A polarization-coded laser radar with its own local oscillator light

Abstract

The present invention belongs to the technical field of laser radar ranging and speed measurement, and discloses a polarization-encoded laser radar with its own local oscillator light, including a laser Laser, a polarizer POL, an adjustable polarization rotation module, a transmitting telescope, a receiving telescope, a filter Filter, a half-wave plate HWP, a polarization beam splitter PBS, a first photodetector PD1, a second photodetector PD2 and a main control module. Compared with the prior art, the present invention can significantly reduce the background noise in the echo signal and improve the signal-to-noise ratio of the system by randomly rotating the linearly polarized light by two opposite small angles, which is equivalent to modulating the local oscillator light and the signal in the same pulse, and detecting through a balanced detector. In addition, since the local oscillator light and the signal experience the same path, the Doppler effect of the target motion has the same effect on the two, and will not affect the coherent detection.

Description

Technical Field

[0001] The present invention relates to the technical field of laser radar ranging and speed measurement, and in particular to a polarization coded laser radar with its own local oscillator light. 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 be lost to a certain extent. Therefore, the signal-to-noise ratio is low during the day and it is difficult to work normally. The Chinese invention patent with the authorization announcement number CN118011415B proposes a method of phase encoding and interfering the echo signal and performing differential, which can achieve a better noise reduction effect. However, this scheme requires the use of two lasers, and phase compensation is required during phase encoding and decoding due to the slow phase drift between the transmitting and receiving interferometers, which increases the complexity of the system. 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 polarization coded laser radar with its own local oscillator light.

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

[0006] A polarization-encoded laser radar with its own local oscillator light, comprising a laser Laser, a polarizer POL, an adjustable polarization rotation module, a transmitting telescope, a receiving telescope, a filter Filter, a half-wave plate HWP, a polarization beam splitter PBS, a first photodetector PD1, a second photodetector PD2 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 adjustable polarization rotation module is used to randomly rotate the polarization state of the laser pulse signal into a first polarization state or a second polarization state to form a coded optical signal; the first polarization state and the second polarization state have opposite vertical polarization components;

[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 angle between the main axis direction of the half-wave plate HWP and the horizontal polarization direction is 22.5°, which is used to rotate the polarization state of the echo signal by 45°;

[0014] The polarization beam splitter PBS is used to perform polarization beam splitting on the echo signal after polarization rotation to generate a first polarization component and a second polarization component;

[0015] The first photodetector PD1 and the second photodetector PD2 are used to detect the first polarization component and the second polarization component respectively, and output a differential electrical signal;

[0016] The main control module is used to control the adjustable polarization rotation 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.

[0017] Preferably, the angles between the first polarization state and the second polarization state and the horizontal polarization direction are θ and −θ respectively, and θ<<1 is satisfied.

[0018] Preferably, the adjustable polarization rotation module is an electrically controlled magneto-optical modulator EMOM.

[0019] Preferably, the adjustable polarization rotation module is an electrically controlled half-wave plate EHWP.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention proposes a polarization-coded laser radar with local oscillator light. By randomly rotating the linear polarized light into two opposite tiny angles, it is equivalent to modulating the local oscillator light and the signal in the same pulse, and detecting them through a balanced detector, which can greatly reduce the background noise in the echo signal and improve the signal-to-noise ratio of the system. In addition, since the local oscillator light and the signal have experienced the same path, the Doppler effect of the target motion has the same effect on the two and will not affect the coherent detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the polarization coded laser radar with its own local oscillator light of the present invention;

[0023] Figure 2 It is a schematic diagram of signal modulation of the present invention;

[0024] Figure 3 Schematic diagram of the first embodiment of the polarization coded laser radar with its own local oscillator light of the present invention

[0025] Figure 4 This is a schematic diagram of the second embodiment of the polarization coded laser radar with its own local oscillator light of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] like Figure 1 As shown, a polarization-encoded laser radar with its own local oscillator light includes a laser Laser, a polarizer POL, an adjustable polarization rotation module, a transmitting telescope, a receiving telescope, a filter Filter, a half-wave plate HWP, a polarization beam splitter PBS, a first photodetector PD1, a second photodetector PD2 and a main control module.

[0028] The laser is used to generate a linearly polarized laser pulse signal;

[0029] The polarizer POL is used to pass a horizontally polarized laser pulse signal;

[0030] The adjustable polarization rotation module is used to randomly rotate the polarization state of the laser pulse signal into a first polarization state or a second polarization state to form a coded optical signal; the first polarization state and the second polarization state have opposite vertical polarization components;

[0031] The transmitting telescope is used to expand the coded light signal and illuminate the target;

[0032] The receiving telescope is used to receive the echo signal reflected from the target;

[0033] The filter is used to filter out the background light noise outside the passband in the echo signal;

[0034] The angle between the main axis direction of the half-wave plate HWP and the horizontal polarization direction is 22.5°, which is used to rotate the polarization state of the echo signal by 45°;

[0035] The polarization beam splitter PBS is used to perform polarization beam splitting on the echo signal after polarization rotation to generate a first polarization component and a second polarization component;

[0036] The first photodetector PD1 and the second photodetector PD2 are used to detect the first polarization component and the second polarization component respectively, and output a differential electrical signal;

[0037] The main control module is used to control the adjustable polarization rotation 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.

[0038] The angles between the first polarization state and the second polarization state and the horizontal polarization direction are θ and −θ respectively, and θ<<1 is satisfied.

[0039] The specific working process is as follows:

[0040] The laser generates a linearly polarized laser pulse signal, and its horizontal polarization component passes through the polarizer POL, and then passes through the adjustable polarization rotation module to rotate the polarization state by an angle θ or -θ to become the first polarization state P1 or the second polarization state P2, forming a coded optical signal. The two polarization states can be written as

[0041] ,

[0042] Among them, PLO=Acosθ, PS1=Asinθ, PS2=-Asinθ.

[0043] like Figure 2 As shown in the figure, P1 can be decomposed into the horizontal polarization component PLO and the vertical polarization component PS1, and P2 can be decomposed into the horizontal polarization component PLO and the vertical polarization component PS2. Since the rotation angles are the same, the amplitudes of PS1 and PS2 are equal and the signs are opposite. Therefore, the coded optical signal can be regarded as the synthesis of the local oscillator light PLO and the signal PS1 or PS2, that is, the coded optical signal has its own local oscillator light. The coded optical signal is then expanded by the transmitting telescope and irradiated to the target.

[0044] 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 to filter out some background noise and then passes through the half-wave plate HWP for polarization rotation. Since the angle between the main axis direction of the half-wave plate HWP and the horizontal polarization direction is 22.5°, its Jones matrix is:

[0045] ,

[0046] Then the polarization state of the echo signal after passing through the half-wave plate HWP becomes

[0047] ,

[0048] Then the echo signal enters the polarization beam splitter PBS for polarization beam splitting. The horizontal polarization component is transmitted from the polarization beam splitter PBS and enters the first photodetector PD1 for detection; the vertical polarization component is reflected from the polarization beam splitter PBS and enters the second photodetector PD2 for detection. Since the background noise is non-polarized light, the polarization components entering the first photodetector PD1 and the second photodetector PD2 after polarization beam splitting by the polarization beam splitter PBS have equal amplitudes, that is, .

[0049] for , the difference between the first photodetector PD1 and the second photodetector PD2 is

[0050] ,

[0051] for , the difference between the first photodetector PD1 and the second photodetector PD2 is

[0052] ,

[0053] When θ<<1, PLO≈A, PS1≈θ, PS2≈-θ. It can be seen that the differential detection result is the product of the local oscillator light and the signal, which is equivalent to the PLO amplifying PS1 and PS2, which is consistent with the coherent detection result of the balanced zero difference. Therefore, the local oscillator light and the signal can be transmitted and received for detection at the same time. Since the local oscillator light and the signal have experienced the same path, the Doppler effect of the target motion has the same effect on the two and will not affect the coherent detection.

[0054] The differential detection result corresponds to the coded polarization states PS1 and PS2, so the decoding sequence can be obtained. The coded 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 by one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0055] like Figure 3 As shown, embodiment 1:

[0056] The adjustable polarization rotation module is an electrically controlled magneto-optical modulator EMOM.

[0057] The specific working process is as follows:

[0058] The laser generates a linearly polarized laser pulse signal, and its horizontal polarization component passes through the polarizer POL and then passes through the electrically controlled magneto-optical modulator EMOM. The electromagnetic field of the EMOM is controlled by the main control module, and the polarization state of the laser pulse signal is rotated by an angle of θ or -θ using the Faraday effect. Its Jones matrix can be written as

[0059] ,

[0060] After rotation, it becomes the first polarization state P1 or the second polarization state P2 to form a coded optical signal. The two polarization states can be written as

[0061] ,

[0062] Among them, PLO=Acosθ, PS1=Asinθ, PS2=-Asinθ.

[0063] like Figure 2 As shown in the figure, P1 can be decomposed into the horizontal polarization component PLO and the vertical polarization component PS1, and P2 can be decomposed into the horizontal polarization component PLO and the vertical polarization component PS2. Since the rotation angles are the same, the amplitudes of PS1 and PS2 are equal and the signs are opposite. Therefore, the coded optical signal can be regarded as the synthesis of the local oscillator light PLO and the signal PS1 or PS2, that is, the coded optical signal has its own local oscillator light. The coded optical signal is then expanded by the transmitting telescope and irradiated to the target.

[0064] 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 to filter out some background noise and then passes through the half-wave plate HWP for polarization rotation. Since the angle between the main axis direction of the half-wave plate HWP and the horizontal polarization direction is 22.5°, its Jones matrix is:

[0065] ,

[0066] Then the polarization state of the echo signal after passing through the half-wave plate HWP becomes

[0067] ,

[0068] Then the echo signal enters the polarization beam splitter PBS for polarization beam splitting. The horizontal polarization component is transmitted from the polarization beam splitter PBS and enters the first photodetector PD1 for detection; the vertical polarization component is reflected from the polarization beam splitter PBS and enters the second photodetector PD2 for detection. Since the background noise is non-polarized light, the polarization components entering the first photodetector PD1 and the second photodetector PD2 after polarization beam splitting by the polarization beam splitter PBS have equal amplitudes, that is, .

[0069] for , the difference between the first photodetector PD1 and the second photodetector PD2 is

[0070] ,

[0071] for , the difference between the first photodetector PD1 and the second photodetector PD2 is

[0072] ,

[0073] When θ<<1, PLO≈A, PS1≈θ, PS2≈-θ. It can be seen that the differential detection result is the product of the local oscillator light and the signal, which is equivalent to the PLO amplifying PS1 and PS2, which is consistent with the coherent detection result of the balanced zero difference. Therefore, the local oscillator light and the signal can be transmitted and received for detection at the same time. Since the local oscillator light and the signal have experienced the same path, the Doppler effect of the target motion has the same effect on the two and will not affect the coherent detection.

[0074] The differential detection result corresponds to the coded polarization states PS1 and PS2, so the decoding sequence can be obtained. The coded 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 by one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0075] like Figure 4 As shown, Example 2:

[0076] The adjustable polarization rotation module is an electrically controlled half-wave plate EHWP.

[0077] The specific working process is as follows:

[0078] The laser generates a linearly polarized laser pulse signal, and its horizontal polarization component passes through the polarizer POL and then passes through the electrically controlled half-wave plate EHWP. The main control module controls the angle between the main axis of the electrically controlled half-wave plate EHWP and the horizontal polarization direction to be θ / 2 or -θ / 2, so that the polarization state of the laser pulse signal rotates by an angle of θ or -θ. Its Jones matrix can be written as

[0079] ,

[0080] After rotation, it becomes the first polarization state P1 or the second polarization state P2 to form a coded optical signal. The two polarization states can be written as

[0081] ,

[0082] Among them, PLO=Acosθ, PS1=Asinθ, PS2=-Asinθ.

[0083] like Figure 2As shown in the figure, P1 can be decomposed into the horizontal polarization component PLO and the vertical polarization component PS1, and P2 can be decomposed into the horizontal polarization component PLO and the vertical polarization component PS2. Since the rotation angles are the same, the amplitudes of PS1 and PS2 are equal and the signs are opposite. Therefore, the coded optical signal can be regarded as the synthesis of the local oscillator light PLO and the signal PS1 or PS2, that is, the coded optical signal has its own local oscillator light. The coded optical signal is then expanded by the transmitting telescope and irradiated to the target.

[0084] 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 to filter out some background noise and then passes through the half-wave plate HWP for polarization rotation. Since the angle between the main axis direction of the half-wave plate HWP and the horizontal polarization direction is 22.5°, its Jones matrix is:

[0085] ,

[0086] Then the polarization state of the echo signal after passing through the half-wave plate HWP becomes

[0087] ,

[0088] Then the echo signal enters the polarization beam splitter PBS for polarization beam splitting. The horizontal polarization component is transmitted from the polarization beam splitter PBS and enters the first photodetector PD1 for detection; the vertical polarization component is reflected from the polarization beam splitter PBS and enters the second photodetector PD2 for detection. Since the background noise is non-polarized light, the polarization components entering the first photodetector PD1 and the second photodetector PD2 after polarization beam splitting by the polarization beam splitter PBS have equal amplitudes, that is, .

[0089] for , the difference between the first photodetector PD1 and the second photodetector PD2 is

[0090] ,

[0091] for , the difference between the first photodetector PD1 and the second photodetector PD2 is

[0092] ,

[0093] When θ<<1, PLO≈A, PS1≈θ, PS2≈-θ. It can be seen that the differential detection result is the product of the local oscillator light and the signal, which is equivalent to the PLO amplifying PS1 and PS2, which is consistent with the coherent detection result of the balanced zero difference. Therefore, the local oscillator light and the signal can be transmitted and received for detection at the same time. Since the local oscillator light and the signal have experienced the same path, the Doppler effect of the target motion has the same effect on the two and will not affect the coherent detection.

[0094] The differential detection result corresponds to the coded polarization states PS1 and PS2, so the decoding sequence can be obtained. The coded 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 by one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0095] It can be seen from the various embodiments of the present invention that the present invention proposes a polarization-coded laser radar with local oscillator light. By randomly rotating the linear polarized light by two opposite small angles, it is equivalent to modulating the local oscillator light and the signal in the same pulse, and detecting it through a balanced detector, which can greatly reduce the background noise in the echo signal and improve the signal-to-noise ratio of the system. In addition, since the local oscillator light and the signal have experienced the same path, the Doppler effect of the target motion has the same effect on the two and will not affect the coherent detection.

Claims

1. A polarization coded laser radar with its own local oscillator light, 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; An adjustable polarization rotation module, used for randomly rotating the polarization state of the laser pulse signal into a first polarization state or a second polarization state to form a coded optical signal; the first polarization state and the second polarization state have opposite vertical polarization components; 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 half-wave plate HWP, wherein the angle between the main axis direction of the half-wave plate HWP and the horizontal polarization direction is 22.5°, and is used to rotate the polarization state of the echo signal by 45°; A polarization beam splitter PBS, used for performing polarization beam splitting on the echo signal after polarization rotation to generate a first polarization component and a second polarization component; The first photodetector PD1 and the second photodetector PD2 are used to detect the first polarization component and the second polarization component respectively, and output differential electrical signals; The main control module is used to control the adjustable polarization rotation 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 angles between the first polarization state and the second polarization state and the horizontal polarization direction are θ and -θ respectively, and satisfy θ<<1, The specific working process is as follows: The laser generates a linearly polarized laser pulse signal, and its horizontal polarization component passes through the polarizer POL, and then passes through the adjustable polarization rotation module to rotate the polarization state by an angle θ or -θ to become the first polarization state P1 or the second polarization state P2, forming a coded optical signal. The two polarization states can be written as ， Among them, PLO=Acosθ, PS1=Asinθ, PS2=-Asinθ, P1 can be decomposed into the horizontal polarization component PLO and the vertical polarization component PS1, and P2 can be decomposed into the horizontal polarization component PLO and the vertical polarization component PS2. Since the rotation angles are the same, the amplitudes of PS1 and PS2 are equal and the signs are opposite. Therefore, the coded optical signal can be regarded as the synthesis of the local oscillator light PLO and the signal PS1 or PS2, that is, the coded optical signal has its own local oscillator light. Then the coded optical signal is expanded by the transmitting telescope and irradiated to the target. After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal. After that, it passes through the filter to filter out some background noise and then passes through the half-wave plate HWP for polarization rotation. Since the angle between the main axis direction of the half-wave plate HWP and the horizontal polarization direction is 22.5°, its Jones matrix is: ， Then the polarization state of the echo signal after passing through the half-wave plate HWP becomes , Then the echo signal enters the polarization beam splitter PBS for polarization beam splitting. The horizontal polarization component is transmitted from the polarization beam splitter PBS and enters the first photodetector PD1 for detection; the vertical polarization component is reflected from the polarization beam splitter PBS and enters the second photodetector PD2 for detection. Since the background noise is non-polarized light, the polarization components entering the first photodetector PD1 and the second photodetector PD2 after polarization beam splitting by the polarization beam splitter PBS have equal amplitudes, that is, , for , the difference between the first photodetector PD1 and the second photodetector PD2 is ， for , the difference between the first photodetector PD1 and the second photodetector PD2 is ， When θ<<1, PLO≈A, PS1≈θ, PS2≈-θ, and the differential detection result is the product of the local oscillator light and the signal, which is equivalent to PLO amplifying PS1 and PS2, which is consistent with the coherent detection result of balanced zero difference, realizing the simultaneous transmission and reception detection of the local oscillator light and the signal.

2. The polarization coded laser radar with its own local oscillator light according to claim 1, characterized in that: The adjustable polarization rotation module is an electrically controlled magneto-optical modulator EMOM.

3. The polarization coded laser radar with its own local oscillator light according to claim 1, characterized in that: The adjustable polarization rotation module is an electrically controlled half-wave plate EHWP.

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