Polarization Stokes measuring device and method for underwater light scattering

Abstract

The invention provides a polarization Stokes measurement device and method for underwater light scattering. The device provided by the invention comprises a laser incidence module, a laser scattering module, a first beam splitter, a second beam splitter, a polarization spectroscope and a polarization module, the laser incidence module is used for emitting laser beams in different polarization states towards a water area; the laser scattering module is used for sending the composite scattering signal to the first beam splitter; the first beam splitter is used for separating the composite scattering signal to obtain first transmission light and first reflection light; the polarizing beam splitter is used for separating the first transmission light to obtain second transmission light and second reflected light; the second beam splitter is used for separating the first reflected light to obtain third transmission light and third reflected light; the polarization module is used for carrying out polarization state separation on the optical signals and outputting a plurality of light beams to a plurality of corresponding photoelectric detectors. The device and method provided by the invention are used for solving the problem of photoelectric detector saturation caused by sunlight interference of the laser radar, and improving the accuracy of underwater target detection.

Description

Technical Field

[0001] This application relates to the field of laser measurement technology, and in particular to a polarization Stokes measurement device and method for underwater light scattering. Background Technology

[0002] LiDAR has significant applications in marine surveying, enabling it to detect complex structures of seawater profiles, underwater targets, and topography. It can also precisely analyze the composition and distribution of seaweed, providing technical support for key areas such as marine engineering planning, seabed resource exploration, and marine environmental protection. Characterized by high precision and a large dynamic range, this technology plays an indispensable role in revealing the physical and chemical properties of the underwater environment and the patterns of biological distribution.

[0003] However, in practical applications, when using lidar for high-precision and wide dynamic range measurements, marine lidar relies on highly sensitive photodetectors (such as photomultiplier tubes and single-photon avalanche diodes) to capture weak signals. These photodetectors are susceptible to interference from strong sunlight reflections from the water surface and near the water's edge, leading to signal superposition and causing the photodetector to saturate. This not only reduces signal detection accuracy but may also accelerate the aging of the photodetector, affecting the long-term stability and reliability of the system.

[0004] Therefore, there is an urgent need for a device to solve the problem of photodetector saturation caused by sunlight interference in lidar, and to improve the accuracy of lidar in underwater target detection. Summary of the Invention

[0005] In view of this, this application provides a polarization Stokes measurement device and method for underwater light scattering to solve the problem of photodetector saturation caused by sunlight interference in lidar, and to improve the accuracy of lidar in underwater target detection.

[0006] Specifically, this application is implemented through the following technical solution:

[0007] The first aspect of this application provides a polarization Stokes measurement device for underwater light scattering. The device includes a laser incident module, a laser scattering module, a first beam splitter, a second beam splitter, a polarization beam splitter, and multiple polarization modules. The output of the first beam splitter is connected to the second beam splitter and the polarization beam splitter, respectively. The multiple outputs of the second beam splitter and the multiple outputs of the polarization beam splitter are respectively linked to different polarization modules. Each polarization module includes multiple polarization units, and each polarization unit includes a third beam splitter and a photodetector. The number of third beam splitters and photodetectors in each polarization unit is the same. Different polarization modules contain different types of polarizers, and the polarization processing characteristics of different types of polarizers are different. Different polarization modules separate laser signals into different polarization states.

[0008] The laser incident module is used to emit laser beams containing different polarization states toward the water area;

[0009] The laser scattering module is used to receive the laser signal of the laser beam after being scattered by the underwater target, and the composite signal of sunlight and background light reflected from the water surface, and send the composite scattering signal composed of the laser signal and the composite signal to the first beam splitter.

[0010] The first beam splitter is used to separate the composite scattering signal to obtain a first transmitted light and a first reflected light. The first transmitted light passes through the polarizing beam splitter, and the first reflected light passes through the second beam splitter. The light intensity of the composite scattering signal is greater than the upper limit of the range of a single photodetector.

[0011] The polarizing beam splitter is used to separate the first transmitted light to obtain a second transmitted light and a second reflected light; the second beam splitter is used to separate the first reflected light to obtain a third transmitted light and a third reflected light; the second transmitted light, the second reflected light, the third transmitted light and the third reflected light are respectively sent to different polarization modules;

[0012] Each polarization module is used to separate the polarization state of the received optical signal and output multiple beams of light with different polarization states to multiple corresponding photodetectors; wherein, the light intensity of the beam entering each photodetector is not greater than the upper limit of the range of the photodetector, and the sum of the light intensity output by the photodetectors of all polarization modules is the same as the light intensity of the composite scattering signal.

[0013] A second aspect of this application provides a polarization Stokes measurement method for underwater light scattering, the method being applied to the polarization Stokes measurement device for underwater light scattering as described in any one of the first aspects of this application, the method comprising:

[0014] The laser incident module emits laser beams containing different polarization states toward the water.

[0015] The laser scattering module receives the laser signal of the laser beam after being scattered by the underwater target, and the composite signal of sunlight and background light reflected from the water surface, and sends the composite scattering signal composed of the laser signal and the composite signal to the first beam splitter.

[0016] The first beam splitter separates the composite scattering signal to obtain a first transmitted light and a first reflected light. The first transmitted light is sent to a polarizing beam splitter, and the first reflected light is sent to a second beam splitter.

[0017] The polarizing beam splitter separates the first transmitted light to obtain a second transmitted light and a second reflected light. The second beam splitter separates the first reflected light to obtain a third transmitted light and a third reflected light. The second transmitted light, the second reflected light, the third transmitted light, and the third reflected light are then sent to different polarization modules.

[0018] Each polarization module separates the polarization state of the received optical signal and outputs multiple beams of light with different polarization states to the corresponding multiple photodetectors.

[0019] The polarization Stokes measurement device and method for underwater light scattering provided in this application, in a first aspect, achieves effective separation of laser scattering echo signals and background interference signals in complex underwater environments through a structural design that combines multi-stage beam splitting with polarization characteristic separation. This application emits laser beams containing different polarization states through a laser incident module. Utilizing the difference in polarization state characteristics between the underwater target scattered light and the background light, a physical basis is provided for subsequent signal separation. After being collected by the laser scattering module, the composite scattering signal contains the effective laser signal scattered by the underwater target and interference signals from sunlight or the environmental background. Furthermore, the total intensity of this composite signal typically exceeds the dynamic range of a single photodetector, making direct detection prone to saturation or information loss. To this end, this application utilizes a combination of a first beam splitter, a polarizing beam splitter, and a second beam splitter to perform multi-stage beam splitting and polarization state separation based on the differences in spatial direction, polarization state, and light intensity of different components in the composite scattering signal. The first beam splitter spatially separates the composite scattering signal, initially reducing the intensity of a single path. The polarizing beam splitter further divides the transmitted light into optical paths with different polarization directions based on the difference in polarization states between the background light and the effective signal, effectively separating the background light with significantly different polarization characteristics from the target scattering signal into different channels. The second beam splitter further spatially splits the first reflected light, ensuring that the overall composite signal can be reasonably distributed to multiple polarization modules, so that the light intensity in each channel is controlled within the range of the corresponding photodetector, while maintaining the integrity of the overall signal. This multi-stage beam splitting and polarization separation design based on light intensity and polarization characteristics, compared to existing technologies that only use single-stage beam splitting or single polarization processing, can more effectively achieve reasonable splitting of composite scattering signals and independent extraction of effective signals under strong background light conditions. It reduces background light interference to the detector, avoids detector saturation due to excessive light intensity, and improves the device's ability to extract underwater target scattering signals and the complete measurement effect of polarization Stokes information under strong interference environments, thereby significantly improving measurement accuracy, environmental adaptability, and the stability of the detection system. Secondly, this application achieves polarization Stokes measurement by setting up polarization modules containing different types of polarizers, allowing the polarization Stokes measurement device to capture and analyze signals from different polarization states, thereby obtaining complete polarization information. Firstly, the polarization Stokes measurement device uses different polarization modules, with different types of polarizers within each module to process different polarization components. For example, linear polarizers are used to acquire signals associated with linearly polarized light in a specific direction, while quarter-wave plates are used to convert certain polarization states (such as circularly polarized light) into linearly polarized light. Further utilizing linear polarizers to acquire signals in a specific direction allows the system to more effectively measure circularly polarized signals. The polarization units in each polarization module divide the light beam into multiple different polarization components, each detected by a photodetector. This allows each polarization module to measure scattered signals in different polarization states separately.Secondly, through the collaboration of multiple polarization modules, the polarization-Stokes measurement device can achieve polarization-Stokes measurements of underwater targets. Since each polarization module processes signals of different polarization states, the device can measure the scattered signal from multiple polarization angles using different combinations of polarizers, obtaining more comprehensive underwater target information. The signal superposition between different polarization modules further improves the detection accuracy of the polarization-Stokes measurement device, ensuring efficient measurement of the target's scattered signal. Attached Figure Description

[0020] Figure 1 A schematic diagram of the underwater light scattering polarization Stokes measurement device provided in Embodiment 1 of this application;

[0021] Figure 2 A flowchart of the underwater light scattering polarization Stokes measurement method provided in Embodiment 2 of this application;

[0022] Explanation of reference numerals in the attached figures:

[0023] 1: Pulsed laser;

[0024] 2: First wave of films;

[0025] 3: Second wave of films;

[0026] 4: Water surface;

[0027] 5: Receiver;

[0028] 6: Filters;

[0029] 7: First beam splitter;

[0030] 8: Polarizing beam splitter;

[0031] 9, 10, 11, 15, 16, 17, 23, 24, 25, 31, 32, 33: Third beam splitter;

[0032] 12, 13, 14, 18, 19, 20, 26, 27, 28, 34, 35, 36: Photodetectors;

[0033] 21: Second beam splitter;

[0034] 22: 45° linear polarizer;

[0035] 29: Quarter-wave plate;

[0036] 30: Linear polarizer. Detailed Implementation

[0037] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0038] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used herein are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0039] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0040] The following specific embodiments are given to illustrate the technical solution of this application in detail.

[0041] Figure 1 This is a schematic diagram of the underwater light scattering polarization Stokes measurement device provided in Embodiment 1 of this application. Please refer to... Figure 1 The device provided in this embodiment includes a laser incident module, a laser scattering module, a first beam splitter 7, a second beam splitter 21, a polarizing beam splitter 8, and multiple polarization modules. The output of the first beam splitter 7 is connected to the second beam splitter 21 and the polarizing beam splitter 8, respectively. The multiple outputs of the second beam splitter 21 and the multiple outputs of the polarizing beam splitter 8 are respectively linked to different polarization modules. Each polarization module includes multiple polarization units, and each polarization unit includes a third beam splitter and a photodetector. The number of third beam splitters and photodetectors in each polarization unit is the same. Different polarization modules contain different types of polarizers, and the polarization processing characteristics of different types of polarizers are different. Different polarization modules separate laser signals into different polarization states.

[0042] The laser incident module is used to emit laser beams containing different polarization states toward the water area;

[0043] The laser scattering module is used to receive the laser signal of the laser beam after being scattered by the underwater target, and the composite signal of sunlight and background light reflected from the water surface, and send the composite scattering signal composed of the laser signal and the composite signal to the first beam splitter 7.

[0044] The first beam splitter 7 is used to separate the composite scattering signal to obtain a first transmitted light and a first reflected light. The first transmitted light passes through the polarizing beam splitter 8, and the first reflected light passes through the second beam splitter 21. The light intensity of the composite scattering signal is greater than the upper limit of the range of a single photodetector.

[0045] The polarizing beam splitter 8 is used to separate the first transmitted light to obtain a second transmitted light and a second reflected light; the second beam splitter 21 is used to separate the first reflected light to obtain a third transmitted light and a third reflected light; the second transmitted light, the second reflected light, the third transmitted light and the third reflected light are respectively sent to different polarization modules;

[0046] Each polarization module is used to separate the polarization state of the received optical signal and output multiple beams of light with different polarization states to multiple corresponding photodetectors; wherein, the light intensity of the beam entering each photodetector is not greater than the upper limit of the range of the photodetector, and the sum of the light intensity output by the photodetectors of all polarization modules is the same as the light intensity of the composite scattering signal.

[0047] For details, please refer to Figure 1 The underwater light scattering polarization Stokes measurement device includes a laser incident module, a laser scattering module, a first beam splitter 7, a second beam splitter 21, a polarization beam splitter 8, and multiple polarization modules. The laser incident module is connected to the laser scattering module, the laser scattering module is connected to the first beam splitter 7, the first beam splitter 7 is connected to the second beam splitter 21 and the polarization beam splitter 8, and the multiple polarization modules are respectively connected to the second beam splitter 21 or the polarization beam splitter 8.

[0048] The function and structure of each module will be introduced below.

[0049] Specifically, the laser incident module is used to emit laser beams containing different polarization states towards the water. Polarization state refers to the characteristic of the direction of electric field vibration in electromagnetic waves. For lasers, polarization state characterizes the state of the electric field vector of light as it changes over time and space. Common polarization states include linearly polarized light, circularly polarized light, and elliptically polarized light. In the laser incident module, emitting laser beams with different polarization states is to obtain multidimensional information about the scattered light from the target during detection. By analyzing this multidimensional information, the physical and chemical properties of the target can be identified.

[0050] For further details, please refer to [link / reference]. Figure 1The laser incident module includes a pulsed laser 1, a first waveplate 2, and a second waveplate 3 connected in sequence; wherein the first waveplate 2 is a half-waveplate, and the second waveplate 3 is a quarter-waveplate;

[0051] The pulsed laser 1 is used to emit a detection laser toward the water area;

[0052] The first waveplate 2 is used to adjust the polarization direction of the probe laser;

[0053] The second waveplate 3 is used to modulate the probe laser after it has been adjusted by the first waveplate 2, thereby generating a laser beam with multiple polarization states.

[0054] Specifically, the laser incident module includes a pulsed laser 1, a first waveplate 2, and a second waveplate 3. The pulsed laser 1 is connected to the first waveplate 2, and the first waveplate 2 is connected to the second waveplate 3. The first waveplate 2 is a half-wave plate, and the second waveplate 3 is a quarter-wave plate.

[0055] Furthermore, pulsed laser 1 is used to emit a high-intensity, short-pulse probe laser with a stable, single initial polarization state, providing a basis for subsequent polarization adjustment and modulation. First waveplate 2 (i.e., half-wave plate) is used to adjust the polarization direction of the probe laser. By changing the polarization angle of the incident light, it directionally controls the linear polarization state of the probe laser, preparing for the generation of multiple polarization states. Second waveplate 3 (i.e., quarter-wave plate) is used to further modulate the probe laser adjusted by the half-wave plate, converting it from linearly polarized light to circularly polarized light, ellipsoidally polarized light, or other polarization states, achieving laser beam output with multiple polarization states.

[0056] In practice, pulsed laser 1 emits a probe laser with stable linear polarization toward the water surface, providing the basic light source for the entire device. The probe laser passes through a first waveplate 2 (half-wave plate), which adjusts the polarization direction of the probe laser by rotating its angle, thus changing the direction of the photoelectric field vibration. The adjusted probe laser then enters a second waveplate 3 (quarter-wave plate), which, based on the polarization angle of the incident laser and its own optical properties, performs phase delay on the light wave, generating a laser beam with circularly polarized light, elliptically polarized light, or other composite polarization states.

[0057] Optionally, the purpose of setting the first waveplate 2 is to utilize its phase delay characteristics, depending on different rotation angles. The polarization direction of the incident ray-polarized laser is controlled and adjusted. Specifically, the first waveplate 2 adjusts the polarization angle of the incident ray-polarized light by 2... The rotation allows the polarization direction of the probe laser to be flexibly changed according to the detection requirements. The formula for calculating the rotation angle is:

[0058] ;

[0059] Among them, the The rotation angle of the first waveplate 2; The angle between the polarization directions to be changed.

[0060] By precisely controlling the rotation angle, the polarization direction of the laser can be offset from the main polarization direction of the background light, minimizing interference from the background light in the same polarization direction.

[0061] Furthermore, the second waveplate 3 is designed based on the differences in scattering characteristics of lasers with different polarization states in the target and background media within an underwater scattering environment. The second waveplate 3 can further convert the linearly polarized light adjusted by the first waveplate 2 into circularly polarized or elliptically polarized light. Its specific control principle utilizes… Waveplates exist in the fast and slow axis directions The phase difference is used to modulate different polarization states. The key parameter is the angle between the incident light and the fast axis of the waveplate. The formula for calculating the rotation angle is:

[0062] ;

[0063] Among them, the The rotation angle of the second waveplate 3; The angle between the principal axis of the polarization ellipse and the linearly polarized light, representing the desired elliptical or circular polarization state.

[0064] The device provided in this embodiment achieves dynamically controllable output of laser beams with multiple polarization states through the synergistic effect of a pulsed laser, a half-wave plate, and a quarter-wave plate, overcoming the limitations of existing technologies that rely solely on fixed waveplate parameters or empirical adjustments. Specifically, the laser incident module first emits a probe laser with stable linear polarization characteristics via a pulsed laser, providing a basic light source for subsequent polarization control. Unlike traditional methods that only achieve polarization state conversion by rotating the waveplate, this embodiment introduces the polarization characteristics of ambient background light and target light as the basis for adjustment when adjusting the waveplate parameters. By real-time monitoring of the main polarization direction of the underwater ambient background light and the polarization direction required for target detection, combined with the principle of optical polarization control, the optimal rotation angles of the half-wave plate and quarter-wave plate are calculated. Specifically, the rotation angle of the half-wave plate is calculated based on the main polarization direction of the underwater ambient background light and the polarization direction required for target detection, enabling rapid adjustment of the incident laser linear polarization direction to achieve optimal deviation from the main polarization direction of the background light, thereby enhancing the contrast between the target signal and background noise. The rotation angle of the quarter-wave plate is calculated based on the angle between the desired output composite polarization state and the incident light polarization state, enabling flexible conversion of the incident linearly polarized light to circular polarization, elliptical polarization, or a specific composite polarization state. Through the aforementioned dynamic calculation and adjustment mechanism, the laser incident module can flexibly generate laser beams with various polarization states, such as linear, circular, and elliptical polarization. This enables the polarization Stokes measurement device to comprehensively acquire the light scattering and reflection characteristics of underwater targets and the environment, significantly improving the accuracy and integrity of the detection. At the same time, it has extremely high environmental adaptability and can automatically adjust the optimal polarization output strategy according to different aquatic environmental conditions (such as water quality, depth, and background light changes). This effectively distinguishes target signals from background noise, reduces the impact of external interference on detection accuracy, and avoids saturation of the detector due to strong echo signals. This ensures that the device has underwater detection capabilities with high dynamic range, high signal fidelity, and strong environmental adaptability.

[0065] Specifically, the laser scattering module is used to receive the laser signal of the laser beam after being scattered by the underwater target, and the composite signal of sunlight and background light reflected from the water surface, and sends the composite scattering signal composed of the laser signal and the composite signal to the first beam splitter.

[0066] For further details, please refer to [link / reference]. Figure 1 The laser scattering module includes a receiver 5 and a filter 6. The receiver 5 is connected to the filter 6, and the filter 6 is connected to the first beam splitter 7.

[0067] The receiver 5 is used to receive the laser signal of the laser beam after being scattered by the underwater target. The receiver 5 is also used to receive a composite signal including sunlight reflected from the water surface and background light, and send the composite scattering signal composed of the laser signal and the composite signal to the filter 6.

[0068] The filter 6 is used to filter the composite scattering signal and remove stray light outside the laser operating wavelength.

[0069] Specifically, the laser scattering module includes a receiver 5 and a filter 6. The receiver 5 is connected to the filter 6, and the filter 6 is connected to the first beam splitter 7.

[0070] Furthermore, receiver 5 receives the laser signal scattered by the underwater target, and simultaneously receives a composite signal including sunlight reflected from the water surface and background light. These signals are then integrated into a composite scattered signal and transmitted to filter 6. The underwater target includes underwater particles and molecules. Filter 6 filters the composite scattered signal transmitted by receiver 5, removing stray light outside the laser's operating wavelength, including strong reflections of sunlight and ambient background light, retaining only the effective laser scattered signal within the laser's operating wavelength range to ensure the accuracy of subsequent signal detection.

[0071] It should be noted that sunlight and background light from the water surface can severely interfere with the laser scattering signal during reflection and propagation, reducing the detection signal-to-noise ratio and potentially causing photodetector saturation. To effectively suppress this interference, the device incorporates a filter in the laser scattering module. Through its precise wavelength-selective filtering function, the filter processes the composite scattering signal received by receiver 5, removing stray light outside the laser's operating wavelength (including strong reflection components of sunlight and ambient background light), effectively preserving the target scattering signal within the laser's operating wavelength range, thereby ensuring the device's measurement accuracy and stability.

[0072] In practice, receiver 5 receives laser scattering echo signals from underwater targets, as well as sunlight reflected from the water surface and ambient light from the water environment. These signals are then integrated to form a composite scattering signal. This composite scattering signal is transmitted to filter 6, which performs spectral selective filtering on the composite scattering signal, removing stray light outside the laser's operating wavelength, including strong reflection components of sunlight and ambient light, retaining only the effective echo signal within the laser's operating wavelength for use by subsequent signal separation and detection units.

[0073] The apparatus provided in this embodiment optimizes the measurement capabilities of the polarization-Stokes measurement device in complex environments through the collaborative design of the laser scattering module and the receiver and filter. The receiver comprehensively receives the effective laser signal scattered by the underwater target while integrating interference signals from the environment, such as sunlight reflected from the water surface and background light, ensuring the integrity and diversity of the input signal and providing comprehensive data support for subsequent processing. The filter effectively removes background light and stray light from the interference signal through precise spectral selective filtering, retaining only the target laser signal, thereby improving the signal-to-noise ratio. This design not only solves the problem of interference from sunlight and environmental noise on measurement accuracy but also avoids the risk of detector saturation or distortion caused by strong light interference, significantly improving the dynamic range and measurement stability of the system. Simultaneously, by clearly separating the useful signal and the interference signal, the laser scattering module lays a high-quality input foundation for subsequent signal beam splitting and detection, enhancing the adaptability and reliability of the polarization-Stokes measurement device in complex marine environments.

[0074] Specifically, the first beam splitter 7 is used to separate the composite scattering signal to obtain a first transmitted light and a first reflected light. The first transmitted light passes through the polarizing beam splitter 8, and the first reflected light passes through the second beam splitter 21. The first beam splitter 7 is usually made of a material with specific optical properties (such as a reflecting mirror or a transmitting mirror), and can split the incident beam into two or more beams in different directions as required according to certain optical principles (such as reflection, refraction, or transmission).

[0075] Optionally, the first beam splitter, through a dielectric thin-film structure designed for a specific wavelength (e.g., 532 nm), utilizes the interference effect of multiple high- and low-refractive-index materials to stably split the composite scattering signal into a first transmitted light and a first reflected light under a 45° incident condition, which propagate in different directions. This beam splitting behavior is based on the principle of reflection-transmission wavefront phase interference and is independent of the polarization state and incident intensity of the incident light. It can effectively ensure the polarization Stokes characteristics and energy balance of the composite light field, providing a reliable physical basis for subsequent multi-channel detection.

[0076] For further details, please refer to [link / reference]. Figure 1 The first beam splitter 7 is connected to the filter 6. The first beam splitter 7 is used to separate the composite scattered signal after it has been filtered by the filter 6, resulting in two beams with different polarization states: a first transmitted light and a first reflected light. The first transmitted light passes through a polarizing beam splitter 8 for further polarization component separation. The first reflected light passes through a second beam splitter 21 for further optical path separation.

[0077] In practice, during the separation process, the composite scattering signal first hits the surface of the first beam splitter 7. According to the design and properties of the first beam splitter 7, some of the light will be reflected (first reflected light), while the other part of the light will pass through the first beam splitter 7 (first transmitted light).

[0078] Specifically, the polarizing beam splitter 8 is used to separate the first transmitted light into a second transmitted light and a second reflected light. The polarizing beam splitter 8 can separate light according to its polarization state, separating beams with different polarization directions. It is typically used to transmit or reflect beams with specific polarization directions, while blocking or processing beams with other polarization directions. The working principle of the polarizing beam splitter 8 is based on the different reflection and transmission characteristics of polarized light. Since polarized light has a fixed vibration direction, light waves with different polarization directions will exhibit different reflection and transmission phenomena when passing through the polarizing beam splitter, depending on the design of the mirror surface and the polarization direction. The polarizing beam splitter 8 utilizes the special properties of its materials or coatings to process light with different polarization directions differently.

[0079] For further details, please refer to [link / reference]. Figure 1 The polarizing beam splitter 8 is connected to the first beam splitter 7. The polarizing beam splitter 8 is used to separate the first transmitted light after it has been split by the first beam splitter 7, so as to obtain two beams with two polarization states, namely the second transmitted light and the second reflected light.

[0080] In practice, when the first transmitted light enters the polarizing beam splitter 8, it carries a certain polarization state (including different types such as linearly polarized light and circularly polarized light). The polarizing beam splitter 8 typically contains specific optical coatings or materials, which have different reflectivities and transmittances for light with different polarization directions. The polarizing beam splitter 8 splits the first transmitted light into two parts according to the polarization direction of the light. Light whose polarization direction matches the mirror design of the polarizing beam splitter 8 is transmitted, i.e., the second transmitted light. Light whose polarization direction is opposite to or does not match the mirror design of the polarizing beam splitter 8 is reflected, i.e., the second reflected light.

[0081] Optionally, the polarization beam splitter, based on the multilayer film interference effect, exhibits different reflectivities and transmittances for light with different polarization directions under the operating wavelength (532nm) and a specific incident angle of 45°. The physical mechanism lies in the film structure design, which allows P-polarized light to achieve near-total transmission through multiple interferences, while S-polarized light is almost entirely reflected due to phase interference, thus achieving efficient polarization separation.

[0082] Specifically, the second beam splitter 21 is used to separate the first reflected light into a third transmitted light and a third reflected light. It should be noted that the structure and working principle of the second beam splitter 21 are similar to those of the first beam splitter 7, and will not be repeated here. However, the application scenarios and subsequent paths of the second beam splitter 21 differ from those of the first beam splitter 7. Based on the above description, the first beam splitter 7 separates the composite scattered signal, which includes laser echo signals from the underwater target, as well as sunlight and background light reflected from the water surface. The first beam splitter 7 needs to separate these composite scattered signals into a first transmitted light and a first reflected light for further processing. The second beam splitter 21 processes the first reflected light, further separating it into a third transmitted light and a third reflected light, thus further subdividing the first reflected light to provide more information for subsequent polarization analysis.

[0083] It should be noted that after the polarizing beam splitter 8 and the second beam splitter 21 separate the first transmitted light and the first reflected light to obtain the second transmitted light, the second reflected light, the third transmitted light, and the third reflected light, the subsequent paths of the different transmitted and reflected lights are different. The second transmitted light, the second reflected light, the third transmitted light, and the third reflected light are sent to different polarization modules.

[0084] Specifically, each polarization module includes multiple polarization units, and each polarization unit includes a third beam splitter and a photodetector. The number of third beam splitters and photodetectors in each polarization unit is the same. Different polarization modules contain different types of polarizers, and the polarization light processing characteristics of different types of polarizers are different. Different polarization modules separate laser signals into different polarization states.

[0085] For further details, please refer to [link / reference]. Figure 1 The multiple polarization modules include a first polarization module, a second polarization module, a third polarization module, and a fourth polarization module. The second transmitted light passes through the first polarization module, the second reflected light passes through the second polarization module, the third transmitted light passes through the third polarization module, and the third reflected light passes through the fourth polarization module.

[0086] Specifically, the multiple polarization modules include a first polarization module, a second polarization module, a third polarization module, and a fourth polarization module. Each of the first, second, third, and fourth polarization modules contains three polarization units. Each polarization unit contains a third beam splitter and a photodetector that are interconnected. Different polarization units within the same polarization module are connected sequentially.

[0087] Furthermore, the first polarization module is used to receive the second transmitted light after being separated by the polarizing beam splitter 8, the second polarization module is used to receive the second reflected light after being separated by the polarizing beam splitter 8, the third polarization module is used to receive the third transmitted light after being separated by the second beam splitter 21, and the fourth polarization module is used to receive the fourth reflected light after being separated by the second beam splitter 21.

[0088] It should be noted that different polarization modules may contain different types of polarizers (for example, the third polarization module contains a linear polarizer, and the fourth polarization module contains a 45° linear polarizer, which will be described in the following embodiments). Polarizers allow light polarized in one direction to pass through while blocking or absorbing light in other directions (light polarized in directions other than the specified one). Different types of polarizers have different polarization processing characteristics, and they can separate different components in the optical signal according to the desired polarization state. Because different polarization modules use different polarizers, each polarization module can separate or filter specific polarized light components according to its specific polarization processing characteristics, thereby achieving the separation of different polarization states of the laser signal.

[0089] Furthermore, different polarization modules receive different reflected or transmitted light, and their subsequent processing of the reflected or transmitted light also differs. The following discussion will focus on the first and second polarization modules as examples. Since the first and second polarization modules are structurally identical, their subsequent processing of the second transmitted or reflected light is also the same. Therefore, in this embodiment, only the first polarization module will be described as an example; the second polarization module is similar and will not be described in detail here.

[0090] Specifically, the first polarization module includes multiple polarization units connected in sequence; each polarization unit consists of a pair of third beam splitters and a photodetector, the third beam splitter in each polarization unit is connected to the photodetector, and the third beam splitter in each polarization unit is connected to the third beam splitter in the adjacent polarization unit; the third beam splitter of the first polarization unit in the first polarization module is connected to the polarization beam splitter.

[0091] For further details, please refer to [link / reference]. Figure 1 The first polarization module includes three polarization units connected in sequence. These three polarization units are: a first polarization unit composed of a third beam splitter 9 and a photodetector 12; a second polarization unit composed of a third beam splitter 10 and a photodetector 13; and a third polarization unit composed of a third beam splitter 11 and a photodetector 14. The third beam splitters in adjacent polarization units are connected in sequence, i.e., third beam splitter 9, third beam splitter 10, and third beam splitter 11 are connected in sequence. The third beam splitter 9 of the first polarization unit is connected to the polarizing beam splitter 8.

[0092] In practice, the first polarization module separates the second transmitted light using a third beam splitter based on multiple polarization units to obtain multiple beams with different polarization states. The photodetectors based on multiple polarization units detect the separated multiple beams. The signals detected by the multiple photodetectors in the first polarization module are superimposed to determine the parallel polarization component scattering signal corresponding to the first polarization module.

[0093] Specifically, in the first polarization unit of the first polarization module, the third beam splitter 9 transmits the second transmitted light from the polarizing beam splitter 8 and separates it into two beams, each with a different polarization direction. The photodetector 12 detects the beams separated by the third beam splitter 9, converts the received optical signal into an electrical signal, and outputs intensity information. In the second polarization unit of the first polarization module, the third beam splitter 10 receives the beam separated by the first polarization unit and further splits it into two beams with different polarization states. The photodetector 13 detects the beams separated by the third beam splitter 10, converts the received optical signal into an electrical signal, and outputs intensity information. In the third polarization unit of the first polarization module, the third beam splitter 11 receives the beam separated by the second polarization unit and continues to separate it into two beams with different polarization states. The photodetector 14 detects the beams separated by the third beam splitter 11, converts the received optical signal into an electrical signal, and outputs intensity information. Finally, the first polarization module superimposes the signals from the photodetectors in the three polarization units, synthesizing multiple signals with different polarization states to obtain a total scattered signal, namely, the parallel polarization component scattered signal.

[0094] Based on the above description, since the first polarization module and the second polarization module are structurally identical, their subsequent processing of the second transmitted light or the second reflected light is also the same. This embodiment only describes the structure of the second polarization module. Please continue to refer to... Figure 1 The second polarization module includes three polarization units connected in sequence. These three polarization units are: a first polarization unit composed of a third beam splitter 15 and a photodetector 18; a second polarization unit composed of a third beam splitter 16 and a photodetector 19; and a third polarization unit composed of a third beam splitter 17 and a photodetector 20. The third beam splitters in adjacent polarization units are connected in sequence, i.e., third beam splitter 15, third beam splitter 16, and third beam splitter 17 are connected in sequence. The third beam splitter 15 of the first polarization unit is connected to the polarizing beam splitter 8.

[0095] Specifically, the third polarization module includes a quarter-wave plate 29, a linear polarizer 30, and multiple polarization units connected in sequence. The quarter-wave plate 29 is connected to the second beam splitter 21. Each polarization unit consists of a pair of third beam splitters and a photodetector. The third beam splitter in each polarization unit is connected to the photodetector, and the third beam splitter in each polarization unit is connected to the third beam splitter in the adjacent polarization unit. The third beam splitter of the first polarization unit in the third polarization module is connected to the linear polarizer 30.

[0096] For further details, please refer to [link / reference]. Figure 1 The third polarization module includes a quarter-wave plate 29, a linear polarizer 30, and three polarization units. The quarter-wave plate 29 is connected to the second beam splitter 21, and the linear polarizer 30 is connected to the first polarization unit among the three polarization units. The three polarization units are: the first polarization unit composed of the third beam splitter 31 and photodetector 34; the second polarization unit composed of the third beam splitter 32 and photodetector 35; and the third polarization unit composed of the third beam splitter 33 and photodetector 36. The third beam splitters in adjacent polarization units are connected sequentially, i.e., the third beam splitter 31, the third beam splitter 32, and the third beam splitter 33 are connected sequentially. The third beam splitter 31 of the first polarization unit is connected to the linear polarizer 30.

[0097] Specifically, the quarter-wave plate 29 is used to convert the third transmitted light, converting the third transmitted light containing circularly polarized light components into linearly polarized light in a specified direction; the linearly polarized plate 30 is used to extract the linearly polarized components in a specified direction from the linearly polarized light; each polarization unit in the third polarization module is used to separate the linearly polarized components based on the third beam splitter, and to detect the separated linearly polarized components using the photodetector to obtain a photodetector signal; the third polarization module is used to superimpose the photodetector signals from all polarization units in the third polarization module, and then convert the superimposed signal according to the matching relationship between the fast and slow axis directions of the quarter-wave plate and the polarization state of the incident light, and calculate the circularly polarized component scattering signal corresponding to the third polarization module.

[0098] Furthermore, the quarter-wave plate 29 is used to convert the third transmitted light containing circularly polarized light components into linearly polarized light. The fast and slow axis directions of the quarter-wave plate 29 determine its conversion method. The corresponding conversion form is determined by matching the polarization state of the third transmitted light. When the polarization direction of the third transmitted light matches the axis of the quarter-wave plate 29, the quarter-wave plate 29 converts the linearly polarized light into circularly polarized light, or vice versa. The linear polarizer 30 is used to extract the linearly polarized component in a specified direction from the linearly polarized light converted by the quarter-wave plate 29. The linear polarizer 30 extracts the light component with the same polarization direction from the beam from the quarter-wave plate 29 by selectively allowing linearly polarized light in a specific direction to pass through.

[0099] In practice, the third transmitted light enters a quarter-wave plate 29. The quarter-wave plate 29 adjusts the phase of the third transmitted light according to the different refractive indices along the fast and slow axes, converting the third transmitted light, which includes circularly polarized light separation, into linearly polarized light with a specified direction. The linearly polarized light processed by the quarter-wave plate 29 enters a linear polarizer 30. The linear polarizer 30 extracts the linearly polarized components in the same direction according to the transmission direction of the linearly polarized light, filtering out polarized light components that do not match that direction. The extracted linearly polarized light enters the first polarization unit in the third polarization module. The third beam splitter 31 in the first polarization unit separates the linearly polarized light into two beams, each with a different polarization direction. A photodetector 34 detects the beams separated by the third beam splitter 31, converts the received optical signal into an electrical signal, and outputs intensity information. The third beam splitter 32 in the second polarization unit receives the beams separated by the first polarization unit and further splits them into two beams with different polarization states. A photodetector 35 detects the beams separated by the third beam splitter 32, converts the received optical signal into an electrical signal, and outputs intensity information. The third beam splitter 33 in the third polarization unit receives the beam separated by the second polarization unit and further separates it into two beams with different polarization states. The photodetector 36 detects the beam separated by the third beam splitter 33, converts the received optical signal into an electrical signal, and outputs intensity information. Finally, the third polarization module superimposes the signals from the photodetectors in the three polarization units, synthesizing multiple signals with different polarization states to obtain a total scattered signal, namely the linearly polarized component scattered signal. At this point, based on the polarization conversion characteristics of the quarter-wave plate 29, the third polarization module performs a conversion according to the fast and slow axis directions of the quarter-wave plate 29 and the polarization state of the third transmitted light, converting the linearly polarized component scattered signal back into a circularly polarized component scattered signal.

[0100] The apparatus provided in this embodiment offers significant advantages for achieving polarization-Stokes measurements, particularly in capturing circularly polarized component scattered signals, through the use of a quarter-wave plate and a linear polarizer. The quarter-wave plate converts circularly polarized light into linearly polarized light, allowing for further measurement via a linear polarizer. Circularly polarized light is inherently difficult to separate and detect directly using conventional polarizers because it contains two mutually perpendicular linearly polarized components with a phase difference. The quarter-wave plate adjusts the phase relationship of the light, converting circularly polarized light into linearly polarized light, making it easier to identify and separate in subsequent measurements. The linear polarizer then selectively measures this converted light, allowing only linearly polarized components in specific directions to pass through. In this way, the quarter-wave plate and linear polarizer ensure effective extraction and measurement of the circularly polarized components, enabling the entire polarization-Stokes measurement apparatus to comprehensively measure scattered signals of different polarization states. Ultimately, this design improves the accuracy and reliability of polarization-Stokes measurements, ensuring the system can accurately capture various polarization component signals, thereby enhancing the performance of marine lidar systems in complex environments.

[0101] Specifically, the fourth polarization module includes a 45° linear polarizer 22 and multiple polarization units. The 45° linear polarizer 22 is connected to the first polarization unit among the multiple polarization units. Each polarization unit consists of a pair of third beam splitters and a photodetector. The third beam splitter in each polarization unit is connected to the photodetector, and the third beam splitter in each polarization unit is connected to the third beam splitter in the adjacent polarization unit. The third beam splitter of the first polarization unit in the fourth polarization module is connected to the 45° linear polarizer 22.

[0102] For further details, please refer to [link / reference]. Figure 1 The fourth polarization module includes a 45° linear polarizer 22 and three polarization units. The 45° linear polarizer 22 is connected to the first of the three polarization units. The three polarization units are, respectively, a first polarization unit composed of a third beam splitter 23 and a photodetector 26, a second polarization unit composed of a third beam splitter 24 and a photodetector 27, and a third polarization unit composed of a third beam splitter 25 and a photodetector 28. The third beam splitters in adjacent polarization units are connected sequentially, that is, the third beam splitter 23, the third beam splitter 24, and the third beam splitter 25 are connected sequentially. The third beam splitter 23 of the first polarization unit is connected to the 45° linear polarizer 22.

[0103] Specifically, the 45° linear polarizer 22 is used to filter the third reflected light and extract linearly polarized light in the 45° direction; each polarization unit in the fourth polarization module is used to separate the linearly polarized light based on the third beam splitter, and the photodetector is used to detect the separated linearly polarized light signals to obtain photodetector signals; the fourth polarization module is used to superimpose the photodetector signals from all polarization units in the fourth polarization module, and combine them with the beam separation characteristics of the third beam splitter to determine the 45° linearly polarized component scattering signal corresponding to the fourth polarization module.

[0104] Furthermore, the 45° linear polarizer 22 only allows the third reflected light with a polarization direction of 45° to pass through, blocking polarized light in other directions. When the third reflected light passes through the 45° linear polarizer, its polarization direction is adjusted to be consistent with the transmission direction of the 45° linear polarizer 22. The 45° linear polarizer 22 is used to adjust the polarization direction of the third reflected light, making it linearly polarized at 45°, ensuring that the third reflected light entering the fourth polarization module has a specific polarization direction, thus guaranteeing accuracy in subsequent separation and detection processes.

[0105] In practice, the third reflected light enters the fourth polarization module and passes through a 45° linear polarizer 22. The 45° linear polarizer 22 adjusts the polarization direction of the third reflected light, resulting in linearly polarized light with a polarization direction of 45°. The adjusted linearly polarized light enters the first polarization unit in the fourth polarization module. The third beam splitter 23 in the first polarization unit separates the linearly polarized light into two beams, each with a different polarization direction. The photodetector 26 detects the beams separated by the third beam splitter 23, converts the received optical signal into an electrical signal, and outputs intensity information. The third beam splitter 24 in the second polarization unit receives the beam separated by the first polarization unit and further splits it into two beams with different polarization states. The photodetector 27 detects the beams separated by the third beam splitter 24, converts the received optical signal into an electrical signal, and outputs intensity information. The third beam splitter 25 in the third polarization unit receives the beam separated by the second polarization unit and continues to separate it into two beams with different polarization states. The photodetector 28 detects the beam separated by the third beam splitter 25, converts the received optical signal into an electrical signal, and outputs intensity information. Finally, the fourth polarization module superimposes the signals from the photodetectors in the three polarization units, synthesizing signals with multiple different polarization states to obtain a total scattered signal, namely the 45° linear polarization component scattered signal.

[0106] The apparatus provided in this embodiment, with its 45° linear polarizer, is of great significance for achieving polarization Stokes measurements. Polarization Stokes measurements require acquiring light scattering information from multiple polarization states of the target to comprehensively analyze and accurately identify the characteristics of underwater targets. The 45° linear polarizer adjusts the polarization state of the incident light to 45° linear polarization, allowing subsequent polarization modules to focus on measuring the scattered signal in this specific polarization direction. Through the 45° linear polarizer, the polarization Stokes measurement device can acquire scattered signals at different polarization angles, particularly in the 45° polarization direction, thus providing more details about the target's optical characteristics. This setup not only ensures the measurement of specific polarization components but also improves the overall measurement accuracy and reliability of the system by utilizing signals from different polarization angles, ultimately achieving comprehensive and high-precision polarization Stokes measurement functionality.

[0107] It should be noted that the polarization states of the scattered signals corresponding to different polarization modules are different. Based on the above description, the first polarization module corresponds to the parallel polarization component scattered signal, the second polarization module corresponds to the perpendicular polarization component scattered signal, the third polarization module corresponds to the circular polarization component scattered signal, and the fourth polarization module corresponds to the 45° linear polarization component scattered signal.

[0108] Optionally, the light intensity of the composite scattering signal is greater than the upper limit of the range of a single photodetector; the light intensity of the beam entering each photodetector is not greater than the upper limit of the range of the photodetector, and the sum of the light intensities output by the photodetectors of all polarization modules is the same as the light intensity of the composite scattering signal.

[0109] The device provided in this embodiment, when faced with a complex scattering signal whose intensity exceeds the upper limit of a single photodetector's range, utilizes reasonable optical beam splitting and polarization separation techniques to ensure the complete acquisition of all effective scattering information while avoiding detector saturation or damage due to light intensity overload. Specifically, the complex scattering signal includes the target laser signal, sunlight interference, and background stray light, and the overall light intensity exceeds the upper limit that a single photodetector can withstand. Through a combined beam splitting and polarization control method, the overall signal is decomposed into multiple sub-beams with controlled intensity and distinguishable polarization states. The parameters of the first beam splitter are designed based on the detector's dynamic range. By adjusting its reflectivity and transmittance, the complex optical signal is initially separated into transmitted and reflected light in space, with the intensity of each part controlled within the detector's allowable range. Subsequently, the polarization beam splitter, based on the different polarization directions of the light in the complex signal, utilizes the physical characteristics of high transmission of P-polarized light and high reflection of S-polarized light to further achieve polarization state separation of the beam, while also taking into account further balanced energy distribution. This design ensures that the intensity of a single beam entering each detector does not exceed the maximum capacity of that detector, while the sum of the light intensities measured by each detector along all beam-splitting paths remains equivalent to the total intensity of the initial composite scattering signal, demonstrating the overall energy conservation characteristics and measurement integrity of the system. This design not only guarantees the high dynamic range and high signal-to-noise ratio measurement requirements of the scattered signal, but also achieves system-level multi-channel dynamic control and energy management through the reverse engineering of optical device physical parameters and detector performance parameters, ensuring that laser scattering signals in complex underwater environments can be acquired and processed completely, accurately, and safely.

[0110] Optionally, after the polarization module outputs multiple beams of light with different polarization states to corresponding photodetectors, it is also used to correct the detection results, including: determining the output channel signal based on the correlation between the measurement results of the photodetectors and the background noise; performing energy integration on the output channel signal using the same time window to obtain a stable calibration quantity; calibrating using multiple standard polarization states to establish the correspondence between the measurement signal results of each polarization module and the standard polarization state; fitting the measurement data of all known standard polarization states using the least squares method to obtain the optimal instrument matrix; combining the optimal instrument matrix with the measurement of the lidar echo signal, introducing matrix weights, and inverting the polarization state of the water profile; outputting normalized polarization parameters based on the inversion results, and using the normalized polarization parameters to classify suspended particles in the water.

[0111] Specifically, after obtaining the detection results from multiple polarization modules, the detection results need to be corrected, and the output channel signal can be denoted as:

[0112] ;

[0113] in, For output channel signals; , , , The measurement results are from the photodetector. , , , This is background noise.

[0114] To obtain a stable calibration value, energy integration is performed using the same time window:

[0115] ;

[0116] in, To stabilize the calibration quantity; This is the output channel signal.

[0117] Furthermore, the instrument was calibrated using six standard polarization states: 0°, 45°, 90°, 135°, right-handed, and left-handed. Given the relationship between the measurement signal results of each polarization module and the standard polarization state, the inverse of the matrix was solved using the least squares method. To accurately calculate the inverse matrix, the least squares method was used to optimize the process. By performing least squares fitting on the measurement data of all known standard polarization states, an optimal instrument matrix was obtained.

[0118] ;

[0119] in, The optimal instrument matrix; To stabilize the calibration quantity; This is the standard polarization state matrix.

[0120] After obtaining the optimal instrument matrix through calibration, the polarization state of the water profile can be retrieved by measuring the echo signal of the lidar. Due to differences in noise, detector sensitivity, and gain, matrix weights are introduced, expressed as follows:

[0121] ;

[0122] in, The optimal instrument matrix; These are the matrix weights; , , , The measurement results are from the photodetector. , , , This is a Stokes vector.

[0123] After obtaining the inversion results, the normalized polarization parameters can be output as follows:

[0124] ;

[0125] in, Normalization parameters for the 0° / 90° linear polarization components; The difference between the 0° and 90° linear polarization components obtained by inversion; The total intensity of scattered light from the water body obtained by inversion; Normalized parameters for the 45° / 135° linear polarization components; The difference between the 45° and 135° linear polarization components obtained by inversion; These are the normalization parameters for the circular polarization components; The difference between the right-hand and left-hand circular polarization components obtained from the inversion; This represents the total degree of polarization.

[0126] The device provided in this embodiment, in a first aspect, achieves effective separation of laser scattering echo signals and background interference signals in complex underwater environments through a structural design that combines multi-stage beam splitting and polarization characteristic separation. This application emits laser beams containing different polarization states through a laser incident module. Utilizing the difference in polarization state characteristics between the underwater target scattered light and the background light, a physical basis is provided for subsequent signal separation. After being collected by the laser scattering module, the composite scattering signal contains the effective laser signal scattered by the underwater target and interference signals from sunlight or the environmental background. Furthermore, the total intensity of this composite signal typically exceeds the dynamic range of a single photodetector, making direct detection prone to saturation or information loss. To this end, this application utilizes a combination of a first beam splitter, a polarizing beam splitter, and a second beam splitter to perform multi-stage beam splitting and polarization state separation based on the differences in spatial direction, polarization state, and light intensity of different components in the composite scattering signal. The first beam splitter spatially separates the composite scattering signal, initially reducing the intensity of a single path. The polarizing beam splitter further divides the transmitted light into optical paths with different polarization directions based on the difference in polarization states between the background light and the effective signal, effectively separating the background light with significantly different polarization characteristics from the target scattering signal into different channels. The second beam splitter further spatially splits the first reflected light, ensuring that the overall composite signal can be reasonably distributed to multiple polarization modules, so that the light intensity in each channel is controlled within the range of the corresponding photodetector, while maintaining the integrity of the overall signal. This multi-stage beam splitting and polarization separation design based on light intensity and polarization characteristics, compared to existing technologies that only use single-stage beam splitting or single polarization processing, can more effectively achieve reasonable splitting of composite scattering signals and independent extraction of effective signals under strong background light conditions. It reduces background light interference to the detector, avoids detector saturation due to excessive light intensity, and improves the device's ability to extract underwater target scattering signals and the complete measurement effect of polarization Stokes information under strong interference environments, thereby significantly improving measurement accuracy, environmental adaptability, and the stability of the detection system. Secondly, this application achieves polarization Stokes measurement by setting up polarization modules containing different types of polarizers, allowing the polarization Stokes measurement device to capture and analyze signals from different polarization states, thereby obtaining complete polarization information. Firstly, the polarization Stokes measurement device uses different polarization modules, with different types of polarizers within each module to process different polarization components. For example, linear polarizers are used to acquire signals associated with linearly polarized light in a specific direction, while quarter-wave plates are used to convert certain polarization states (such as circularly polarized light) into linearly polarized light. Further utilizing linear polarizers to acquire signals in a specific direction allows the system to more effectively measure circularly polarized signals. The polarization units in each polarization module divide the light beam into multiple different polarization components, each detected by a photodetector. This allows each polarization module to measure scattered signals in different polarization states separately.Secondly, through the collaboration of multiple polarization modules, the polarization-Stokes measurement device can achieve polarization-Stokes measurement of underwater targets. Since each polarization module processes signals of different polarization states, the device can measure scattered signals from multiple polarization angles using different combinations of polarizers, obtaining more comprehensive underwater target information. Signal superposition between different polarization modules further improves the detection accuracy of the polarization-Stokes measurement device, ensuring efficient measurement of target scattered signals. Thirdly, the laser incident module, through the synergistic effect of a pulsed laser, a half-wave plate, and a quarter-wave plate, enables the generation of laser beams with multiple polarization states. Firstly, the laser incident module can flexibly generate laser beams with various polarization states, such as linear, circular, and elliptical polarization, allowing the polarization-Stokes measurement device to comprehensively acquire the light scattering and reflection characteristics of underwater targets and the environment, significantly improving detection accuracy and information integrity. Secondly, by adjusting the waveplate parameters, the laser incident module possesses extremely high environmental adaptability, capable of coping with complex and changing underwater environmental conditions, such as different water qualities, depths, and background light interference, thereby improving the reliability of the detection results. Furthermore, the multi-polarization laser beam can effectively distinguish between target signals and background noise, reducing the impact of external interference on detection accuracy. It also avoids detector saturation due to strong echo signals, ensuring the device has high dynamic range and high signal fidelity. Fourthly, the laser scattering module, through the collaborative design of the receiver and filter, comprehensively optimizes the measurement capabilities of the polarization-Stokes measurement device in complex environments. The receiver can comprehensively receive the effective laser signal scattered by the underwater target, while integrating interference signals from the environment, such as sunlight reflected from the water surface and background light, ensuring the integrity and diversity of the input signal and providing comprehensive data support for subsequent processing. The filter, through precise spectral selective filtering, effectively removes background light and stray light from the interference signal, retaining only the target laser signal, thereby improving the signal-to-noise ratio. This design not only solves the problem of interference from sunlight and environmental noise on measurement accuracy but also avoids the risk of detector saturation or distortion caused by strong light interference, significantly improving the system's dynamic range and measurement stability. Meanwhile, by clearly separating useful signals from interference signals, the laser scattering module lays a high-quality input foundation for subsequent signal beam splitting and detection, enhancing the adaptability and reliability of the polarization Stokes measurement device in complex marine environments.

[0127] Corresponding to the aforementioned embodiment of a polarization Stokes measurement device for underwater light scattering, this application also provides an embodiment of a polarization Stokes measurement method for underwater light scattering.

[0128] Figure 2 This is a flowchart of the underwater light scattering polarization Stokes measurement method provided in Embodiment 2 of this application. Please refer to... Figure 2The method provided in this embodiment is applied to the underwater light scattering polarization Stokes measurement device according to any one of the first aspects of this application, and the method includes:

[0129] S201, The laser incident module emits laser beams containing different polarization states toward the water.

[0130] S202, The laser scattering module receives the laser signal of the laser beam after being scattered by the underwater target, and the composite signal of sunlight and background light reflected from the water surface, and sends the composite scattering signal composed of the laser signal and the composite signal to the first beam splitter.

[0131] S203. The first beam splitter separates the composite scattering signal to obtain a first transmitted light and a first reflected light. The first transmitted light is sent to a polarizing beam splitter, and the first reflected light is sent to a second beam splitter.

[0132] S204. The polarizing beam splitter separates the first transmitted light to obtain a second transmitted light and a second reflected light. The second beam splitter separates the first reflected light to obtain a third transmitted light and a third reflected light. The second transmitted light, the second reflected light, the third transmitted light, and the third reflected light are then sent to different polarization modules.

[0133] S205. Each polarization module separates the polarization state of the received optical signal and outputs multiple beams of light with different polarization states to the corresponding multiple photodetectors.

[0134] The method in this embodiment can be used to execute Figure 1 The steps of the device embodiment shown are similar in principle and process, and will not be repeated here.

[0135] For details on the implementation process of the corresponding steps in the above method, please refer to the implementation process of the functions and roles of each unit in the above device, which will not be repeated here.

[0136] For the method embodiments, since they basically correspond to the device embodiments, the relevant parts can be referred to in the description of the device embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and 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 modules can be selected to achieve the purpose of this application according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0137] The above description is merely a preferred embodiment of this application and is not intended to limit this application. 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 polarization Stokes measurement device for underwater light scattering, characterized in that, The device includes a laser incident module, a laser scattering module, a first beam splitter, a second beam splitter, a polarizing beam splitter, and multiple polarization modules. The output of the first beam splitter is connected to the second beam splitter and the polarizing beam splitter, respectively. The multiple outputs of the second beam splitter and the multiple outputs of the polarizing beam splitter are respectively linked to different polarization modules. Each polarization module includes multiple polarization units, and each polarization unit includes a third beam splitter and a photodetector. The number of third beam splitters and photodetectors in each polarization unit is the same. Different polarization modules contain different types of polarizers, and the polarization processing characteristics of different types of polarizers are different. Different polarization modules separate laser signals into different polarization states. The laser incident module is used to emit laser beams containing different polarization states toward the water area; The laser scattering module is used to receive the laser signal of the laser beam after being scattered by the underwater target, and the composite signal of sunlight and background light reflected from the water surface, and send the composite scattering signal composed of the laser signal and the composite signal to the first beam splitter. The first beam splitter is used to separate the composite scattering signal to obtain a first transmitted light and a first reflected light. The first transmitted light passes through the polarizing beam splitter, and the first reflected light passes through the second beam splitter. The light intensity of the composite scattering signal is greater than the upper limit of the range of a single photodetector. The polarizing beam splitter is used to separate the first transmitted light to obtain a second transmitted light and a second reflected light; the second beam splitter is used to separate the first reflected light to obtain a third transmitted light and a third reflected light; the second transmitted light, the second reflected light, the third transmitted light and the third reflected light are respectively sent to different polarization modules; Each polarization module is used to separate the polarization state of the received optical signal and output multiple beams of light with different polarization states to multiple corresponding photodetectors; wherein, the light intensity of the beam entering each photodetector is not greater than the upper limit of the range of the photodetector, and the sum of the light intensity output by the photodetectors of all polarization modules is the same as the light intensity of the composite scattering signal.

2. The apparatus according to claim 1, characterized in that, The multiple polarization modules include a first polarization module, a second polarization module, a third polarization module, and a fourth polarization module. The second transmitted light passes through the first polarization module, the second reflected light passes through the second polarization module, the third transmitted light passes through the third polarization module, and the third reflected light passes through the fourth polarization module.

3. The apparatus according to claim 1, characterized in that, After the polarization module outputs multiple beams of light with different polarization states to corresponding photodetectors, it is also used to correct the detection results, including: The output channel signal is determined based on the correlation between the measurement results of the photodetector and the background noise. The output channel signal is integrated using the same time window to obtain a stable calibration value. Calibration was performed using multiple standard polarization states to establish the correspondence between the measurement signal results of each polarization module and the standard polarization state; The optimal instrument matrix is ​​obtained by fitting the measurement data of all known standard polarization states using the least squares method. By combining the optimal instrument matrix with the measured lidar echo signal, matrix weights are introduced to invert the polarization state of the water profile. The normalized polarization parameters are output based on the inversion results, and the normalized polarization parameters are used to classify suspended particles in water.

4. The apparatus according to claim 2, characterized in that, The first polarization module includes multiple polarization units connected in sequence; each polarization unit consists of a pair of third beam splitters and a photodetector, the third beam splitter in each polarization unit is connected to the photodetector, and the third beam splitter in each polarization unit is connected to the third beam splitter in the adjacent polarization unit; the third beam splitter of the first polarization unit in the first polarization module is connected to the polarization beam splitter.

5. The apparatus according to claim 2, characterized in that, The third polarization module includes a quarter-wave plate, a linear polarizer, and multiple polarization units connected in sequence. The quarter-wave plate is connected to the second beam splitter. Each polarization unit consists of a pair of third beam splitters and a photodetector. The third beam splitter in each polarization unit is connected to the photodetector, and the third beam splitter in each polarization unit is connected to the third beam splitter in the adjacent polarization unit. The third beam splitter of the first polarization unit in the third polarization module is connected to the linear polarizer.

6. The apparatus according to claim 2, characterized in that, The fourth polarization module includes a 45° linear polarizer and multiple polarization units. The 45° linear polarizer is connected to the first polarization unit among the multiple polarization units. Each polarization unit consists of a pair of third beam splitters and a photodetector. The third beam splitter in each polarization unit is connected to the photodetector, and the third beam splitter in each polarization unit is connected to the third beam splitter in the adjacent polarization unit. The third beam splitter of the first polarization unit in the fourth polarization module is connected to the 45° linear polarizer.

7. The apparatus according to claim 5, characterized in that, The quarter-wave plate is used to convert the third transmitted light, converting the third transmitted light containing circularly polarized light components into linearly polarized light in a specified direction. The linear polarizer is used to extract the linear polarization component in a specified direction from the linearly polarized light; Each polarization unit in the third polarization module is used to separate the linear polarization component based on the third beam splitter, and the photodetector is used to detect the separated linear polarization component to obtain the photodetector signal. The third polarization module is used to superimpose the photodetector signals from all polarization units in the third polarization module, and then convert the superimposed signals according to the matching relationship between the fast axis and slow axis directions of the quarter-wave plate and the polarization state of the incident light, and calculate the circular polarization component scattering signal corresponding to the third polarization module.

8. The apparatus according to claim 6, characterized in that, The 45° linear polarizer is used to filter the third reflected light and extract linearly polarized light in the 45° direction; Each polarization unit in the fourth polarization module is used to separate the linearly polarized light based on the third beam splitter, and the photodetector is used to detect the separated linearly polarized light signals to obtain the photodetector signal. The fourth polarization module is used to superimpose the photodetector signals from all polarization units in the fourth polarization module, and then combine them with the beam separation characteristics of the third beam splitter to determine the 45° linear polarization component scattering signal corresponding to the fourth polarization module.

9. The apparatus according to claim 1, characterized in that, The laser incident module includes a pulsed laser, a first waveplate, and a second waveplate connected in sequence; wherein the first waveplate is a half-waveplate and the second waveplate is a quarter-waveplate; The pulsed laser is used to emit a detection laser toward the water area; The first waveplate is used to adjust the polarization direction of the probe laser; The second waveplate is used to modulate the probe laser after it has been adjusted by the first waveplate, thereby generating a laser beam with multiple polarization states.

10. A polarization Stokes measurement method for underwater light scattering, characterized in that, The method is applied to the underwater light scattering polarization Stokes measurement device according to any one of claims 1-9, and the method includes: The laser incident module emits laser beams containing different polarization states toward the water. The laser scattering module receives the laser signal of the laser beam after being scattered by the underwater target, and the composite signal of sunlight and background light reflected from the water surface, and sends the composite scattering signal composed of the laser signal and the composite signal to the first beam splitter. The first beam splitter separates the composite scattering signal to obtain a first transmitted light and a first reflected light. The first transmitted light is sent to a polarizing beam splitter, and the first reflected light is sent to a second beam splitter. The polarizing beam splitter separates the first transmitted light to obtain a second transmitted light and a second reflected light. The second beam splitter separates the first reflected light to obtain a third transmitted light and a third reflected light. The second transmitted light, the second reflected light, the third transmitted light, and the third reflected light are then sent to different polarization modules. Each polarization module separates the polarization state of the received optical signal and outputs multiple beams of light with different polarization states to the corresponding multiple photodetectors.

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