Miniaturized three-dimensional dual-wavelength multifunctional laser radar device

Abstract

The invention relates to a miniaturized three-dimensional dual-wavelength multifunctional laser radar device, which comprises an upper computer, a digital signal processor, a laser, a first light path module, a second light path module and a scattered light collection module, the laser outputs two paths of laser to enter the first light path module and the second light path module respectively, the second light path module performs frequency doubling and beam expanding collimation on the input laser and then emits the laser to the atmosphere, and the scattered light collection module collects scattered light signals and inputs the scattered light signals to the digital signal processor after photoelectric conversion; the digital signal processor uploads the data to an upper computer for product calculation; the first light path module carries out beam expansion and collimation on the input laser, then emits the laser to the atmosphere, collects a backward scattering light signal at the same time, carries out frequency mixing and signal photoelectric conversion, and then carries out fast Fourier transform to obtain power spectrum data. According to the invention, efficient and accurate data such as wind field environment and aerosol concentration can be provided for the aircraft, and important guidance and guarantee are provided for take-off and landing and flight safety of the aircraft.

Description

Technical Field

[0001] The present invention relates to the field of meteorological monitoring, and in particular to a miniaturized three-dimensional dual-wavelength multifunctional laser radar device. Background Art

[0002] In low-altitude economic applications, aircraft rely on good weather conditions and stable wind fields. However, in reality, low-altitude wind fields are often unpredictable due to human activities or natural environment. In particular, dense buildings in cities have a great impact on the direction of regional wind fields, often forming short-term severe wind fields such as turbulence and shear, which pose a great threat to aircraft takeoff and landing. Therefore, how to provide aircraft with efficient and accurate data such as wind field environment and aerosol concentration, and provide important guidance and guarantee for aircraft takeoff and landing and flight safety is a problem that needs to be considered at present. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a miniaturized three-dimensional dual-wavelength multifunctional laser radar device to solve the deficiencies of the prior art.

[0004] The object of the present invention is achieved by the following technical solutions: a miniaturized three-dimensional dual-wavelength multifunctional laser radar device, the device comprising a host computer, a digital signal processor, a laser, a first optical path module, a second optical path module and a scattered light collection module; The laser is configured to output two laser beams which enter the first optical path module and the second optical path module respectively. The second optical path module performs frequency doubling and beam expansion and collimation on the input laser beam and then emits the laser beam into the atmosphere, which acts on aerosol particles in the air to cause Mie scattering. The scattered light collection module collects the scattered light signal and completes the photoelectric conversion before inputting it into the digital signal processor. The digital signal processor uploads the signal to the host computer for product calculation. The first optical path module expands and collimates the input laser and then emits it into the atmosphere. At the same time, it collects the backscattered light signal superimposed with the Doppler shift, performs frequency mixing and signal photoelectric conversion, and then performs fast Fourier transform on the signal through a digital signal processor to obtain power spectrum data, thereby extracting the radial wind speed of the aerosol particles.

[0005] The device also includes a servo system, which receives instructions sent by a host computer to realize rotation in azimuth and elevation directions, change the direction of transmitting and receiving beams, and thus complete space scanning.

[0006] The second optical path module includes a frequency doubler, a second telescope and two reflectors. The wavelength of one laser is halved after passing through the frequency doubler, and then it is expanded and collimated by the second telescope and emitted into the atmosphere through two reflectors, acting on aerosol particles in the air to cause Mie scattering.

[0007] The scattered light collection module includes a third telescope, an interference filter and a photomultiplier tube. Part of the scattered light signal enters the third telescope and is focused and collimated, and then passes through the interference filter to be incident on the photomultiplier tube to complete the photoelectric conversion of the signal. The electrical signal is collected by the digital signal processor and uploaded to the host computer for calculation of backscattering coefficient, extinction coefficient and optical thickness related products.

[0008] The first optical path module includes an optical circulator, a balanced detector and a first telescope. The laser is injected into the first telescope through the optical circulator. The first telescope expands and collimates the light beam and then emits it into the atmosphere. Due to the movement of aerosol particles, the light signal acting on the aerosol particles is superimposed with the Doppler frequency shift. Part of the backscattered light signal is mixed with the local oscillator (LO) signal after passing through the first telescope and the optical circulator. A 180° phase difference is introduced when the two optical signals are output. After the signal is photoelectrically converted by the balanced detector, an intermediate frequency electrical signal is output, which is collected by a digital signal processor and then the power spectrum data is obtained through fast Fourier transform, thereby extracting the radial wind speed of the aerosol particles to reflect the atmospheric wind field conditions.

[0009] The first telescope includes a transmission structure consisting of an objective lens and an eyepiece. The incident divergent laser is expanded through the eyepiece and then collimated through the objective lens before being emitted.

[0010] The balanced detector includes an optical fiber coupler, two pairs of PIN diodes and a transimpedance amplifier; when the optical signal and the local oscillator signal (LO) enter the optical fiber coupler for beat frequency, two signals with a phase difference of 180° are output, which respectively enter the photosensitive surfaces of two parallel PIN diodes to generate two current signals with opposite phases, and then the two current signals are differentially processed, and finally the current and voltage output are converted by the transimpedance amplifier to obtain a voltage signal.

[0011] The third telescope comprises a Cassegrain optical telescope, the front end of which is a secondary mirror and the rear end is a primary mirror. When the returning light beam enters the telescope tube, the rear end primary mirror reflects the light beam and converges it on the secondary mirror. The secondary mirror reflects and converges the light beam again, and a pinhole diaphragm is installed at the focal position. A convex lens is arranged behind the diaphragm. The divergent light beam is collimated by the convex lens and then filtered out light of other wavelengths by an interference filter before being incident on a photomultiplier tube.

[0012] The present invention has the following advantages: a miniaturized three-dimensional dual-wavelength multifunctional laser radar device that can provide aircraft with efficient and accurate data such as wind field environment and aerosol concentration, provide important guidance and guarantee for aircraft take-off and landing and flight safety, and has the characteristics of high temporal and spatial resolution, light weight and small blind spots. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of the present invention; Figure 2 It is a schematic diagram of the balanced detector structure; Figure 3 This is a schematic diagram of the structure of the third telescope. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application provided below in conjunction with the drawings is not intended to limit the scope of protection of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. The present invention is further described below in conjunction with the drawings.

[0015] like Figure 1 As shown, the present invention specifically relates to a miniaturized three-dimensional dual-wavelength multifunctional laser radar device, which includes a host computer (PC), a digital signal processor, a servo system, a laser, a balanced detector, a telescope, a frequency multiplier and a photomultiplier tube (PMT), etc., to complete the reception and transmission of optical signals.

[0016] The laser radar uses optical fiber as the gain medium and can generate narrow-linewidth, high-power pulsed lasers. The 1550nm laser is divided into two paths by an optical coupler. One path generates a 775nm laser through double frequency. The laser of this wavelength is emitted into the atmosphere after beam expansion and collimation, and acts on the aerosol particles in the air to cause Mie scattering. Part of the scattered light signal enters the telescope 3. After focusing and collimation, the light beam is incident on the photomultiplier tube (PMT) to complete the photoelectric conversion process. The electrical signal is collected by the digital signal processor and uploaded to the host computer (PC) for calculation of related products such as backscattering coefficient, extinction coefficient and optical thickness.

[0017] The other path is 1550nm wavelength, which is injected into telescope 1 through an optical circulator. Telescope 1 expands and collimates the light beam and then emits it into the atmosphere. Due to the movement of aerosol particles, the light signal acting on the aerosol particles is superimposed with the Doppler frequency shift. Part of the backscattered light signal is mixed with the local oscillator light signal after passing through telescope 1 and the optical circulator. The output of the two optical signals introduces a 180° phase difference, and the photoelectric conversion is completed through the balanced detector (PD), and an 80MHz intermediate frequency electrical signal is output. The signal is collected by the digital signal processor and the power spectrum data is obtained through the fast Fourier transform (FFT), and then the radial wind speed of the aerosol particles is extracted. Due to the small size and light weight of aerosol particles, their movement in space reflects the atmospheric wind field. At the same time, the servo system can receive instructions from the host computer (PC) to realize rotation in azimuth and pitch directions, change the direction of the transmitting and receiving beams, and thus complete space scanning.

[0018] Furthermore, the optical circulator has a common port for receiving and transmitting, and can replace the transceiver switch to realize time-sharing application, reduce the switch conversion time, effectively reduce the detection blind area, and has the characteristics of low insertion loss and high isolation between channels.

[0019] Furthermore, the telescope 1 adopts a transmission structure, which is composed of an objective lens and an eyepiece. The divergent light beam can be expanded through the eyepiece and finally collimated by the objective lens before being emitted, and the same is true for receiving.

[0020] Furthermore, if Figure 2 As shown, the function of the laser radar balanced detector is to perform beat frequency and photoelectric conversion of the returned optical signal. It contains a fiber coupler, two pairs of analog PIN diodes and a transimpedance amplifier, and has the characteristics of large bandwidth, large dynamic range and high gain.

[0021] When the optical signal and the local oscillator signal (LO) enter the fiber coupler for beat frequency, two signals with a phase difference of 180° are output and incident on the photosensitive surfaces of two parallel PIN diodes respectively, generating two current signals with opposite phases. The two current signals are then differentially processed, which greatly improves the amplitude of the output signal and suppresses noise. Finally, the current and voltage output is converted through a transimpedance amplifier (TIA) to obtain a voltage signal, which greatly improves the sensitivity of the detector.

[0022] Furthermore, the telescope 2 adopts a Galilean structure, which expands and collimates the optical signal and then transmits it into the air, and has the advantages of low loss and small divergence angle.

[0023] Furthermore, if Figure 3As shown, the function of telescope 3 is to receive the optical signal emitted by the telescope into the air and scattered back. Telescope 3 is a Cassegrain optical telescope, with a secondary mirror at the front end and a primary mirror at the rear end. When the returning light beam enters the telescope tube, the primary mirror at the rear end reflects the light beam and converges it on the secondary mirror. The secondary mirror reflects and converges the light beam again. In order to reduce the interference light in the environment entering the photomultiplier tube, a small aperture diaphragm is installed at its focal position. While ensuring that the signal light passes completely, the aperture of the diaphragm is as small as possible to block the interference light in the environment to the greatest extent. The rear stage of the diaphragm is a convex lens, the purpose of which is to collimate the divergent light beam. The collimated light beam passes through the interference filter to filter out the light of other wavelength components, and the desired wavelength light signal is incident on the photomultiplier tube.

[0024] Furthermore, the interference filter uses a special process and multi-layer coating on the surface to reflect and interfere with light of different wavelengths, thereby interfering and enhancing the desired 775nm wavelength of light, while the remaining wavelengths of light are noise or interference signals and are reflected into the atmosphere.

[0025] Furthermore, the photomultiplier tube has high sensitivity and noise, and can achieve single photon level reception, so it can effectively improve the reception signal-to-noise ratio and sensitivity in this radar application. The photomultiplier tube mainly uses the photoelectric effect. When the photon passes through the incident window and enters the cathode, it excites the cathode to produce electrons. The electrons enter the electron multiplier under the attraction of the focusing electrode, achieving multi-stage electron multiplication. Finally, the anode collects and derives the current. The output current is further amplified by the transimpedance amplifier and the output voltage signal is collected by the digital signal processor.

[0026] Furthermore, the laser radar laser uses an all-fiber laser, which includes a seed light source, an acousto-optic modulator, a coupler, and an amplifier. The seed light source can generate a 1550nm narrow-linewidth laser source, which is divided into two paths through a 1*2 fiber coupler. One path is the local oscillator light signal for receiving the beat frequency; the other path is the excitation signal, which is pulse modulated by an acousto-optic modulator (AOM) and subjected to 80MHz frequency shift processing. The frequency-shifted signal is power amplified by EDFA. The amplified laser signal is again divided into two paths by the fiber coupler, one for frequency doubling processing and the other for transmission to the atmosphere by telescope 1.

[0027] The laser is controlled by serial port. The host computer sends instructions through the signal processor and then forwarded to the laser through the serial port. It can control control information such as pulse output energy and pulse width. At the same time, the laser has an external trigger interface. The signal processor generates a TTL level with a repetition frequency of 10KHz to achieve pulse repetition frequency control and acquisition synchronization.

[0028] Furthermore, the servo system consists of a motor, a reducer, an encoder, a power system, and a communication control board, and can provide low-ripple DC power for the optical transceiver components. The servo system adopts a two-dimensional structure design and can rotate in azimuth and pitch directions. The servo system has multiple observation modes including PPI, RPI, RHI, DBS, LOS, VAD, and custom scanning.

[0029] The servo motor has the advantages of high torque and high precision, which can ensure that the servo system is not affected in severe weather such as strong winds, and can withstand gusts of up to 50m / s. The servo system has a safety design. After power failure, the brake is rotated to prevent rotation due to gravity during transportation or maintenance, avoiding safety hazards. The servo system can be manually controlled by the host computer or external handle for easy maintenance.

[0030] Furthermore, the digital signal processor is responsible for collecting and processing the intermediate frequency signal output by the balanced detector and the voltage signal output by the photomultiplier tube, and outputting the processed data. The laser radar digital signal processor has dual-channel signal acquisition capabilities, a channel sampling bit of 14 bits, and a sampling frequency of up to 1GHz. Its main algorithm is the fast Fourier transform, which can convert the echo message into the frequency domain for Doppler frequency analysis and supports large overlap operations. The digital signal processor has the function of performing spectrum accumulation operations for the same position distance library under multiple working cycles, with a maximum accumulation number of more than 6000. After completing the spectrum processing, the processing results are transmitted to the host computer via Gigabit Ethernet.

[0031] The signal processor has RS422 / RS232 / TTL serial communication function. The communication interface supports the communication protocol of servo turntable, laser and other auxiliary equipment. It can send azimuth and pitch angle positioning, azimuth uniform speed scanning, azimuth fan scanning, pitch fan scanning and azimuth volume scanning functions to the servo turntable. At the same time, it can obtain the turntable azimuth and pitch angle information and other sensor information transferred by the servo turntable from the servo turntable. The feedback cycle interval is 20ms.

[0032] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used for various other combinations, modifications and improvements, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A miniaturized three-dimensional dual-wavelength multifunctional laser radar device, characterized in that: The device comprises a host computer, a digital signal processor, a laser, a first optical path module, a second optical path module and a scattered light collection module; The laser is configured to output two laser beams which enter the first optical path module and the second optical path module respectively. The second optical path module performs frequency doubling and beam expansion and collimation on the input laser beam and then emits the laser beam into the atmosphere, which acts on aerosol particles in the air to cause Mie scattering. The scattered light collection module collects the scattered light signal and completes the photoelectric conversion before inputting it into the digital signal processor. The digital signal processor uploads the signal to the host computer for product calculation. The first optical path module expands and collimates the input laser and then emits it into the atmosphere. At the same time, it collects the backscattered light signal superimposed with the Doppler shift, performs frequency mixing and signal photoelectric conversion, and then performs fast Fourier transform on the signal through a digital signal processor to obtain power spectrum data, thereby extracting the radial wind speed of the aerosol particles.

2. A miniaturized three-dimensional dual-wavelength multifunctional laser radar device according to claim 1, characterized in that: The device also includes a servo system, which receives instructions sent by a host computer to realize rotation in azimuth and elevation directions, change the direction of transmitting and receiving beams, and thus complete space scanning.

3. The miniaturized three-dimensional dual-wavelength multifunctional laser radar device according to claim 1, characterized in that: The second optical path module includes a frequency doubler, a second telescope and two reflectors. The wavelength of one laser is halved after passing through the frequency doubler, and then it is expanded and collimated by the second telescope and emitted into the atmosphere through two reflectors, acting on aerosol particles in the air to cause Mie scattering.

4. The miniaturized three-dimensional dual-wavelength multifunctional laser radar device according to claim 1, characterized in that: The scattered light collection module includes a third telescope, an interference filter and a photomultiplier tube. Part of the scattered light signal enters the third telescope and is focused and collimated, and then passes through the interference filter to be incident on the photomultiplier tube to complete the photoelectric conversion of the signal. The electrical signal is collected by the digital signal processor and uploaded to the host computer for calculation of backscattering coefficient, extinction coefficient and optical thickness related products.

5. The miniaturized three-dimensional dual-wavelength multifunctional laser radar device according to claim 1, characterized in that: The first optical path module includes an optical circulator, a balanced detector and a first telescope. The laser is injected into the first telescope through the optical circulator. The first telescope expands and collimates the light beam and then emits it into the atmosphere. Due to the movement of aerosol particles, the light signal acting on the aerosol particles is superimposed with the Doppler frequency shift. Part of the backscattered light signal is mixed with the local oscillator (LO) signal after passing through the first telescope and the optical circulator. A 180° phase difference is introduced when the two optical signals are output. After the signal is photoelectrically converted by the balanced detector, an intermediate frequency electrical signal is output, which is collected by a digital signal processor and then the power spectrum data is obtained through fast Fourier transform, thereby extracting the radial wind speed of the aerosol particles to reflect the atmospheric wind field conditions.

6. The miniaturized three-dimensional dual-wavelength multifunctional laser radar device according to claim 5, characterized in that: The first telescope includes a transmission structure consisting of an objective lens and an eyepiece. The incident divergent laser is expanded through the eyepiece and then collimated through the objective lens before being emitted.

7. The miniaturized three-dimensional dual-wavelength multifunctional laser radar device according to claim 5, characterized in that: The balanced detector includes an optical fiber coupler, two pairs of PIN diodes and a transimpedance amplifier; when the optical signal and the local oscillator signal (LO) enter the optical fiber coupler for beat frequency, two signals with a phase difference of 180° are output, which respectively enter the photosensitive surfaces of two parallel PIN diodes to generate two current signals with opposite phases, and then the two current signals are differentially processed, and finally the current and voltage output are converted by the transimpedance amplifier to obtain a voltage signal.

8. The miniaturized three-dimensional dual-wavelength multifunctional laser radar device according to claim 4, characterized in that: The third telescope comprises a Cassegrain optical telescope, the front end of which is a secondary mirror and the rear end is a primary mirror. When the returning light beam enters the telescope tube, the rear end primary mirror reflects the light beam and converges it on the secondary mirror. The secondary mirror reflects and converges the light beam again, and a pinhole diaphragm is installed at the focal position. A convex lens is arranged behind the diaphragm. The divergent light beam is collimated by the convex lens and then filtered out light of other wavelengths by an interference filter before being incident on a photomultiplier tube.

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