Laser imaging system, Lidar
By introducing a vortex coherent filter structure at the lidar receiver, the spatial coherence difference between the target echo and the scattering noise is utilized to effectively suppress the scattering noise, solving the problem of reduced signal-to-noise ratio in environments such as fog and rain, and improving imaging performance and signal-to-noise ratio.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INST OF OPTICS & ELECTRONICS CHINESE ACAD OF SCI
- Filing Date
- 2026-05-29
- Publication Date
- 2026-07-21
AI Technical Summary
In scattering environments such as fog and rain, existing lidar systems suffer from strong scattering and absorption of laser light by water droplets, resulting in a large amount of non-target echo noise at the receiver. This leads to a sharp drop in the signal-to-noise ratio, limiting imaging distance and accuracy.
A vortex coherent filter structure is set at the receiving end. By using vortex phase modulation and spatial filtering, the spatial coherence difference between the target echo signal and the scattered noise signal is utilized to effectively suppress the scattered noise signal.
Without relying on time gating or complex post-processing algorithms, it significantly improves imaging performance and signal-to-noise ratio in complex environments, and enhances the detection probability and imaging quality of target echo signals.
Smart Images
Figure CN122430871A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the fields of photoelectric detection and lidar technology, and more specifically, to a laser imaging system and lidar. Background Technology
[0002] In scattering environments such as fog and rain, existing lidar systems generate a large amount of non-target echo noise at the receiver due to the strong scattering and absorption of laser light by water droplets. This leads to a sharp drop in the signal-to-noise ratio, severely limiting the imaging distance and accuracy.
[0003] Existing technologies have improved the aforementioned problems through high-power laser technology, time-gating technology, algorithm post-processing methods, and spectral, polarization, and field-of-view filtering, but they still cannot effectively suppress scattering noise, resulting in poor imaging effects. Summary of the Invention
[0004] The purpose of this application is to provide a laser imaging system and a lidar, which uses a vortex coherent filter structure at the receiving end based on the spatial coherence difference between the target echo signal and the scattered noise signal to effectively suppress the scattered noise signal and improve the imaging performance in complex environments.
[0005] In a first aspect, embodiments of this application provide a laser imaging system, including: a laser emitting module, a vortex coherent filtering module, and an imaging module; the laser emitting module is used to emit a laser coherent signal toward a target to be detected; the vortex coherent filtering module is used to receive a scattered noise signal and a target echo signal reflected from the target to be detected, and based on the spatial coherence difference between the target echo signal and the scattered noise signal, performs phase modulation and spatial filtering on the target echo signal and the scattered noise signal to obtain a noise-suppressed target echo signal; the imaging module is used to receive the noise-suppressed target echo signal and perform imaging.
[0006] This application embodiment sets up a vortex coherent filtering module at the signal receiving end to perform vortex phase modulation and spatial filtering on the scattered noise signal and the target echo signal. In this process, based on the difference in spatial coherence between the target echo signal and the scattered noise signal, the optical front end of the scattered noise signal is suppressed, thereby improving the imaging performance in complex environments.
[0007] In some embodiments, the vortex coherent filtering module includes a vortex modulation module and a filtering module; the vortex modulation module is used to receive the scattered noise signal and the target echo signal, and to perform phase modulation on the scattered noise signal and the target echo signal to generate a modulated target echo signal and a modulated scattered noise signal; the filtering module is used to suppress the modulated scattered noise signal based on the difference in spatial energy distribution between the modulated target echo signal and the modulated scattered noise signal, so as to obtain a noise-suppressed target echo signal.
[0008] In this embodiment, the vortex coherent filtering module includes a vortex modulation module and a filtering module. The vortex modulation module applies vortex phase modulation to the received scattered noise signal and the target echo signal, causing them to form different spatial energy distributions. Then, the filtering module preferentially transmits the modulated target echo signal and effectively suppresses the modulated scattered noise signal, achieving physical blocking of noise photons, thereby increasing the detection probability of the target echo signal and improving imaging performance in complex environments.
[0009] In some embodiments, the length of the propagation optical path between the vortex modulation module and the filtering module is configured such that the modulated target echo signal forms a stable ring energy distribution when it reaches the filtering module.
[0010] In this embodiment, the propagation optical path between the vortex modulation module and the filtering module enables the modulated target echo signal to form a stable ring energy distribution when it reaches the filtering module, thereby improving the spatial selectivity of the filtering module for the target echo signal and the scattered noise signal, and thus improving the noise suppression effect.
[0011] In some embodiments, the vortex modulation module includes a vortex phase plate, a diffractive optical element, a liquid crystal device, a metasurface structure, a spatial light modulator, a grating, or a prism assembly.
[0012] In this embodiment, the vortex modulation module can be implemented in various ways and is not limited to a single device form, which improves the implementation flexibility of the vortex modulation module and thus improves the universality of the laser imaging system.
[0013] In some embodiments, the filtering module includes a masked window, an aperture group, an annular aperture, an adjustable aperture, an optical fiber coupling structure, or a mode-selective coupling structure.
[0014] In this embodiment, the filtering module can be implemented in various ways and is not limited to a single device. The filtering module can selectively transmit the target echo signal through spatial obstruction or selectively transmit the target echo signal through spatial mode selective coupling, thereby improving the implementation flexibility of the filtering module and the applicability of the laser imaging system.
[0015] In some embodiments, the laser imaging system further includes a transmitting optical path and a receiving optical path; the laser coherent signal is transmitted to the target to be detected via the transmitting optical path; the target echo signal is transmitted via the receiving optical path and enters the vortex coherent filtering module.
[0016] In this embodiment, by setting up a transmitting optical path and a receiving optical path, the laser coherent signal is transmitted to the target to be detected, and the target echo signal is transmitted to the vortex coherent filtering module. The transmitting and receiving optical paths can adopt either a coaxial or non-coaxial structure, thereby enabling the laser imaging system of this application to be adapted to different optical path layouts.
[0017] In some embodiments, the transmitting optical path and the receiving optical path are scanning and transmitting coaxial optical paths; the scanning and transmitting coaxial optical path includes a polarizing beam splitter prism, a fast reflector, and an adjustable focus lens arranged sequentially along the optical path.
[0018] In this embodiment, when the transmitting optical path and the receiving optical path are coaxial optical paths, the propagation paths of the transmitting light and the receiving light in space are basically coincident, which is beneficial to maintaining the spatial matching relationship between the target echo signal and the vortex coherent filter module during scanning or imaging, and improving noise suppression and imaging stability.
[0019] Furthermore, the coherent laser signal output by the laser emitting module is coupled into the coaxial optical path through a polarization beam splitter prism, undergoes spatial deflection under the control of a fast reflector, and then exits through an adjustable focus lens to the target to be detected. The target echo signal reflected back from the target to be detected returns along the original path, passes through the adjustable focus lens and the fast reflector, and returns to the polarization beam splitter prism. The polarization beam splitter prism guides the signal to the receiving end and the subsequent vortex coherent filter module, which helps to maintain the spatial matching relationship between the target echo signal and the vortex coherent filter module during the scanning process, thereby improving noise suppression and imaging stability.
[0020] In some embodiments, the imaging module includes a detector and an imaging processing module; wherein the detector is used to detect the noise-suppressed target echo signal; and the imaging processing module is used to perform imaging based on the noise-suppressed target echo signal.
[0021] In this embodiment, the imaging module includes a detector and an imaging processing module; wherein, the detector detects the target echo signal after noise suppression, and the imaging processing module images the target echo signal, thereby improving the imaging performance in complex environments.
[0022] In some embodiments, the laser imaging system further includes a collimator; wherein the collimator is disposed in the emitted light path and is used to collimate the laser coherent signal.
[0023] In this embodiment, by setting a collimator in the emission optical path, the coherent laser signal emitted by the laser emission module is converted into an approximately parallel collimated beam, thereby improving the quality of the emitted beam.
[0024] Secondly, embodiments of this application provide a lidar, which includes the laser imaging system of any embodiment of the first aspect.
[0025] Other features and advantages of this application will be set forth in the following description, and some features and advantages may be learned by practicing the embodiments of this application. Attached Figure Description
[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a schematic diagram of the structure of a first laser imaging system provided in an embodiment of this application; Figure 2 This is a schematic diagram of the structure of a second laser imaging system provided in an embodiment of this application; Figure 3 The figure shows the experimental results of a single-photon lidar vortex coherent filtering comparison in a dense fog scene, as provided in the embodiments of this application.
[0028] Icons: 10-Laser imaging system, 11-Laser emission module, 12-Vortex coherent filter module, 13-Imaging module, 14-Scanning and transmitting coaxial optical path, 15-Collimator, 16-Target to be detected, 121-Vortex modulation module, 122-Filtering module, 131-Detector, 132-Imaging processing module, 141-Polarization beam splitter prism, 142-Fast reflecting mirror, 143-Adjustable focusing lens. Detailed Implementation
[0029] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.
[0030] It should be noted that all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.
[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0032] In scattering environments such as fog and rain, existing lidar systems generate significant non-target echo noise at the receiver due to the scattering and absorption of laser light by fog droplets and raindrops. This leads to a decrease in the signal-to-noise ratio, limiting imaging distance and accuracy. To address these issues, existing technologies primarily improve upon them through the following methods: (1) High-power laser technology: Increasing the laser power can compensate for the energy attenuation caused by atmospheric scattering and absorption during propagation, ensuring sufficient energy to return to the detector and extending the effective detection range. However, when the active illumination laser power is increased, the intensity of backscatter noise will also increase with the increase of laser power. For systems using single-photon detectors, excessively strong backscatter noise may increase the probability of noise triggering and reduce the effective detection efficiency of the target signal.
[0033] (2) Time gating technology, also known as time gate or range gate: This technology controls the detector to operate within a predetermined time window when the reflected light from the target arrives through precise delay and fast gating, in order to suppress some noise in the non-target time domain range. However, time gating technology limits the time window for detector signal acquisition and is difficult to suppress noise in the same or similar time domain range as the target echo, such as amplified spontaneous emission noise during laser operation, environmental noise, or multiple scattering noise generated inside the scattering medium. When the target is inside the scattering medium, some backscattering noise may be distributed in the same or similar time domain range as the target echo signal, resulting in a reduced suppression effect of time gating on this type of noise.
[0034] (3) Post-processing methods of algorithms: such as first photon imaging, few photon imaging, depth sensing fusion and computational imaging, etc. Their effectiveness is essentially limited by the signal-to-noise ratio level of the original echo signal, which cannot improve the quality of the original signal at the detector receiver. They also have a real-time bottleneck and are difficult to meet the high-speed response requirements of scenarios such as autonomous driving.
[0035] (4) Spectral, polarization, and field-of-view filtering: This type of method can suppress some background noise, but when the noise and the target echo are similar in terms of spectral, polarization, or spatial field-of-view characteristics, the ability to suppress fog-induced multiple scattering noise is limited.
[0036] Therefore, existing technologies generally have the following shortcomings: they cannot effectively suppress scattering noise across the entire time domain without shortening the detection time window.
[0037] To address the shortcomings of existing technologies, this application provides a laser imaging system and a lidar system. Based on the spatial coherence difference between the target echo signal and the scattered noise signal, a vortex coherent filter structure is set at the receiving end to suppress the optical front-end of the scattered noise signal, thereby improving imaging performance in complex environments. This application is applicable to three-dimensional imaging and target detection in complex propagation environments such as fog, rain, and scattering media, and is also applicable to other imaging fields involving active illumination using coherent light. Specifically, it can be applied to scenarios requiring the removal of scattered noise and other incoherent noise, such as coherent light illumination detection and imaging. Specific scenarios include, but are not limited to, the following: (1) All-weather environmental perception in autonomous driving and advanced driver assistance systems; (2) Navigation and monitoring in low-visibility conditions such as ports, waterways, and airports; (3) Three-dimensional detection of drones and unmanned ships in fog and rain environments.
[0038] Figure 1 This is a schematic diagram of the structure of the first laser imaging system provided in the embodiments of this application, as shown below. Figure 1 As shown, the laser imaging system 10 includes: a laser emitting module 11, a vortex coherent filtering module 12, and an imaging module 13; the laser emitting module 11 is used to emit a laser coherent signal to the target 16 to be detected; the vortex coherent filtering module 12 is used to receive the scattered noise signal and the target echo signal reflected from the target to be detected, and based on the spatial coherence difference between the target echo signal and the scattered noise signal, it performs phase modulation and spatial filtering on the target echo signal and the scattered noise signal to obtain the target echo signal after noise suppression; the imaging module 13 is used to receive the target echo signal after noise suppression and perform imaging.
[0039] The vortex coherent filter module 12 is an optical filter structure with vortex coherent characteristics. For example... Figure 1 As shown, the vortex coherent filter module 12 is set at the signal receiving end to receive the scattered noise signal and the target echo signal reflected from the target to be detected, and to perform phase modulation and spatial filtering on the scattered noise signal and the target echo signal to obtain the target echo signal after noise suppression.
[0040] The scattering noise signal includes non-target noise signals such as backscattering and multiple scattering caused by fog droplets, raindrops or other scattering media during the transmission of the laser coherent signal to the target to be detected, and scattering noise signals generated or superimposed by the scattering medium as the target echo signal returns from the target to the receiver; and may also include other non-target echo components introduced by the scattering medium and background noise components that enter the receiver along with the target echo signal.
[0041] The laser emitting module 11 can be a distributed feedback laser, a distributed Bragg reflector laser, a fiber laser, etc. The specific type can be selected and configured according to the actual situation; this application does not impose any specific limitations on this.
[0042] The imaging module 13 receives the noise-suppressed target echo signal and converts it into an electrical signal to ultimately form a target image. The imaging module 13 can be composed of a photodetector, a front-end readout circuit, a spatial multi-pixel array (optional), and a signal processing unit.
[0043] This application embodiment introduces an optical filtering structure based on vortex coherence characteristics at the signal receiving end, which enables effective suppression of noise signals based on "spatial coherence difference" without relying on time gating or complex algorithm post-processing, thus significantly improving imaging performance in complex environments.
[0044] In some embodiments, the vortex coherent filtering module 12 includes a vortex modulation module 121 and a filtering module 122; the vortex modulation module 121 is used to receive the scattered noise signal and the target echo signal, and to perform phase modulation on the scattered noise signal and the target echo signal to generate a modulated target echo signal and a modulated scattered noise signal; the filtering module 122 is used to suppress the modulated scattered noise signal based on the difference in spatial energy distribution between the modulated target echo signal and the modulated scattered noise signal to obtain a noise-suppressed target echo signal.
[0045] In the above implementation process, the vortex modulation module 121 is used to apply helical phase modulation to the received signal to generate a beam carrying a helical phase structure, the intensity distribution of which is usually "a ring with a dark core". By changing the modulation phase of the vortex modulation module 121, various irregular rings can be generated, such as: elliptical rings, C-rings, polygonal rings, nested multi-rings, etc.
[0046] In specific implementation, the vortex modulation module 121 can be configured as a vortex phase plate, a diffractive optical element, a liquid crystal device, a metasurface structure, a spatial light modulator, a grating, or a prism group.
[0047] The working principle of the vortex modulation module 121 is as follows: (1) The target echo signal is spatially coherent light, which can form a stable ring vortex energy distribution after passing through the vortex modulation module 121; (2) The scattered noise signal is spatially incoherent light. After passing through the vortex modulation module 121, it is still randomly distributed and cannot form a stable vortex structure.
[0048] The filtering module 122 is a spatial filtering kit. Its core function is to achieve selective transmission of the modulated target echo signal and suppression of the modulated noise signal based on the difference in spatial energy distribution between the target echo signal after vortex phase modulation and the scattered noise signal.
[0049] Therefore, the filtering module 122 is used to selectively transmit the modulated target echo signal and suppress the modulated scattering noise signal based on the difference in spatial energy distribution between the modulated target echo signal and the modulated scattering noise signal, so as to obtain the noise-suppressed target echo signal.
[0050] In the specific implementation process, the filter module 122 is a ring spatial filter, which can be set as a window with a mask or an aperture group.
[0051] The working principle of filter module 122 is as follows: By using a ring-shaped spatial filter matched with the vortex energy ring, most of the incoherent noise is blocked, and the target coherent echo is efficiently transmitted.
[0052] Through the aforementioned vortex modulation module 121 and filtering module 122, full-time domain noise suppression is achieved without introducing time gating or compressing the detection time window.
[0053] In the specific implementation process, since the vortex modulation module 121 can generate ring structures of different shapes by modulating the phase, in order for the filter module 122 to effectively transmit the vortex energy ring and suppress the scattered noise signal, the filter module 122 should be matched with the vortex modulation module 121.
[0054] Furthermore, since the target echo signal modulated by the vortex modulation module 121 usually needs to travel a certain distance to form a stable ring energy distribution suitable for spatial selection by the filter module 122, there is a propagation optical path between the vortex modulation module 121 and the filter module 122.
[0055] The propagation optical path refers to the optical path between the vortex modulation module 121 and the filtering module 122 for the propagation of the modulated light field. It can be a free-space optical path, a folded optical path, or other optical path that can maintain the propagation of the modulated light field. The length of the propagation optical path is configured to ensure that the modulated target echo signal forms a stable ring energy distribution when it reaches the filtering module 122.
[0056] The filter module 122 is positioned to match the stable ring energy distribution in order to improve the selective transmission capability of the target echo signal and enhance the suppression effect on the scattered noise signal.
[0057] To clarify how to determine the matching filter module 122 based on the vortex modulation module 121 and the propagation optical path between them, the specific steps are as follows: (1) Add a vortex light conversion element to the signal receiving end as a vortex modulation module 121. When adding the vortex light conversion element, make sure that the center of the vortex light conversion element is aligned with the center of the beam at the signal receiving end.
[0058] (2) The vortex-modulated light field is measured using a graduated aperture, CCD, or CMOS camera to obtain relevant parameters of the vortex light. These parameters include the propagation distance required to form a stable annular energy distribution, the diameter of the dark core at the center of the vortex light, and the diameter of the outer ring of the vortex light. The propagation distance required to form a stable annular energy distribution refers to the distance or range from the vortex modulation module 121 to the location where the stable annular energy distribution is formed. The diameter of the dark core at the center of the vortex light refers to the diameter of the low-intensity region at the center of the vortex ring at the location of the stable annular energy distribution. The diameter of the outer ring of the vortex light refers to the diameter corresponding to the outer boundary of the vortex light energy ring at the location of the stable annular energy distribution.
[0059] (3) Fabricate a spatial filtering kit that matches the diameter of the dark core at the center of the vortex beam and the diameter of the outer ring of the vortex beam. The spatial filtering kit is used to preferentially transmit the target echo signal corresponding to the vortex beam ring region and suppress non-target noise signals.
[0060] (4) At the location where a stable annular energy distribution is formed, the spatial filter kit prepared in (3) above is set to form filter module 122. When adding the spatial filter kit, pay attention to aligning it with the center of the beam at the signal receiving end to ensure that the vortex light conversion-spatial filter kit group works normally.
[0061] As described above, the relevant parameters of vortex light include the propagation distance required to form a stable annular energy distribution, the diameter of the dark core at the center of the vortex light, and the diameter of the outer ring of the vortex light. These parameters are related to the order of the vortex light conversion element, the incident beam parameters, the incident beam wavelength, and the propagation distance. To enable those skilled in the art to implement the technical solution of this application, the parameter matching relationship is explained using a vortex phase plate (VPP) as an example.
[0062] In one specific implementation, the signal receiver employs a 20th-order vortex phase plate (VPP) to modulate the target echo signal and scattered noise signal using vortex phase modulation. Experimental measurements, combined with system setup, show that under an incident beam wavelength of 1550 nm, the vortex-modulated received light field, after passing through a 0.6 m folded propagation path, forms a stable annular energy distribution. Therefore, an annular spatial filter is placed at this location for spatial filtering. The annular through-hole mask used in the annular spatial filter has the following parameters: inner diameter 6.2 mm (determined by the diameter of the dark core at the center of the vortex beam), and outer diameter 18 mm (determined by the diameter of the outer ring of the vortex beam). This annular through-hole mask is fabricated using methods such as 3D printing and is used to selectively transmit the vortex energy ring, blocking scattered noise signals that have not formed a stable annular distribution.
[0063] It should be understood that when the order of the vortex phase plate decreases (e.g., to 10th order), the size of the vortex dark core decreases, and the outer ring diameter decreases accordingly. The size of the spatial filter needs to be scaled proportionally to ensure that only a stable annular energy distribution region is transmitted. When the incident beam aperture increases, the outer ring diameter of the vortex increases accordingly, and the size of the spatial filter needs to be enlarged to match the vortex energy distribution.
[0064] As can be seen from the above, both the vortex modulation module 121 and the filtering module 122 can be implemented in various ways. Therefore, in this embodiment, the vortex modulation module 121 and the filtering module 122 are not limited to a single device form. The inventive concept is to apply helical phase modulation to the received echo, so that the target echo signal and the scattered noise signal form different spatial energy distributions after propagation, and to achieve preferential transmission of the target signal and suppression of the noise signal through subsequent spatial filtering. Therefore, any device combination that can achieve the above-mentioned "vortex phase modulation + spatial selective filtering" function can be used to implement the technical solution of this application.
[0065] Here are some examples illustrating different combinations of devices: In one embodiment, the vortex modulation module 121 can be implemented using diffractive optical elements, and the filtering module 122 can be implemented using a window with an annular mask or an annular aperture. In this combination, the target echo signal with good spatial coherence forms a stable annular energy distribution after propagation over a certain distance after vortex phase modulation; while the scattered noise signal with poor spatial coherence usually cannot form a stable and clear annular structure after the same modulation. At this time, by setting an annular spatial filter that matches the annular energy distribution of the target echo, the target echo can be preferentially transmitted and noise suppressed. This combination has a simple structure, good stability, is easy to manufacture and integrate, and is suitable for engineering implementation.
[0066] In one embodiment, the vortex modulation module 121 can be implemented using a spatial light modulator, and the filtering module 122 can be implemented using an adjustable aperture or a replaceable mask. This combination is suitable for parameter adjustment and experimental verification under different operating conditions. The spatial light modulator can generate vortex phase distributions with different parameters by loading different phase patterns, while the adjustable aperture or replaceable mask can be matched according to the diameter of the dark core and the outer ring diameter formed after modulation, thereby achieving selective transmission of the target echo signal. The advantage of this method is its high flexibility, which makes it easy for those skilled in the art to optimize it according to different wavelengths, different beam parameters, and different propagation distances.
[0067] In one embodiment, the vortex modulation module 121 can be implemented using a metasurface structure, and the filtering module 122 can be implemented using a window with an annular mask, a micro / nano-fabricated annular aperture, or other equivalent spatial selection structures. This combination offers advantages such as compact devices and high integration, making it suitable for scenarios with high requirements for system size and stability. Its working mechanism is the same as the aforementioned methods, utilizing the difference in spatial energy distribution between the target echo signal and the scattered noise signal after vortex phase modulation, and achieving noise suppression through a subsequent matched spatial filtering structure.
[0068] It should be noted that although the specific implementations of the above-mentioned different device combinations differ, their working principles are consistent. They all utilize vortex phase modulation to form a stable and identifiable ring-shaped energy distribution in the target echo signal, and then selectively transmit this distribution through a spatial filtering structure, thereby suppressing scattering noise signals. Therefore, different vortex modulation devices such as diffractive optical elements, spatial light modulators, and metasurfaces, as well as different spatial filtering devices such as masked windows, ring apertures, and adjustable apertures, are all specific implementations or equivalent alternatives of the inventive concept of this application.
[0069] Furthermore, all of the above-mentioned combinations can suppress scattering noise signals at the signal receiver without relying on time gating or compressing the detection time window. This increases the proportion of target echo signals entering the detector, improves the original signal-to-noise ratio, and enhances subsequent imaging quality. Among these, the combination of diffractive optical elements and annular apertures is more suitable for engineering implementation, the combination of spatial light modulators and adjustable apertures is more suitable for experimental debugging and parameter optimization, and the combination of metasurfaces and matched spatial filter structures is more suitable for system miniaturization and integration.
[0070] In this embodiment, the vortex coherent filtering module includes a vortex modulation module and a filtering module. The vortex modulation module applies vortex phase modulation to the received scattered noise signal and the target echo signal, causing them to form different spatial energy distributions, thus obtaining modulated target echo signals and modulated scattered noise signals. Then, the filtering module preferentially transmits the modulated target echo signal and effectively suppresses the modulated scattered noise signal, achieving physical blocking of noise photons, thereby increasing the detection probability of the target echo signal and improving imaging performance in complex environments.
[0071] It should be noted that the filter module 122 can also be replaced by an annular aperture, an adjustable aperture, an optical fiber coupling structure, or a mode-selective coupling structure.
[0072] The essence of this optical fiber structure is a spatial mode-selective coupling mechanism. Specifically, spatial selective coupling based on single-mode fiber is achieved as follows: adjusting the fiber coupling position to align it with the energy concentration region of the vortex ring; utilizing the mode-selective characteristics of single-mode fiber for the incident light field, only light satisfying specific spatial distribution and mode matching conditions is allowed to couple into the fiber; for target echo signals forming a stable ring structure, their local region can effectively match the fiber's fundamental mode, thus achieving partial coupling; for spatially randomly distributed scattered noise signals, their mode matching with the fiber's guided mode is low, significantly reducing coupling efficiency. This achieves prioritized transmission of the target signal and suppression of noise signals.
[0073] In some embodiments, the laser imaging system 10 further includes a transmitting optical path and a receiving optical path; the laser coherent signal is transmitted to the target to be detected via the transmitting optical path; the target echo signal is transmitted via the receiving optical path and enters the vortex coherent filtering module 12.
[0074] In the above implementation, the transmitting and receiving optical paths are set up independently. In this case, the system typically includes independent transmitting mirror groups, scanning mirror groups, and receiving mirror groups. The transmitted beam illuminates the target through an independent transmitting optical path, while the target echo enters the receiving end through another independent receiving optical path. At this time, the vortex coherent filter module 12 is set in the receiving optical path to separate the target signal from the scattered noise in the echo, while the transmitting optical path does not need to pass through this filter module.
[0075] Figure 2 This is a schematic diagram of the structure of the second laser imaging system provided in the embodiments of this application, as shown below. Figure 2As shown, in some embodiments, the transmitting optical path and the receiving optical path are a scanning and transmitting coaxial optical path 14; the scanning and transmitting coaxial optical path 14 is located between the laser transmitting module 11 and the vortex coherent filter module 12; the laser coherent signal is transmitted to the target to be detected through the scanning and transmitting coaxial optical path 14, and the target echo signal is transmitted to the vortex coherent filter module 12 through the scanning and transmitting coaxial optical path 14.
[0076] In the above implementation process, the scanning and transmitting coaxial optical path 14 includes a polarizing beam splitter prism 141, a fast reflector 142, and a focusable lens 143 arranged sequentially.
[0077] like Figure 2 As shown, its basic working process is as follows: the coherent laser signal output by the laser emitting module 11 is coupled into the coaxial optical path through the polarization beam splitter prism 141, and spatially deflected under the control of the fast reflector 142, and then emitted to the target area through the adjustable focus lens 143; the target echo signal reflected back from the target returns along the original path, and returns to the polarization beam splitter prism 141 after passing through the adjustable focus lens 143 and the fast reflector 142, and is guided by the polarization beam splitter prism 141 to the subsequent vortex coherent filter module 12.
[0078] By setting a scanning and transmitting coaxial optical path 14 between the laser emitting module 11 and the vortex coherent filter module 12, the propagation paths of the emitted light and the received light in space are basically coincident. This is beneficial to maintaining the spatial matching relationship between the target echo and the vortex coherent filter module during the scanning process, thereby improving noise suppression and imaging stability.
[0079] like Figure 2 As shown, in some embodiments, the imaging module 13 includes a detector 131 and an imaging processing module 132; wherein, the detector 131 is used to detect the target echo signal after noise suppression; and the imaging processing module 132 is used to perform imaging based on the target echo signal after noise suppression.
[0080] In the above implementation process, detector 131 can be a single-photon detector. It can also be other types of detectors, as long as they can detect the target echo signal after noise suppression. This application does not make any specific limitations in this regard.
[0081] The imaging processing module 132 can be a control and processing module. In addition to imaging the target echo signal after noise suppression, it can also send control commands to other modules.
[0082] like Figure 2As shown, the "imaging processing module 132" serves as the core control unit of the entire system, and it has signal interaction relationships with the detector 131, the laser emission module 11, and the scanning component (fast reflector) 142. Its functions are, on the one hand, to perform unified timing control of the laser emission, scanning process, and detector detection process, and on the other hand, to receive, process, and reconstruct the echo data output by the detector.
[0083] Specifically, if detector 131 is a single-photon detector, the detection result-related information sent by detector 131 to imaging processing module 132 includes single-photon arrival time information, photon count information, and detection trigger response information. This information is used by imaging processing module 132 to construct a time-of-flight histogram, extract the target echo peak position, calculate the target distance, and further combine it with scanning position information to complete three-dimensional imaging reconstruction. Conversely, imaging processing module 132 sends operating control signals to detector 131, including detector operating mode settings, synchronization trigger signals, time window parameter settings, and control commands to start or stop data acquisition.
[0084] The imaging processing module 132 sends the following signals to the laser emission module 11: a laser trigger signal, a pulse emission timing control signal, and a laser repetition frequency control signal. These signals control the laser to emit pulsed laser light at predetermined times and synchronize the emission time with the data acquisition process at the single-photon detection end, thus providing a unified time reference for subsequent time-of-flight ranging. This achieves timing coordination of the entire system, ensuring that the transmitting, scanning, and receiving ends work collaboratively under unified control.
[0085] The imaging processing module 132 sends scanning control signals to the fast reflector 142. These control signals may include scanning angle commands, scanning path commands, and step control signals. Their function is to control the laser beam to perform point-by-point or continuous scanning within the target area along a predetermined trajectory, enabling the system to sequentially acquire echo signals from corresponding positions in different spatial directions. The imaging processing module 132 drives the fast reflector 142 according to the set scanning range and resolution, and correlates the spatial position information corresponding to each scanning angle with the time-of-flight information obtained by the single-photon detector, thereby achieving joint reconstruction of the target's two-dimensional position and depth information, ultimately obtaining a three-dimensional image or point cloud result.
[0086] Based on the above, it can be concluded that Figure 2The arrows do not represent simple functional connections, but rather the flow directions of control signals, synchronization signals, scan drive signals, and detection data signals in the actual system. Specifically, the imaging processing module 132 is responsible for sending emission control signals to the laser emission module 11, scanning control signals to the fast reflector 142, and operating control and synchronization trigger signals to the detector 131. Simultaneously, it receives photon arrival time and counting data returned by the detector 131 and completes imaging processing based on this data. These signal flow relationships collectively constitute a complete closed-loop working process of the system from laser emission, target scanning, echo detection to image reconstruction, improving imaging performance in complex environments.
[0087] like Figure 2 As shown, in some embodiments, the laser imaging system 10 further includes a collimator 15; wherein the collimator 15 is disposed on the emission optical path and is used to collimate the laser coherent signal output by the laser emission module 11.
[0088] In this embodiment, by setting a collimator in the emission optical path, the coherent laser signal emitted by the laser emission module is converted into an approximately parallel collimated beam, thereby improving the quality of the emitted beam.
[0089] To further verify the performance of the laser imaging system provided in the embodiments of this application, the results of a comparative experiment are presented below. Figure 3 The figure shows the experimental results of a single-photon lidar vortex coherent filtering comparison in a dense fog scene, as provided in the embodiments of this application.
[0090] like Figure 3 As shown in Figure 'a', the target to be detected is placed in the fog chamber of the rain and fog simulation platform. The fog chamber uses an ultrasonic atomizer to generate controllable water mist, forming a dense fog scene with a one-way energy transmittance of T=4.35%. This scene corresponds to the fog-penetrating imaging scenario commonly used in autonomous driving.
[0091] like Figure 3 As shown in c1 and d1, the image camera has difficulty identifying the target to be detected.
[0092] like Figure 3 As shown in Figure b, the echo signals of the target detection were compared before and after using a vortex coherent filtering module (e.g., a vortex phase plate, VPP). The solid line represents the signal without the vortex coherent filtering module (No VPP), showing a high overall noise level where the target signal is submerged in noise and cannot be identified. The dashed line represents the signal received after using the vortex coherent filtering module (With VPP). The comparison shows a reduction in overall noise level, with a clear target signal peak visible between 2000 and 4000 ps. This indicates that the vortex coherent filtering module can effectively suppress various types of noise caused by water mist scattering and improve the quality of the original detection signal.
[0093] Figure 3 Figures c2 and d2 demonstrate the 3D reconstruction results of single-photon lidar imaging in dense fog. c2 shows the 3D reconstruction result without the vortex coherent filtering module; in this case, single-photon detection is severely affected by noise, and the target outline is completely indistinguishable in the reconstructed depth map. Figure d2 shows the 3D reconstruction result with the vortex coherent filtering module; the module effectively suppresses noise received by single-photon detection and reduces the impact of fog scattering. The panda's outline is clearly distinguishable in the reconstructed depth map, achieving effective single-photon 3D imaging.
[0094] In some embodiments, this application provides a lidar, which includes the laser imaging system of any of the above embodiments.
[0095] In summary, the beneficial effects of this application are as follows: (1) Achieving suppression of scattering noise across the entire time domain, overcoming the limitations of existing time-gating techniques: Utilizing the essential difference in spatial coherence between target echo and fog scattering noise, the noise is physically distinguished and suppressed at the receiving end through the synergistic effect of vortex phase modulation and spatial filtering. Unlike time-gating techniques that can only suppress noise within a limited time window, the technical solution of this application does not impose any restrictions on the detection time window, thus achieving continuous suppression of scattering noise across the entire time domain, effectively solving the problem of difficulty in suppressing scattering noise when it overlaps with the target echo in time.
[0096] (2) Directly improving the original signal-to-noise ratio at the receiving end, significantly improving single-photon detection conditions: By structurally controlling the light field in front of the detector, physical blocking of noise photons is achieved, thereby increasing the detection probability of the target photon before the single-photon detector. Compared with existing technologies that rely on algorithms to process the detected data, the technical solution of this application can directly improve the original echo signal-to-noise ratio, effectively alleviate the problem of "first photon being triggered by noise" in single-photon detection, and enable a stable target echo peak value to be obtained even in a strong scattering environment.
[0097] (3) Achieving 3D imaging under extremely low visibility conditions significantly expands the application boundaries of the system: Due to the improved signal-to-noise ratio brought about by noise suppression in the entire time domain, multiple scattered photons are effectively filtered, enabling 3D point cloud reconstruction and intensity imaging of targets even in strong scattering environments with visibility as low as sub-meter level. Compared with the situation where traditional lidar fails to image in dense fog or can only obtain scattered echo points, the technical solution of this application significantly expands the effective working range of single-photon lidar under adverse weather conditions.
[0098] (4) Improved temporal resolution and distance measurement accuracy, and improved 3D reconstruction quality: Under the condition that noise is effectively suppressed, the temporal distribution of the target echo is more concentrated and the echo pulse width is reduced, thereby improving the resolution of time-of-flight ranging. This makes the technical solution of this application exhibit higher depth consistency and spatial compactness in 3D point cloud imaging, which is beneficial to the identification and reconstruction of fine structures.
[0099] (5) Simple structure, modular integration, and good engineering adaptability and scalability: The vortex coherent filter module adopted has a simple structure and can be integrated as an independent optical module into the receiver of the existing single-photon lidar system without changing the basic workflow of the original system. At the same time, this technical solution is highly adaptable to laser wavelength, detector type and scanning method, and has the potential for promotion in a variety of coherent optical detection systems.
[0100] Furthermore, noise suppression is achieved entirely through passive optical components, making it easy to integrate. It eliminates the need for time gating of the signal, computational processing, and additional noise separation devices such as acousto-optic modulators. Without affecting the detector's dynamic range, it does not increase the system's computational burden or slow down the system's detection speed.
[0101] In the embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.
[0102] Furthermore, the units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.
[0103] Furthermore, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.
[0104] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.
Claims
1. A laser imaging system, characterized in that, Includes: a laser emission module, a vortex coherent filter module, and an imaging module; The laser emitting module is used to emit coherent laser signals toward the target to be detected; The vortex coherent filtering module is used to receive the scattered noise signal and the target echo signal reflected from the target to be detected, and based on the spatial coherence difference between the target echo signal and the scattered noise signal, performs phase modulation and spatial filtering on the target echo signal and the scattered noise signal to obtain the target echo signal after noise suppression. The imaging module is used to receive the noise-suppressed target echo signal and perform imaging.
2. The laser imaging system according to claim 1, characterized in that, in, The vortex coherent filtering module includes a vortex modulation module and a filtering module; The vortex modulation module is used to receive the scattered noise signal and the target echo signal, and to perform phase modulation on the scattered noise signal and the target echo signal to generate a modulated target echo signal and a modulated scattered noise signal. The filtering module is used to suppress the modulated scattering noise signal based on the spatial energy distribution difference between the modulated target echo signal and the modulated scattering noise signal, so as to obtain the noise-suppressed target echo signal.
3. The laser imaging system according to claim 2, characterized in that, The length of the propagation optical path between the vortex modulation module and the filtering module is configured such that the modulated target echo signal forms a stable ring energy distribution when it reaches the filtering module.
4. The laser imaging system according to claim 3, characterized in that, The vortex modulation module includes a vortex phase plate, diffractive optical elements, liquid crystal devices, metasurface structures, spatial light modulators, and gratings or prism groups.
5. The laser imaging system according to claim 3, characterized in that, The filtering module includes a masked window, an aperture group, an annular aperture, an adjustable aperture, an optical fiber coupling structure, or a mode-selective coupling structure.
6. The laser imaging system according to any one of claims 1-5, characterized in that, The laser imaging system also includes a transmitting optical path and a receiving optical path; The laser coherent signal is transmitted to the target to be detected via the transmitting optical path; the target echo signal is transmitted via the receiving optical path and enters the vortex coherent filtering module.
7. The laser imaging system according to claim 6, characterized in that, The transmitting optical path and the receiving optical path are coaxial scanning and transmitting optical paths; the coaxial scanning and transmitting optical path includes a polarizing beam splitter prism, a fast reflector, and an adjustable focus lens arranged sequentially along the optical path.
8. The laser imaging system according to claim 6, characterized in that, The imaging module includes a detector and an imaging processing module; The detector is used to detect the noise-suppressed target echo signal; the imaging processing module is used to perform imaging based on the noise-suppressed target echo signal.
9. The laser imaging system according to claim 6, characterized in that, The laser imaging system also includes a collimator; The collimator is disposed on the emitted optical path and is used to collimate the laser coherent signal.
10. A lidar, characterized in that, The lidar includes the laser imaging system as described in any one of claims 1-9.