A method and device for detecting targets in turbid media based on annular circularly polarized light

Abstract

The present application provides a method and device for detecting a target in a turbid medium based on annular circularly polarized light. The method provided by the present application includes: modulating circularly polarized light to obtain a target laser beam, irradiating a target to be measured based on the target laser beam to obtain reflected light; wherein the target laser beam is annular circularly polarized light; determining the receiving angle of the reflected light according to the characteristic that the backscattering polarization of the circularly polarized light is invariant; receiving and modulating the reflected light based on the receiving angle, detecting the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity contained in the reflected light; calculating the circular polarization component based on the intensity difference between the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity, detecting the target to be measured based on the circular polarization component, and calculating the distance of the target to be measured. The method and device for detecting a target in a turbid medium based on annular circularly polarized light provided by the present application are used to accurately, quickly, and reliably complete target detection and ranging.

Description

Technical Field

[0001] The present application relates to the technical field of target detection, and in particular to a method and device for detecting a target in a turbid medium based on annular circularly polarized light. Background Art

[0002] Turbid media, such as sandstorms and underwater environments, are widely present in the atmosphere, oceans, and many industrial sites. The particles and suspended matter in these media can produce strong multiple scattering effects on the light beam, seriously interfering with the accuracy of the target measurement signal.

[0003] At present, common target detection and ranging technologies in turbid media mostly rely on laser technology. The traditional laser ranging method calculates the distance between the target and the measuring device by emitting a straight laser beam and receiving its reflected signal. However, this method faces huge challenges in turbid media. Due to the existence of the scattering effect, the laser beam will diverge rapidly during the transmission process, and the reflected signal is often submerged by noise, making the received effective signal extremely weak and difficult to distinguish, and it is impossible to complete the target ranging. In addition, the scattering of particles in turbid media will further aggravate the attenuation and distortion of the signal. For linear light sources, only targets within a very small range can be detected, and the detection efficiency is low. In addition, the scattering in turbid media will seriously affect the accuracy and stability of ranging, and cannot meet the needs of target detection. Summary of the invention

[0004] In view of this, the present application provides a method and device for target detection in turbid media based on annular circularly polarized light, so as to accurately, quickly and reliably complete target detection and ranging.

[0005] Specifically, the present application is implemented through the following technical solutions:

[0006] The first aspect of the present application provides a method for detecting a target in a turbid medium based on annular circularly polarized light, the method comprising:

[0007] Modulating circularly polarized light to obtain a target laser beam, irradiating a target to be measured based on the target laser beam to obtain reflected light; wherein the circularly polarized light is in a circular polarization state, the target laser beam is an annular circularly polarized light, and under the same spacing distance condition, a single detection range of the circularly polarized light is smaller than a single detection range of the target laser beam;

[0008] According to the polarization invariance characteristic of the backscattering of circularly polarized light, the receiving angle of the reflected light is determined;

[0009] Wherein, within the first angle range, the change in polarization direction of the reflected light polarization compared with the target laser beam is less than a first threshold, and the reflected light polarization is consistent with the polarization type of the target laser beam; the receiving angle is within the first angle range;

[0010] receiving and modulating the reflected light based on the receiving angle, and detecting the intensity of left-handed circularly polarized light and the intensity of right-handed circularly polarized light contained in the reflected light;

[0011] A circular polarization component is calculated based on the light intensity difference between the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity, and a distance of the target to be measured is calculated based on the circular polarization component.

[0012] The second aspect of the present application provides a target detection device in a turbid medium based on annular circularly polarized light, the device comprising an irradiation module, a modulation module and a calculation module; wherein,

[0013] The irradiation module is used to modulate circularly polarized light to obtain a target laser beam, and irradiate the target to be measured based on the target laser beam to obtain reflected light; wherein the circularly polarized light is in a circular polarization state, and the target laser beam is an annular circularly polarized light, and under the same spacing distance condition, the single detection range of the circularly polarized light is smaller than the single detection range of the target laser beam;

[0014] The modulation module is used to determine the receiving angle of the reflected light according to the characteristic that the backscattered polarization of the circularly polarized light remains unchanged;

[0015] Wherein, within the first angle range, the change in polarization direction of the reflected light polarization compared with the target laser beam is less than a first threshold, and the reflected light polarization is consistent with the polarization type of the target laser beam; the receiving angle is within the first angle range;

[0016] The modulation module is further used to receive and modulate the reflected light based on the receiving angle, and detect the intensity of left-handed circularly polarized light and the intensity of right-handed circularly polarized light contained in the reflected light;

[0017] The calculation module is used to calculate the circular polarization component based on the light intensity difference between the left-handed circular polarized light intensity and the right-handed circular polarized light intensity, and calculate the distance of the target to be measured based on the circular polarization component.

[0018] The target detection method and device in turbid medium based on annular circular polarized light provided by the present application modulates the circular spot produced by a linear laser into an annular spot by modulation, and uses an annular target laser beam for detection at the same irradiation distance. Compared with the traditional linear laser beam, the annular target laser beam can cover a larger detection area, so that the target to be detected can be more effectively covered and found in one detection, thereby improving the detection efficiency. Furthermore, since the received circular polarization components all come from the annular circular polarized light itself as the detection light, measuring the circular polarization components can greatly suppress environmental noise and scattered light, because in the calculation of the circular polarization components, the interference of linear polarized light and non-polarized light in the environment is completely excluded, and only the circular polarization components of the annular circular polarized light can be received, thereby simplifying the system structure and reducing the detection cost on the basis of improving the detection accuracy. Furthermore, according to the characteristic of the invariant backscattered polarization of circularly polarized light, the receiving angle of the reflected light is determined, because only the backscattered light within a specific angle range has sufficient circular polarization components, so that the circular polarization components of the circularly polarized light after being reflected by the target to be measured are used for measurement, so that the circularly polarized light can greatly reduce the interference of environmental noise in the target distance measurement, which not only ensures that the target detection can be completed stably and reliably in any environment and any medium, but also improves the measurement accuracy of the target detection. In this way, the distance of the target to be measured can be calculated by the circular polarization component, and the detection and identification can be completed efficiently and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A flow chart of a method for detecting a target in a turbid medium based on annular circularly polarized light provided by an exemplary embodiment of the present application;

[0020] Figure 2 A schematic diagram of a target detection device in a turbid medium based on annular circularly polarized light provided by an exemplary embodiment of the present application;

[0021] Figure 3 A schematic diagram of a target detection device in a turbid medium based on annular circularly polarized light provided by another exemplary embodiment of the present application;

[0022] Figure 4 A schematic diagram of a target detection device in a turbid medium based on annular circularly polarized light provided by an exemplary embodiment of the present application;

[0023] Description of reference numerals:

[0024] 1: Laser generator;

[0025] 2: Polarizer;

[0026] 3: Second quarter wave plate;

[0027] 4: Axis lens;

[0028] 5: turbid medium;

[0029] 6: Target to be tested;

[0030] 7: first quarter wave plate;

[0031] 8: Wollaston polarizing filter;

[0032] 9: filter;

[0033] 10: first photomultiplier tube;

[0034] 11: second photomultiplier tube;

[0035] 12: Circularly polarized light. DETAILED DESCRIPTION

[0036] Here, exemplary embodiments are described in detail, and examples thereof are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application.

[0037] The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in this article refers to and includes any or all possible combinations of one or more associated listed items.

[0038] It should be understood that although the terms first, second, third, etc. may be used in the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0039] The present application provides a method and device for detecting a target in a turbid medium based on annular circularly polarized light, which are used to accurately, quickly and reliably complete target detection and ranging.

[0040] Specific embodiments are given below to introduce the technical solution of the present application in detail.

[0041] Figure 1 This is a flow chart of a method for detecting a target in a turbid medium based on annular circularly polarized light provided by an exemplary embodiment of the present application. Figure 1 , the method provided in this embodiment may include:

[0042] S101. Modulate circularly polarized light to obtain a target laser beam, and irradiate a target to be measured based on the target laser beam to obtain reflected light; wherein, the circularly polarized light is in a circular polarization state, and the target laser beam is an annular circularly polarized light. Under the same spacing distance condition, a single detection range of the circularly polarized light is smaller than a single detection range of the target laser beam.

[0043] Specifically, circularly polarized light is a special form of light wave. During the propagation of the electric vector of the circularly polarized light wave, its terminal trajectory forms a circle or a nearly circular light wave on a plane perpendicular to the direction of light propagation. The magnitude of the electric vector of the circularly polarized light wave remains unchanged at any moment, but its direction changes continuously with time.

[0044] Furthermore, the circularly polarized light is shaped to obtain a target laser beam, which is a circularly polarized light. In specific implementation, the target laser beam retains the optical properties of the circularly polarized light and has a circular distribution shape.

[0045] It should be noted that, at the same irradiation distance, the annular structure of the target laser beam can cover a wider area, so that targets within a larger range can be detected in one detection process.

[0046] A specific embodiment is given below to introduce the generation process of the target laser beam in detail:

[0047] (1) Determine the type of light source according to the type of turbid medium, generate a detection laser based on a laser beam generator, the detection laser matches the type of the light source, and modulate the detection laser to obtain the circularly polarized light.

[0048] Specifically, a laser beam generator is a laser that can release a high-energy laser beam in a very short time. The laser beam generated by the laser beam generator is not continuous, but appears in the form of a series of pulses.

[0049] It should be noted that the specific model of the laser beam generator is determined according to actual needs, and is not limited in this embodiment. In specific implementation, the laser beam generator provides energy through a pump source to make the particles in the gain medium transition from a low energy level to a high energy level, forming a population inversion. When the population inversion reaches a certain level, stimulated radiation is generated through the feedback of the resonant cavity to form a detection laser.

[0050] Furthermore, the detection laser generated by the laser beam generator is an unmodulated and unshaped laser beam. In specific implementation, different detection lasers can be generated according to the specific type of the laser beam generator. The type of light source is determined according to the type of turbid medium. Specifically, different light sources should be used reasonably in different occasions. For example, blue-green light should be used for underwater detection to reduce absorption, and red light should be used for environmental measurement with low visibility in the air to enhance penetration.

[0051] In this step, the detection laser is modulated so that the detection laser has a consistent polarization direction.

[0052] A specific embodiment is given below to introduce in detail the process of modulating the detection laser: adjusting the polarization state of the detection laser based on the polarizer and the second quarter-wave plate to obtain the circularly polarized laser as circularly polarized light.

[0053] Optionally, the polarization state of the detection laser is adjusted based on a polarizer to obtain a second linearly polarized light.

[0054] Specifically, the vibration direction of the light wave in the second linear polarized light is limited to a specific direction, which may be a polarization direction or a transmission direction. It is understood that the electric field vector of the light wave of the second linear polarized light vibrates in a plane perpendicular to the propagation direction, and the vibration direction remains consistent and does not change with time.

[0055] Furthermore, the polarizer is an optical element that can selectively transmit light waves in the same direction as its transmission direction and block polarized light components in other directions. In specific implementation, the polarizer adjusts the polarization state of the detection laser generated by the laser beam generator to convert it from an arbitrary polarization state to a consistent second linear polarized light.

[0056] The target detection method in turbid medium based on annular circular polarized light provided in this embodiment adjusts the polarization state of the detection laser based on the polarizer to obtain the second linear polarized light. In this way, the polarization state of the detection laser is accurately controlled by the polarizer, which reduces the measurement error that may be introduced due to the change of polarization state, thereby improving the stability and measurement accuracy of the entire detection and ranging system. Furthermore, the detection laser is adjusted to the second linear polarized light with consistent polarization state by the polarizer, which provides the necessary conditions for the subsequent conversion of the second linear polarized light into circular polarized light, ensuring the accuracy and efficiency of the conversion process.

[0057] A specific embodiment is given below to introduce the modulation process of the second linear polarized light in detail:

[0058] Optionally, the second linearly polarized light is modulated based on a second quarter wave plate to obtain the circularly polarized light.

[0059] Specifically, the second quarter wave plate is a birefringent crystal plate with specific thickness and optical properties.

[0060] Furthermore, when the second linear polarized light is vertically incident on the second quarter wave plate, and the polarization direction of the second linear polarized light forms an angle of 45° with a main axis of the second quarter wave plate, the polarization state of the second linear polarized light will become a circular polarization state.

[0061] In specific implementation, since the second quarter wave plate generates a 90° phase difference in the second linearly polarized light, the end trajectory of the electric field vector of the second linearly polarized light in the propagation direction forms a circle, thereby obtaining circularly polarized light.

[0062] The target detection method in turbid medium based on annular circularly polarized light provided in this embodiment is based on modulating the second linearly polarized light by the second quarter wave plate to obtain circularly polarized light. In this way, the circularly polarized light obtained by modulating the second linearly polarized light by the second quarter wave plate can ensure the reliability and accuracy of measurement in complex and changeable environments.

[0063] (2) The circularly polarized light is shaped based on an axicon to obtain the target laser beam.

[0064] Specifically, the aconic lens is a lens with a conical surface. It should be noted that the specific model of the aconic lens can be selected according to actual needs, and this is not limited in this embodiment. In specific implementation, the bottom surface of the aconic lens can be a circle, and the side surface of the aconic lens can be a continuous inclined surface, so that the aconic lens is formed into a cone shape.

[0065] Furthermore, the light is refracted inside the axicon and spreads out along the side of the axicon, thereby forming a target laser beam on the exit surface of the axicon.

[0066] It is understandable that the smaller the taper of the axon lens, the smaller the size of the ring of emitted light. In actual detection, the specific taper of the axon lens can be set based on actual conditions, and this is not limited in this embodiment.

[0067] The target detection method in turbid medium based on annular circular polarized light provided in this embodiment shapes the circular polarized light based on an aconic lens to obtain a target laser beam. In this way, the circular polarized light is shaped into an annular target laser beam, and the annular target laser beam maintains its annular shape and a certain divergence angle during the propagation process, thereby expanding the range of a single detection and improving the detection efficiency. Furthermore, the annular target laser beam generated by the aconic lens can cover a larger detection area, so that the target to be measured can be accurately found and located in the turbid medium, improving the accuracy and stability of the measurement results.

[0068] Figure 2This is a schematic diagram of a target detection device in a turbid medium based on annular circularly polarized light provided by an exemplary embodiment of the present application. Figure 2 After the laser generator 1 generates the detection laser, the polarization state of the detection laser is adjusted by the polarizer 2 to obtain a second linear polarized light, and then the second linear polarized light is modulated by the second quarter-wave plate 3 to obtain circular polarized light, which is then input into the conical lens 4 and shaped by the conical lens 4 to obtain the target laser beam 12.

[0069] Furthermore, the target laser beam 12 is annular circularly polarized light. Figure 2 The single detection range of annular circularly polarized light is larger than that of circularly polarized light. Therefore, when the target laser beam irradiates the target 6 to be measured, the target 6 to be measured can be completely covered.

[0070] Please continue to refer to Figure 2 After the axon lens 4 emits the target laser beam 12, the target laser beam 12 can be gradually enlarged during the forward propagation by adjusting the angle of the axon lens 4. In this way, it can be ensured that the target laser beam 12 can cover the target 6 when detecting the target 6.

[0071] Optionally, the target to be detected is surrounded by a turbid medium.

[0072] For details, please continue to refer to Figure 2 Turbid medium 5 is a medium that can scatter, absorb or interfere with the propagation of light beams. Turbid medium 5 is widely present in nature and industrial environments.

[0073] In specific implementation, in deep sea or turbid waters, suspended particles, plankton, dissolved substances, etc. contained in the water will scatter and absorb light, forming a turbid medium 5. It is understandable that when performing target detection of the target to be detected, it is necessary to overcome the interference of the turbid medium on the target detection to ensure the accuracy of the target detection.

[0074] As an optional embodiment, when the target to be detected is not detected, the direction of the target laser beam can be moved so that the target laser beam scans a new area and re-detection is performed until the target to be detected in the area to be detected.

[0075] In this step, after the target laser beam irradiates the target to be measured, the reflected light is obtained by reflection.

[0076] S102, determining a receiving angle of reflected light according to a characteristic of invariant polarization of backscattered circularly polarized light;

[0077] Wherein, within the first angle range, the change in polarization direction of the reflected light polarization compared with the target laser beam is less than a first threshold, and the reflected light polarization is consistent with the polarization type of the target laser beam; and the receiving angle is within the first angle range.

[0078] Specifically, after the circular polarized light irradiates the target to be detected, it reflects back the reflected light. It should be noted that the characteristic of the invariant backscattering polarization is: since the target laser beam is annular circular polarized light, the reflected light rarely degenerates at a certain angle (i.e., the first angle range), and the reflected light still contains a large amount of circular polarization components with sufficient information. In essence, the incident light is circular polarized light. After irradiating the target to be detected and reflecting, it is necessary to detect enough circular polarization components from the reflected light to complete the identification of the target to be detected. At this time, within the first angle region, the circular polarization component of the received reflected light mainly comes from the circular polarized light, and the circular polarized light rarely degenerates or even partially degenerates into elliptical polarized light, so there are enough circular polarization components to achieve detection with a high signal-to-noise ratio; outside the first angle range, the original circular polarized light will quickly degenerate into linear polarized light, that is, the circular polarization component of the circular polarized light will quickly degenerate into a linear polarization component, resulting in a large amount of linear polarization components in the reflected light, and the detected circular polarization components are very few, and it is impossible to obtain enough circular polarization component information to achieve the detection of the target to be detected. It is understandable that the non-polarized light intensity and linear polarization components in the reflected light are noise, and if the circular polarization component contained in the reflected light is too small, it cannot be used for target detection. Different from other similar circular polarization detection methods, this application limits the angle range of detection.

[0079] In a specific implementation, the receiving angle may be the angle between a device receiving the reflected light and a device emitting the target laser beam.

[0080] It should be noted that circularly polarized light is the superposition of two plane polarized light beams with the same frequency, perpendicular vibration directions and a constant phase difference of (2m±1 / 2)π (where m is an integer). This superposition causes the endpoints of the light vector to describe a circular trajectory on a plane perpendicular to the direction of light propagation.

[0081] In specific implementation, in this step, the target laser beam based on the annular circularly polarized light irradiates the target to be measured to obtain reflected light. The reflected light within the first angle range has more circular polarization components. At this time, the reflected light can be circularly polarized light or elliptically polarized light. The light outside the first angle range contains linear polarization components that affect the detection effect. During detection, the reflected light is received within the first angle range. In other words, the circular polarization component of the reflected light within the first angle range is detected. Further, the polarization form of the reflected light is not the only limitation. It is only required that the circular polarization component information obtained by reflection after irradiation by the incident annular circularly polarized light in the reflected light accounts for more than a threshold value in the light intensity information of the entire reflected light.

[0082] Optionally, determining the receiving angle of the reflected light based on the characteristic of the invariant backscattered polarization of circularly polarized light includes: adjusting the position of the reflected light detector, the receiving angle corresponding to the propagation path of the reflected light detector and the target laser beam is within a first angle range; at each value of the first angle range, the reflected light detector receives the reflected light generated by the target laser beam irradiating the target to be measured; determining the maximum angle and minimum angle at which the difference in polarization characteristics between the reflected light and the target laser beam is less than a threshold, and taking the angle range between the maximum angle and the minimum angle as the first angle range, as the receiving angle range of the reflected light. During the reflection process of the reflected light, the reflected light within the first angle range is mainly circularly polarized components, and beyond the first angle range, a large number of linearly polarized components appear in the reflected light, that is, the proportion of noise is too large, which will seriously affect the accuracy of recognition.

[0083] As an optional embodiment, the first angle range matches the backscattering polarization invariant characteristic, and the first angle range is 0° to 5°.

[0084] The method provided by the present invention, due to the complex reflection characteristics of turbid media, is difficult to completely receive all information at a fixed angle. The present invention directly determines the receiving range containing ambient noise light according to the noise information in the reflected light, thereby receiving the reflected light within the specific range. On the one hand, the amount of received information is increased, and the accuracy of target detection is improved. At the same time, it also avoids adding other ambient light sources to illuminate the object to increase the amount of irrelevant information, further simplifies the system structure, and optimizes the detection process.

[0085] S103 , receiving and modulating the reflected light based on the receiving angle, and detecting the intensity of the left-handed circularly polarized light and the intensity of the right-handed circularly polarized light contained in the reflected light.

[0086] Specifically, the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity are parameters that describe the light intensity characteristics of circularly polarized light in different rotation directions.

[0087] Furthermore, the rotating electric vector in elliptically polarized light is synthesized by two electric vector vibrations with the same frequency, perpendicular vibration directions, and a fixed phase difference.

[0088] Furthermore, circularly polarized light is a special type of elliptically polarized light, whose polarization plane rotates with a circular frequency over time relative to the propagation direction, and the trajectory of the end of the light vector lies on a circle.

[0089] A specific embodiment is given below to introduce in detail the process of obtaining the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity:

[0090] (1) Modulating the reflected light based on a first quarter-wave plate to obtain a first linearly polarized light.

[0091] Specifically, the specific model of the first quarter wave plate can be determined according to actual needs, and is not limited in this embodiment. For example, in one embodiment, the first quarter wave plate can be set to the same model as the second quarter wave plate.

[0092] Furthermore, the first quarter wave plate is used to convert the circularly polarized light reflected by the target to be measured into linearly polarized light. In specific implementation, after the circularly polarized light is reflected by the target, its polarization state may remain unchanged or undergo complex changes, but after being processed by the first quarter wave plate 8, it can be uniformly converted into linearly polarized light, which is convenient for subsequent optical processing and measurement.

[0093] Furthermore, the first quarter wave plate generates a phase difference between the two light intensities passing through the wave plate through a specific phase delay, so as to realize the conversion of the reflected light into the first linear polarized light. For example, in one embodiment, the first quarter wave plate generates a phase difference of π / 2 by introducing a phase delay of one quarter of the wavelength of the light, so as to convert the incident reflected light into the first linear polarized light.

[0094] (2) Modulating the first linearly polarized light based on a Wollaston polarizer to obtain left-handed circularly polarized light intensity and right-handed circularly polarized light intensity in the reflected light.

[0095] Specifically, the Wollaston polarizer is a prism made of two birefringent crystals with excellent optical properties glued or photo-bonded together through a specific process.

[0096] Further, the specific material of the Wollaston polarizer is determined according to actual needs, and is not limited in this embodiment. For example, in one embodiment, calcite or BBO crystal can be used to make the Wollaston polarizer.

[0097] The target detection method in a turbid medium based on annular circularly polarized light provided in the present embodiment first modulates the reflected light based on the first quarter wave plate to obtain the first linearly polarized light, and then modulates the first linearly polarized light based on the Wollaston polarizer to obtain the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity. In this way, the reflected light reflected back is converted into the first linearly polarized light by the first quarter wave plate, which helps to reduce the influence of scattered light and environmental noise on the measurement result. Further, the first linearly polarized light is easier to be processed and detected in subsequent components, thereby improving the measurement accuracy and stability of the entire target detection. In this way, by modulating the reflected light by the first quarter wave plate and the Wollaston polarizer, the accuracy and reliability of target detection can be guaranteed.

[0098] Figure 3 This is a schematic diagram of a target detection device in a turbid medium based on annular circularly polarized light provided by another exemplary embodiment of the present application. Figure 3After the target laser beam irradiates the target 6 to be measured, the reflected light is converted into the first linear polarized light by the first quarter wave plate 7, and then the first linear polarized light is modulated by the Wollaston polarizer 8 to obtain the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity.

[0099] S104, calculating a circular polarization component based on a light intensity difference between the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity, and calculating a distance of the target to be measured based on the circular polarization component.

[0100] Specifically, the circular polarization component refers to the intensity difference between the left-hand circular polarization intensity and the right-hand circular polarization intensity during the propagation and reflection of the target laser beam. The circular polarization component is obtained by measuring the intensity difference between the left-hand circular polarization intensity and the right-hand circular polarization intensity.

[0101] In specific implementation, the reflection time of the target laser beam during target detection can be determined based on the circular polarization component, and the distance of the target to be detected can be calculated.

[0102] A specific embodiment is given below to describe in detail the process of obtaining the light intensity difference between the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity:

[0103] (1) After filtering the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity, the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity are respectively input into two photomultiplier tubes to enhance the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity.

[0104] Specifically, filtering processing can suppress or block other useless wavelengths of light. Through filtering processing, the interference of ambient light and other stray light can be reduced, and the signal-to-noise ratio of the signal can be improved, thereby improving the accuracy and stability of ranging.

[0105] In specific implementation, filtering processing can be performed through a filter. It should be noted that the filter is used to selectively transmit or reflect light of a specific wavelength, thereby achieving filtering processing of the optical signal.

[0106] Furthermore, a photomultiplier tube is a highly sensitive photoelectric detection device that can convert weak light signals into electrical signals and amplify the output. In specific implementation, a photomultiplier tube can be composed of a photocathode, a dynode and an anode. The photomultiplier tube realizes the conversion and amplification of light signals into electrical signals through the photoelectric effect and the secondary electron emission effect.

[0107] Furthermore, the specific number of photomultiplier tubes is set according to actual needs, and is not limited in this embodiment. For example, in one embodiment, the number of photomultiplier tubes can be set to 2, which are used to process left-handed circularly polarized light intensity and right-handed circularly polarized light intensity respectively.

[0108] In specific implementation, the photoelectrons on the photocathode are excited and escape, and then undergo multiple collisions and secondary electron emissions between the photomultiplier tubes to form an electron flow and amplify step by step. Finally, the amplified electron flow is received by the anode and converted into an electrical signal output. In this way, the intensity of the left-handed circularly polarized light and the right-handed circularly polarized light can be determined by the output electrical signal intensity.

[0109] Please continue to refer to Figure 3 , through the photomultiplier tube 10 and the photomultiplier tube 11, the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity are obtained.

[0110] (2) Calculating the difference between the intensity of the left-handed circularly polarized light and the intensity of the right-handed circularly polarized light to obtain the intensity difference.

[0111] Specifically, the light intensity difference can be calculated by a traditional light intensity difference calculation method, or by a neural network light intensity difference calculation method, which is not limited in this embodiment. For example, in one embodiment, in combination with the above embodiment, the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity are subtracted to obtain the light intensity difference corresponding to the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity.

[0112] The target detection method in the turbid medium based on annular circular polarized light provided by the present embodiment, first filtering process obtains left-handed circular polarization intensity and right-handed circular polarization intensity, and then calculates the difference between left-handed circular polarization intensity and right-handed circular polarization intensity, and obtains light intensity difference. In this way, by the filtering effect of the optical filter, the light signal passing through the optical filter can be made purer, and the spectral characteristics are more consistent, which is conducive to the accurate detection and measurement of the light signal by the subsequent photomultiplier tube. Further, the distance of the target can be more accurately detected and measured in a complex environment by the optical filter, which improves the overall performance and reliability, and makes target detection more suitable for various practical application scenarios. Further, by two different positions, it is a photomultiplier tube, and the left-handed circular polarization intensity and the right-handed circular polarization intensity obtained by the Wollaston polarizing prism are detected. In this way, by the high sensitivity and low noise characteristics of the photomultiplier tube, the left-handed circular polarization intensity and the right-handed circular polarization intensity can be accurately detected and amplified, thereby improving measurement accuracy and stability.

[0113] A specific embodiment is given below to introduce in detail the calculation process of the distance of the target to be measured:

[0114] (1) Calculating a first time of receiving the reflected light based on the circular polarization component.

[0115] Specifically, the circular polarization component carries information about the propagation time of the light wave, and the first moment of receiving the reflected light is determined by the circular polarization component.

[0116] In specific implementation, the moment when the change degree of the circular polarization light intensity value exceeds the first threshold is determined as the first moment. For example, in one embodiment, the circular polarization component is 30 when the target to be detected is not encountered, and the circular polarization component is 50 when the target to be detected is encountered. At this time, the first moment can be determined based on the difference. It can be understood that for the reflected light from the target to be detected, its polarization state can be characterized by four Stokes parameters I, Q, U, and V. Among them, I is the unpolarized light intensity, Q and U represent the linear polarization intensity in two directions respectively, and V represents the circular polarization component. Combined with the above example, when the circular polarization component V of the target laser beam is 100 milliwatts, it passes through the turbid medium and reflects. At this time, if there is no target to be measured, the original 100 milliwatt circular polarization component V will be reduced to 30 milliwatts during backward measurement. It should be noted that in the absence of a target to be measured, the circular polarization component V will be stable at 30 milliwatts. When there is a target to be measured, the circular polarization component V becomes 50, so the first moment can be determined by the change of the circular polarization component V. The non-polarized light intensity I and the linearly polarized light intensities Q and U are seriously affected by external interference and other scattered light and can be ignored in actual measurement, but their existence will not affect the accurate measurement of the circular polarization component at all.

[0117] In specific implementation, the circular polarization component V can be determined by subtracting the right-handed circularly polarized light intensity from the left-handed circularly polarized light intensity. In other words, the circular polarization component V is the light intensity value containing the right hand rotation minus the light intensity value containing the left hand rotation.

[0118] It should be noted that when performing detection, all sources of the circular polarization component V are the target laser beam, so whether the reflected light is circularly polarized light or elliptically polarized light does not affect the accuracy of the detection. In other words, the non-polarized light intensity I, the linearly polarized light intensity Q and U will not affect the value of the circular polarization component V, and the influence of the non-polarized light intensity I and the linearly polarized light intensity Q and U on the detection can be avoided. It can be understood that the non-polarized light intensity I, the linearly polarized light intensity Q and U contained in the non-circularly polarized light in all environments such as noise, external light intensity, scattered light intensity, etc. are all irrelevant to the circular polarization component V.

[0119] As an optional embodiment, the calculating the first moment of receiving the reflected light based on the circular polarization component includes:

[0120] Determining the degree of change of the circular polarization component between adjacent detection cycles;

[0121] The moment corresponding to the subsequent detection cycle when the change degree exceeds a preset threshold is determined as the first moment, wherein the preset threshold is greater than the change degree of the circular polarization component caused by environmental interference.

[0122] Specifically, the specific value of the preset threshold is set according to actual needs, and is not limited in this embodiment. It should be noted that since the circular polarization component is almost not affected by the environment, the preset threshold can be set to a smaller value.

[0123] (2) Based on the second moment when the target laser beam is emitted and the first moment, the target time of the light wave flight is calculated; wherein the target time is the total time corresponding to the emission and reception of the light wave.

[0124] Specifically, the second moment is the time when the target laser beam is emitted. In specific implementation, the moment of generation can be recorded when the target laser beam is generated, and it is determined as the second moment.

[0125] Furthermore, the target time is the time taken from transmitting to receiving. In specific implementation, the second moment can be subtracted from the first moment to obtain the target time.

[0126] (3) Calculating the distance based on the target time and the circular polarization component.

[0127] Specifically, the target time is the time it takes for the light wave to propagate during the detection process. It is understandable that since the propagation speed of the light wave is always equal to the speed of light, the distance of the target to be detected can be determined by the target time and the circular polarization component.

[0128] In specific implementation, the distance of the target to be measured can be calculated based on the following formula:

[0129] ;

[0130] Wherein, D is the distance of the target to be measured, T1 is the first moment, T2 is the second moment, and c is the speed of light.

[0131] The target detection method in turbid medium based on annular circular polarized light provided in this embodiment first calculates the first moment of receiving reflected light based on the circular polarization component, then calculates the target time taken by the light wave to fly based on the second moment when the target laser beam is emitted, and finally calculates the distance based on the target time and the circular polarization component. In this way, since the circular polarization component is derived solely from the target laser beam itself, this characteristic can greatly reduce the interference of environmental noise and scattered light when measuring distance in turbid media. In this way, by accurately measuring the circular polarization component, the time taken by the light wave to propagate in the medium can be accurately calculated, thereby improving the accuracy of ranging.

[0132] Optionally, a target angle is determined based on the circular polarization component, and an angle between the laser beam generator and the laser beam receiver is adjusted to the target angle.

[0133] Specifically, the laser beam receiver is a component that receives reflected light. Figure 2, all components on the left side of the first quarter wave plate 7 can be identified as laser beam receivers

[0134] In specific implementation, the angle corresponding to the reflected light containing the least noise is determined by the circular polarization component of the reflected light, and this angle is determined as the target angle. For example, in one embodiment, the circular polarization component of the reflected light of 175° to 180° is almost entirely derived from the target laser beam, so the target angle is determined to be 0° to 5°.

[0135] The target detection method in turbid medium based on annular circular polarized light provided in this embodiment determines the target angle based on the circular polarization component, and adjusts the angle between the laser beam generator and the laser beam receiver to the target angle. In this way, when the reflected light detector is set at the target angle, the interference from ambient light and other non-target sources of light can be reduced, and the signal-to-noise ratio is improved. In this way, by reducing errors, the target detection is more reliable and robust.

[0136] Please continue to refer to Figure 3 , a detection laser is generated by a laser generator 1, and the detection laser is adjusted by a polarizer 2 and a second quarter-wave plate 3 to obtain circularly polarized light. The circularly polarized light is shaped by a conical lens 4 to obtain a target laser beam. After the target laser beam passes through a turbid medium 5 and irradiates a target 6 to be measured, reflection occurs to generate reflected light, and the reflected light is modulated by a first quarter-wave plate 7 to obtain a first linearly polarized light. The first linearly polarized light is then modulated by a Wollaston polarizer 8 to obtain left-handed circularly polarized light intensity and right-handed circularly polarized light intensity. After filtering by a filter 9, target detection and ranging are completed by a first photomultiplier tube 10 and a second photomultiplier tube 11.

[0137] Furthermore, circularly polarized light has the characteristic of being invariant in the backward direction of circular polarization. It should be noted that at 180 degrees, the circular polarization component V is entirely derived from the emitted circularly polarized light. At 45 degrees, etc., in the lateral direction and other directions, the circular polarization component V will quickly degenerate into linear polarization intensities Q and U. Therefore, sufficient circular polarization components V cannot be received in the lateral direction and other directions. Only in the backward direction can sufficient circular polarization components be received, based on which target detection can be completed. In the backward direction, the circular polarization component V does not change.

[0138] The target detection method in turbid medium based on annular circular polarized light provided in this embodiment first modulates the circular polarized light to obtain a target laser beam, irradiates the target to be measured based on the target laser beam to obtain reflected light, and then modulates the reflected light, calculates the circular polarization component based on the light intensity difference between the left-handed circular polarized light intensity and the right-handed circular polarized light intensity, and calculates the distance of the target to be measured based on the circular polarization component. In this way, the annular target laser beam is used for detection. Compared with the traditional linear laser beam, the annular target laser beam can cover a larger detection area, so that the target to be measured can be more effectively covered and found in one detection, thereby improving the efficiency of detection. Further, detection and ranging are performed through the circular polarization component. Since the circular polarization component is derived solely from the target laser beam itself, the interference of environmental noise and scattered light is reduced, making the ranging signal purer, thereby improving the ranging accuracy. Further, by optimizing the receiving angle of the detector to the target angle, the interference of ambient light and other non-target sources of light is reduced, and the stability and reliability of the system are enhanced. In this way, through the anti-interference ability of circularly polarized light and the coverage advantage of annular light beams, target detection and ranging can be effectively carried out in turbid media, improving the reliability and accuracy of target detection.

[0139] Corresponding to the aforementioned embodiment of a method for detecting a target in a turbid medium based on annular circularly polarized light, the present application also provides an embodiment of a device for detecting a target in a turbid medium based on annular circularly polarized light.

[0140] Figure 4 This is a schematic diagram of a target detection device in a turbid medium based on annular circularly polarized light provided by an exemplary embodiment of the present application. Figure 4 The device provided in this embodiment includes an irradiation module 410, a modulation module 420 and a calculation module 430; wherein,

[0141] The irradiation module 410 is used to modulate circularly polarized light to obtain a target laser beam, and irradiate the target to be measured based on the target laser beam to obtain reflected light; wherein the circularly polarized light is in a circular polarization state, and the target laser beam is an annular circularly polarized light. Under the same spacing distance condition, the single detection range of the circularly polarized light is smaller than the single detection range of the target laser beam;

[0142] The modulation module 420 is used to determine the receiving angle of the reflected light according to the characteristic that the backscattered polarization of the circularly polarized light is constant; wherein, within a first angle range, the change in polarization direction of the reflected light polarization is less than a first threshold value compared with the target laser beam, and the reflected light polarization is consistent with the target laser beam polarization type; and the receiving angle is within the first angle range;

[0143] The modulation module 420 is further used to receive and modulate the reflected light based on the receiving angle, and detect the intensity of the left-handed circularly polarized light and the intensity of the right-handed circularly polarized light contained in the reflected light;

[0144] The calculation module 430 is used to calculate the circular polarization component based on the light intensity difference between the left-handed circular polarized light intensity and the right-handed circular polarized light intensity, and calculate the distance of the target to be measured based on the circular polarization component.

[0145] The device of this embodiment can be used to perform Figure 1 The steps, specific implementation principles and implementation processes of the method embodiment shown are similar and will not be repeated here.

[0146] Optionally, the modulation module 420 is specifically configured to modulate the reflected light based on a first quarter wave plate to obtain a first linearly polarized light;

[0147] The modulation module 420 is further specifically configured to modulate the first linearly polarized light based on a Wollaston polarizer to obtain the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity in the reflected light.

[0148] Optionally, the modulation module 420 is further specifically configured to modulate the first linearly polarized light based on a Wollaston polarizer to obtain left-handed circularly polarized light intensity and right-handed circularly polarized light intensity in the reflected light.

[0149] Optionally, the calculation module 430 is further specifically used to filter and process the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity, and then input the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity into two photomultiplier tubes respectively to enhance the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity;

[0150] The calculation module 430 is further specifically used to calculate the difference between the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity to obtain the light intensity difference.

[0151] Optionally, the modulation module 420 is further specifically configured to calculate a first time of receiving the reflected light based on the circular polarization component;

[0152] The modulation module 420 is further specifically used to calculate the target time of the light wave flight based on the second time when the target laser beam is emitted and the first time; wherein the target time is the total time corresponding to the light wave from emission to reception.

[0153] The modulation module 420 is further specifically configured to calculate the distance based on the target time and the circular polarization component.

[0154] Optionally, the modulation module 420 is further specifically configured to adjust the polarization state of the detection laser based on a polarizer to obtain a second linearly polarized light.

[0155] Optionally, the modulation module 420 is further specifically used to determine the type of light source according to the type of turbid medium;

[0156] The modulation module 420 is further specifically configured to generate a detection laser based on a laser beam generator, the detection laser being matched with the light source type, and adjusting the polarization state of the detection laser based on a polarizer and a second quarter wave plate to obtain the circularly polarized laser as circularly polarized light;

[0157] The modulation module 420 is further specifically configured to shape the circularly polarized light based on an axicon to obtain the target laser beam.

[0158] Optionally, the calculation module 430 is further specifically used to adjust the position of the reflected light detector, and the receiving angle corresponding to the propagation path of the reflected light detector and the target laser beam is within a first angle range;

[0159] The calculation module 430 is further specifically configured to cause the reflected light detector to receive the reflected light generated when the target laser beam irradiates the target to be measured at each value of the first angle range;

[0160] The calculation module 430 is further specifically used to modulate the reflected light to obtain the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity;

[0161] The calculation module 430 is further specifically used to determine a maximum angle and a minimum angle at which the difference in polarization characteristics between the reflected light and the target laser beam is less than a threshold, and to use an angle range between the maximum angle and the minimum angle as a first angle range, as a receiving angle range of the reflected light.

[0162] Optionally, the first angle range matches the backscattering polarization invariant characteristic, and the first angle range is 0° to 5°.

[0163] Optionally, the calculation module 430 is further specifically used to determine the degree of change of the circular polarization component between adjacent detection cycles;

[0164] The calculation module 430 is further specifically used to determine the moment corresponding to the subsequent detection cycle when the degree of change exceeds a preset threshold as the first moment, wherein the preset threshold is greater than the degree of change of the circular polarization component caused by environmental interference.

[0165] Optionally, a detection laser is generated by the laser generator, and the detection laser is adjusted by the polarizer and the second quarter-wave plate to obtain circularly polarized light, and the circularly polarized light is shaped by the conical lens to obtain a target laser beam; after the target laser beam passes through the turbid medium and irradiates the target to be measured, reflection occurs to generate reflected light, and the reflected light is modulated by the first quarter-wave plate to obtain a first linearly polarized light, and the first linearly polarized light is modulated by the Wollaston polarizer to obtain left-handed circularly polarized light intensity and right-handed circularly polarized light intensity, and after filtering by the filter, the first photomultiplier tube and the second photomultiplier tube are used to complete the detection and ranging of the target to be measured.

[0166] The implementation process of the functions and effects of each unit in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, and will not be repeated here.

[0167] For the device embodiment, since it basically corresponds to the method embodiment, the relevant parts can refer to the partial description of the method embodiment. The device embodiment described above is only schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present application scheme. A person of ordinary skill in the art can understand and implement it without paying any creative work.

[0168] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for detecting a target in a turbid medium based on annular circularly polarized light, characterized in that: The method comprises: Modulate the circularly polarized light to obtain a target laser beam, and irradiate the target to be measured based on the target laser beam to obtain reflected light; wherein the circularly polarized light is in a circular polarization state, and the target laser beam is annular circularly polarized light. Under the same irradiation distance, the annular structure of the target laser beam can make its single detection cover a wider area than the circularly polarized light, and the single detection range of the annular circularly polarized light is greater than that of the circularly polarized light. When the target laser beam irradiates the target to be measured, it can completely cover the target to be measured; According to the polarization invariance characteristic of the backscattering of circularly polarized light, the receiving angle of the reflected light is determined; The method of determining the receiving angle of the reflected light according to the characteristic that the backscattered polarization of the circularly polarized light is invariant comprises: Adjusting the position of the reflected light detector, wherein the receiving angle corresponding to the propagation path of the target laser beam and the reflected light detector is within a first angle range; At each value of the first angle range, the reflected light detector receives reflected light generated when the target laser beam irradiates the target to be measured; According to the proportion of the circular polarization component and the noise, determine the maximum angle and the minimum angle at which the noise is less than a threshold, and use the angle range between the maximum angle and the minimum angle as the first angle range, which is used as the receiving angle range of the reflected light; Wherein, within the first angle range, the change in polarization direction of the reflected light polarization compared with the target laser beam is less than a first threshold, and both the reflected light polarization and the target laser beam are circularly polarized light; and the receiving angle is within the first angle range; receiving and modulating the reflected light based on the receiving angle, and detecting the intensity of left-handed circularly polarized light and the intensity of right-handed circularly polarized light contained in the reflected light; Calculating a circular polarization component based on a light intensity difference between the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity, and calculating a distance of the target to be measured based on the circular polarization component; The calculating the distance of the target to be measured based on the circular polarization component includes: Calculate a first time of receiving the reflected light based on the circular polarization component; Based on the second moment when the target laser beam is emitted and the first moment, the target time for the light wave to fly is calculated; wherein the target time is the total time corresponding to the emission and reception of the light wave; The distance is calculated based on the target time.

2. The method according to claim 1, characterized in that The receiving and modulating the reflected light based on the receiving angle, and detecting the intensity of left-handed circularly polarized light and the intensity of right-handed circularly polarized light contained in the reflected light, comprises: Modulating the reflected light based on a first quarter wave plate to obtain a first linearly polarized light; The first linearly polarized light is modulated based on a Wollaston polarizer to obtain the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity in the reflected light.

3. The method according to claim 2, characterized in that The calculating of the circular polarization component based on the light intensity difference between the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity comprises: After filtering the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity, the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity are respectively input into two photomultiplier tubes to enhance the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity; The difference between the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity is calculated to obtain the light intensity difference.

4. The method according to claim 1, characterized in that: The method of modulating the circularly polarized light to obtain a target laser beam comprises: Determine the type of light source according to the type of turbid medium. Generate a detection laser based on a laser beam generator, the detection laser matches the light source type, and adjust the polarization state of the detection laser based on a polarizer and a second quarter wave plate to obtain the circularly polarized laser as circularly polarized light; The circularly polarized light is shaped based on an aconic lens to obtain the target laser beam.

5. The method according to claim 1, characterized in that The first angle range matches the backscattering polarization invariant characteristic, and the first angle range is 0° to 5°.

6. The method according to claim 1, characterized in that The calculating the first time of receiving the reflected light based on the circular polarization component comprises: Determining the degree of change of the circular polarization component between adjacent detection cycles; The moment corresponding to the subsequent detection cycle when the change degree exceeds a preset threshold is determined as the first moment, wherein the preset threshold is greater than the change degree of the circular polarization component caused by environmental interference.

7. The method according to claim 1, characterized in that The device for detecting the target to be measured comprises a laser generator, a polarizing plate, a second quarter wave plate, an aconic lens, a turbid medium, a target to be measured, a first quarter wave plate, a Wollaston polarizer, a filter, a first photomultiplier tube and a second photomultiplier tube; Detecting the target to be detected includes: The detection laser is generated by the laser generator, and the detection laser is adjusted by the polarizer and the second quarter-wave plate to obtain circularly polarized light. The circularly polarized light is shaped by the conical lens to obtain a target laser beam. After the target laser beam passes through the turbid medium and irradiates the target to be measured, reflection occurs to generate reflected light, the reflected light is modulated by the first quarter-wave plate to obtain a first linearly polarized light, the first linearly polarized light is modulated by the Wollaston polarizer to obtain left-handed circularly polarized light intensity and right-handed circularly polarized light intensity, and after filtering by the filter, the target to be measured is detected and measured by the first photomultiplier tube and the second photomultiplier tube.

8. A target detection device in turbid medium based on annular circularly polarized light, characterized in that: The device comprises an irradiation module, a modulation module and a calculation module; wherein, The irradiation module is used to modulate circularly polarized light to obtain a target laser beam, and irradiate the target to be measured based on the target laser beam to obtain reflected light; wherein the circularly polarized light is in a circular polarization state, and the target laser beam is annular circularly polarized light. At the same irradiation distance, the annular structure of the target laser beam can make its single detection cover a wider area than the circularly polarized light, and the single detection range of the annular circularly polarized light is greater than that of the circularly polarized light. When the target laser beam irradiates the target to be measured, it can completely cover the target to be measured; The modulation module is used to determine the receiving angle of the reflected light according to the characteristic that the backscattered polarization of the circularly polarized light remains unchanged; The method of determining the receiving angle of the reflected light according to the characteristic that the backscattered polarization of the circularly polarized light is invariant comprises: Adjusting the position of the reflected light detector, wherein the receiving angle corresponding to the propagation path of the target laser beam and the reflected light detector is within a first angle range; At each value of the first angle range, the reflected light detector receives reflected light generated when the target laser beam irradiates the target to be measured; According to the proportion of the circular polarization component and the noise, determine the maximum angle and the minimum angle at which the noise is less than a threshold, and use the angle range between the maximum angle and the minimum angle as the first angle range, which is used as the receiving angle range of the reflected light; Wherein, within the first angle range, the change in polarization direction of the reflected light polarization compared with the target laser beam is less than a first threshold, and both the reflected light polarization and the target laser beam are circularly polarized light; and the receiving angle is within the first angle range; The modulation module is further used to receive and modulate the reflected light based on the receiving angle, and detect the intensity of left-handed circularly polarized light and the intensity of right-handed circularly polarized light contained in the reflected light; The calculation module is used to calculate the circular polarization component based on the light intensity difference between the left-handed circular polarized light intensity and the right-handed circular polarized light intensity, and calculate the distance of the target to be measured based on the circular polarization component; The calculating the distance of the target to be measured based on the circular polarization component includes: Calculate a first time of receiving the reflected light based on the circular polarization component; Based on the second moment when the target laser beam is emitted and the first moment, the target time for the light wave to fly is calculated; wherein the target time is the total time corresponding to the emission and reception of the light wave; The distance is calculated based on the target time.

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