Design of a Transmitting Optical System for Large-Angle MEMS Lidar with High Spatial Resolution

Abstract

Lidar has been extensively used in various applications, such as autonomous driving, robot navigation, and drone obstacle avoidance, due to its advantages of a high resolution, high-ranging accuracy, and strong anti-interference ability. The micro-electro-mechanical systems (MEMS) lidar technology approach has gained popularity due to its miniaturization and semi-solid state. However, the small scanning angle of the MEMS scanning micromirror and the associated radar system cause issues, such as a limited scanning range and low spatial resolution, which hinder the wider use of MEMS lidar. To address the problems caused by the small scanning angle of the MEMS micromirror and the limitations of the current optical system, this study suggests a new MEMS lidar transmitting optical system that offers a wide scanning angle and high spatial resolution. It is based on an array reflector group and a Fresnel lens, which enables the large-angle scanning of the target area while maintaining high spatial resolution. The scanning range is 120° × 60°, the spatial resolution is 0.05° × 0.25°, and the beam-filling ratio reaches 90.63%.

1. Introduction

Lidar has been widely used in various applications, including autonomous driving, robot navigation, and drone obstacle avoidance, due to its advantages of a high resolution, high-ranging accuracy, and strong anti-interference capability [1,2,3,4]. MEMS micromirror laser radar is the most mature semi-solid laser radar at present due to its advantages such as miniaturization and a fast scanning speed. It is also the technical solution for large-scale applications and mass production. However, the main disadvantage of this solution is that the mechanical scanning angle of the micromirror is relatively small, which limits the scanning angle of the radar system, thereby limiting the overall performance and wide application of MEMS scanning laser radar. Therefore, if MEMS laser radar can achieve wide-angle scanning and a broad field of view for detection while maintaining a high scanning speed, high resolution, and long-range detection performance, the application scope of MEMS scanning imaging laser radar will be significantly expanded. It can be applied in various fields, including autonomous driving, target detection and tracking, drones, intelligent logistics, and smart transportation.

In addition to its mature production technology, MEMS scanning mirrors have advantages in terms of their cost and lifespan. MEMS reflectors can modulate, switch the light, and control the phase of the beam [5,6,7,8,9]. The small scanning angle restricts the application range of MEMS imaging lidar to a certain extent. Therefore, it is necessary to add auxiliary devices to increase its scanning angle, thereby meeting the needs of practical applications. Currently, there are three primary design methods to increase the system scanning angle: (1) Add scanning devices and utilize multiple MEMS micromirrors for combined scanning. (2) Use a mechanical turntable with a two-dimensional MEMS scanning micromirror for horizontal panoramic scanning. (3) Add an angle expansion optical system to the MEMS scanning micromirror to expand the scanning range.

The solution proposed in reference [10] involves using multiple MEMS micromirrors for combined scanning. The structure of this solution is simple. However, this solution requires the use of multiple MEMS scanning systems. If the number of combined systems is small, the scanning angle expansion is limited. When multiple systems are used in combination, synchronizing them and stitching together several frame point cloud images presents a significant challenge.

Reference [11] utilizes a mechanical turntable to drive the MEMS scanning system, enabling it to rotate horizontally and achieve a 360° panoramic scan. This solution is similar to the principle of mechanical rotating laser radar, except that MEMS scanning micromirrors replace the array of light sources and detectors. Therefore, in actual use, it will encounter the same problems as mechanical rotating laser radar, such as its large size and the strong influence of mechanical vibration.

Reference [12] uses the Snell window effect of the scanning beam to achieve two-dimensional spatial scanning. This solution immerses the MEMS micromirror in a liquid of mineral oil. While allowing the MEMS micromirror to vibrate, the liquid provides the Snell window effect, thereby expanding the scanning angle. Then, the laser spot is converted into plane light through a customized cylindrical prism, which can expand the scanning angle of the MEMS scanning micromirror to 150°. This method significantly expands the scanning angle of the MEMS micromirror; however, since the MEMS micromirror is immersed in liquid, its scanning frequency is greatly limited, and it cannot scan at high speeds. Furthermore, the quality of the beam significantly decreases after it has undergone refraction and reflection in the liquid, and the plane light becomes more divergent after passing through the cylindrical prism, making it difficult to detect distant targets. In summary, the scanning speed and detection distance of this solution are greatly limited. To improve this solution, consider replacing the mineral oil with a curved dome prism to expand the scanning angle of the MEMS micromirror; however, this approach still leaves a problem with large beam divergence.

Reference [13] proposes a solution that involves placing a positive lens in front of and a negative lens behind the MEMS micromirror to form an inverted Galileo system, thereby expanding the optical scanning angle of the MEMS micromirror. Although this method has a simple structure, the laser beam emitted after passing through the negative lens will increase the beam divergence angle. After long-distance transmission, the light spot becomes significantly larger, and energy dispersion becomes more pronounced. Moreover, the expanded scanning beam is unevenly distributed within the scanning range, resulting in dense beams in the center and sparse beams at the edges, which leads to a decrease in the quality of the point cloud image. Furthermore, when the number of scanning pulse laser beams remains unchanged, the scanning angle increases, resulting in a proportional decrease in the system’s spatial resolution. Moreover, the spatial beam-filling ratio also decreases, which may cause missed detection and a loss of the detection target. This is a problem faced by all solutions that utilize optical systems to expand the scanning angle.

References [14,15] are improvements on the above-mentioned positive and negative lens combination system, in which an F-θ lens is added to the optical system. The F-θ lens is also called a flat-field focusing lens. Its function is to make the image height of the beam after passing through the lens proportional to the field of view of the lens, ensuring that the laser beam is evenly distributed after passing through the lens. This solution addresses the issue of uneven scanning beams and significantly compresses the divergence angle of the outgoing laser beam, which is beneficial for long-distance transmission. After passing through the F-θ lens, it is transmitted to a wide-angle lens or a fisheye lens to achieve large-angle scanning. However, due to the addition of the F-θ lens system, the number of lenses in the entire optical system increases significantly, making system installation more difficult, the cost higher, and the overall system volume larger. Additionally, this solution still has the disadvantage of reducing the system’s spatial resolution.

References [16,17] describe a design that uses a MEMS micromirror to move in a spiral trajectory, along with a catadioptric optical system, to achieve panoramic scanning in the horizontal direction. This solution can achieve 360° detection in the horizontal direction, significantly expanding the scanning range, and has a simple structure. However, this solution has high requirements for the alignment of the prism center and the MEMS micromirror center, making the system difficult to assemble and adjust. Furthermore, due to the existence of the refracting and reflecting cone surface, the outgoing light beam will have a large beam divergence in the meridian or sagittal direction. The laser beam, after long-distance transmission, exhibits a flat spot, which significantly affects the energy distribution of the laser beam and the signal-to-noise ratio of the echo signal.

In addition, reference [18] proposes a new type of wedge structure to expand the system scanning angle. The magnifying structure is composed of a wedge structure made of glass and a reflector with a highly reflective film on the glass (called a back mirror). The incident laser is first reflected by the MEMS reflector to the back mirror, and these beams are referred to as first-order reflected beams. After the first reflection by the back mirror, the laser beam returns to the MEMS mirror. The beam reflected twice by the MEMS micromirror is referred to as a secondary reflected beam. The second-order beam is used as the scanning beam, and the secondary beam can be reflected more times to obtain a higher scanning level. This method does not contain any complex optical lenses or structures. Compared to other methods, the system is more compact and only requires a 1 mm increase in package height. However, this solution requires a larger MEMS reflector surface, and after several reflections, the quality of the outgoing beam deteriorates, and the scanning angle becomes deformed, which does not meet the requirements of high-performance navigation laser radar.

Due to the small mechanical scanning angle of the MEMS scanning micromirror, current technical solutions for achieving large-angle scanning in MEMS laser radar primarily include adding more scanning components, integrating mechanical turntable systems, and using optical angle expansion systems to increase the optical scanning angle of the MEMS micromirror. However, the above technical solutions all have some defects. For example, the quality of the scanning beam decreases after the scanning angle is extended, making it impossible to detect at a long distance. After adding the optical system, the overall system has several disadvantages, including an increased volume and assembly difficulty, as well as a decreased spatial resolution. Therefore, achieving the large-angle scanning of MEMS micromirrors while ensuring system miniaturization, a high spatial resolution, high frame rate, and long-distance detection remains a technical challenge.

Table 1. Different options for extending the scanning angle.

References	Technical Solution	Scan Angle	Spatial Resolution	Advantage	Disadvantages
[10]	multiple MEMS	/	/	Easy to operate	Limited expansion effect
[11]	mechanical turntable	360°	/	Panoramic imaging	Mechanical turntable structure
[12]	Snell window	150°	/	Simple structure	Beam quality deteriorates
[13]	Galileo system	53°	/	Simple structure	Resolution reduction
[14]	F-θ lens	57°	/	Small divergence angle	Resolution reduction
[15]	F-θ lens	60°	/	Small divergence angle	Resolution reduction
[16]	Panoramic Prism	360°	/	Panoramic imaging	Beam quality deteriorates
[17]	Panoramic Prism	360°	/	Panoramic imaging	Beam quality deteriorates
[18]	wedge structure	45.3° × 42.6°	/	Compact structure	Resolution reduction
This article	Fresnel prism	120° × 60°	0.05° × 0.25°	Both scanning angle and resolution	Multiple lasers

compares various technical solutions. All of these solutions achieve the expansion of the MEMS scanning mirror. Each solution has its own advantages and disadvantages, allowing users to choose the appropriate solution based on the specific scenario. However, these solutions fail to consider the system’s spatial resolution when considering angle expansion. Many solutions experience a proportional decrease in the spatial resolution after expanding the scanning angle, which is unacceptable for radar systems. The solution proposed in this paper addresses the issue of system spatial resolution while achieving extended scanning angles.

This study proposes a MEMS lidar transmitting optical system with a large angle and high spatial resolution based on an array reflector group and a Fresnel lens. The system uses an array reflector group to convert a sparse array laser beam into a compact array laser beam, overcoming the gaps between beams caused by the mechanical structure. The relationship between the laser beam divergence angle and spatial resolution is analyzed to determine the optimal system parameters and scanning scheme, achieving the highest beam space-filling ratio and maximizing the system’s detection efficiency. The Fresnel lens and a single MEMS micromirror are designed to work together to achieve the large-angle scanning of the array laser beam. While maintaining a high spatial resolution, the system achieves the large-angle scanning of the target area. This paper achieves a large scanning angle, high spatial resolution, and high beam-filling rate simultaneously through the combination of array laser beam, Fresnel prism, and scanning mirror.

2. Theoretical Analysis

2.1. Scanning Space Beam-Filling Ratio

During the imaging process with lidar detection, the beam divergence angle and spatial scanning resolution of the laser beam are two crucial parameters that, together, determine the scanning beam-filling ratio of the radar system for the target within the detection range. A good imaging lidar system will have both a small laser beam divergence angle and a high spatial scanning resolution. The higher the spatial resolution of the system, the stronger the ability to resolve target details, which is determined by the scanning range and the number of data points. A laser beam with a small divergence angle can ensure that the lidar system can detect at a longer distance. For example, when the divergence angle of the laser beam is 3 mrad, the spot becomes 3 m after transmitting 1 km. Although the divergence angle is only a few mrad, if it is not collimated, the spot diameter will be very large after reaching the distant target. Its shape and unit energy cannot meet the signal detection requirements. When the beam divergence angle is relatively large, the spot on the target may appear repeatedly, resulting in a waste of beam energy. The spot energy divergence is large, resulting in an echo signal that is too weak to be detected. Moreover, the beam divergence angle should not be too small. When the laser beam divergence angle is smaller than its spatial resolution, the target object may be missed due to the small beam spot and small beam filling in space, resulting in system decision errors. Therefore, when designing an imaging lidar system, the spatial scanning resolution and laser beam divergence angle of the system must be considered comprehensively.

The scanning space-filling ratio is defined as the ratio of the area of all the spots within the scanning angle to the area of the target area. Let the divergence angle of the laser beam be θ, the scanning angle is $(2{\omega }_x,2{\omega }_y)$, and the unit is mrad. The number of spots in the horizontal and vertical directions within the scanning angle is n and m, respectively. Then the area of a single spot at a distance of R is

$$S_i={\displaystyle \frac{\pi R^2{\theta }^2}{4}}$$

(1)

Therefore, the sum of all spot areas within the scanning range is

$${\displaystyle \sum S}={\displaystyle \frac{nm\pi R^2{\theta }^2}{4}}$$

(2)

The scanning space beam-filling ratio (${\eta }_s$) can be expressed as

$${\eta }_S={\displaystyle \frac{nm\pi R^2{\theta }^2}{4\times 2R\tan {\omega }_{x}2R\tan {\omega }_y}}\approx {\displaystyle \frac{nm\pi {\theta }^2}{16{\omega }_x{\omega }_y}}$$

(3)

The definition of the spatial angular resolution is the scanning angle divided by the number of laser beams collected in that direction. Its value is directly related to the target sampling rate. The horizontal angular resolution (${\delta }_x$) and vertical angular resolution (${\delta }_y$) are expressed as follows:

$${\delta }_x={\displaystyle \frac{2{\omega }_x}{n}},{\delta }_y={\displaystyle \frac{2{\omega }_y}{m}}$$

(4)

Assuming that in the scanning space, the horizontal and vertical scanning angles and the number of scanning laser beams are equal,

$${\omega }_x={\omega }_y,n=m$$

(5)

We are then able to obtain

$${\eta }_S={\displaystyle \frac{\pi {\theta }^2}{4{\delta }_x{\delta }_y}}={\displaystyle \frac{\pi {\theta }^2}{4{\delta }^2}}$$

(6)

Therefore, the scanning space-filling ratio is determined by the laser beam divergence angle and the system angular resolution. Figure 1 depicts the relationship between the filling ratio and the beam divergence angle and angular resolution. We can increase the laser beam pulse emission repetition frequency, reduce the scanning angle, and adjust the laser beam divergence angle to improve the scanning beam space-filling ratio. In the design, the laser beam divergence angle should be slightly smaller than the system spatial resolution, but not too much smaller. This ensures the system’s high beam space-filling ratio and high sampling rate for the detection target simultaneously.

The ratio of the beam divergence angle to the system spatial angular resolution is denoted as g and the scanning beam-filling rate can be expressed as

$${\eta }_S={\displaystyle \frac{\pi g^2}{4}}$$

(7)

The relationship curve between the scanning space beam-filling ratio and the dimensionless quantity (g) is shown in Figure 2. As the ratio g gradually increases, the beam-filling ratio also increases. However, a larger beam-filling ratio is preferable. If the beam-filling ratio becomes too large, the beams will overlap, significantly wasting the laser beam energy. Consequently, the performance requirements for components such as lasers and detectors will also become very high. Therefore, it is necessary to reasonably design the beam-filling ratio of the overall scanning angle. While ensuring a high sampling rate for the detection target, it is also necessary to minimize the loss of light energy caused by the overlap of beams.

As shown in Figure 3, the beam scanning conditions for the dimensionless quantity g are 2, 1.15, and 1. It can be obtained that when g is 2, the beams overlap significantly. When g is 1.15, although the beam-filling rate is close to 100%, it does not fully cover the scanning range. Since the beams are circular, some overlap occurs, but gaps remain between the beams. When g is 1, the scanning beams do not overlap, and the beam-filling rate is 78.5%. There is a relatively high sampling rate for the detection target and no beam overlap occurs. Simultaneously, the collimation requirements for the output beam are also reduced. Therefore, this system sets the ratio of the divergence angle of the laser beam to the spatial angular resolution of the system to 1.

When the laser beams are aligned in both the horizontal and vertical directions, the gap in the middle remains large. To further improve the filling ratio of the beams in the scanning space, this study proposes a hexagonal splicing method. During the scanning process, the starting positions of the laser beams in two adjacent rows differ by half a laser beam, as shown in Figure 4. Through calculation, the space-filling rate of this scheme can be increased to 90.63%.

2.2. Design of Emission Optical System with Large Angle and High Spatial Resolution

The scanning system utilizes a Fresnel prism to achieve a high filling ratio for a MEMS micromirror with a large angle, as illustrated in Figure 5. The light source of the system adopts an array of fiber laser beams that pass through a special Fresnel prism. After passing through the prism, the laser beams at different positions have different deflection angles. The outgoing beam can be converged onto the MEMS scanning micromirror via a reflector to ensure that the beam remains collimated. The MEMS micromirror then transmits appropriate control signals to scan the target area. Due to the mechanical structure and other factors, a large gap exists between the array laser beams. Such an arrangement will require a larger Fresnel prism, which is not conducive to the processing of the Fresnel prism and miniaturization design. Therefore, this study proposes using a reflector group to transform the laser beam array from a sparse array to a compact laser beam, thereby achieving beam deflection. The two sets of scanning systems are combined up and down to further improve the spatial resolution. When the upper and lower scanning systems are assembled and fixed, the two sets of array laser beams are arranged in a staggered manner in the vertical direction, with a spacing of half the distance between spots, meeting the requirements of the high filling ratio of the system.

The Fresnel lens described in this article differs from traditional Fresnel lenses, which are designed to better focus light beams. The primary function of the Fresnel lens designed in this article is to deflect the light beam, as the MEMS micromirrors are very small. Scanning the entire array laser beam at different angles through the MEMS micromirrors is a challenge. Therefore, the Fresnel prism designed in this article needs to deflect laser beams at different positions onto the MEMS micromirrors, while also distributing the array laser beams at different scanning angles. Furthermore, it is necessary to ensure that the emitted laser beams are parallel, without compromising the beam quality.

The system can use either a single-axis scanning mirror or a two-dimensional scanning mirror. The single-axis scanning mirror has a low cost, simple control, and a large horizontal scanning angle. The two-dimensional scanning mirror has a higher cost, but has a higher spatial resolution, as shown in Figure 6. The array laser beam can provide a denser laser dot matrix, and the scalability of this system is high.

The working principle of the reflector array is shown in Figure 7. The array reflector can be used to convert a sparse laser beam array into a compact laser beam array. This design can better match the subsequent Fresnel lens. By reasonably arranging the reflectors, the array laser beam with the original spacing of h₁ is converted into an array laser beam with a spacing of h₂. The distance h between the two reflectors and h₁ and h₂ form a right triangle. The relationship between the spacing of the sparse beam and the spacing of the compact beam is shown in Equation (9). Through two sets of reflector arrays, it can be achieved that the laser beam array and the Fresnel lens are not on the same plane, which reduces the difficulty of the system assembly process and makes the overall system more flexible.

$${\mathit{h}}_2=\sqrt{h^2-h_1^2}$$

(8)

The Fresnel lens in the system of this study serves as the flat Fresnel lens, which is the research object. The center of the lens is called the 0-th ring, the one immediately outside it is the 1st ring, and so on from the inside to the outside. The radius of the 0-th ring of the lens center is represented by h₀, and the distance from the midpoint of the i-th ring to the center of the lens is recorded as hi. Figure 8a illustrates a diagram of the convergent light path of vertically incident parallel light after traversing the Fresnel lens plane.

When parallel light is incident from the i-th ring prism, since the light is incident vertically, no deflection occurs at point M. However, when the light passes through the lens and reaches point N, the light is not perpendicular to the exit interface, and deflection occurs at this time.

Among them, θ_i is the inclination angle of the i-th annular surface, φ_i is the angle between the light and the optical axis when it converges to the focus, and φ_i is also the deflection angle of the light. As shown in Figure 8b, the refraction of the light at point N is magnified. At point N, when the light is transmitted from the i-th annular surface of the lens to the air, the incident angle is i₁, the exit angle is i₂, and the deflection angle of the light is φ_i. It can be obtained from the geometric relationship of the angles in the figure and the law of refraction.

$$\left\{\begin{array}{l}{i}_2=i_1+{\phi }_i\\ {\theta }_i=i_1\\ n\cdot \sin i_1=\sin (i_1+{\phi }_i)\\ \tan {\phi }_i={\displaystyle \raisebox{1ex}{$h_i$}\!\left/ \!\raisebox{-1ex}{$f$}\right.}\end{array}\right.$$

(9)

After the calculation, we obtain

$$\tan {\phi }_i=\tan {\theta }_i={\displaystyle \frac{\sin {\phi }_i}{n-\cos {\phi }_i}}$$

(10)

3. Optical Design and Parametric Analysis

The array reflector group proposed in this project enables the conversion of a sparse beam array into a compact beam array. Its structure and optical path tracing are shown in Figure 9 and Figure 10. From the optical path diagram, it can be seen that the sparse array beam is well converted into a compact beam through two sets of array reflectors, and the beam direction is rotated 90°. The spacing of the array laser beam is converted from 8 mm to a compact laser beam array of 3 mm.

A high-performance Fresnel prism that meets the requirements is designed through theoretical calculation. Using Zemax optical design software for simulation analysis, the overall optical path of the system is shown in Figure 11. After the array laser beam passes through the Fresnel lens, it remains parallel to the lens. All laser beams are reflected to the MEMS micromirror via a reflector. The MEMS micromirror performs one-dimensional scanning to achieve the large-angle and high-spatial-resolution scanning of the target plane. It can be seen that all laser beams are reflected onto the very small MEMS micromirrors. The beam quality of the laser beams after reflection does not deteriorate, and they remain parallel beams, with different beams distributed at different angles.

The three-dimensional structure of the Fresnel prism is shown in Figure 12. By designing the angles of different subunits, the precise control of the laser beam array is achieved.

Table 2. The angle parameter values.

Number of Rings	Tilt Angle (°)	Number of Rings	Tilt Angle (°)
0-th	0	±8-th	±11.96
±1-th	±1.56	±9-th	±13.33
±2-th	±3.11	±10-th	±14.65
±3-th	±4.57	±11-th	±15.94
±4-th	±6.14	±12-th	±17.11
±5-th	±7.63	±13-th	±18.40
±6-th	±9.10	±14-th	±19.57
±7-th	±10.55	±15-th	±20.66

lists the angle parameter values.

To verify the correctness of our design, we fabricated a simplified Fresnel prism and paired it with red and green lasers. The laser beams were deflected by the prism onto the MEMS micromirror, where they were reflected and scanned. The experimental schematic is shown in Figure 13, and the scanning results are shown in Figure 14. The figure shows that the red and green laser beams achieve alternating scanning, resulting in a higher spatial resolution for the system. Figure 15 illustrates a three-dimensional model of the array reflector group and the Fresnel lens.

4. Discussion

This study designed a MEMS laser radar-transmitting optical system with a large angle, high spatial resolution, and high filling ratio. By designing an array reflector group, the sparse laser beam array is converted into a compact laser beam array and the beam is folded 90°. The overall structure is more compact, which reduces the requirements for the subsequent Fresnel lens. The subsequent design of the matching Fresnel lens converges the array laser beam onto a MEMS micromirror with a very small facet, while maintaining the divergence angle of the laser beam. The relationship between the laser beam divergence angle and spatial resolution is analyzed, and a high-filling-ratio solution for hexagonal staggered scanning is proposed. The MEMS laser radar transmitting system designed in this study achieves large-angle scanning while ensuring the spatial resolution and using only a single MEMS micromirror. Furthermore, the system proposed in this study can be used in conjunction with the large-field-of-view-receiving optical system we proposed earlier [19], as presented in Figure 16.

The overall system allows for large-angle, high-spatial-resolution scanning and wide-field-of-view, high-efficiency reception in the MEMS laser radar system. The scanning system forms a laser beam spot on the target surface through an array laser beam. In the receiving optical system, the system uses a combination of an image–space telecentric system and a microlens array to correct the spatial lattice beams in different fields of view, achieving a parallel light output. This also overcomes the influence of the incident angle on the interference filter. In addition, after the echo signals from different fields of view pass through the image–space telecentric objective lens, the main light is parallel to the optical axis, and the converging light spot falls on the focal plane. The spatial lattice corresponds one-to-one to the unit lenses of the microlens array. Then, the echo beam is converged to a small-area element detector through a high-performance aspheric focusing lens to achieve large-field-of-view detection. The scanning system in this article and the above-mentioned receiving optical system together constitute a lidar system with a large field of view and high spatial resolution. Although the optical system in this article has the performance of a large scanning angle and high spatial resolution, the system currently requires the use of array laser beams and prism systems for beam deflection, which places high demands on the assembly and adjustment of the optical system. In the future, we will further optimize it using laser array chips and meta-lenses to continuously improve the performance parameters of the lidar system.

5. Conclusions

Lidar has been widely used in various applications, such as autonomous driving, robot navigation, and drone obstacle avoidance, due to its advantages of a high resolution, high-ranging accuracy, and strong anti-interference ability. The MEMS lidar technology route has been widely adopted due to its miniaturization and solid-state nature.

To address the small scanning angles in MEMS micromirrors and the limitations of the current supporting optical system, which cannot optimize both the scanning angle and spatial resolution simultaneously, this study proposes a MEMS lidar-transmitting optical system that uses a group of reflectors and a Fresnel lens to achieve wide scanning angles and high spatial resolution.

The array reflector group is used to convert the sparse array laser beam into a compact array laser beam, overcoming the gap between the beams caused by the mechanical structure. This study analyzed the relationship between the laser beam divergence angle and spatial resolution, determined the scanning scheme with the highest beam space-filling ratio, and achieved the highest system detection efficiency. Here, we designed a Fresnel lens and used a single MEMS micromirror to achieve the large-angle scanning of the array laser beam. While ensuring high spatial resolution, the system achieves large-angle scanning of the target area. The scanning range is 120° × 60°, the spatial resolution is 0.05° × 0.25°, and the beam-filling ratio reaches 90.63%.