A small facet element large field of view high condensing receiving optical system with anti-background light interference

Abstract

The application discloses a facet element large-view-field high-condensing light receiving optical system which is anti-background light interference and comprises a large-view-field image far field lens system, a microlens array and an aspheric focusing lens; the large-view-field image far field lens system converges receiving light beams of different view fields on the same focal plane, and main rays of echo light beams are parallel to an optical axis; the distance between the microlens array and the echo light beam focusing plane is the focal length of a sub-lens of the microlens array; the microlens array collimates and corrects echo light beams of different view fields, so that the outgoing light beams are parallel light beams; the corrected parallel light beams are focused through the aspheric focusing lens; and finally, the signal receiving of the large-view-field high-condensing light is realized through a small light-sensitive surface element detector. The application overcomes the problem that the view field of the small surface element detector is limited, guarantees high-condensing light receiving, overcomes the influence of the system caused by background light interference, and has strong expansibility.

Description

Technical Field

[0001] This invention belongs to the field of non-imaging optical system technology, and more specifically, it is a small-area, large-field-of-view, high-focusing light receiving optical system that resists background light interference. Background Technology

[0002] In recent years, driven by technologies such as internet information technology, optoelectronic sensors, optical communication technology, and automation control, artificial intelligence has entered a new stage of development. LiDAR, as an active depth sensor, is a product of the combination of traditional radar technology and modern laser technology. After decades of development, it has been widely applied and developed in fields such as laser mapping, laser tracking, laser space rendezvous and docking, laser remote sensing, and laser 3D imaging. Benefiting from the advantages of laser's good directionality and concentrated energy, LiDAR possesses unique advantages that traditional microwave radar and cameras lack: extremely high angular resolution, extremely high range resolution and ranging accuracy, the ability to acquire multiple images of the target, and strong anti-interference capabilities. Compared to microwave radar, it is smaller in size and mass, and has attracted widespread attention from research institutions both domestically and internationally.

[0003] For traditional imaging optical systems, several design methods exist to expand their signal receiving field of view, such as wide-angle lenses and fisheye lenses, and the size of charge-coupled image sensors (CCDs) is continuously increasing. However, in applications such as lidar systems, the photodetectors are not traditional CCD devices, but rather avalanche photodiode (APD) detectors with high response speed and high gain. The photosensitive surface diameter of an APD is much smaller than that of a CCD element, significantly reducing its receiving field of view and making it difficult to achieve large field of view detection. Furthermore, large-area array APD technology is not yet mature, and its manufacturing process is complex and costly. The element size of the InGaAs-APD detector corresponding to the 1550nm laser beam in the human eye-safe wavelength band is even smaller, making its manufacturing even more difficult. In addition, since the pulse width of the emitted laser pulse is generally only a few nanoseconds, the detector and subsequent signal readout circuit must also have very fast response speed and bandwidth, which is also a significant challenge. The staring receiver system with a single element has a simple structure, which can greatly simplify the design of the system and enable miniaturization, thereby improving the overall stability and practicality of imaging lidar and expanding its application range.

[0004] Currently, a relatively mature technique for increasing the receiving field of view of small-area detectors involves adding auxiliary optical systems such as field lenses, light cones, or immersion lenses after the receiving objective. While using field lenses, light cones, and immersion lenses to expand the receiving field of view can appropriately increase its range while maintaining focusing capability, these methods have limited effectiveness in expanding the receiving field of view for small-area detectors, cannot meet the system requirements for a large receiving field of view, and cannot overcome the influence of background light radiation. Summary of the Invention

[0005] In view of the above-mentioned problems in the existing technology, the present invention proposes a small-area-size, high-focusing optical receiving system that resists background light interference. It solves the problem of small receiving field of view of existing lidar small-area detectors, while ensuring that the system can achieve high-focusing detection and overcome background light interference.

[0006] The present invention can be solved by the following technical solutions:

[0007] A small-area, large-field-of-view, high-focusing optical receiving system with anti-background light interference includes a large-field-of-view image-side telecentric lens system, a microlens array, and an aspherical focusing lens. The large-field-of-view image-side telecentric lens system converges received beams from different fields of view onto the same focal plane, and the principal rays of the echo beams are all parallel to the optical axis. The distance between the microlens array and the focusing plane of the echo beam is the focal length of the sub-lens of the microlens array. The microlens array collimates and corrects the echo beams from different fields of view, making the outgoing beam a parallel beam. The corrected parallel beam is then focused by the aspherical focusing lens, and finally, a large-field-of-view, high-focusing signal is received through a small-photosensitive surface element detector.

[0008] Furthermore, the large field-of-view telecentric lens system consists of five lenses and an aperture stop, with a receiving field of view of 40°. When the field of view of the echo beams differs by 0.5°, the distance between the focal points is 260µm.

[0009] Furthermore, the entire microlens array is composed of a number of sub-lenses arranged in a regular pattern. Each sub-lens is plano-convex, with its four sides and bottom surface being flat, and its top surface being curved, which enables beam converging. The flat side surfaces of the sub-lenses ensure seamless connections between them.

[0010] Furthermore, the central radius of the microlens array is 13 mm, the diameter of a single microlens unit is 260 μm, and the focal length is 65 μm.

[0011] Furthermore, the material of the microlens array is glass BK7, n = 1.52.

[0012] Furthermore, it also includes an interference filter, which is disposed after the microlens array. The interference filter is formed by coating an optical thin film layer of a specific thickness on the glass surface using a vacuum coating method. It uses the interference principle to allow light waves in a specific spectral range to pass through, and the passed light waves are then focused by the aspherical focusing lens onto the small photosensitive surface element detector.

[0013] Furthermore, it also includes a semi-reflective prism, a second aspherical focusing lens, and a second detector. The semi-reflective prism is made of glass BK7 with a refractive index n of 1.52.

[0014] Beneficial effects:

[0015] This invention enables wide-field, high-focus broadband detection while overcoming the influence of different echo laser beams on the interference filter and overcoming background light interference. An image-side telecentric lens converges echo beams from different angles, ensuring the principal ray of the echo beam is parallel to the optical axis. The convergence points of echo beams from different angles are on the same focal plane. A microlens array collimates the converged beams from different angles, making the outgoing beam a parallel beam. The collimated parallel beam is then converged onto a small-area APD detector by an aspherical focusing lens, achieving wide-field, high-focus, and background light interference-resistant echo signal reception. This optical system can be widely applied in many non-imaging detection systems, such as lidar. This system overcomes the limited field of view of small-area detectors while ensuring high-focus reception and overcoming the influence of background light interference, and it has strong scalability. Attached Figure Description

[0016] Figure 1 This is a structural diagram of the present invention.

[0017] Figure 2 Schematic diagram of optical path design for image-side telecentric lens

[0018] Figure 3 Solid image of a microlens array

[0019] Figure 4 Optical path diagram after correction by microlens array

[0020] Figure 5 The graph shows the filtering performance of the interference filter for different incident angles and different wavelength laser beams.

[0021] Figure 6 System architecture diagram to overcome background light interference

[0022] Figure 7 Diagram of a small-area, large-field-of-view, high-concentration coherent receiving optical system Detailed Implementation

[0023] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Specific implementation method one:

[0025] This embodiment of the small-area, large-field-of-view, high-concentration light-receiving optical system includes a large-field-of-view image-side telecentric lens system 101, a microlens array 102, and an aspherical focusing lens 103. Combined with... Figures 1-4 This implementation method is described below.

[0026] The small-area, large-field-of-view, high-concentration light-receiving optical system described above, such as Figure 1 As shown, the system includes a large field-of-view image-side telecentric lens system 101. For received beams from different fields of view, the beams converge at the same focal plane after passing through the large field-of-view image-side telecentric lens system 101, and the principal rays of the echo beams are all parallel to the optical axis. Then, the distance between the microlens array 102 and the focusing plane of the echo beam is determined, and the distance is the focal length of the sub-lens of the microlens array. The microlens array collimates and corrects the echo beams from different fields of view, making the outgoing beam a parallel beam. The corrected parallel beam is then focused by an aspherical focusing lens 103, and finally, a large field-of-view, high-focus signal is received through a small photosensitive surface element detector 104.

[0027] The large field-of-view image-side telecentric lens system 101, as described above... Figure 2 As shown, it consists of five lenses 201, 202, 203, 204, and 205, and an aperture stop 206. It can be seen that echo beams from different fields of view converge onto the same focal plane, and each principal ray is parallel to the optical axis. When the fields of view of the echo beams differ by 0.5°, the distance between the focal points is 260µm. This distance is used to match the diameter and focal length of the sub-lenses in the microlens array.

[0028] The microlens array 102, as described above Figure 3 As shown, the entire microlens array 102 is composed of several sub-lenses arranged in a regular pattern. Each sub-lens is plano-convex, with its four sides and bottom surface being flat, and its top surface being curved, which enables beam converging. The flat side surface design of the sub-lenses ensures seamless connections between them. The sub-lenses have a side length of 260 μm, a focal length of 65 μm, and are made of BK7 material.

[0029] The aforementioned large field-of-view image-side telecentric lens system 101 and microlens array 102 combined system, such as Figure 4 As shown, the echo beam converges at the focal plane after passing through the image-side telecentric lens, and the principal ray is parallel to the optical axis. The microlens array is placed one focal length behind the focal plane, and the light rays are corrected into parallel beams after passing through the microlens array.

[0030] The aforementioned small-area, large-field-of-view, high-concentration light-receiving optical system as a whole, such as Figure 1As shown, the system consists of an image-side telecentric lens system 101, a microlens array 102, an aspherical focusing lens 103, and a small photosensitive surface element detector 104. The light beam is corrected into a parallel beam after passing through the microlens array 102. The aspherical focusing lens 103 is placed after the microlens array 102, and it converges the light beam onto the small photosensitive surface element detector 104. The distance between the detector 104 and the focusing lens 103 is the back focal length of the aspherical focusing lens. Specific Implementation Method Two:

[0032] This embodiment is a small-area, large-field-of-view, high-concentration optical receiving system that overcomes background light interference. The small-area, large-field-of-view optical receiving system that overcomes background light interference is based on Embodiment 1 by adding an interference filter 105.

[0033] Narrowband filters are mainly of two types: absorptive and interferometric. Absorptive filters are primarily based on colored glass, utilizing its ability to absorb specific wavelengths of light. The advantages of absorptive filters are good stability and uniformity, good beam quality, and low manufacturing cost. However, their disadvantage is a relatively large passband, typically greater than 30 nm, resulting in poor detection performance for weak signals. Interferometric filters are made by vacuum coating an optical thin film layer of a specific thickness onto the glass surface. A single piece of glass consists of multiple thin films, using the principle of interference to allow light waves within a specific spectral range to pass through. They have a narrow passband and better filtering performance. However, based on the principle of interference, different incident angles lead to different optical path differences, making interferometric filters very sensitive to the incident angle. Figure 5 The image shows the filtering performance of a narrowband filter for laser beams of different wavelengths at different incident angles. As the incident angle increases, the center wavelength shifts and the filtering performance decreases.

[0034] The receiving optical system of this invention corrects echo beams from different fields of view into parallel beams by placing an interference filter behind a microlens array. The system avoids the performance degradation of the interference filter due to varying incident angles and overcomes background light interference encountered during large field-of-view reception. The system structure is as follows: Figure 6 As shown.

[0035] Specific implementation method three: Combining Figure 3 This implementation method is described below.

[0036] This embodiment is a small-area, large-field-of-view, high-concentration coherent receiving optical system.

[0037] This embodiment is a coherent receiving system. Based on Embodiment 1, the coherent receiving system adds a reference beam, a semi-reflective prism 106, an aspherical focusing lens 107, and a detector 108. Its structure is as follows: Figure 7 As shown.

[0038] In very weak signal detection, coherent detection is often required, necessitating both spatial and temporal coherence between the reference and received beams. To achieve effective optical interference on the detector's photosensitive surface, heterodyne detection requires not only that the local oscillator beam and the incident signal beam have the same polarization direction and consistent energy flux vector (i.e., spatial angular collimation, coaxiality), but also that the wavefronts of the two beams have matching curvature. Studies show that to ensure spatial coherence, the incident angle θ between the local oscillator beam and the signal beam satisfies:

[0039]

[0040] Where λ is the laser wavelength and D is the diameter of the detector photosensitive surface.

[0041] The coherent system described in this invention corrects echo beams from different fields of view into parallel beams. After passing through a semi-reflective mirror, the received beam and the reference beam converge onto the detector, ensuring that the two beams can achieve good coherence.

[0042] This invention may have other embodiments. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A small-area, large-field-of-view, high-concentration light-receiving optical system with resistance to background light interference, characterized in that, This includes large field-of-view image-side telecentric lens systems, microlens arrays, and aspherical focusing lenses; The large field-of-view image-side telecentric lens system converges the received beams from different fields of view onto the same focal plane, and the principal rays of the echo beams are all parallel to the optical axis. The distance between the microlens array and the focusing plane of the echo beam is the focal length of the sub-lens of the microlens array. The microlens array collimates and corrects the echo beams for different fields of view, making the outgoing beam a parallel beam. The corrected parallel beam is then focused by the aspherical focusing lens, and finally the signal reception of a large field of view and high light concentration is achieved through a small photosensitive surface element detector.

2. The small-area, large-field-of-view, high-concentration light-receiving optical system with anti-background light interference according to claim 1, characterized in that, The large field-of-view telecentric lens system consists of five lenses and an aperture stop. Its receiving field of view is 40°. When the field of view of the echo beams differs by 0.5°, the distance between the focal points is 260µm.

3. The small-area, large-field-of-view, high-concentration light-receiving optical system with anti-background light interference according to claim 1, characterized in that, The entire microlens array is composed of several sublenses arranged in a regular pattern. Each sublens is plano-convex in shape, with its four sides and bottom surface being flat, and its top surface being curved, which enables beam convergence.

4. The small-area, large-field-of-view, high-concentration light-receiving optical system with anti-background light interference according to claim 1, characterized in that, The microlens array has a central radius of 13 mm, a diameter of 260 μm for each microlens unit, and a focal length of 65 μm.

5. The small-area, large-field-of-view, high-concentration optical receiving system with anti-background light interference according to claim 1, characterized in that, The microlens array is made of glass BK7, n = 1.

52.

6. The small-area, large-field-of-view, high-concentration light-receiving optical system with anti-background light interference according to claim 1, characterized in that, It also includes an interference filter, which is disposed after the microlens array. The interference filter is formed by coating an optical thin film layer of a specific thickness on the glass surface using a vacuum coating method. It uses the interference principle to allow light waves in a specific spectral range to pass through, and the passed light waves are then focused by the aspherical focusing lens onto the small photosensitive surface element detector.

7. The small-area, large-field-of-view, high-concentration light-receiving optical system with anti-background light interference according to claim 1, characterized in that, It also includes a semi-reflective prism, a second aspherical focusing lens, and a second detector. The semi-reflective prism is made of glass BK7 with a refractive index n of 1.52.

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