A scanning imaging system based on a vortex beam in a scattering medium

Abstract

A scanning imaging system based on vortex beam scattering medium belongs to the field of optical imaging. It is composed of vortex beam emission system, vortex beam receiving system, digital signal processing, synchronization system and imaging system. The vortex beam emission system includes vortex beam generation system, two-dimensional beam scanning system, emission optical system and modulation. The vortex beam receiving system includes receiving optical system, spatial light filtering, single photon detection, photoelectric detection, etc. It is also applicable to target imaging in non-scattering medium.

Description

Technical Field

[0001] This invention relates to the application of vortex beams, and more specifically, to scanning imaging of vortex beams in scattering media, belonging to the field of optical imaging. Background Technology

[0002] In some special environments, such as dense smoke, dust, and underwater environments with strong scattering media, visibility is extremely low, making it difficult for human vision or existing machine vision to operate. Other technologies, such as terahertz imaging, microwave imaging, ultrasonic imaging, and far-infrared imaging, either have problems such as overly bulky imaging equipment, low imaging speed, or low imaging resolution, which cannot meet the practical requirements.

[0003] In the field of autonomous driving, existing LiDAR systems lack specific technical measures for weather conditions such as fog and dense fog, as exemplified by standards such as "CN109946707B - LiDAR Receiver, Transmitter, System and Distance Measurement Method". The standards "WO2020182024A1-Laser transceiver module and lidar system" and "CN115840210A-Transmitting module, transceiver module, lidar and system for lidar" require that, as automotive-grade radar systems, they must meet all-weather operating conditions and safety requirements.

[0004] Vortex beams have a unique optical field structure, and their orbital angular momentum (OAM) provides a powerful technical means for the research and application of vortex beams. Summary of the Invention

[0005] In view of at least some problems existing in the prior art, the present invention provides a scanning imaging system based on vortex beam scattering media. By employing vortex beams, spatial light filtering, electrical signal filtering, single-photon detection, and other measures, target imaging in scattering media, especially strongly scattering media, is achieved, thereby improving imaging clarity.

[0006] The present invention is characterized in that the vortex beam generation system (1) is used to generate vortex beams, including Gaussian beams, or Laguerre beams, or Bessel beams, or Airy beams, and their derivative beams. The probe beam is generated after modulation by the modulation (9).

[0007] Furthermore, one method of generating a Bessel-Gaussian beam consists of a fiber laser, a polarization-maintaining fiber and its fast / slow axis 45° alignment, a beam collimator, an aperture, a pair of conical lenses, etc., which outputs an orthogonally polarized Bessel-Gaussian beam.

[0008] The present invention is characterized in that the two-dimensional beam scanning system (2) is used for two-dimensional imaging scanning of the detection beam and is adapted to the imaging optical field of view.

[0009] The present invention is characterized in that the emission optical system (3) includes a beam expanding optical system adapted to the scanning imaging optical field of view.

[0010] Furthermore, the receiving optical system (4) is adapted to the scanning imaging optical field of view, collects and focuses the spatially propagating light field to the spatial light filter (5). It can transmit and receive coaxially or off-axis with the transmitting optical system (3).

[0011] The present invention is characterized in that the modulation (9) is used for pulse modulation, or multi-channel wavelength division multiplexing (WDM), or wavelength tuning, or orthogonal polarization transformation, etc., of the vortex beam generation system (1) to generate a probe beam.

[0012] The present invention is characterized in that the spatial light filter (5) filters the spatial light output of the receiving optical system (4), including: polarization detection, spatial light low-pass filtering, orbital angular momentum (OAM) spectrum filtering, radial Hilbert transform, etc. This filters out backscattered light from the probe beam and scattered light from the scattering medium, improving the target imaging resolution and clarity.

[0013] Furthermore, the spatial light filter (5) outputs two paths to the single-photon detector (6) and the photoelectric detector (61), respectively.

[0014] Furthermore, the single-photon detector (6) is used for single-photon counting in the TOF (Time of Flight) imaging system; the photoelectric detector (61) is used for light pulse detection in the TOF (Time of Flight) imaging system. Alternatively, the photoelectric detector (61) is used for photoelectric conversion in the continuous light (CW) imaging system, simulating electrical signal output. The single-photon detector (6) has automatic saturation intensity protection; based on the saturation intensity threshold of the single-photon detector (6), the single-photon detector (6) and the photoelectric detector (61) automatically switch to each other.

[0015] The present invention is characterized in that the digital signal processing (7) includes: generating the counting timestamp of the single-photon detector (6) of the TOF (Time of Flight) imaging system; the light pulse detection timestamp of the photoelectric detector (61); or generating the digital signal of the ADC analog-to-digital conversion of the photoelectric detector (61) continuous light (CW) imaging system; generating the saturation light intensity control signal and detection switching threshold of the single-photon detector (6); quantization and background noise filtering; further filtering of backscattered light noise of the detector beam and scattered light noise of the scattering medium, etc.

[0016] The present invention is characterized in that the digital signal processing (7) includes: pixel and image frame generation; pixel interpolation and correction of photodetector (61); multi-channel image stitching; image display or output, etc.

[0017] The invention is characterized in that the synchronization system (10) generates clock signals, synchronization signals, control signals, etc., and controls and synchronizes the modulation (9), the two-dimensional beam scanning system, the digital signal processing (7), the imaging system (8), etc.

[0018] Furthermore, the synchronization system (10) includes a central processing unit, memory, and system software, etc.

[0019] The present invention is characterized by being configured either as TOF (Time of Flight) 3D imaging; or as continuous light (CW) 2D imaging; or as a switch between the two; or as simultaneous imaging of multiple channels. Attached Figure Description Figure 1 This is a schematic diagram of a scanning imaging system based on a vortex beam scattering medium; Figure 2 A schematic diagram of a basic 3D imaging system for TOF (Time of Flight) pulse depth detection; Figure 3 This is a schematic diagram of a basic 2D imaging system using continuous light (CW) scanning. Detailed Implementation

[0020] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0021] Example 1 Figure 2 A basic 3D imaging system for TOF (Time of Flight) pulse depth detection. It consists of a 1550nm single-mode fiber laser, polarization-maintaining fiber and its fast / slow axis 45° alignment, beam collimation, aperture, and conical lens pair, generating a Bessel-Gaussian beam. A Q-switched (91) electrical pulse is generated by a synchronization system (10) to Q-modulate the fiber laser of the Bessel-Gaussian beam generation system (11), outputting an orthogonally polarized Bessel-Gaussian pulse detection beam.

[0022] The two-dimensional MEMS deflection system (21) consists of two MEMS micromirrors along the X and Y axes, and is adapted to the target detection field of view. The transmitting optical system (3) includes a beam expanding optical system to ensure that the laser beam can be effectively emitted and cover the required optical field of view; the corresponding receiving optical system (4) is adapted to the scanning imaging optical field of view, collects and focuses the spatially propagating light field to the spatial light filter (5). It can be coaxially transmitted and received or off-axis transmitted and received with the transmitting optical system (3). Coaxial transmission and reception means that the receiving optical system (4) and the transmitting optical system (3) share a set of optical systems, separated by a semi-transparent mirror or a half-lens optical path. No further examples will be given.

[0023] Spatial light filtering (5) filters the output signal light of the receiving optical system (4), including: polarization detection, spatial light low-pass filtering, orbital angular momentum (OAM) spectrum filtering, radial Hilbert transform, etc.; filtering of background light, backscattered light of the probe beam, scattered light of the scattering medium, etc., extracting the reflected light of the target object and improving image resolution.

[0024] The spatial light filter (5) outputs two channels to the gated IDQ single-photon detector (6) and the SiPM photodetector (61), respectively. The gated IDQ single-photon detector (6) has a saturation intensity gate protection function. The gated IDQ single-photon detector (6) and the SiPM photodetector (61) are hot backups of each other. The gated IDQ single-photon detector (6) is the main detector. When the intensity exceeds its saturation intensity threshold, it automatically switches to the SiPM photodetector (61). When the intensity is below its saturation intensity threshold, it automatically switches back to the gated IDQ single-photon detector (6).

[0025] Digital signal processing (7) receives the photon counting signal from the gated IDQ single-photon detector (6) and the optical pulse signal from the SiPM photodetector (61), respectively; generates the photon counting timestamp of the gated IDQ single-photon detector (6) and the optical pulse detection timestamp of the SiPM photodetector (61). It generates the saturation intensity control signal and detection switching threshold for the gated IDQ single-photon detector (6). Quantization noise and background noise are filtered using finite-length unit impulse response (FIR) digital filters, Fourier digital filters, etc.; further filtering is applied to the backscattered light noise of the probe beam and the scattered light noise of the scattering medium, etc.

[0026] The imaging system (8) includes pixel and image frame generation; pixel interpolation and correction of the SiPM photodetector (61) under detection switching; multi-channel image stitching; image display or output, etc.

[0027] The synchronization system (10) generates clock signals, synchronization signals, control signals, etc. Synchronization and control Q-switching (91), two-dimensional MEMS beam deflection system, digital signal processing (7), imaging system (8), etc.; the synchronization system (10) includes a central processing unit ARM, FPGA, memory, drive circuit and system software, etc.

[0028] Example 2 Figure 3 A basic 2D imaging system for continuous light (CW) scanning. The Bessel-Gaussian beam generation system (11) consists of a 1550nm single-mode fiber laser, polarization-maintaining fiber and its fast / slow axis 45° docking, beam collimation, aperture, conical lens pair, etc., and outputs an orthogonally polarized Bessel-Gaussian continuous light (CW) beam.

[0029] The two-dimensional MEMS deflection system (21) is a two-dimensional deflection system composed of two MEMS micro mirrors along the X and Y axes, and is adapted to the target detection field of view.

[0030] The transmitting optical system (3) includes a beam-expanding optical system to ensure that the laser beam can be effectively emitted and cover the required optical field of view; the corresponding receiving optical system (4) is adapted to the scanning imaging optical field of view, collecting and focusing the spatially propagating light field to the spatial light filter (5). It can be coaxially or off-axis with the transmitting optical system (3). Coaxial transmission means that the receiving optical system (4) and the transmitting optical system (3) share a single optical system, separated by a semi-transparent mirror or a translucent mirror optical path, which will not be exemplified further.

[0031] Spatial light filtering (5) filters the output signal light of the receiving optical system (4), including: polarization detection, spatial light low-pass filtering, orbital angular momentum (OAM) spectrum filtering, radial Hilbert transform, etc.; filtering of background light, backscattered light of the probe beam, scattered light of the scattering medium, etc., extracting the reflected light of the target object, and improving image resolution. Spatial light filtering (5) outputs to SiPM photodetector (61).

[0032] The digital signal processing (7) receives the analog electrical signal output from the SiPM photodetector (61) and generates a digital signal through high-speed A / D conversion. The quantization noise and background noise are filtered by finite-length unit impulse response (FIR) digital filters, Fourier digital filters, etc.; the backscattered light noise of the probe beam and the scattered light noise of the scattering medium are further filtered, etc.

[0033] The imaging system (8) includes pixel and image frame generation; multi-channel image stitching; image display or output, etc.

[0034] The synchronization system (10) generates clock signals, synchronization signals, control signals, etc. Control and synchronization Q-switching (91), two-dimensional MEMS beam deflection system, digital signal processing (7), imaging system (8); the synchronization system (10) includes a central processing unit ARM, FPGA; memory, drive circuit and system software, etc.

[0035] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A scanning imaging system based on a vortex beam scattering medium, characterized in that: The vortex beam generation system (1) generates vortex beams including Gaussian beams, Laguerre beams, Bessel beams, Airy beams, and their derivative beams. The probe beam is generated after modulation by the modulation (9). It consists of a fiber laser, a polarization-maintaining fiber and its fast and slow axes aligned at 45°, a beam collimator, an aperture, a pair of conical lenses, etc., to generate a Bessel-Gaussian orthogonally polarized beam. A two-dimensional beam scanning system (2) is used for two-dimensional imaging scanning of the vortex beam generated by the vortex beam generating system (1), and is adapted to the imaging optical field of view; a transmitting optical system (3) includes a beam expander system, and is adapted to the scanning imaging optical field of view. A receiving optical system (4) is adapted to the scanning imaging optical field of view, and collects and focuses the spatially propagating light field to the spatial light filter (5). It can transmit and receive coaxially or off-axis with the transmitting optical system (3); modulation (9) is used for pulse modulation, or multi-channel wavelength division multiplexing (WDM), or wavelength tuning, or orthogonal polarization transformation, etc., of the vortex beam generating system (1).

2. The scanning imaging system based on a vortex beam scattering medium according to claim 1, characterized in that: The spatial light filter (5) filters the spatial light output of the receiving optical system (4), including polarization detection, spatial light low-pass filtering, orbital angular momentum (OAM) spectrum filtering, radial Hilbert transform, etc.

3. The scanning imaging system based on a vortex beam scattering medium according to claim 2, characterized in that: The spatial optical filter (5) is split into two outputs to the single-photon detector (6) and the photoelectric detector (61).

4. A scanning imaging system based on a vortex beam scattering medium according to claim 3, characterized in that: The single-photon detector (6) is used for single-photon counting in a TOF (Time of Flight) imaging system, and the photoelectric detector (61) is used for light pulse detection in a TOF (Time of Flight) imaging system. Alternatively, the photoelectric detector (61) is used for photoelectric conversion in a continuous light (CW) imaging system, simulating electrical signal output. The single-photon detector (6) has automatic saturation intensity protection; based on the saturation intensity threshold of the single-photon detector (6), the single-photon detector (6) and the photoelectric detector (61) automatically switch to each other.

5. A scanning imaging system based on a vortex beam scattering medium according to claims 2-4, characterized in that: The digital signal processing (7) includes: generating the single-photon detection (6) counting timestamp of the TOF (Time of Flight) imaging system; the photoelectric detection (61) light pulse detection timestamp; or generating the ADC analog-to-digital conversion digital signal of the photoelectric detection (61) continuous light (CW) imaging system; generating the saturation light intensity control signal and detection switching threshold of the single-photon detection (6); quantization and background noise filtering; further filtering of backscattered light noise of the detection beam and scattered light noise of the scattering medium, etc.

6. A scanning imaging system based on a vortex beam scattering medium according to claim 5, characterized in that: The imaging system (8) includes pixel and image frame generation; pixel interpolation and correction of the photodetector (61); multi-channel image stitching; image display or output, etc.

7. A scanning imaging system based on a vortex beam scattering medium according to claims 4 to 6, characterized in that: The synchronization system (10) generates clock signals, synchronization signals, control signals, etc.; including a central processing unit, memory and system software, etc.

8. A scanning imaging system based on a vortex beam scattering medium according to claims 1 to 7, characterized in that: It can be configured as TOF (Time of Flight) 3D imaging; or as continuous light (CW) 2D imaging; or a switch between the two; or simultaneous imaging of multiple channels.

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