A polarization lidar based on diffractive film reception

Abstract

The present invention discloses a polarization lidar based on a diffractive thin film receiver, which includes a laser (1), a beam splitting prism (BS) (2), a polarization modulation system (3), an optical emission system (4), a quarter-wave plate (5), a diffractive thin film (6), a polarization beam splitter (7), a collimator (8), a filter (9), a first photodetector (10), a second photodetector (11) and a signal acquisition and processing module (12). In the system, the diffractive thin film (6), the polarization beam splitter (7), the collimator (8) and the filter (9) form a polarization diffraction system (13), which, combined with the photodetector, can measure information such as the target distance and the degree of polarization. Compared with the lenses made of materials such as quartz used in traditional optical receiving systems, the mass areal density of the diffractive thin film is 4 orders of magnitude lower. In addition, the diffractive thin film can modulate the propagation direction of light waves and is insensitive to the polarization state of light within a certain scale range. Applying it to the receiving end of the polarization lidar can reduce the complexity of the system and achieve miniaturization, integration and lightweight of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of lidar, and in particular to a polarization lidar based on diffractive thin film reception. Background Art

[0002] As a new type of active detection technology, lidar has advantages such as high sensitivity and high time resolution, and has many applications in ranging, three-dimensional imaging, etc. As a type of lidar, polarization lidar loads the polarization state on the laser, which is beneficial to obtaining the characteristic information of the target. In the existing polarization lidar solutions, the optical receiving system generally uses optical lenses, polarizers, etc. for reception. The system is relatively complex, and the optical lens has a large weight, which is not conducive to the application of lidar in aerospace, vehicle-mounted, etc. In recent years, based on the diffraction principle of light, an optical element that realizes diffraction by etching a relief structure on a thin film substrate using micro-nano processing technology. The surface relief structure of it can be made below the order of 10 μm, and the areal mass density is 4 orders of magnitude lower than that of lenses made of materials such as quartz used in traditional optical reception. In addition, the diffractive thin film has a modulation effect on the propagation direction of the light beam and is insensitive to the polarization state of light within a certain scale range. Combined with a polarization beam splitting device to form a polarization diffraction receiving system, applying this system to the receiving end of a polarization lidar and combining it with a photodetector can realize the acquisition of information such as the target distance and polarization degree. At the same time, it can reduce the complexity of the polarization lidar system, which is beneficial to the integration, light weight and miniaturization of the system, and further beneficial to the application of the polarization lidar. Summary of the Invention

[0003] The purpose of the present invention is to reduce the system weight of the polarization lidar and the complexity of the system, and provide a polarization lidar based on diffractive thin film reception. The invention has the characteristics of clear principle, convenient operation, simple structure, etc. It combines a diffractive thin film element that has a modulation effect on the propagation direction of the light beam and is insensitive to the polarization state within a certain scale range with a polarization beam splitting device to form a polarization diffraction receiving system as the receiving end of the polarization lidar. Compared with the traditional optical receiving system, it can effectively reduce the weight of the lidar system and the complexity of the system.

[0004] The technical solution of the present invention is as follows: A polarization lidar based on diffractive thin film reception. The laser emitted by the laser passes through the beam splitting prism BS. A small part of the laser energy enters the photodetector and serves as the reference signal of the signal acquisition and processing module. Most of the laser energy enters the polarization modulation system, loads a predetermined polarization state, and is emitted by the optical emission system to reach the target. The echo signal after being reflected by the target surface passes through a quarter-wave plate, then passes through the polarization diffraction system, and the P light and S light are respectively focused on the first photodetectors a and b. At the same time, the generated electrical signals enter the signal acquisition and processing module for signal processing.

[0005] Furthermore, when the diffractive thin film element with a focusing effect is used at the receiving end of the lidar, it can effectively reduce the weight of the system compared with the traditional optical receiving lens.

[0006] Furthermore, by combining the diffractive thin film element with a photodetector, information such as the distance and polarization degree of the target can be received.

[0007] Furthermore, the diffractive thin film element has a small areal density, is easy to fold, and can easily achieve a large aperture. At the same time, the weight of the system will not increase significantly.

[0008] Furthermore, the diffractive thin film element is fabricated using optical design and can be designed differently according to application requirements.

[0009] Furthermore, when the diffractive thin film element is used at the receiving end of the lidar, chromatic aberration in thin film imaging does not need to be considered.

[0010] Furthermore, the diffractive thin film element can modulate the propagation direction of light waves and is insensitive to polarization states within a certain scale range. When combined with a polarization beam splitter to form a polarization diffraction system and applied at the receiving end of a polarization lidar, it can reduce the complexity of the system and achieve miniaturization, integration, and lightweighting of the system.

[0011] Furthermore, the combination of the polarization diffraction system and the first photodetector can measure the distance and polarization degree information of the target.

[0012] Furthermore, the diffractive thin film element is fabricated using optical design and can be designed differently according to different application requirements.

[0013] Furthermore, affected by its own dispersion, the diffractive thin film is more suitable for applications of monochromatic light such as lasers, which is beneficial for the separation of background light in the receiving system, thereby improving the signal-to-noise ratio.

[0014] The principle of the present invention is as follows:

[0015] Existing polarization lidar systems generally use lenses, polarizers, etc. as the optical receiving system, and the lenses are relatively heavy. The diffractive thin film used in the present invention can modulate the propagation direction of the light beam and form a polarization diffraction system with a polarization beam splitter. When applied at the receiving end of the polarization lidar, it can achieve beam splitting and focusing of polarized light, reduce the complexity of the polarization lidar system, and realize miniaturization and integration of the system. In addition, the areal density of the diffractive thin film is 4 orders of magnitude lower than that of lenses made of materials such as quartz used in traditional receivers. Compared with the receiving end of traditional polarization lidar systems, it can effectively reduce the weight of the lidar system and achieve lightweighting.

[0016] The advantages of the present invention compared with the prior art are as follows:

[0017] (1) Compared with the traditional optical receiving end, the thin film of the present invention can modulate the propagation direction of the light beam.

[0018] (2) Compared with the traditional optical receiving end, the thin film of the present invention can, through a polarization beam splitter and in combination with a photodetector, obtain information such as the target distance and polarization degree.

[0019] (3) Compared with the lenses made of materials such as quartz used in the traditional optical receiving end, the thin film of the present invention has a mass areal density 4 orders of magnitude lower and is lighter in mass under the same aperture.

[0020] (4) Compared with the traditional optical receiving end, the thin film of the present invention is fabricated using optical design and can be designed differently according to system requirements.

[0021] (5) When the thin film of the present invention is applied to a lidar, taking advantage of the monochromatic light of the laser, the problem of chromatic aberration in thin film imaging does not need to be considered.

[0022] (6) The thin film used in the present invention has a mature processing technology. The thin film is easy to fold, can achieve a large aperture, and can be applied to lidars with large-aperture reception, facilitating the detection of lidars at longer distances.

[0023] (7) The present invention has a clear principle and a simple structure, can effectively reduce the weight of the lidar system, and can achieve the lightweight, integration, and miniaturization of the lidar. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. is a schematic diagram of a lidar based on diffractive thin film reception according to the present invention. Among them, 1 is a laser, 2 is a beam splitter prism (BS), 3 is a polarization modulation system, 4 is an optical emission system, 5 is a quarter-wave plate, 6 is a diffractive thin film, 7 is a polarization beam splitter, 8 is a collimator, 9 is a filter, 10 is a first photodetector, 11 is a second photodetector, 12 is a signal acquisition and processing module, and 13 is a polarization diffraction system.

[0025] Figure 2 FIG. is a conceptual diagram of a polarization diffraction system. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0027] Embodiment 1

[0028] As Figure 1 shown, the present invention is a lidar based on diffractive film reception, comprising a laser 1, a beam splitter prism (BS) 2, a polarization modulation system 3, an optical emission system 4, a quarter-wave plate 5, a polarization diffraction system 13, a first photodetector 10, a second photodetector 11, and a signal acquisition and processing module 12. The first photodetector 10 includes first photodetectors a and b, and the polarization diffraction system 13 includes a diffractive film 6, a polarization beam splitter 7, two collimators 8, and two filters 9. The laser emits laser light, and after passing through the beam splitter prism BS, a small portion of the laser energy enters the second photodetector as a reference signal for the signal acquisition and processing module. Most of the laser energy enters the polarization modulation system, is loaded with a predetermined polarization state, and is emitted by the optical emission system to reach the target. The echo signal obtained after reflection from the target surface, after passing through the quarter-wave plate, passes through the polarization diffraction system 13, is received by the diffractive film 6, and then passes through the polarization beam splitter 7 to obtain P light and S light. The P light is focused on the first photodetector a through the collimator 8 and the filter 9, and the S light is focused on the first photodetector b through the collimator 8 and the filter 9. At the same time, the generated electrical signals enter the signal acquisition and processing module for signal processing. The present invention is a polarization lidar based on diffractive film reception. The diffractive film 6 and the polarization beam splitter 7 used in the system, in combination with the photodetectors a and b, can achieve the acquisition of information such as the target distance and polarization degree. Compared with lenses made of materials such as quartz used in traditional optical reception systems, the mass per unit area of the diffractive film is 4 orders of magnitude lower. In addition, it can modulate the propagation direction of light waves and is insensitive to the polarization state within a certain range. Applying it to the receiving end of a polarization lidar can reduce the complexity of the system and achieve miniaturization, integration, and lightweight of the system.

Claims

1. A polarization lidar based on diffractive film reception, characterized in that: It includes a laser (1), a beam splitter prism (BS) (2), a polarization modulation system (3), an optical emission system (4), a quarter-wave plate (5), a diffraction film (6), a polarization beam splitter (7), a collimator (8), a filter (9), a first photodetector (10), a second photodetector (11) and a signal acquisition and processing module (12). The first photodetector (10) includes first photodetectors a and b. The laser (1) emits laser light. After passing through the beam splitter prism BS (2), a small part of the laser energy enters the second photodetector (11) and serves as a reference signal for the signal acquisition and processing module (12). Most of the laser energy enters the polarization modulation system (3), is loaded with a predetermined polarization state, and is emitted by the optical emission system (4) to reach the target. The echo signal reflected from the target surface, after passing through the quarter-wave plate (5), passes through the polarization diffraction system (13), and the P light and S light are respectively focused on the first photodetectors a and b. The generated electrical signals enter the signal acquisition and processing module (12) for signal processing.

2. The polarization lidar based on diffractive film reception according to claim 1, characterized in that: Applying a thin-film optical element with a focusing effect to the receiving end of a lidar, compared with the quartz lens used in a traditional optical receiving system, the mass per unit area of the diffraction film is 4 orders of magnitude lower. Under the same large aperture, using the diffraction film is lighter in weight and can effectively reduce the weight of the system.

3. The polarization lidar based on diffractive film reception according to claim 1, characterized in that: The polarization beam splitter is a Glan laser polarization prism, a polarization beam splitter, or a Wollaston prism.

4. The polarization lidar based on diffractive film reception according to claim 1, characterized in that: The diffraction film element is insensitive to the polarization state within a certain scale range. Combined with the polarization beam splitter, it can form a new device, the polarization diffraction system (13). Among them, the echo signal passes through the polarization diffraction system (13), and the P light and S light are respectively focused on the first photodetectors a and b; it can be used as the receiving end of a polarization lidar, reducing the complexity of the polarization lidar system and facilitating the miniaturization, integration, and lightweight of the system.

5. The polarization lidar based on diffractive film reception according to claim 1, characterized in that: The combination of the polarization diffraction system (13) and the first photodetector (10) can realize the measurement of the distance and polarization degree information of the target.

6. The polarization lidar based on diffractive film reception according to claim 1, characterized in that: The diffraction film (6) is fabricated using optical design and can be designed differently according to different application requirements.

7. The polarization lidar based on diffractive film reception according to claim 1, characterized in that: Affected by its own dispersion, the diffraction film is more suitable for the application of monochromatic light such as laser, which is beneficial to the separation of background light in the receiving system, thereby improving the signal-to-noise ratio.

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