A laser radar and ranging method based on polarization noise reduction

Abstract

The present invention belongs to the field of laser radar ranging technology, and discloses a laser radar based on polarization noise reduction and a ranging method. The laser radar includes a laser, a polarizer, a polarization modulation module, a transmitting telescope, a receiving telescope, a filter, a polarization beam splitter, a first detection module, a second detection module and a main control module, wherein the polarization modulation module can randomly modulate the laser pulse signal into a coded light signal having a first polarization state or a second polarization state, and the first polarization state and the second polarization state are mutually orthogonal. Compared with the prior art, the present invention uses a polarization encoding and decoding sequence for ranging, and detects the decoded echo signal through a high-sensitivity balanced detector for differential, which can greatly reduce the background noise in the echo signal and improve the signal-to-noise ratio of the system. In addition, the Doppler effect of the target motion has no effect on the decoding.

Description

Technical Field

[0001] The present invention relates to the technical field of laser radar ranging, and in particular to a laser radar and ranging method based on polarization noise reduction. Background Art

[0002] Radar plays a very important role in the fields of military, civil aviation, and autonomous driving. LiDAR uses short-wavelength lasers as information carriers, so it has a higher resolution and can be used to detect, track, and identify targets, as well as perform distance measurement and imaging.

[0003] The signal-to-noise ratio is a very important indicator in lidar detection and can directly affect the performance of the system. For daylight background noise, it can only be filtered through a filter. While filtering the noise, the real signal will have a certain loss. Therefore, the signal-to-noise ratio is low during the day and it is difficult to work normally. Patent CN118011415B proposes a method of phase encoding and interfering the echo signal and then performing differential, which can achieve a better noise reduction effect. However, this solution requires the use of two lasers, and when performing phase encoding and decoding, there will be a slow phase drift between the transmitting and receiving interferometers, so phase compensation is required, which increases the complexity of the system. Patent CN118191861B uses the same interferometer for encoding and decoding, which can eliminate phase drift, but still requires two lasers. In addition, for moving targets, the Doppler effect will change the phase difference of the echo photons during the transmission of the long and short arms of the interferometer, reducing the accuracy of decoding. Summary of the invention

[0004] In view of the above defects in the prior art, the present invention proposes a laser radar and ranging method based on polarization noise reduction.

[0005] The technical solution of the present invention is achieved in this way:

[0006] A laser radar based on polarization noise reduction includes a laser Laser, a polarizer POL, a polarization modulation module, a transmitting telescope, a receiving telescope, a filter Filter, a polarization beam splitter PBS, a first detection module D1, a second detection module D2 and a main control module.

[0007] The laser is used to generate a linearly polarized laser pulse signal;

[0008] The polarizer POL is used to pass a horizontally polarized laser pulse signal;

[0009] The polarization modulation module is used to randomly modulate the laser pulse signal into a coded light signal having a first polarization state or a second polarization state; the first polarization state and the second polarization state are orthogonal to each other;

[0010] The transmitting telescope is used to expand the coded light signal and illuminate the target;

[0011] The receiving telescope is used to receive the echo signal reflected from the target;

[0012] The filter is used to filter out the background light noise outside the passband in the echo signal;

[0013] The polarization beam splitter PBS is used to perform polarization beam splitting on the filtered echo signal to generate a first polarization component and a second polarization component;

[0014] The first detection module D1 and the second detection module D2 are used to detect the amplitudes of the first polarization component and the second polarization component respectively, and output differential electrical signals to eliminate background noise signals;

[0015] The main control module is used to control the polarization modulation module to perform polarization encoding to obtain a coding sequence, collect differential electrical signals to generate a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain distance information of the target.

[0016] Preferably, the first polarization state and the second polarization state are a horizontal polarization state and a vertical polarization state, respectively.

[0017] Preferably, the polarization modulation module comprises a beam splitter BS, a first half-wave plate HWP1, an electro-optic modulator EOM, a second quarter-wave plate QWP2 and a reflector M,

[0018] The beam splitter BS is used to transmit the horizontally polarized laser pulse signal transmitted through the polarizer POL to the first half-wave plate HWP1; and to transmit the coded light signal reversely passed through the first half-wave plate HWP1 to the transmitting telescope;

[0019] The angle between the main axis direction of the first half-wave plate HWP1 and the horizontal polarization direction is 22.5°;

[0020] The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the first half-wave plate HWP1 to be 0 or π;

[0021] The angle between the main axis direction of the second quarter wave plate QWP2 and the horizontal polarization direction is 45°;

[0022] The second quarter wave plate QWP2 and the reflector M are used to rotate the horizontal polarization and the vertical polarization by 90 degrees respectively.

[0023] Preferably, the polarization modulation module comprises a second half-wave plate HWP2, an electro-optical modulator EOM, and a third half-wave plate HWP3.

[0024] The included angles between the main axis directions of the second half-wave plate HWP2 and the third half-wave plate HWP3 and the horizontal polarization direction are both 22.5°;

[0025] The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the second half-wave plate HWP2 to be 0 or π.

[0026] Preferably, the first polarization state and the second polarization state are respectively a left-handed circular polarization state and a right-handed circular polarization state;

[0027] A first quarter wave plate QWP1 is also arranged between the filter Filter and the receiving telescope;

[0028] The angle between the main axis direction of the first quarter wave plate QWP1 and the horizontal polarization direction is 45°.

[0029] Preferably, the polarization modulation module comprises a fourth half-wave plate HWP4 and an electro-optical modulator EOM.

[0030] The angle between the main axis direction of the fourth half-wave plate HWP4 and the horizontal polarization direction is 22.5°;

[0031] The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the fourth half-wave plate HWP4 to π / 2 or 3π / 2.

[0032] Preferably, the first detection module D1 and the second detection module D2 are both single-photon balanced detectors.

[0033] The present invention also discloses a laser radar ranging method, comprising the following steps:

[0034] S1: The laser emits a laser pulse signal, which passes through the polarizer POL and generates a driving signal by preparing a random sequence to control the polarization modulation module to perform polarization encoding, and randomly modulates the signal into a coded light signal having a first polarization state or a second polarization state orthogonal thereto, thereby forming a coding sequence;

[0035] S2: The encoded laser pulse signal is expanded by the transmitting telescope and then irradiated to the target, and the receiving telescope is used to receive the echo signal reflected from the target;

[0036] S3: After being filtered, the echo signal enters the polarization beam splitter PBS for polarization decoding to obtain a decoding sequence;

[0037] S4: performing a shift cross-correlation operation on the coding sequence and the decoding sequence, and obtaining the distance information of the target according to the position corresponding to the peak value of the cross-correlation operation result.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention proposes a laser radar and ranging method based on polarization noise reduction, which uses a polarization encoding and decoding sequence for ranging, and uses a high-sensitivity balanced detector to detect the decoded echo signal for differential, which can greatly reduce the background noise in the echo signal and improve the signal-to-noise ratio of the system. In addition, the Doppler effect of the target movement has no effect on the decoding. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram of a first embodiment of a laser radar based on polarization noise reduction according to the present invention;

[0041] Figure 2 This is a schematic diagram of Embodiment 2 of the laser radar based on polarization noise reduction of the present invention;

[0042] Figure 3 This is a schematic diagram of the third embodiment of the laser radar based on polarization noise reduction of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0044] like Figure 1 As shown, embodiment 1:

[0045] A laser radar based on polarization noise reduction includes a laser Laser, a polarizer POL, a polarization modulation module, a transmitting telescope, a receiving telescope, a filter Filter, a polarization beam splitter PBS, a first detection module D1, a second detection module D2 and a main control module.

[0046] The laser is used to generate a linearly polarized laser pulse signal;

[0047] The polarizer POL is used to pass a horizontally polarized laser pulse signal;

[0048] The polarization modulation module is used to randomly modulate the laser pulse signal into a coded light signal having a first polarization state or a second polarization state; the first polarization state and the second polarization state are orthogonal to each other;

[0049] The transmitting telescope is used to expand the coded light signal and illuminate the target;

[0050] The receiving telescope is used to receive the echo signal reflected from the target;

[0051] The filter is used to filter out the background light noise outside the passband in the echo signal;

[0052] The polarization beam splitter PBS is used to perform polarization beam splitting on the filtered echo signal to generate a first polarization component and a second polarization component;

[0053] The first detection module D1 and the second detection module D2 are used to detect the amplitudes of the first polarization component and the second polarization component respectively, and output differential electrical signals to eliminate background noise signals;

[0054] The main control module is used to control the polarization modulation module to perform polarization encoding to obtain a coding sequence, collect differential electrical signals to generate a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain distance information of the target.

[0055] The first polarization state and the second polarization state are a horizontal polarization state and a vertical polarization state, respectively.

[0056] The polarization modulation module includes a beam splitter BS, a first half-wave plate HWP1, an electro-optic modulator EOM, a second quarter-wave plate QWP2 and a reflector M.

[0057] The beam splitter BS is used to transmit the horizontally polarized laser pulse signal transmitted through the polarizer POL to the first half-wave plate HWP1; and to transmit the coded light signal reversely passed through the first half-wave plate HWP1 to the transmitting telescope;

[0058] The angle between the main axis direction of the first half-wave plate HWP1 and the horizontal polarization direction is 22.5°;

[0059] The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the first half-wave plate HWP1 to be 0 or π;

[0060] The angle between the main axis direction of the second quarter wave plate QWP2 and the horizontal polarization direction is 45°;

[0061] The second quarter wave plate QWP2 and the reflector M are used to rotate the horizontal polarization and the vertical polarization by 90 degrees respectively.

[0062] The specific working process is as follows:

[0063] The laser Laser generates a linearly polarized laser pulse signal, and its horizontal polarization component passes through the polarizer POL, and then passes through the first half-wave plate HWP1, the electro-optic modulator EOM, the second quarter-wave plate QWP2 and the reflector M in sequence through the beam splitter BS, and is reflected, and then passes through the second quarter-wave plate QWP2, the electro-optic modulator EOM, and the first half-wave plate HWP1 again. Since the angle between the main axis direction of HWP1 and the horizontal polarization direction is 22.5°, and the angle between the main axis direction of the second quarter-wave plate QWP2 and the horizontal polarization direction is 45°, the Jones matrices of the two are respectively

[0064] ,

[0065] The Jones matrices of the reflector M and the electro-optic modulator EOM are

[0066] ,

[0067] Where θ is the phase difference modulated by the electro-optic modulator EOM. Then the polarization state of the coded optical signal after polarization modulation is

[0068] ,

[0069] When 2θ=0 or π, the polarization state of the coded optical signal is vertical polarization or horizontal polarization. Then the beam is expanded through the transmitting telescope and irradiated to the target.

[0070] After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal. It then passes through the filter Filter to filter out some background noise and enters the polarization beam splitter PBS for decoding. The horizontal polarization component AH of the echo signal is transmitted through the polarization beam splitter PBS and enters the first detection module D1 for detection; the vertical polarization component AV is reflected from the polarization beam splitter PBS and enters the second detection module D2 for detection. Since the background noise is non-polarized light, the polarization component amplitudes entering the first detection module D1 and the second detection module D2 after polarization beam splitting by the polarization beam splitter PBS are equal, that is, .

[0071] When 2θ=0, the polarization state of the transmitted coded light signal is vertical polarization, and the detection results of the first detection module D1 and the second detection module D2 are respectively and , the difference between the two is -A. When 2θ=π, the polarization state of the transmitted coded light signal is horizontal polarization, and the detection results of the first detection module D1 and the second detection module D2 are respectively and , the difference between the two is A. It can be seen that the background noise has been eliminated in the difference result, and only the real reflection signal is included. Replace A and -A in the difference result sequence with 0 and 1 respectively, and the decoded sequence can be obtained.

[0072] The coding sequence is shifted bit by bit and cross-correlated with the decoding sequence to obtain the cross-correlation value at each shift. When the cross-correlation value reaches the peak, it indicates that the sending and receiving sequences correspond one to one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0073] like Figure 2 As shown, Example 2:

[0074] A laser radar based on polarization noise reduction includes a laser Laser, a polarizer POL, a polarization modulation module, a transmitting telescope, a receiving telescope, a filter Filter, a polarization beam splitter PBS, a first detection module D1, a second detection module D2 and a main control module.

[0075] The laser is used to generate a linearly polarized laser pulse signal;

[0076] The polarizer POL is used to pass a horizontally polarized laser pulse signal;

[0077] The polarization modulation module is used to randomly modulate the laser pulse signal into a coded light signal having a first polarization state or a second polarization state; the first polarization state and the second polarization state are orthogonal to each other;

[0078] The transmitting telescope is used to expand the coded light signal and illuminate the target;

[0079] The receiving telescope is used to receive the echo signal reflected from the target;

[0080] The filter is used to filter out the background light noise outside the passband in the echo signal;

[0081] The polarization beam splitter PBS is used to perform polarization beam splitting on the filtered echo signal to generate a first polarization component and a second polarization component;

[0082] The first detection module D1 and the second detection module D2 are used to detect the amplitudes of the first polarization component and the second polarization component respectively, and output differential electrical signals to eliminate background noise signals;

[0083] The main control module is used to control the polarization modulation module to perform polarization encoding to obtain a coding sequence, collect differential electrical signals to generate a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain distance information of the target.

[0084] The first polarization state and the second polarization state are a horizontal polarization state and a vertical polarization state, respectively.

[0085] The polarization modulation module includes a second half-wave plate HWP2, an electro-optic modulator EOM, and a third half-wave plate HWP3.

[0086] The included angles between the main axis directions of the second half-wave plate HWP2 and the third half-wave plate HWP3 and the horizontal polarization direction are both 22.5°;

[0087] The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the second half-wave plate HWP2 to be 0 or π.

[0088] The specific working process is as follows:

[0089] The laser generates a linearly polarized laser pulse signal, and its horizontal polarization component passes through the polarizer POL, and then passes through the second half-wave plate HWP2, the electro-optic modulator EOM, and the third half-wave plate HWP3 in sequence. The Jones matrices of the second half-wave plate HWP2 and the third half-wave plate HWP3 are both

[0090] ,

[0091] The Jones matrices of the electro-optic modulator EOM are

[0092] ,

[0093] Where θ is the phase difference modulated by the electro-optic modulator EOM. Then the polarization state of the coded optical signal after polarization modulation is

[0094] ,

[0095] When θ=0 or π, the polarization state of the coded optical signal is horizontal polarization or vertical polarization. Then the beam is expanded through the transmitting telescope and irradiated to the target.

[0096] After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal. It then passes through the filter Filter to filter out some background noise and enters the polarization beam splitter PBS for decoding. The horizontal polarization component AH of the echo signal is transmitted through the polarization beam splitter PBS and enters the first detection module D1 for detection; the vertical polarization component AV is reflected from the polarization beam splitter PBS and enters the second detection module D2 for detection. Since the background noise is non-polarized light, the polarization component amplitudes entering the first detection module D1 and the second detection module D2 after polarization beam splitting by the polarization beam splitter PBS are equal, that is, .

[0097] When θ = 0, the polarization state of the transmitted coded light signal is horizontal polarization, and the detection results of the first detection module D1 and the second detection module D2 are respectively and , the difference between the two is A. When θ=π, the polarization state of the transmitted coded light signal is vertical polarization, and the detection results of the first detection module D1 and the second detection module D2 are respectively and , the difference between the two is -A. It can be seen that the background noise has been eliminated in the difference result, and only the real reflection signal is included. Replace A and -A in the difference result sequence with 0 and 1 respectively, and the decoded sequence can be obtained.

[0098] The coding sequence is shifted bit by bit and cross-correlated with the decoding sequence to obtain the cross-correlation value at each shift. When the cross-correlation value reaches the peak, it indicates that the sending and receiving sequences correspond one to one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0099] like Figure 3 As shown, Example 3:

[0100] A laser radar based on polarization noise reduction includes a laser Laser, a polarizer POL, a polarization modulation module, a transmitting telescope, a receiving telescope, a filter Filter, a polarization beam splitter PBS, a first detection module D1, a second detection module D2 and a main control module.

[0101] The laser is used to generate a linearly polarized laser pulse signal;

[0102] The polarizer POL is used to pass a horizontally polarized laser pulse signal;

[0103] The polarization modulation module is used to randomly modulate the laser pulse signal into a coded light signal having a first polarization state or a second polarization state; the first polarization state and the second polarization state are orthogonal to each other;

[0104] The transmitting telescope is used to expand the coded light signal and illuminate the target;

[0105] The receiving telescope is used to receive the echo signal reflected from the target;

[0106] The filter is used to filter out the background light noise outside the passband in the echo signal;

[0107] The polarization beam splitter PBS is used to perform polarization beam splitting on the filtered echo signal to generate a first polarization component and a second polarization component;

[0108] The first detection module D1 and the second detection module D2 are used to detect the amplitudes of the first polarization component and the second polarization component respectively, and output differential electrical signals to eliminate background noise signals;

[0109] The main control module is used to control the polarization modulation module to perform polarization encoding to obtain a coding sequence, collect differential electrical signals to generate a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain distance information of the target.

[0110] The first polarization state and the second polarization state are respectively a left-hand circular polarization state and a right-hand circular polarization state;

[0111] A first quarter wave plate QWP1 is also arranged between the filter Filter and the receiving telescope;

[0112] The angle between the main axis direction of the first quarter wave plate QWP1 and the horizontal polarization direction is 45°.

[0113] The polarization modulation module includes a fourth half-wave plate HWP4 and an electro-optic modulator EOM.

[0114] The angle between the main axis direction of the fourth half-wave plate HWP4 and the horizontal polarization direction is 22.5°;

[0115] The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the fourth half-wave plate HWP4 to π / 2 or 3π / 2.

[0116] The specific working process is as follows:

[0117] The laser generates a linearly polarized laser pulse signal, and its horizontal polarization component passes through the polarizer POL, and then passes through the fourth half-wave plate HWP4 and the electro-optic modulator EOM in sequence. The Jones matrix of the fourth half-wave plate HWP4 is

[0118] ,

[0119] The Jones matrices of the electro-optic modulator EOM are

[0120] ,

[0121] Where θ is the phase difference modulated by the electro-optic modulator EOM. Then the polarization state of the coded optical signal after polarization modulation is

[0122] ,

[0123] When θ=π / 2 or 3π / 2, the polarization state of the coded optical signal is left-hand circular polarization state and right-hand circular polarization state. Then the beam is expanded through the transmitting telescope and irradiated to the target.

[0124] The coded light signal is reflected by the target and enters the receiving telescope, becoming an echo signal. After passing through the first quarter-wave plate QWP1, the polarization state becomes

[0125] ,

[0126] After filtering part of the background noise through the filter, it enters the polarization beam splitter PBS for decoding. The horizontal polarization component AH of the echo signal is transmitted through the polarization beam splitter PBS and enters the first detection module D1 for detection; the vertical polarization component AV is reflected from the polarization beam splitter PBS and enters the second detection module D2 for detection. Since the background noise is non-polarized light, the polarization component amplitudes entering the first detection module D1 and the second detection module D2 after polarization beam splitting by the polarization beam splitter PBS are equal, that is, .

[0127] When θ=π / 2, the polarization state of the transmitted coded light signal is left-handed circular polarization, and the echo signal becomes horizontally polarized after passing through the first quarter-wave plate QWP1. The detection results of the first detection module D1 and the second detection module D2 are respectively and , the difference between the two is A. When θ=3π / 2, the polarization state of the transmitted coded light signal is right-hand circular polarization, and the echo signal becomes vertical polarization after passing through the first quarter-wave plate QWP1. The detection results of the first detection module D1 and the second detection module D2 are respectively and , the difference between the two is -A. It can be seen that the background noise has been eliminated in the difference result, and only the real reflection signal is included. Replace A and -A in the difference result sequence with 0 and 1 respectively, and the decoded sequence can be obtained.

[0128] The coding sequence is shifted bit by bit and cross-correlated with the decoding sequence to obtain the cross-correlation value at each shift. When the cross-correlation value reaches the peak, it indicates that the sending and receiving sequences correspond one to one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0129] It can be seen from the various embodiments of the present invention that the present invention proposes a laser radar and ranging method based on polarization noise reduction, which uses a polarization encoding and decoding sequence for ranging, and detects the decoded echo signal through a high-sensitivity balanced detector for differential, which can greatly reduce the background noise in the echo signal and improve the signal-to-noise ratio of the system. In addition, the Doppler effect of the target motion has no effect on the decoding.

Claims

1. A laser radar based on polarization noise reduction, characterized in that: include: Laser, used to generate linearly polarized laser pulse signals; A polarizer POL, used for passing a horizontally polarized laser pulse signal; A polarization modulation module, used for randomly modulating a laser pulse signal into a coded light signal having a first polarization state or a second polarization state; the first polarization state and the second polarization state are orthogonal to each other; A transmitting telescope is used to expand the coded light signal and illuminate the target; a receiving telescope for receiving an echo signal reflected from a target; Filter, used to filter out the background light noise outside the passband of the echo signal; A polarization beam splitter PBS, used for performing polarization beam splitting on the filtered echo signal to generate a first polarization component and a second polarization component; The first detection module D1 and the second detection module D2 are used to detect the amplitudes of the first polarization component and the second polarization component respectively, and output differential electrical signals to eliminate background noise signals; The main control module is used to control the polarization modulation module to perform polarization encoding to obtain a coding sequence, collect differential electrical signals to generate a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain the distance information of the target. The first polarization state and the second polarization state are a horizontal polarization state and a vertical polarization state, respectively. The polarization modulation module includes a beam splitter BS, a first half-wave plate HWP1, an electro-optic modulator EOM, a second quarter-wave plate QWP2 and a reflector M. The beam splitter BS is used to transmit the horizontally polarized laser pulse signal transmitted through the polarizer POL to the first half-wave plate HWP1; and to transmit the coded light signal reversely passed through the first half-wave plate HWP1 to the transmitting telescope; The angle between the main axis direction of the first half-wave plate HWP1 and the horizontal polarization direction is 22.5°; The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the first half-wave plate HWP1 to be 0 or π; The angle between the main axis direction of the second quarter wave plate QWP2 and the horizontal polarization direction is 45°; The second quarter wave plate QWP2 and the reflector M are used to rotate the horizontal polarization and the vertical polarization by 90 degrees respectively.

2. The laser radar based on polarization noise reduction according to claim 1, characterized in that: The first detection module D1 and the second detection module D2 are both single-photon balanced detectors.

3. A laser radar based on polarization noise reduction, characterized in that: include: Laser, used to generate linearly polarized laser pulse signals; A polarizer POL, used for passing a horizontally polarized laser pulse signal; A polarization modulation module, used for randomly modulating a laser pulse signal into a coded light signal having a first polarization state or a second polarization state; the first polarization state and the second polarization state are orthogonal to each other; A transmitting telescope is used to expand the coded light signal and illuminate the target; a receiving telescope for receiving an echo signal reflected from a target; Filter, used to filter out the background light noise outside the passband of the echo signal; A polarization beam splitter PBS, used for performing polarization beam splitting on the filtered echo signal to generate a first polarization component and a second polarization component; The first detection module D1 and the second detection module D2 are used to detect the amplitudes of the first polarization component and the second polarization component respectively, and output differential electrical signals to eliminate background noise signals; The main control module is used to control the polarization modulation module to perform polarization encoding to obtain a coding sequence, collect differential electrical signals to generate a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain the distance information of the target. The first polarization state and the second polarization state are a horizontal polarization state and a vertical polarization state, respectively. The polarization modulation module includes a second half-wave plate HWP2, an electro-optic modulator EOM, and a third half-wave plate HWP3. The included angles between the main axis directions of the second half-wave plate HWP2 and the third half-wave plate HWP3 and the horizontal polarization direction are both 22.5°; The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the second half-wave plate HWP2 to be 0 or π.

4. The laser radar based on polarization noise reduction according to claim 3, characterized in that: The first detection module D1 and the second detection module D2 are both single-photon balanced detectors.

5. A laser radar based on polarization noise reduction, characterized in that: include: Laser, used to generate linearly polarized laser pulse signals; A polarizer POL, used for passing a horizontally polarized laser pulse signal; A polarization modulation module, used for randomly modulating a laser pulse signal into a coded light signal having a first polarization state or a second polarization state; the first polarization state and the second polarization state are orthogonal to each other; A transmitting telescope is used to expand the coded light signal and illuminate the target; a receiving telescope for receiving an echo signal reflected from a target; Filter, used to filter out the background light noise outside the passband of the echo signal; A polarization beam splitter PBS, used for performing polarization beam splitting on the filtered echo signal to generate a first polarization component and a second polarization component; The first detection module D1 and the second detection module D2 are used to detect the amplitudes of the first polarization component and the second polarization component respectively, and output differential electrical signals to eliminate background noise signals; The main control module is used to control the polarization modulation module to perform polarization encoding to obtain a coding sequence, collect differential electrical signals to generate a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain the distance information of the target. The first polarization state and the second polarization state are respectively a left-hand circular polarization state and a right-hand circular polarization state; A first quarter wave plate QWP1 is also arranged between the filter Filter and the receiving telescope; The angle between the main axis direction of the first quarter wave plate QWP1 and the horizontal polarization direction is 45°. The polarization modulation module includes a fourth half-wave plate HWP4 and an electro-optic modulator EOM. The angle between the main axis direction of the fourth half-wave plate HWP4 and the horizontal polarization direction is 22.5°; The electro-optic modulator EOM is used to modulate the phase difference between the horizontal polarization component and the vertical polarization component of the laser pulse signal after polarization rotation by the fourth half-wave plate HWP4 to π / 2 or 3π / 2.

6. The laser radar based on polarization noise reduction according to claim 5, characterized in that: The first detection module D1 and the second detection module D2 are both single-photon balanced detectors.

7. A laser radar ranging method, implemented by using any one of the laser radars in claims 1 to 6, characterized in that: The following steps are involved: S1: The laser emits a laser pulse signal, which passes through the polarizer POL and generates a driving signal by preparing a random sequence to control the polarization modulation module to perform polarization encoding, and randomly modulates the signal into a coded light signal having a first polarization state or a second polarization state orthogonal thereto, thereby forming a coding sequence; S2: The encoded laser pulse signal is expanded by the transmitting telescope and then irradiated to the target, and the receiving telescope is used to receive the echo signal reflected from the target; S3: After being filtered, the echo signal enters the polarization beam splitter PBS for polarization decoding to obtain a decoding sequence; S4: performing a shift cross-correlation operation on the coding sequence and the decoding sequence, and obtaining the distance information of the target according to the position corresponding to the peak value of the cross-correlation operation result.

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