Laser scanning device and method based on transmission metasurface-wedge mirror dynamic coupling

Abstract

The invention discloses a laser scanning device and method based on transmission metasurface-wedge mirror dynamic coupling, and relates to the technical field of optical scanning. The transmission-type metasurface divides a single beam of laser into multiple beams of transmission laser with the same light intensity, the propagation direction of the multiple beams of transmission laser has a deflection angle relative to the incidence direction of the single beam of laser, and the wedge-shaped prism is arranged on an emergent light path of the transmission-type metasurface, conducts secondary deflection on the multiple beams of transmission laser and then emits the multiple beams of transmission laser to a target surface. By controlling the transmission-type metasurface and the wedge-shaped prism to rotate at the same or different rotating speeds, a corresponding scanning track is generated to cover a target surface for laser scanning. The transmission-type metasurface is coupled with the wedge-shaped prism, a single laser beam is divided into multiple transmission laser beams, the scanning angle is remarkably increased in cooperation with the rotation process, the data size obtained in the scanning process is increased, and the scanning precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical scanning, and in particular to a laser scanning device and method based on dynamic coupling of a transmissive metasurface - wedge prism. Background Art

[0002] Laser scanning technology is one of the core technologies of airborne lidar, and is also an indispensable part of fields such as remote sensing mapping and 3D reconstruction, with wide practical value. Currently, the main laser scanning methods used in airborne lidar include: line scanning method, rotary scanning method, and fiber scanning method.

[0003] In the application of airborne lidar, although the line scanning method can provide high - precision scanning data, its disadvantages are also obvious. First, the scanning speed is limited. Due to the limitations of mechanical moving parts, it cannot meet the requirements of high - speed scanning, which to a certain extent affects the efficiency of data acquisition. Second, long - term use will cause wear of mechanical components, increase the failure rate, and reduce the reliability and stability of the device. In addition, environmental factors such as temperature and humidity may cause slight deformation of mechanical components, thus affecting the scanning accuracy. At the same time, the physical limitations of the scanning mirror result in a limited scanning range, making it difficult to meet the requirements of large - range scanning. Finally, the scanning lines may overlap on the ground, resulting in data redundancy, increasing the complexity and time cost of data processing.

[0004] As a new type of laser scanning method, the fiber scanning method still has some obstacles in the application of airborne lidar. First, the technical maturity is insufficient, with potential technical risks and reliability problems, which restricts its promotion in practical applications. Second, high - performance fiber components and precise control devices lead to high costs, and the device complexity increases, increasing the difficulty of use and maintenance. In addition, the fiber scanning method is sensitive to environmental factors, which may lead to performance degradation or instability. At the same time, the limitation of the fiber length results in a limited scanning range, unable to meet the requirements of long - distance scanning. Finally, there may be losses and attenuation in the transmission process of the fiber, affecting the intensity and stability of the scanning signal, which further restricts the application range of the fiber scanning method.

[0005] The rotary scanning method circumvents the disadvantages of the above two methods to a certain extent, but its scanning range is not flexible, restricted by the fixed tilt angle of the scanning mirror, lacking flexibility. Moreover, the polarization angle of the wedge prism in the rotary scanning method is limited, which also restricts the scanning range and efficiency of the rotary scanning method. And when the aircraft is flying at high speed, there may be missing data acquisition, resulting in a decrease in the 3D reconstruction accuracy due to insufficient data volume, which is also a common problem of single - laser scanning. Therefore, it is urgent to optimize and improve the existing rotary scanning method to solve problems such as limited scanning angle and few scanning laser beams. Summary of the Invention

[0006] To address the deficiencies in the background art, the present invention provides a laser scanning device and method based on the dynamic coupling of a transmissive metasurface and a wedge prism. By coupling the transmissive metasurface with the wedge prism, a single laser beam is divided into multiple transmitted laser beams. During the rotation process, the scanning angle is significantly increased, resulting in an increase in the amount of data obtained during the scanning process and improving the scanning accuracy.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A laser scanning device based on the dynamic coupling of a transmissive metasurface and a wedge prism includes a transmissive metasurface and a wedge prism arranged at intervals along the axial direction. The transmissive metasurface can divide a single laser beam into multiple transmitted laser beams with the same light intensity, and the propagation directions of the multiple transmitted laser beams all have deflection angles relative to the incident direction of the single laser beam. The wedge prism is disposed on the outgoing light path of the transmissive metasurface and performs secondary deflection on the multiple transmitted laser beams and then emits them to the target surface. By controlling the transmissive metasurface and the wedge prism to rotate at the same or different speeds, corresponding scanning trajectories are generated to cover the target surface for laser scanning.

[0009] Further, the material of the transmissive metasurface is single-crystalline silicon, and the material of the wedge prism is BK7 optical glass.

[0010] A laser scanning method based on the dynamic coupling of a transmissive metasurface and a wedge prism includes the following steps:

[0011] First, a single laser beam is split into multiple transmitted laser beams with different deflection angles by the transmissive metasurface;

[0012] Second, the multiple transmitted laser beams are incident on the wedge prism for secondary deflection;

[0013] Finally, the transmissive metasurface and the wedge prism are rotated at the same speed or different speeds in the axial direction to dynamically adjust the laser scanning path. Among them, the mathematical expression of the deflection angle during the dynamic coupling of the transmissive metasurface and the wedge prism is as follows:

[0014]

[0015] In the formula: θ m is the total deflection angle of a single laser beam after passing through the transmissive metasurface and the wedge prism, is the deflection angle of a single laser beam after passing through the transmissive metasurface, m is the beam order, n is the refractive index of the wedge prism, and α is the wedge angle of the wedge prism.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. In the single-wedge prism laser scanning method of the present invention, a transmissive metasurface is added for beam splitting, increasing the number of scanning laser beams, thereby increasing the amount of data obtained during scanning, improving scanning accuracy, and significantly increasing the scanning angle compared to the single-wedge prism laser scanning method. The width of the scanning area covered by the scanning trajectory can reach more than 22 times that of the single-wedge prism scanning method, enabling large-range scanning tasks;

[0018] 2. Compared with the double-wedge prism laser combined scanning method, the present invention not only obtains a relatively large laser scanning angle, but also has a compact structure, greatly reducing the volume and weight, which helps to reduce the load of the vehicle. At the same time, a faster rotation speed can be obtained during the laser scanning process, facilitating miniaturization and making the application more extensive;

[0019] 3. The present invention couples a transmissive metasurface with a wedge prism to achieve multiple scanning beams during rotation, greatly increasing the scanning area of the beams during laser scanning. It is particularly suitable for use as the laser scanning part of an airborne lidar and can also be applied to more laser scanning scenarios. Description of the Drawings

[0020] Figure 1 is a schematic structural diagram of the laser scanning device of the present invention;

[0021] Figure 2 is a schematic diagram of the beam propagation path of the laser scanning device in the embodiment;

[0022] Figure 3 is a distribution diagram of the laser landing point positions on the target surface one meter away after a single laser beam only passes through the transmissive metasurface in the embodiment;

[0023] Figure 4 is a distribution diagram of the laser landing point positions on the target surface one meter away after a single laser beam passes through the laser scanning device of the present invention in a stationary state in the embodiment;

[0024] Figure 5 is a trajectory diagram of the laser landing points on the target surface one meter away when the laser scanning device of the present invention is in a rotating state in the embodiment;

[0025] Figure 6 is a trajectory diagram of the laser landing points on the target surface one kilometer away when the laser scanning device of the present invention is in a rotating state in the embodiment;

[0026] Figure 7 is a comparison schematic diagram of the scanning areas of the laser scanning device of the present invention, the single-transmissive metasurface scanning method, and the single-wedge prism scanning method in the embodiment;

[0027] Figure 8It is the laser landing point trajectory diagram of the transmissive metasurface of the laser scanning device of the present invention in the embodiment at a rotation speed of 1 rad / s and a wedge prism with a deflection angle of 8 degrees at a rotation speed of 8 rad / s;

[0028] Figure 9 It is the laser landing point trajectory diagram of the transmissive metasurface of the laser scanning device of the present invention in the embodiment at a rotation speed of 1 rad / s and a wedge prism with a deflection angle of 8 degrees at a rotation speed of 3 rad / s;

[0029] Figure 10 It is the laser landing point trajectory diagram of the transmissive metasurface of the laser scanning device of the present invention in the embodiment at a rotation speed of 1 rad / s and a wedge prism with a deflection angle of 8 degrees at a rotation speed of 6 rad / s;

[0030] Figure 11 It is the laser landing point trajectory diagram of the transmissive metasurface of the laser scanning device of the present invention in the embodiment at a rotation speed of 1 rad / s and a wedge prism with a deflection angle of 8 degrees at a rotation speed of 15 rad / s;

[0031] Figure 12 It is the laser landing point trajectory diagram of the transmissive metasurface of the laser scanning device of the present invention in the embodiment at a rotation speed of 1 rad / s and a wedge prism with a deflection angle of 8 degrees at a rotation speed of 30 rad / s;

[0032] Figure 13 It is the laser landing point trajectory diagram of the transmissive metasurface of the laser scanning device of the present invention in the embodiment at a rotation speed of 1 rad / s and a wedge prism with a deflection angle of 2 degrees at a rotation speed of 8 rad / s.

[0033] In the figure: 1. Single-beam laser; 2. Transmissive metasurface; 3. Wedge prism; 4. Laser. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0035] Such as Figure 1As shown in the figure, a laser scanning device based on the dynamic coupling of a transmissive metasurface and a wedge prism includes a transmissive metasurface 2 and a wedge prism 3 arranged at intervals along the axis direction. The transmissive metasurface 2 can divide a single beam of laser 1 into multiple transmissive lasers with the same light intensity. The propagation directions of the multiple transmissive lasers all have deflection angles relative to the incident direction of the single beam of laser 1. The wedge prism 3 is arranged on the outgoing light path of the transmissive metasurface 2 and performs secondary deflection on the multiple transmissive lasers. For example, the transmissive metasurface 2 divides the single beam of laser 1 into seven transmissive lasers with the same light intensity and deflection angles of a°, ±b°, ±c°, and ±d° relative to the incident direction. The seven transmissive lasers are incident from the plane of the wedge prism 3 with a fixed wedge angle and are deflected by its inclined plane and then exit to the target surface. By controlling the transmissive metasurface 2 and the wedge prism 3 to rotate at the same or different speeds, corresponding scanning trajectories are generated to cover the target surface for laser scanning. Since the rotation speeds of the transmissive metasurface 2 and the wedge prism 3 are independently adjustable, the dynamic control of the scanning density can be achieved by adjusting the speed difference.

[0036] Preferably, the material of the transmissive metasurface 2 is single crystal silicon, and the material of the wedge prism 3 can be selected as BK7. BK7 is a common optical glass, widely used in the visible light and near-infrared bands, and has good transmittance and excellent processing performance.

[0037] As Figure 1 shown in the figure, a laser scanning method based on the dynamic coupling of a transmissive metasurface and a wedge prism includes the following steps:

[0038] First, a single beam of laser 1 is split into multiple transmissive lasers with different deflection angles by the transmissive metasurface 2;

[0039] Second, the multiple transmissive lasers are incident on the wedge prism 3 for secondary deflection, and the secondary deflection angle is determined by the refractive index and wedge angle of the wedge prism 3;

[0040] Finally, the transmissive metasurface 2 and the wedge prism 3 are rotated at the same speed or different speeds in the axis direction to dynamically adjust the laser scanning path. Among them, the mathematical expression of the deflection angle during the dynamic coupling of the transmissive metasurface 2 and the wedge prism 3 is as follows:

[0041]

[0042] In the formula: θ m is the total deflection angle of a single beam of laser after passing through the transmissive metasurface and the wedge prism, is the deflection angle of a single beam of laser after passing through the transmissive metasurface, m is the beam order, n is the refractive index of the wedge prism, and α is the wedge angle of the wedge prism.

[0043] Embodiment

[0044] In this embodiment, the material of the transmissive metasurface 2 is single-crystalline silicon with a thickness of 525 ± 15 μm. The material of the wedge prism 3 is BK7 optical glass, with a refractive index of 1.51 at a wavelength of 1064 nm and a wedge angle of 5.318° ± 0.002°.

[0045] As shown in Figure 2 , the laser 4 emits a single beam of laser 1 with a wavelength of 1064 nm. The transmissive metasurface 2 divides the single beam of laser 1 into seven transmitted lasers with the same light intensity and deflection angles of 0°, ±10°, ±30°, and ±50° relative to the incident direction. These seven laser beams then enter the wedge prism 3 and are deflected again to expand the scanning angle.

[0046] As shown in Figure 3 , it shows the distribution of the laser landing point positions on the target surface one meter away from the transmissive metasurface 2 after the single beam of laser 1 passes only through the transmissive metasurface 2.

[0047] Through the coupling of the transmissive metasurface 2 and the wedge prism 3, the present invention can further deflect the transmitted laser based on the transmissive metasurface 2. As shown in Figure 4 , it shows the distribution of the laser landing point positions on the target surface one meter away from the transmissive metasurface 2 after the single beam of laser 1 passes through the stationary transmissive metasurface 2 and the wedge prism 3. The common rotation of the transmissive metasurface 2 and the wedge prism 3 can generate a landing point trajectory in the form of concentric circles. As shown in Figure 5 , it shows the laser landing point trajectory formed on the target surface one meter away from the transmissive metasurface 2 in the rotating state. Move the target surface away from the transmissive metasurface 2 to a position of one kilometer. As shown in Figure 6 , it shows the laser landing point trajectory formed on the target surface one kilometer away from the transmissive metasurface 2 in the rotating state.

[0048] Compared with the single transmissive metasurface scanning method and the single wedge prism scanning method, the laser scanning device of the present invention can greatly increase the scanning area of the light beam during the scanning operation. As shown in Figure 7As shown, it presents the comparison of the scanning areas among the laser scanning device of the present invention, the single-transmissive metasurface scanning method, and the single-wedge prism scanning method. The conditions for the three scanning methods are the same, with a rotational speed of 20 rad / s, a distance of 100 m from the ground, and a working duration of 3 seconds. The direction indicated by the arrow in the figure is the flight direction of the aircraft. Among them, part (a) shows the scanning trajectory of the transmitted laser with the largest deflection angle of the laser scanning device of the present invention, part (b) shows the scanning trajectory of the single-transmissive metasurface scanning method, and part (c) shows the scanning trajectory of the single-wedge prism scanning method. The scanning area width of the laser scanning device of the present invention is 320 meters, while the scanning area width of the single-transmissive metasurface scanning method is 119.17 meters, and the scanning area width of the single-wedge prism scanning method is 14.06 meters, verifying that the present invention significantly increases the scanning area during the scanning operation.

[0049] In addition, the transmissive metasurface 2 and the wedge prism 3 in the laser scanning device of the present invention can also rotate at different speeds. With the change of the differential speed, the trajectory of the laser scanning landing point will also be adjusted accordingly. As shown in Figure 8 it presents the laser landing point trajectory when the transmissive metasurface 2 rotates at a speed of 1 rad / s and the wedge prism 3 with a deflection angle of 8 degrees rotates at a speed of 8 rad / s; as shown in Figure 9 it presents the laser landing point trajectory when the transmissive metasurface 2 rotates at a speed of 1 rad / s and the wedge prism 3 with a deflection angle of 8 degrees rotates at a speed of 3 rad / s; as shown in Figure 10 it presents the laser landing point trajectory when the transmissive metasurface 2 rotates at a speed of 1 rad / s and the wedge prism 3 with a deflection angle of 8 degrees rotates at a speed of 6 rad / s; as shown in Figure 11 it presents the laser landing point trajectory when the transmissive metasurface 2 rotates at a speed of 1 rad / s and the wedge prism 3 with a deflection angle of 8 degrees rotates at a speed of 15 rad / s; as shown in Figure 12 it presents the laser landing point trajectory when the transmissive metasurface 2 rotates at a speed of 1 rad / s and the wedge prism 3 with a deflection angle of 8 degrees rotates at a speed of 30 rad / s; as shown in Figure 13 it presents the laser landing point trajectory when the transmissive metasurface 2 rotates at a speed of 1 rad / s and the wedge prism 3 with a deflection angle of 2 degrees rotates at a speed of 8 rad / s.

[0050] In summary, the laser scanning device and method based on the dynamic coupling of transmissive metasurface - wedge mirror designed by the present invention have significant advantages compared with other laser scanning methods. It can achieve a large laser scanning angle and multiple scanning beams, and the device structure is compact. During the laser scanning process, it significantly increases the scanning area of the beam, and is particularly suitable for use as the laser scanning part of an airborne lidar, and can also be applied to more laser scanning scenarios.

[0051] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent conditions of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0052] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A laser scanning device based on dynamic coupling of a transmission metasurface and a wedge mirror, characterized in that: The invention comprises a transmissive metasurface (2) and a wedge-shaped prism (3) arranged at intervals along an axial direction. The transmissive metasurface (2) can split a single laser beam (1) into multiple transmissive laser beams with the same light intensity, and the propagation directions of the multiple transmissive laser beams have a deflection angle relative to the incident direction of the single laser beam (1). The wedge-shaped prism (3) is arranged on the outgoing light path of the transmissive metasurface (2) and performs secondary deflection on the multiple transmissive laser beams before emitting them to a target surface. By controlling the transmissive metasurface (2) and the wedge-shaped prism (3) to rotate at the same or different rotation speeds, a corresponding scanning track is generated to cover the target surface for laser scanning.

2. The laser scanning device based on dynamic coupling of transmission metasurface and wedge mirror according to claim 1, characterized in that: The material of the transmission type metasurface (2) is single crystal silicon, and the material of the wedge-shaped prism (3) is BK7 optical glass.

3. A laser scanning method based on dynamic coupling of a transmission metasurface and a wedge mirror, characterized in that: According to the laser scanning device of claim 1, the scanning method thereof comprises the following steps: First, a single laser beam (1) is split into multiple transmitted laser beams with different deflection angles by a transmissive metasurface (2); Secondly, multiple beams of transmitted laser light are incident on a wedge-shaped prism (3) for secondary deflection; Finally, the transmissive metasurface (2) and the wedge-shaped prism (3) are rotated at the same speed or different speeds in the axial direction to dynamically adjust the laser scanning path, wherein the deflection angle during the dynamic coupling between the transmissive metasurface (2) and the wedge-shaped prism (3) is mathematically expressed as follows: Where: θ m is the total deflection angle of a single laser beam after passing through the transmissive metasurface and the wedge prism, is the deflection angle of a single laser beam after passing through the transmission metasurface, m is the beam order, n is the refractive index of the wedge prism, and α is the wedge angle of the wedge prism.

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