Balanced detection device for coherent detection laser wind radar

Abstract

This invention discloses a coherent detection laser wind measurement radar balanced detection device. By separating and adjusting the polarization state and phase difference of the depolarized signal light to match the phase difference with the polarization direction of the local oscillator light, the depolarized portion of the signal light participates in coherent balanced detection, enhancing the coherent signal strength and improving the detection signal-to-noise ratio. The device solves the problem of precise phase difference adjustment between the two balanced detection arms using an electro-optic delay crystal, and achieves even energy distribution between the two balanced detection arms using an energy beam-splitting prism, ultimately achieving optimal balanced detection.

Description

Technical Field

[0001] This invention belongs to the field of lidar, specifically relating to a balanced detection device for a coherent detection lidar wind measurement radar. Background Technology

[0002] Atmospheric wind field information is an important parameter of the atmosphere, playing a crucial role in climate and meteorology research, numerical weather prediction, environmental monitoring, and military aviation. Atmospheric wind field measurements are mainly conducted through direct detection and coherent detection. Coherent detection, which utilizes aerosol backscattering signals for heterodyne detection, is a rapid method for detecting low-altitude wind fields, offering advantages such as high sensitivity and high accuracy.

[0003] The basic principle of coherent detection is as follows: After a laser is emitted into the atmosphere, it undergoes elastic scattering with aerosols. This scattered light signal carries Doppler frequency shift information caused by the atmospheric wind field and the local oscillator signal, which beats the signal. By processing the beat signal, the Doppler frequency shift is extracted, thereby retrieving the three-dimensional wind field information. However, because the received scattered signal is extremely weak, and because the signal light depolarizes, this depolarized portion cannot participate in the beat, reducing the coherence efficiency and resulting in a lower signal-to-noise ratio for the detected beat signal.

[0004] The free-space interference optical path device disclosed in patent 201410683013.3 uses a polarization-independent self-coherent method for both beam splitting and beam combining. This requires that the incident light must be polarized; otherwise, different polarizations cannot generate coherent signals. Furthermore, it uses a fixed parallel plate to correct the phase difference between the two balanced probe arms to 180°, which requires a processing accuracy of 10nm for the near-infrared band, making it difficult to achieve. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a balanced detection device for a coherent detection laser wind radar. It adopts a method of polarization beam splitting and then converting to the same polarization state before evenly splitting and combining the beams for balanced detection, which solves the problem that the depolarized signal cannot participate in coherence and the problem that the phase of the optical path of the two arms of balanced detection is not easy to match. By utilizing aerosol scattering of the two parts of the signal, which are both non-depolarized and depolarized, the signal-to-noise ratio of the detection is improved, the detection distance is increased, and the signal-to-noise ratio of the detection signal is improved.

[0006] The basic principle of this invention is to separate the depolarized signal light using a polarization beam splitter, then change the polarization direction of the non-depolarized light and beat it with the local oscillator light. The phase difference between the two arms of the balanced detector is changed by an electro-optic crystal to ensure maximum coherence efficiency.

[0007] The technical solution of the present invention is as follows:

[0008] A coherent detection laser wind-measuring radar balanced detection device, characterized in that it includes:

[0009] The polarization beam splitter module is used to split the signal light into two beams, namely s-polarized signal light and p-polarized signal light;

[0010] The beam combining and reflection module is used to combine the local oscillator light with one of the polarized signal lights to form the first polarized signal light;

[0011] The modulation crystal module is used to modulate another beam of polarized signal light to form a second polarized signal light, and the phase difference between the second polarized signal light and the first polarized signal light is 360° or an integer multiple of 360°.

[0012] A polarization conversion module is used to convert a first polarization signal or a second polarization signal into a polarization signal light with the same polarization as another polarization signal light.

[0013] The energy beam splitter module is used to receive two beams of polarized signal light with the same polarization and split them into two beams of polarized signal light with the same amplitude, phase and polarization and perpendicular propagation directions, namely the third polarized signal light and the fourth polarized signal light.

[0014] Furthermore, it also includes:

[0015] The modulation crystal and reflection module are used to change the propagation direction of the third polarized signal light so that it is parallel to the propagation direction of the fourth polarized signal light, and to ensure that the phase difference between the third polarized signal light and the fourth polarized signal light is constant at 180° or an odd multiple of 180°.

[0016] Or, it may also include:

[0017] The focusing and photoelectric detection module is used to focus and beat frequency process the third polarized signal light and the fourth polarized signal light, and transmit them to the data acquisition and processor module to generate an enhanced Doppler signal frequency spectrum.

[0018] Preferably, the polarization beam splitter module is a polarization beam splitter prism.

[0019] Preferably, the beam combining and reflection module includes a beam combiner and a high-reflection mirror, wherein the beam combiner is a planar beam combiner or a cubic beam combiner.

[0020] Preferably, the energy beam splitting module is an energy beam splitting prism with a splitting ratio of 1:1.

[0021] Compared with existing technologies, the beneficial effects of the invention are as follows:

[0022] (1) By separating and adjusting the polarization state and phase difference of the depolarized signal light to match the phase difference of the polarization direction of the local oscillator light, the depolarized part of the signal light participates in coherent balanced detection, thereby enhancing the coherent signal intensity and improving the detection signal-to-noise ratio.

[0023] (2) The problem of precise adjustment of phase difference between two balanced probe arms is solved by electro-optic delay crystal, and the energy of the two balanced probe arms is evenly distributed by energy beam splitting prism, thus achieving the optimization of balanced probe.

[0024] (3) The non-depolarization signal was used to participate in the beat frequency, which improved the coherence efficiency, increased the detection signal-to-noise ratio, and increased the detection distance by 20%.

[0025] (4) It is related to the polarization of light and can be used in various coherent detection systems. The phase difference of the optical path of the balanced detection double arm is easy to adjust. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of Embodiment 1 of the coherent detection laser wind radar balanced detection device of the present invention;

[0027] Figure 2 yes Figure 1 This is a schematic diagram of Embodiment 2 of the Coherent Detection Laser Wind Measurement Radar Balance Detection Device of the present invention.

[0028] In the figure: 1. Polarizing beam splitter prism, 2. Beam combiner, 3a. First electro-optic modulation crystal, 3b. Second electro-optic modulation crystal, 4a. First electro-optic driver, 4b. Second electro-optic driver, 5a. First half-wave plate, 5b. Second half-wave plate, 6a. First high-reflection mirror, 6b. Second high-reflection mirror, 7. Energy beam splitter prism, 8a. First focusing lens, 8b. Second focusing lens, 9. Balanced detector, 10a. First magnified photodetector, 10b. Second magnified photodetector, 11. Digital acquisition and processor, 12. Phase delay crystal. Detailed Implementation

[0029] The present invention will be further described below with reference to examples and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1

[0031] See Figure 1 , Figure 1 This is a schematic diagram of Embodiment 1 of the coherent detection laser wind radar balanced detection device of the present invention. As shown in the figure, a coherent detection laser wind radar balanced detection device includes a polarization beam splitter prism 1, a beam combiner 2, a first electro-optic modulation crystal 3a, a second electro-optic modulation crystal 3b, a first electro-optic driver 4a, a second electro-optic driver 4b, a first half-wave plate 5, a first high-reflection mirror 6a, a second high-reflection mirror 6b, an energy beam splitter prism 7, a first focusing lens 8a, a second focusing lens 8, and a balanced detector 9.

[0032] The signal light is split into s-polarized and p-polarized signal light after passing through the polarization beam splitter 1, and then enters optical path A and optical path B respectively. The s-polarized signal light passes through the beam combiner 2, where its propagation direction is folded by 90°. Simultaneously, the s-polarized local oscillator light passes through the beam combiner 2 and is combined with the s-polarized signal light. After reflection by the first high-reflection mirror 6a, it is incident perpendicularly onto the energy beam splitter 7. The p-polarized signal light first passes through the first electro-optic modulation crystal 3a, adjusting the voltage of the first electro-optic driver 4a to ensure that the phase difference between optical paths A and B is an integer multiple of 360 degrees and remains constant, guaranteeing good coherence between optical paths A and B. Then, the phase-modulated p-polarized signal light passes through the first half-wave plate 5a (the marked direction of the half-wave plate makes an angle of 45° with the p-polarization direction) and becomes s-polarized signal light, which is then incident perpendicularly onto the energy beam splitter 7. The two beams are split by the energy beam splitter 7 into two beams with the same amplitude, phase, and polarization, and then enter optical path C and optical path D respectively. The light beam in optical path C passes through the second high-reflection mirror 6b, which is parallel to the first high-reflection mirror 6a. The propagation direction of the light beam is then parallel to that in optical path D. Next, it passes through the second electro-optic modulation crystal 3b. The voltage of the second electro-optic driver 4b is adjusted so that the phase difference between optical paths C and D is an odd multiple of 180° and remains constant. Then, it passes through the first focusing lens 8a and is input to the positive electrode of the balanced detector 9. The light beam in optical path D passes directly through the second focusing lens 8b and is input to the negative electrode of the balanced detector 9. Finally, the balanced detection is completed, thereby obtaining a balanced detection signal with enhanced signal-to-noise ratio.

[0033] The following are the parameters of the main components used in one embodiment, and are suitable for, but not limited to, the following parameters:

[0034] The polarizing beam splitter 1 can have a side length of 25mm and is composed of two fused silica prisms, which is suitable for commonly used laser wavelengths.

[0035] The beam combiner 2 is a beam combiner with a reflectivity of 99% and a transmittance of 1%, and the substrate is infrared fused silica.

[0036] The first and second electro-optic modulation crystals 3a and 3b are KDP crystals.

[0037] The first electro-optic driver 4a makes the phase difference between optical paths A and B 360° or an integer multiple of 360° and constant.

[0038] The first half-wave plate 5a is made of quartz half-wave plate and is capable of generating an optical path difference of λ / 2.

[0039] The high-reflectivity mirrors 6a and 6b are coated with a dielectric film, with an average reflectivity greater than 99%.

[0040] The splitting ratio of the energy beam splitter 7 is as close to 1:1 as possible.

[0041] The focusing lenses 8a and 8b are plano-convex lenses to accommodate different working wavelengths.

[0042] The second electro-optic driver 4b makes the phase difference between optical paths C and D an odd multiple of 180° and constant.

[0043] The aforementioned balanced detector 9 is an InGaAs balanced detector, typically with a bandwidth of 100MHz or higher.

[0044] The specific process of using the aforementioned coherent detection laser wind radar digital balance detection device for detection is as follows:

[0045] After the signal light is incident perpendicularly on the polarization beam splitter prism 1, it is split into s-polarized light and p-polarized light, which then enter optical paths A and B, respectively. The s-polarized signal light, upon entering optical path A, is first reflected by a high-reflectivity beam combiner 2. Simultaneously, the local oscillator light, also in an s-polarized state, passes through beam combiner 2 and is combined with the s-polarized signal light. This beam then passes through the first high-reflectivity mirror 6a and is incident perpendicularly on the energy beam splitter prism 7. The p-polarized signal light, upon entering optical path B, passes sequentially through the first electro-optic modulation crystal 3a and the half-wave plate 5 before being incident perpendicularly on the energy beam splitter prism 7. The first electro-optic driver 3b is adjusted to ensure that the phase difference between optical paths A and B is an integer multiple of 360 degrees and remains constant. The half-wave plate 5 changes the polarization state of the p-polarized signal light to s-polarized.

[0046] The energy beam splitter prism 7 splits two beams of light into two beams with the same amplitude, phase, and polarization, which enter optical paths C and D respectively. The beam in optical path C passes through the second high-reflection mirror 6b, and its propagation direction is parallel to that of optical path D. Then, it passes through the second electro-optic modulation crystal 3b and the first focusing lens 8a in sequence, and is input to the positive electrode of the balance detector 9. The second electro-optic driver 4b is adjusted so that the phase difference between optical paths C and D is an odd multiple of 180° and remains constant. The beam in optical path D passes directly through the second focusing lens 8b and is input to the negative electrode of the balance detector 9. Finally, the balance detection is completed, and the balance detection signal is obtained.

[0047] Example 2

[0048] See Figure 2 , Figure 2 This is a schematic diagram of Embodiment 2 of the coherent detection laser wind radar balanced detection device of the present invention. As shown in the figure, a coherent detection laser wind radar balanced detection device includes a polarization beam splitter prism 1, a phase retardation crystal 12, an electro-optic driver 4a, a beam combiner 2, a half-wave plate 5b, a high-reflection mirror 6, an energy beam splitter prism 7, a first focusing lens 8a, a second focusing lens 8b, a first amplified photodetector 10a, a second amplified photodetector 10b, and a digital acquisition and processor 11. The connection relationship of the above components is as follows:

[0049] The signal light is incident perpendicularly on the polarization beam splitter prism 1, and the outgoing light is split into p-polarized signal light and s-polarized signal light, which enter optical path A and optical path B respectively. The p-polarized signal light, after passing through the phase delay crystal 12 controlled by the electro-optic driver 4a, is incident perpendicularly on the energy beam splitter prism 7 to form optical path A. The s-polarized signal light, after being reflected by the beam combiner 2, changes its propagation direction by 90°. Simultaneously, the local oscillator light, which is parallel to the incident direction of the signal light and has s-polarization, passes through the beam combiner 2 and is combined with the s-polarized signal light. It then passes perpendicularly through the half-wave plate 5b (the marked direction of the half-wave plate makes an angle of 45 degrees with the s-polarized light of the signal), converting both s-polarization states to p-polarization states. The light is then deflected 90 degrees by the high-reflection mirror 6 installed at a 45-degree angle and incident perpendicularly on the energy beam splitter prism 7 to form optical path B. The electro-optic driver 4a is adjusted so that the phase difference between optical paths A and B is 360° or an integer multiple thereof, ensuring good coherence. The two beams of light emitted from the energy beam splitter prism 7 have the same amplitude and polarization direction, and enter optical paths C and D respectively for individual detection. The light signal in optical path C is focused by the first focusing lens 8a to the first amplified photodetector 10a and becomes a beat frequency signal; simultaneously, the light beam in optical path D is also focused by the second focusing lens 8b to the second amplified photodetector 10b and becomes a beat frequency signal; then the two electrical signals are simultaneously input to the data acquisition and processor 11 through wires to directly obtain the enhanced Doppler signal frequency spectrum.

[0050] Below are reference values ​​for the parameters of the main components used in one embodiment, but are not limited to these parameters:

[0051] The polarizing beam splitter 1 can have a side length of 25mm and is composed of two fused silica prisms, which is suitable for commonly used laser wavelengths.

[0052] The phase delay crystal 12 makes the phase difference between optical paths A and B 360° or an integer multiple thereof.

[0053] The beam combiner 2 is a beam combiner with a reflectivity of 99% and a transmittance of 1%, and the substrate is infrared fused silica.

[0054] The half-wave plate 5b is made of quartz half-wave plate and is suitable for most wavelengths.

[0055] The surface of the high-reflectivity mirror 6 is coated with a dielectric film, with an average reflectivity greater than 99%.

[0056] The splitting ratio of the energy beam splitter 7 is as close to 1:1 as possible.

[0057] The focusing lenses 8a and 8b are a focusing lens group to adapt to different working wavelengths.

[0058] The amplified photodetectors 10a and 10b are InGaAs amplified photodetectors, typically with a bandwidth of 100MHz or higher.

[0059] The data acquisition and processor 11 includes an AD acquisition card with a sampling rate of 200MS / s or higher.

[0060] The specific operation process of using the above-mentioned coherent detection laser wind radar digital balance detection device is as follows:

[0061] The signal light is incident perpendicularly onto the polarization beam splitter prism 1, where it is split into s-polarized and p-polarized light. The s-polarized signal light passes through the polarization beam splitter prism 1 and enters optical path A, then passes through the phase retardation crystal 12 and is incident perpendicularly onto the power beam splitter prism. The p-polarized signal light is reflected into optical path B, and after reflection by the beam combiner 2, its propagation direction changes by 90°. Simultaneously, the s-polarized local oscillator light passes through the beam combiner 2 and is combined with the s-polarized signal light. It then passes through the half-wave plate 5b and becomes p-polarized, before being reflected 90 degrees by the high-reflection mirror 6 and incident perpendicularly onto the energy beam splitter prism 7. During this process, adjusting the voltage of the electro-optic driver 4a allows the phase difference between optical paths A and B to be 360° or an integer multiple thereof. After passing through the energy beam splitter prism 7, the signal light in optical paths A and B becomes two coherent signal beams, which enter optical paths C and D respectively. In each optical path, each beam sequentially passes through the focusing lens 8, the magnifying photodetector 10, and the data acquisition and processing unit 11 to obtain the Doppler frequency signal.

Claims

1. A balanced detection device of a coherent detection laser wind finding radar, characterized in that, The application relates to a polarization modulation Doppler lidar system, which comprises the following modules: a polarization beam splitting module for splitting signal light into two beams, i.e. s-polarized signal light and p-polarized signal light; a beam combining and reflecting module for combining local oscillator light with one of the two beams of polarized signal light to form first polarized signal light; a modulation crystal module for modulating the other beam of polarized signal light to form second polarized signal light, wherein the phase difference between the second polarized signal light and the first polarized signal light is 360 degrees or an integral multiple of 360 degrees; a polarization conversion module for converting the first polarized signal or the second polarized signal into polarized signal light with the same polarization as the other beam of polarized signal light; an energy beam splitting module for receiving two beams of polarized signal light with the same polarization and splitting them into two beams of polarized signal light with the same amplitude, phase and polarization and perpendicular propagation directions, i.e. third polarized signal light and fourth polarized signal light; a modulation crystal and reflecting module for changing the propagation direction of the third polarized signal light to be parallel to the propagation direction of the fourth polarized signal light and ensuring that the phase difference between the third polarized signal light and the fourth polarized signal light is constantly 180 degrees or an odd multiple of 180 degrees; a focusing and photodetection module for focusing and beat frequency processing of the third polarized signal light and the fourth polarized signal light and transmitting them to a data acquisition and processing module to generate an enhanced Doppler signal frequency spectrum.

2. The balanced detection apparatus of the coherent detection wind lidar according to claim 1, wherein, The polarization beam splitting module is a polarization beam splitting prism (1).

3. The balanced detection apparatus of the coherent detection wind lidar according to claim 1, characterized in that The beam combining and reflecting module comprises a beam combiner (2) and a high-reflectivity mirror, wherein the beam combiner (2) is a flat plate beam combiner or a cubic beam combiner.

4. The balanced detection apparatus of the coherent detection wind lidar according to claim 1, characterized in that The energy beam splitting module is an energy beam splitting prism (7) with a splitting ratio of 1:1.

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