divided into two beams of linearly polarized light P and S with polarization states perpendicular to each other after passing through the polarization splitting film 3013, the P light is transmitted along the original light beam direction after penetrating through the polarization splitting film 3013, and is emitted out through the right-angle side of the second right-angle prism 3012; the S light is reflected by the polarization splitting film 3013 and then exits through the right-angle side of the first right-angle prism 3011.
Fig. 3 shows that when the polarization splitting unit 302 is a polarization splitting prism, a weak S light interference optical path exists in the P light, and a detector 701 at a receiving end of the first receiving optical path interferes with normally returned photons of the weak S light; similarly, when the polarization splitting unit 303 is a polarization splitting prism, a weak P light interference optical path exists in the S light. Noise generated by interference cannot be eliminated through a circuit or an algorithm, and the first polarization beam splitting unit 301 may adopt a polarization beam splitting structure with a higher extinction ratio, so as to avoid the influence of the interference noise on the second polarization beam splitting unit 302 and the third polarization beam splitting unit 303.
Fig. 4 is a schematic structural diagram of the polarization beam splitting unit 301 using a wollaston prism, in which two prisms with optical axes perpendicular to each other are glued together, and for light with the same polarization direction as the optical axis and light with the polarization direction perpendicular to the optical axis, refractive indexes of the two prisms are different, and the birefringence divides an incident light beam into two orthogonal polarization states. When unpolarized light is incident perpendicularly on the optical element, e-light (extraordinary light) and o-light (ordinary light) exit at different angles from opposite sides of the prism. The light is split by using the birefringence of the optical crystal, the split light is pure, light in other polarization states does not exist, and the influence of interference light noise does not exist in the second polarization splitting unit 302 and the third polarization splitting unit 303.
Alternatively, the polarization splitting unit may be a glan prism, a nicols prism, or a rochon prism, etc., which is not limited herein.
The first polarization conversion unit 401 and the second polarization conversion unit 402 are quarter-wave plates, which are birefringent crystal plates having a certain thickness, and when light passes through the plates, the phase difference between o light and e light is pi/2 or an odd multiple thereof, and such plates are called quarter-wave plates or 1/4 wave plates. When incident light vertically enters the quarter-wave plate, the polarization of the light and the optical axis plane of the crystal form an angle theta, and after the light is emitted, the light becomes elliptical or circular polarized light, and when the angle theta is 45 degrees, the emergent light is circular polarized light.
The principle of polarization conversion of the present invention is as follows.
Fig. 5 is a diagram illustrating the principle of polarization conversion of P light in the first emission optical path in which P light enters from the S1 plane of the second polarization splitting unit 302 and exits from the S2 plane along the beam propagation direction, with the polarization state unchanged, and the first reception optical path. The S2 plane and the first polarization conversion unit 401 are connected by gluing, the S2 plane and the first polarization conversion unit 401 can be separately placed, or can be connected by optical gluing or gluing, and fig. 5 illustrates the gluing connection. The first polarization conversion unit 401 is a quarter-wave plate, an angle of 45 degrees is formed between an optical axis and a P light vibration direction, and after a light beam emitted from the S2 plane of the second polarization beam splitting unit 302 passes through the first polarization conversion unit 401, the P light polarization state is converted into a circular polarization state light, and the circular polarization state light enters the projection unit 90. In the first receiving optical path, the first polarization conversion unit 401 receives the light beam returned from the projection unit 90, and after the light beam passes through the first polarization conversion unit 401, the circularly polarized light is converted into S polarized light (S light for short), and the S polarized light enters through the S2 surface of the second polarization beam splitting unit 302, is reflected to the S3 surface by the polarization beam splitting film, exits through the S3 surface, and enters the optical filter 601 and the first focusing unit 801.
Fig. 6 is a diagram illustrating the principle of polarization conversion of the S light in the second emission light path in which the S light enters from the S4 surface of the third polarization splitting unit 303, is reflected by the polarization splitting film, and exits from the S5 surface without changing the polarization state, and the second reception light path. The S5 surface and the second polarization conversion unit 402 are connected by gluing, the S5 surface and the second polarization conversion unit 402 can be separately placed, or can be connected by optical gluing or gluing, and fig. 6 illustrates the gluing connection. The second polarization conversion unit 402 is a quarter-wave plate, an angle of 45 degrees is formed between the optical axis and the S light vibration direction, and after the light beam emitted from the S5 plane of the third polarization beam splitting unit 303 passes through the second polarization conversion unit 402, the S light polarization state is converted into the circular polarization state light, and the circular polarization state light is incident on the projection unit 90. In the second receiving optical path, the second polarization conversion unit 402 receives the light beam returned from the projection unit 90, and after passing through the second polarization conversion unit 402, the circularly polarized light is converted into P polarized light (P light for short), and then exits through the S6 surface of the third polarization beam splitting unit 303, and enters the second optical filter 602 and the second focusing unit 802.
The first optical filter 601 and the second optical filter 602 are implemented by an optical coating mode, wherein the optical coating is a process of coating a plurality of layers of optical coating materials with high refractive index and low refractive index alternately on the surface of glass or an optical part, the aims of increasing the transmittance of certain wavelength light and cutting off certain wavelength light are achieved by utilizing the principle of constructive or destructive interference among the layers, and angle control can be additionally applied to increase the transmittance or cut off the light in a certain area range. The optical filter can greatly reduce the noise influence generated by external interference light at the front end, and lays a foundation for the interference noise removal by using a circuit and a software algorithm at the rear end.
In the present embodiment, the first focusing unit 801 and the second focusing unit 802 are composed of lenses having positive refractive power, or are composed of a combination of lenses having positive refractive power and negative refractive power. The projection unit 90 is a piece of micro-mirror driven by mems (micro electro mechanical system), motor or other electronic means, and the mirror reciprocates in the horizontal and/or vertical directions simultaneously (individually) to project a region with a fixed horizontal FOV (scan angle) and/or vertical FOV scan. The receiving end detector and the image sensor which are related in the text belong to the conventional components; the control actions of the receiving end detector and the image sensor can be realized through simple programming by a person skilled in the art, and belong to the common general knowledge in the field, so that the control actions are not described in more detail.
Fig. 7 is a scanning sequence diagram of the mirror of the projection unit 90, which starts to rotate from the starting position O, and after completing one horizontal mechanical deflection angle scanning in one half cycle along the horizontal X direction, deflects a slight angle along the vertical Y direction, and then completes the scanning in the other half cycle along the horizontal-X direction. Every time one period of scanning is completed in the horizontal X direction, the horizontal scanning rate or frequency is 1Hz, and the period number from the starting point O to the ending point O' is the horizontal scanning rate or frequency. FIG. 7 is a scanning sequence of only one embodiment, and the scanning sequence may also be performed by scanning a half cycle along the vertical Y direction, and then scanning another half cycle along the-Y direction after deflecting a small angle along the horizontal X direction; the scanning sequence can also be a quincunx scanning, and the scanning sequence is not limited. Projection unit 90 may be in the form of a scanning sequence driven in a MEMS-driven manner, or by a motor-driven mirror, or other electronic means, again without limitation.
An important parameter of the projection unit 90 is the scanning rate or frequency, which directly determines the number of output points of each frame, and has a large number of points and high resolution; the horizontal mechanical angle θ' of mirror deflection during the period of time from when the mirror of the projection unit 90 projects a photon to when the photon is reflected by a distant target object to be received by the mirror satisfies the following equation:
where d is the distance of the target object, f is the scanning frequency of the projection unit 90 in the horizontal direction, FOV is the maximum mechanical field angle of view of the projection unit 90 in the horizontal direction, and C is the speed of the photon flying in air.
In this embodiment, under the conditions of high scanning frequency and a far target object, the horizontal mechanical deflection angle θ' of the projection unit 90 is large, and the beam deflection angle is 2 times of the mechanical deflection angle; for the first receiving optical path receiving end detector 701 and the second receiving optical path receiving end detector 702 with micro-size apertures, such as 200 μm apertures, in this embodiment, the first focusing unit 801 and the second focusing unit 802 with a single lens have a beam deflection angle of 2 degrees, the photon receiving efficiency of a target object far away from 300 m is about 40%, and the receiving efficiency of a target object near to 300 m can reach 100%, so that the capability of observing the target object far away is limited.
Fig. 8 is an optical path diagram of the first focusing unit 801 and the second focusing unit 802 of the present embodiment, taking two lenses as an example; it should be noted that the entrance pupil size h of the optical path is the same as the size of the mirror of the projection unit 90, the distance d ' from the entrance pupil to the first mirror is in the first receiving optical path, and L1, L2 in fig. 1, and L1 ' and L2 ' in fig. 5 satisfy the following relations:
d’=L1+L2+(L1’+L2’)/n1
in the above equation, n1 is the refractive index of the second polarization beam splitting unit 302, L1 is the distance from the projection unit 90 to the first polarization conversion unit 401 of the first receiving optical path, L2 is the distance from the S3 plane of the second polarization beam splitting unit 302 to the first focusing unit 801, L1 'is the horizontal distance from the incident plane of the first deflection conversion unit 401 to the polarization beam splitting film of the second polarization beam splitting unit 302 of the first receiving optical path in the second polarization beam splitting unit 302, and L2' is the vertical distance from the reflection of the first receiving optical path from the polarization beam splitting film to the light exit plane S3 plane.
The distance d ' from the entrance pupil to the first lens is in the second receiving light path, and L3, L4 in fig. 1, and L3 ' and L4 ' in fig. 6 satisfy the following relationship:
d’= L3+L4+(L3’+L4’)/n2
in the above equation, n2 is the refractive index of the third polarization beam splitting unit 303, L3 is the distance from the projection unit 90 to the second deflection converting unit 402 for the 0-degree field of view photons in the second receiving optical path, L4 is the distance from the S6 plane of the third polarization beam splitting unit 303 to the second focusing unit 802, and L3' is the distance from the incident plane of the second deflection converting unit 402 to the polarization beam splitting film of the third polarization beam splitting unit 303 for the 0-degree field of view photons in the second receiving optical path. L4' is the distance from the 0-degree field of view photon in the second receiving optical path in the third polarization beam splitting unit 303 to the light-emitting surface S6 of the third polarization beam splitting film 303.
Fig. 8 is an example of variations in the first focusing unit 801 and the second focusing unit 802 in the present embodiment, and the specific structure of the present embodiment is not limited.
Fig. 9 is a schematic diagram of a side surface X direction of the projection unit 90 when the first emission optical path light beam and the second emission optical path light beam are simultaneously incident on the projection unit 90, fig. 10 is a schematic diagram of a scan field distribution of a cross section a1 in fig. 9 in a Z direction, and P1 and P2 respectively represent two off-axis incident light rays of the first emission light beam and the second emission light beam in fig. 1 which are incident on the projection unit 90. There is a transition region D3 between the scanning region D1 of the P1 beam and the scanning region D2 of the P2 beam, and D1, D2 and D3 are all dashed boxes to indicate the scanning regions. The scanning areas of P1 and P2 in the embodiment of fig. 10 are each formed by sampling 4 scanning spots in each of the X and Y directions.
In off-axis incidence, the incident light forms angles α and β with respect to the vertical component and the horizontal component of the reflector of the projection unit 90, the reflector of the projection unit 90 uniformly rotates in the vertical direction and the horizontal direction, namely, the rotation angles are the same in the same unit time, but due to the existence of α and β, the light beams reflected by the reflector of the projection unit 90 exit at different angles in the same unit time, when the reflector of the projection unit 90 rotates to the side where the incident light beam P1 has the largest horizontal and vertical component, the angle difference of the exit light beam of the incident light beam P1 is the largest and the distortion is the largest in the same unit time, when the incident light beam P2 passes through the reflector of the projection unit 90, the exit light beam is at the side where the exit angle difference is the smallest in the same unit time, when the reflector of the projection unit 90 rotates to the side where the incident light beam P2 has the largest horizontal and vertical component, the exit light beam P2 has the largest exit angle difference in the same unit time, the exit light beam P1 passes through the reflector, the top of the horizontal and the exit light beam is distorted.
Fig. 11 is a schematic diagram of a light beam projection area having 2 sets of structures shown in fig. 1, wherein 4 incident light beams are incident on the same mirror of the projection unit 90, the scanning areas of the 4 incident light beams are respectively a first scanning area 1001, a second scanning area 1002, a third scanning area 1003 and a fourth scanning area 1004, and a slight overlapping area is formed between the two adjacent scanning areas, which are indicated by filling oblique lines in the drawing.
Further, the number of the projection units 90 can be extended to 2 or more than 2, so that a full-coverage image of a 360-degree area can be realized, the mode of a plurality of light beams entering the same projection unit 90 can be flexible and changeable, and the first emission light path light beam and the second emission light path light beam of the structure shown in fig. 1 can be independently incident on different 90 reflectors so as to realize the field angle expansion. The specific combination form is not subject to any limitation.
The technical scheme of the invention is realized according to the following principle: in the laser radar coaxial receiving scheme, a transmitting end light path and a receiving end light path need to share part of optical elements for ensuring the coaxiality, a commonly used method is that a reflector is placed at the receiving end, received light is bent and deviates from the transmitting light path by an angle and is converged into a detector unit through a lens, a small hole needs to be reserved in the center of the reflector in the scheme and serves as a transmitting window of the transmitting end light path, and the hole in the receiving end light path can lose part of returned light energy and reduce the number of photons for receiving a remote target object; on the other hand, the light exists in the form of electromagnetic waves, the light wave contains an electric vibration vector E and a magnetic vector H, and both the E and the H are perpendicular to the propagation speed U, so that the light wave is transverse wave and has a polarization phenomenon.
Example two
A second embodiment of the present invention provides a laser radar having a second structure, as shown in fig. 12, including a laser light source 1001, a collimating unit 2001, a first polarization beam splitting unit 3001, a second polarization beam splitting unit 3002, and a third polarization beam splitting unit 3003, a first polarization conversion unit 4001, a second polarization conversion unit 4002, a first optical filter 6001, and a second optical filter 6002, an auxiliary mirror including a first mirror 500, a second mirror 501, and a third mirror 502, a first compensation light source 1002, and a second compensation light source 1003, an auxiliary focusing unit including a first focusing unit 8001, a second focusing unit 8002, a third focusing unit 8003, and a fourth focusing unit 8004, a first receiving light path detector 7001, a second receiving light path detector 7002, an image sensor including a first image sensor 7003, a second image sensor 7004, and a projecting unit 900; the auxiliary system may be located in the first emission light path and the second emission light path, or may be located in the first emission light path or the second emission light path.
In the second embodiment, on the basis of the first embodiment, an auxiliary system is added to each of the first emission light path and the second emission light path, and the auxiliary system includes a first compensation light source 1002, a second compensation light source 1003, a second reflecting mirror 501, a third reflecting mirror 502, a third focusing unit 8003, a fourth focusing unit 8004, a first image sensor 7003, and a second image sensor 7004. The auxiliary system can improve the application precision of the laser radar such as calibration, point cloud fusion and the like.
The spectrum of the compensation light source can be in a visible light spectrum (380 nm-780nm range), or a spectrum range in which near infrared can be sensed by the first image sensor 7003 and the second image sensor 7004, and the spectrum can be a single point or a broad spectrum; the optical power of the compensation light source may dynamically change with the change of the external light intensity in order to compensate for the extra light energy of the first image sensor 7003 and the second image sensor 7004.
The second reflecting mirror 501 and the third reflecting mirror 502 of the auxiliary system are mirrors with a small hole reserved in the middle, and light beams of the compensation light source are respectively incident to the first optical filter 6001 and the second optical filter 6002 through the small holes; meanwhile, the first optical filter 6001 and the second optical filter 6002 receive photons returned by the projection unit 900, wherein the received photons returned by the auxiliary light source are reflected to the reflecting surfaces of the second reflecting mirror 501 and the third reflecting mirror 502; the received photons returned after being emitted through the first emission optical path and the second emission optical path by the laser light source 1001 are transmitted to the first polarization conversion unit 4001 and the second polarization conversion unit 4002. After passing through the second mirror 501 and the third mirror 502, the photons are reflected to the third focusing unit 8003 and the fourth focusing unit 8004, and are captured by the first image sensor 7003 and the second image sensor 7004, respectively.
In the emission light path, the light beam of the first compensation light source 1002 passes through the second reflecting mirror 501, enters the first optical filter 6001, is reflected by the first optical filter 6001 onto the projection unit 900, and is projected onto a remote target object; in a receiving light path, the projection unit 900 receives photons returned by diffuse reflection of a remote target object, the photons are incident on the first optical filter 6001 in a reverse direction along an original emission light path, the photons are reflected to the second reflecting mirror 501 at the first optical filter 6001, the second reflecting mirror 501 reflects the photons to the third focusing unit 8003, and the third focusing unit 8003 converges the photons to the first image sensor 7003; meanwhile, in a receiving optical path, the projection unit 900 receives photons returned by diffuse reflection of a remote target object, the photons are incident on the first optical filter 6001 in a reverse direction along the original emitting optical path, the photons are filtered by the first optical filter 6001 to remove stray light and then incident on the first polarization conversion unit 4001, and the polarization state is converted by the first deflection conversion unit 4001 and then sequentially incident on the first focusing unit 8001 and the first receiving optical path detector 7001 from the second polarization beam splitting unit 3002.
Fig. 13 is a schematic cross-sectional structure of the second reflecting mirror 501 of this embodiment, where the S1 plane is a reflecting plane, the included angle between the S1 plane and the horizontal line is set to be θ, and the value of θ is not limited, and θ is 45 degrees in this embodiment. A small hole is reserved in the center of the second reflecting mirror 501, the height of the small hole in the vertical direction is d, an auxiliary light source horizontal incident beam L penetrates through the small hole to enter the first optical filter 6001, the beam is reflected to the projection unit 900 through the first optical filter 6001, the beam is projected onto a far target object, meanwhile, the projection unit 900 receives photons returned by diffuse reflection of the far target object, the photons are reversely incident on the S1 reflecting surface of the second reflecting mirror 501 along the original emission light path, and the reflected photons are received by the third focusing unit 8003. The S2 plane of the cross section of the second reflecting mirror 501 may be parallel to the S1 plane, or may be trapezoidal or triangular at an angle to the S1 plane, and the embodiment is not limited in any way.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. An off-axis incidence based on-axis transmit and receive lidar comprising: the laser device comprises a laser light source, a collimation unit, a transmitting assembly, a receiving assembly and a projection unit;
the laser light source is used for emitting laser beams;
the collimation unit is used for collimating the light beam emitted by the laser light source, reducing the divergence angle of the laser light beam and generating a collimated light beam;
the emission component is positioned in the emission light path and is used for enabling the collimated light beams to be incident into the projection unit; the transmitting assembly comprises a polarization beam splitting unit, a polarization conversion unit and a reflector; the polarization conversion unit is used for changing the polarization state of the light beam emitted from the polarization beam splitting unit, and the light beam with the changed polarization state enters the projection unit again; the reflector is used for changing the propagation direction angle of the linearly polarized light;
the receiving component is positioned in the receiving light path and used for receiving the photons returned by the projection unit; the receiving assembly comprises a polarization conversion unit, a polarization beam splitting unit, an optical filter, a focusing unit and a receiving end detector; the polarization conversion unit is used for changing the polarization state of the photons returned by the projection unit, the polarization beam splitting unit selects different exit ports according to the polarization state conversion state of the returned photons by the polarization conversion unit, the focusing unit converges the photons received by the receiving light path to the receiving end detector, and the optical filter filters interference photons in the photons returned by the projection unit;
the projection unit is a micro-reflector driven based on MEMS or motor or other electronic modes.
2. An off-axis incidence based on-axis transmit and receive lidar according to claim 1, wherein the polarization splitting unit comprises: the device comprises a first polarization light splitting unit, a second polarization light splitting unit and a third polarization light splitting unit, wherein the first polarization light splitting unit is arranged at the output end of a collimation unit and is used for splitting a collimated light beam into two linearly polarized light beams with orthogonal polarization states, and the two linearly polarized light beams respectively form a first emission light path and a second emission light path; the first emission light path and the second emission light path are projected to the second polarization light splitting unit and the third polarization light splitting unit respectively; the second polarization light splitting unit and the third polarization light splitting unit are provided with polarization conversion units along the emitting direction of the emitting light path.
3. The off-axis incidence based on-axis transmitting and receiving lidar according to claim 2, wherein the polarization conversion unit comprises a first polarization conversion unit and a second polarization conversion unit, the second polarization conversion unit is arranged behind the third polarization splitting unit, and the first polarization conversion unit is arranged behind the second polarization splitting unit; the polarization conversion unit is used for converting the linearly polarized light after passing through the polarization light splitting unit into circularly polarized light or elliptically polarized light in the emitting light path; and the polarization conversion unit is used for converting the photons returned by the projection unit from circularly polarized light or elliptically polarized light into linearly polarized light in the receiving optical path.
4. An off-axis incidence based on-axis transmit and receive lidar according to claim 3, wherein the filter comprises: the focusing unit comprises a first optical filter and a second optical filter, and comprises: the receiving end detector comprises a first focusing unit and a second focusing unit, and comprises: a first receiving light path detector and a second receiving light path detector; the receiving optical path includes: the first optical filter can be positioned among the first polarization conversion unit, the second polarization splitting unit, the first focusing unit, the first receiving light path detector and the projection unit of the first receiving light path; and the second optical filter can be positioned among the second polarization conversion unit, the third polarization light splitting unit, the second focusing unit, the second receiving light path detector and the projection unit of the second receiving light path.
5. An off-axis incidence based on-axis transmit and receive lidar according to claim 1, further comprising an auxiliary system comprising: the auxiliary reflector is provided with a small hole for light beams of the compensation light source to pass through, the auxiliary reflector receives photons returned by the compensation light source reflected by the optical filter and reflects the received photons to the auxiliary focusing unit, and the image sensor is used for acquiring the photons converged by the auxiliary focusing unit.
6. An off-axis incidence based on in-line transmit and receive lidar according to claim 5, wherein the auxiliary system is located in a transmit optical path comprising: a first emission light path and a second emission light path; the auxiliary system may be located in the first emission light path and the second emission light path, or may be located in the first emission light path or the second emission light path.
7. The off-axis incidence based on-axis transmitting and receiving lidar according to claim 1, wherein the polarization beam splitting unit is a polarization beam splitting prism, or a coated polarization beam splitter, or an optical crystal capable of generating o-light and e-light.
8. An off-axis incidence based on in-line transmit and receive lidar according to claim 1, wherein the mirror is located in a transmit optical path comprising: a first emission light path and a second emission light path; the reflecting mirror is positioned in the first emission light path and/or the second emission light path and is used for changing the light transmission direction of the first emission light path and/or the second emission light path.
9. The off-axis incidence based on-axis transmitting and receiving lidar according to claim 5, wherein the optical power of the compensation light source is automatically and dynamically adjusted according to the intensity of the ambient light illumination.
10. The off-axis incidence-based coaxial transmitting and receiving lidar according to claim 1, wherein when the number of the laser light sources is one, one laser beam is divided into two beams by a beam splitter or a coupler, each beam path assembly comprises a collimating unit, a transmitting assembly and a receiving assembly, after the two beams pass through the transmitting assembly, the first transmitting light path and the second transmitting light path of each beam can be incident on the same projecting unit or two or more projecting units, and the modes of the beams incident on the projecting units can be freely combined; when the number of the laser light sources is two or more, the number of the light beams incident to the projection unit is two to four times of the number of the light sources, the number of the projection unit can be one or more, and the light beams and the projection unit can be freely combined to realize the field angle expansion.
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