A coherent detection laser radar array optical structure and ranging laser radar

Abstract

The present invention discloses a coherent detection laser radar array optical structure and a ranging laser radar. The light emitted from the light source enters the first lens group, and after processing, the light is divided into signal light and local oscillator light. The signal light is emitted to the target through the second lens group, and the fourth lens group receives the signal light reflected by the target, and forms a real image on the second image plane. The real image is expanded by a fifth lens group and enters the first beam combiner. After the local oscillator light passes through the third lens group, a laser beam waist is generated at the first image plane, and after being expanded by another fifth lens group, it enters the beam combiner, and then converged by the sixth lens group to achieve coherence, and a sensor array is placed on the third image plane. By making the propagation directions of the signal light and the local oscillator light nearly parallel, the beam combiner focuses them on the image plane, and the sensor array is placed on the image plane to receive the combined coherent light, so as to achieve focal plane array coherent ranging. Reduce the decoherence effect of the coherent laser radar and increase the proportion of the beat frequency AC component in the total signal.

Description

Technical Field

[0001] The invention belongs to the field of electronic information technology and relates to a coherent detection laser radar array optical structure and a ranging laser radar. Background Art

[0002] Coherent ranging is an optical ranging method that uses the coherence of light to measure distance. Its principle is to use the coherence of light to obtain optical signals, and the distance information is obtained from the frequency change loaded on the optical signal.

[0003] Assume that the angular frequencies of the local oscillator light and the signal light are ω L and ω S , the corresponding phase φ L and φ S , the corresponding electric field amplitudes are:

[0004]

[0005] When the local oscillator light and the signal light interfere with each other on the photosensitive surface of the detector, the photocurrent is:

[0006]

[0007] In the formula, α is the photoelectric response rate of the photodetector. It can be obtained that the photocurrent has an AC term with a frequency of ω = ω L -ω S , its phase is φ=φ L -φ S By detecting the frequency of the photocurrent, the distance of the target can be obtained.

[0008] At present, all coherent ranging uses a single-point detection architecture, in which each / one detector needs to be matched with a set of transceiver systems. Although some coherent detection systems use a set of lenses to complete multi-point transmission and reception, in the actual optical path, it is still necessary to perform separate optical collimation and shaping for each ranging channel, that is, each path. In essence, it is still an integration method of a single-channel optical system. If this detection system is required for large-scale ranging, such as large FOV detection, a strict scanning device is still required. Currently commonly used scanning devices include mechanical rotating devices, MEMS scanning devices, optical phased arrays (OPA) and other scanning devices.

[0009] Focal plane array imaging is a structure that can simultaneously image multiple photoelectric sensing elements. The smallest photoelectric detection element is called a pixel. Multiple pixels form an imaging array, which can detect targets within a certain field of view. Its main optical structure is an imaging lens, and the imaging array is placed on the focal plane of the lens to form a complete detector.

[0010] This structure uses a mature focal plane imaging lens, the principle of which is very clear and has been widely used in various optical imaging devices, such as cameras, webcams, mobile phones, and household consumer electronics. In addition, in the field of laser radar, focal plane imaging has also been maturely applied, that is, depth cameras that use time of flight (TOF) ranging. This product has also been deeply applied in the industrial field and consumer electronics such as mobile phones, sweeping robots, smart door locks, and vehicle-mounted obstacle avoidance radars.

[0011] However, up to now, coherent ranging lidar using focal plane array mode has not been reported in any literature or commercial application. The difficulty lies in that when using focal plane array imaging, each sensor unit, that is, each point in the pixel has a different phase φ, and multiple points have different phases φ, the AC component of the photocurrent generated by each point will be misaligned in phase, resulting in the photocurrent generated between different areas of the pixel being summed, and the AC components will cancel each other out, thereby reducing the signal-to-noise ratio. Summary of the invention

[0012] The purpose of the present invention is to solve the problem in the prior art that when focal plane array imaging occurs, due to the different phases of multiple points within a pixel, the AC component of the photocurrent is misaligned in phase, and after the photocurrents in different areas are added, the AC components cancel each other out, resulting in a decrease in the signal-to-noise ratio. A coherent detection laser radar array optical structure and a ranging laser radar are provided.

[0013] In order to achieve the above object, the present invention adopts the following technical solutions:

[0014] A coherent detection laser radar array optical structure, comprising a light source, a first lens group, a second lens group, a third lens group, a fourth lens group, a fifth lens group, a first beam combiner and a sixth lens group;

[0015] The light emitted from the light source enters the first lens group, which collimates, shapes and splits the light into signal light and local oscillator light. The signal light is emitted to the target through the second lens group. The fourth lens group receives the signal light reflected from the target and forms a real image on the second image plane. The real image is expanded by one of the fifth lens groups and then enters the first beam combiner. The local oscillator light is shaped and focused by the third lens group to generate a laser beam waist at the first image plane. The laser beam waist is expanded by another fifth lens group and then enters the first beam combiner. After both the signal light and the local oscillator light pass through the first beam combiner, they are converged by the sixth lens group to achieve coherence of the signal light and the local oscillator light on the third image plane. A sensor array or a detector array is placed on the third image plane.

[0016] A further improvement of the present invention is:

[0017] After the signal light and the local oscillator light pass through the first beam combiner, they enter the first beam splitter, which divides the light into two paths and enters the sixth lens group and the seventh lens group respectively. The first light forms a first real image on the third image plane after passing through the sixth lens group, and the second light forms a second real image on the fourth image plane after passing through the seventh lens group.

[0018] The first real image and the second real image are identical or mirror images of each other.

[0019] The sixth lens group and the seventh lens group have the same structure or the same optical function.

[0020] The light source is a fiber laser or a spatial light laser.

[0021] When the light source is a fiber laser, the first lens group is a fiber beam splitter.

[0022] The light source is a spatial light laser. When the light source emits spatial light, the first lens group is a beam expander or a spatial light beam splitter; when the light source emits optical fiber output, the first lens group is an optical fiber coupler, an optical fiber beam splitter or a spatial light beam splitter.

[0023] The laser beam waist is generated at the first image plane, and 1 / e of the laser beam waist 2 The radius is r1, the fourth lens group receives the signal light reflected from the target, and forms a real image on the second image plane, and the radius of the real image is r2, where r2 <r1。

[0024] The real image on the second image plane is expanded by one of the fifth lens groups to become approximately parallel light with a radius of r4 and a divergence angle of θ4; the laser beam waist is expanded by another fifth lens group and collimated to 1 / e of the divergence angle. 2 Approximately parallel light with a radius of r3 and a divergence angle of θ3, where r4 <r3,θ3<θ4。

[0025] A coherent ranging laser radar adopts the coherent detection array optical structure as described in any of the preceding items.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention proposes a coherent detection laser radar array optical structure, which divides the light emitted by a light source into signal light and local oscillator light, expands, collimates and shapes the light through a lens group respectively, so that the propagation directions of the two are nearly parallel, and then focuses the local oscillator light and the signal light through a beam combiner, and focuses them on an image plane, and realizes coherent ranging of the focal plane array through a sensor array or a detector array on the image plane, effectively avoiding the phase misalignment of the AC component, improving the signal-to-noise ratio, reducing the decoherence effect of the coherent laser radar, and increasing the proportion of the beat frequency AC component in the total signal.

[0028] The present invention proposes a coherent ranging laser radar, which adopts a coherent detection array optical structure and does not require a scanning device, and can simultaneously complete the distance measurement and speed measurement of the target. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 A schematic diagram showing the optical path of the optical structure when the light source is a fiber laser;

[0031] Figure 2 A schematic diagram showing the optical path of the optical structure when the light source is a laser emitting spatial light;

[0032] Figure 3 Schematic diagram of the light path of the optical structure when performing area array balanced detection.

[0033] Among them: 1-light source, 2-first lens group, 3-second lens group, 4-third lens group, 5-first image plane, 6, 9-fifth lens group, 7-fourth lens group, 8-second image plane, 10-first beam combiner, 11-sixth lens group, 12-third image plane. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0037] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0038] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0039] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] The present invention proposes a coherent detection laser radar array optical structure, including a light source 1, a first lens group 2, a second lens group 3, a third lens group 4, a fourth lens group 7, a fifth lens group 6, 9, a first beam combiner 10 and a sixth lens group 11; the light emitted from the light source 1 enters the first lens group 2, and is collimated, shaped and split by the first lens group 2 to divide the light into signal light and local oscillation light, the signal light is emitted to the target through the second lens group 3, the fourth lens group 7 receives the signal light reflected from the target, and forms a real image on the second image plane The real image is expanded by one of the fifth lens groups and then enters the first beam combiner 10; the local oscillation light is shaped and focused by the third lens group 4, and a laser beam waist is generated at the first image plane 5. The laser beam waist is expanded by one of the fifth lens groups and then enters the first beam combiner 10. After both the signal light and the local oscillation light pass through the first beam combiner 10, they are converged by the sixth lens group 11 to achieve coherence of the signal light and the local oscillation light on the third image plane 12, and a sensor array or a detector array is placed on the third image plane 12.

[0041] The present invention adopts six lens groups with different functions, each of which is composed of one or more optical lenses, which together form a complete set of optical equipment to complete the designed function.

[0042] The function of the first lens group is to collimate and shape the laser, which can be applied to spatial light lasers and fiber lasers. Its functions include laser collimation, shaping, and beam splitting. The beam splitting function is to divide the light emitted by the laser into two paths: signal light and local oscillator light. The signal light is emitted through the second lens group, and the local oscillator light is transmitted to the first beam combiner through the third lens group to complete the beam combination of the local oscillator light and the signal light reflected from the target.

[0043] The function of the second lens group is to collimate and shape the emitted signal light, adjust it to the required field of view (FOV) / divergence angle, and project the signal light onto the target to be measured.

[0044] The function of the third lens group is to shape the laser beam obtained by beam splitting, focus the laser beam input by optical fiber or spatial light, and generate a laser beam waist with a radius of r1 at the first image plane.

[0045] The function of the fourth lens group is to receive the signal light reflected from the target and form a real image on the second image plane. The image radius of this lens is r2. There is no fixed relationship between r2 and r1. However, in actual use, r2 is recommended. <r1。

[0046] The function of the fifth lens group is as follows: the fifth lens group is divided into two parts, one of which is used to expand the laser beam waist of the first image plane to a radius of r3 and a divergence angle of θ3. The other fifth lens group is used to expand the laser beam waist of the second image plane to a radius of r4 and a divergence angle of θ4. The purpose of this design is to make the propagation directions of the signal light and the local oscillator light nearly parallel after expansion, collimation and shaping, and then the local oscillator light and the signal light can be better converged on the third image plane at the same time through the sixth lens group.

[0047] The function of the sixth lens group is to focus the local oscillator light and the signal light combined by the first beam combiner onto the third image plane. Finally, a sensor array or a detector array is placed on the third image plane, and each pixel performs the functions of distance measurement and speed measurement.

[0048] Example 1

[0049] See also Figure 1 , which is a schematic diagram of the optical path of the optical structure when the light source is a fiber laser, can realize coherent ranging using a focal plane array. In the figure, the solid arrow represents the local oscillator light, and the dotted arrow represents the signal light.

[0050] The laser emitted by the light source 1 is collimated and shaped by the first lens group 2. The first lens group 2 is a fiber optic beam splitter. The splitting ratio of the fiber optic beam splitter can be adjusted accordingly according to the actual system design. The laser is split into two beams by the fiber optic beam splitter, which serve as the local oscillator light and the signal light respectively.

[0051] After the light passes through the first lens group 2, it is divided into two paths, one is the signal light, which enters the second lens group 3, and the other is the local oscillation light, which enters the third lens group 4.

[0052] The signal light emitted outward passes through the second lens group 3 and is projected toward the target. The divergence angle of the projected light is adjusted according to the system design, and the divergence angle is 1 / e 2 The radius is larger than the receiving field of view.

[0053] When the light source 1 is a fiber laser, the third lens group 4 includes a fiber collimator. The light passes through the fiber collimator and becomes convergent light, and forms a laser beam waist on the first image plane 5. The 1 / e 2 The radius is r1. After that, it is collimated by the fifth lens group 6 to become 1 / e of the divergence angle. 2 The approximately parallel light with a radius of r3 and a divergence angle of θ3, the divergence angle requires |θ3|≈0. Then, it passes through the first beam combiner 10 and enters the sixth lens group 11.

[0054] The signal light reflected from the target is converged on the second image plane 8 through the fourth lens group 7, forming a real image with a radius of r2, preferably r2 <r1。

[0055] The real image on the second image plane 8 is expanded by the fifth lens group 9 to become approximately parallel light with a radius of r4 and a divergence angle of θ4. To ensure better imaging quality, it is preferred that r4 < r3 and θ3 < θ4. Then, it enters the first beam combiner 10.

[0056] After both the local oscillator light and the signal light pass through the first beam combiner 10, they are converged by the sixth lens group 11 and converge into a real image on the third image plane 12 to achieve the coherence of the two beams of light. A photoelectric sensor or a photoelectric sensor array for detection can be placed on the third image plane 12.

[0057] Embodiment 2

[0058] See Figure 2 , which shows the optical path schematic diagram of the optical structure when the light source is a laser emitting spatial light, and realizes the implementation method of coherent ranging using a focal plane array. The solid arrow in the figure represents the local oscillator light, and the dashed arrow represents the signal light.

[0059] The laser emitted by the light source 1 is collimated and shaped by the first lens group 2 and divided into two beams, which are used as the local oscillator light and the signal light respectively. The structure of the first lens group 2 is matched. When the emission form of the light source 1 is spatial light, the first lens group 2 is an expander or a spatial light splitter; when the emission form of the light source 1 is fiber output, the first lens group 2 is a fiber coupler, a fiber splitter or a spatial light splitter.

[0060] After the light passes through the first lens group 2, it is divided into two paths. One path is the signal light, which enters the second lens group 3, and the other path is the local oscillator light, which enters the third lens group 4.

[0061] The signal light emitted outward passes through the second lens group 3 and projects towards the target. The divergence angle of the projected light is adjusted according to the system design. Preferably, the 1 / e 2 radius should be greater than the receiving field of view angle.

[0062] When the light source 1 is a fiber laser, the third lens group 4 includes a fiber collimator. The light passes through the fiber collimator and becomes convergent light, and a laser beam waist is formed on the first image plane 5. The 1 / e 2 radius is r1. Then, it is collimated by the fifth lens group 6 to become approximately parallel light with a 1 / e 2 radius of r3 and a divergence angle of θ3. The divergence angle requirement is |θ3| ≈ 0. Then it passes through the first beam combiner 10 and enters the sixth lens group 11.

[0063] The signal light reflected from the target is converged by the fourth lens group 7 on the second image plane 8 to form a real image with a radius of r2. Preferably, r2 < r1.

[0064] The real image on the second image plane 8 is expanded by the fifth lens group 9 to become approximately parallel light with a radius of r4 and a divergence angle of θ4. To ensure better imaging quality, it is preferred that r4 < r3 and θ3 < θ4. Then, it enters the first beam combiner 10.

[0065] After both the local oscillator light and the signal light pass through the first beam combiner 10, they are converged by the sixth lens group 11 and converge into a real image on the third image plane 12, realizing the coherence of the two beams of light. In addition, a photoelectric sensor or a photoelectric sensor array for detection can be placed on the third image plane 12.

[0066] Embodiment 3

[0067] See Figure 3 , which is a schematic optical path diagram of the optical structure for area array balanced detection. If area array balanced detection is required, that is, two identical sensor arrays are used to obtain the same current signal, and finally the effect of pixel-by-pixel balanced detection is achieved, then after the receiving end, a set of mirror optical paths can be adopted to obtain two image planes, and a sensor is placed on each of these two image planes, and the effect of balanced detection can be obtained. The specific implementation steps are as follows:

[0068] The normal optical path is the same as the foregoing. In addition, a first beam splitter 13, a seventh lens group 14, and a fourth image plane 15 are added. In principle, the seventh lens group 14 and the sixth lens group 11 should have the same structure, and the images received by the fourth image plane 15 and the third image plane 12 should be the same or mirror images of each other.

[0069] The light after passing through the first beam combiner 10 enters the first beam splitter 13 and is divided into two paths, which respectively enter the sixth lens group 11 and the seventh lens group 14.

[0070] The light is converged by the sixth lens group 11 to form a first real image on the third image plane 12. At the same time, the light is converged by the seventh lens group 14 to form a second real image on the fourth image plane 15. The first real image and the second real image are the same or mirror images of each other.

[0071] Two identical sensor arrays are respectively placed at the third image plane 12 and the fourth image plane 15, and beat frequency signals are respectively received.

[0072] The currents output by the pixels of these two sensors corresponding to the same target are differentially output, and then time-frequency domain conversion is performed to obtain ranging and velocity measurement results.

[0073] An embodiment of the present invention discloses a coherent ranging laser radar, which adopts the coherent detection array optical structure as described in any of the preceding items. After the detector array or sensor array receives the light, it converts it into an electrical signal, performs time-frequency domain conversion processing, calculates the spectral characteristics of the output signal, and then calculates the distance, speed, three-dimensional coordinate information, and point cloud information of the corresponding target, and outputs it as the measurement result of the laser radar.

[0074] The present invention divides the light emitted by the light source into signal light and local oscillator light, expands, collimates and shapes the light through a lens group respectively, so that the propagation directions of the two are nearly parallel, and then focuses the local oscillator light and the signal light through a beam combiner, and focuses them on an image plane. Through a sensor array or a detector array on the image plane, coherent ranging of a focal plane array is realized, and the phase misalignment of the AC component is effectively avoided, and the signal-to-noise ratio is improved. At the same time, coherent ranging and speed measurement with a large field of view and multiple channels can be performed, and no scanning device is required, and ranging and speed measurement can be completed simultaneously.

[0075] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A coherent detection laser radar array optical structure, characterized in that: It comprises a light source (1), a first lens group (2), a second lens group (3), a third lens group (4), a fourth lens group (7), a fifth lens group (6, 9), a first beam combiner (10) and a sixth lens group (11); Light emitted from a light source (1) enters a first lens group (2), is collimated, shaped and split by the first lens group (2), and is divided into signal light and local oscillator light. The signal light is emitted to a target through a second lens group (3). The fourth lens group (7) receives the signal light reflected from the target and forms a real image on a second image plane (8). The real image is expanded by one of the fifth lens groups and then enters a first beam combiner (10). The local oscillator light is shaped and focused by a third lens group (4), and a laser beam waist is generated at a first image plane (5). The laser beam waist is expanded by another fifth lens group and then enters the first beam combiner (10). After both the signal light and the local oscillator light pass through the first beam combiner (10), they are converged by a sixth lens group (11), and coherence of the signal light and the local oscillator light is achieved on a third image plane (12). A sensor array or a detector array is placed on the third image plane (12).

2. A coherent detection laser radar array optical structure as claimed in claim 1, characterized in that: After passing through the first beam combiner (10), the signal light and the local oscillator light enter the first beam splitter (13), where the light is split into two paths, which enter the sixth lens group (11) and the seventh lens group (14) respectively; the first path of light forms a first real image on the third image plane (12) after passing through the sixth lens group (11), and the second path of light forms a second real image on the fourth image plane (15) after passing through the seventh lens group (14).

3. A coherent detection laser radar array optical structure as claimed in claim 2, characterized in that: The first real image and the second real image are identical or mirror images of each other.

4. The coherent detection laser radar array optical structure according to claim 2, characterized in that: The sixth lens group (11) and the seventh lens group (14) have the same structure or the same optical function.

5. The coherent detection laser radar array optical structure according to claim 1, characterized in that: The light source (1) is a fiber laser or a spatial light laser.

6. A coherent detection laser radar array optical structure as claimed in claim 5, characterized in that: When the light source (1) is a fiber laser, the first lens group (2) is a fiber beam splitter.

7. The coherent detection laser radar array optical structure according to claim 5, characterized in that: The light source (1) is a spatial light laser. When the light source (1) emits spatial light, the first lens group (2) is a beam expander or a spatial light beam splitter. When the light source (1) emits optical fiber output, the first lens group (2) is an optical fiber coupler, an optical fiber beam splitter or a spatial light beam splitter.

8. The coherent detection laser radar array optical structure according to claim 1, characterized in that: The laser beam waist is generated at the first image plane (5), and 1 / e of the laser beam waist 2 The radius is r1, the fourth lens group (7) receives the signal light reflected from the target and forms a real image on the second image plane, the radius of the real image is r2, wherein r2 <r1。 9. The coherent detection laser radar array optical structure according to claim 1, characterized in that: The real image on the second image plane (8) is expanded by one of the fifth lens groups to become approximately parallel light with a radius of r4 and a divergence angle of θ4; the laser beam waist is expanded by another fifth lens group to be collimated to 1 / e of the divergence angle. 2 Approximately parallel light with a radius of r3 and a divergence angle of θ3, where r4 <r3,θ3<θ4。 10. A coherent ranging laser radar, characterized in that: A coherent detection array optical structure as described in any one of claims 1 to 9 is adopted.

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