Miniaturized three-dimensional dual-wavelength multi-functional laser radar device

Abstract

The application 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 optical path module, a second optical path module and a scattered light collection module; two laser beams output by the laser enter the first optical path module and the second optical path module respectively, the second optical path module emits the input laser into the atmosphere after frequency doubling and beam expansion and collimation, the scattered light collection module collects scattered light signals, the scattered light signals are input to the digital signal processor after photoelectric conversion, and the digital signal processor is uploaded to the upper computer for product calculation; the first optical path module emits the input laser into the atmosphere after beam expansion and collimation, simultaneously collects backscattering light signals, mixes the backscattering light signals, carries out photoelectric conversion of the signals, and then carries out fast Fourier transform to obtain power spectrum data. The application can provide efficient and accurate wind field environment and aerosol concentration data for an aircraft, and provides important guidance and guarantee for take-off and landing and flight safety of the aircraft.

Description

TECHNICAL FIELD

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

[0002] In low-altitude economic applications, aircraft rely on good weather conditions and stable wind fields, but in actual situations, low-altitude wind fields are often unpredictable due to human activities or natural environments, especially in cities, where dense building groups have a great impact on regional wind field trends, often forming short-term adverse wind fields such as turbulence and shear, which pose a great threat to aircraft takeoff and landing. Therefore, how to provide efficient and accurate wind field environment and aerosol concentration data for aircraft to provide important guidance and protection for aircraft takeoff and flight safety is a problem that needs to be considered. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art and provides a miniaturized three-dimensional dual-wavelength multifunctional laser radar device that solves the deficiencies of the prior art.

[0004] The purpose of the present application is achieved by the following technical solution: 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;

[0005] The laser is configured to output two paths of laser into the first optical path module and the second optical path module, respectively, the second optical path module performs frequency doubling and beam expansion collimation on the input laser and emits it into the atmosphere, the Mie scattering occurs on the aerosol particles in the air, the scattered light collection module collects the scattered light signal and completes photoelectric conversion and inputs it to the digital signal processor, and the digital signal processor uploads to the host computer for product calculation;

[0006] The first optical path module performs beam expansion collimation on the input laser and emits it into the atmosphere, simultaneously collects the backscattered light signal superimposed with Doppler shift, and performs mixing and signal photoelectric conversion, then the signal is processed by the digital signal processor to obtain power spectrum data, and the radial wind speed of the aerosol particles is extracted.

[0007] The device further comprises a servo system that receives instructions issued by the host computer, realizes rotation in the azimuth and pitch directions, changes the pointing direction of the transmission and reception beams, and thus completes spatial scanning.

[0008] The second light path module comprises a frequency doubler, a second telescope and two mirrors, one way of laser passes through the frequency doubler to halve the wavelength, then passes through the second telescope to expand and collimate, and then is emitted into the atmosphere through the two mirrors to act on aerosol particles in the air to cause Mie scattering.

[0009] The scattering light collection module comprises a third telescope, an interference filter and a photomultiplier tube, part of the scattered light signal enters the third telescope to be focused and collimated, then passes through the interference filter to be incident into the photomultiplier tube to complete photoelectric conversion of the signal, and the electric signal is collected by a digital signal processor and uploaded to a host computer to calculate the backscattering coefficient, the extinction coefficient and the optical thickness related products.

[0010] The first light path module comprises an optical circulator, a balanced detector and a first telescope, laser is injected into the first telescope through the optical circulator, the first telescope expands and collimates the light beam to emit into the atmosphere, due to the movement of aerosol particles, the light signal acting on the aerosol particles is superimposed with a Doppler frequency shift, part of the backscattered light signal passes through the first telescope and the optical circulator, and then is mixed with a local oscillator (LO) signal, two light signals with a phase difference of 180° are introduced, an intermediate frequency electric signal is output after photoelectric conversion of the signal by the balanced detector, power spectrum data is obtained by fast Fourier transform after the electric signal is collected by a digital signal processor, and then the radial wind speed of the aerosol particles is extracted to reflect the atmospheric wind field.

[0011] The first telescope comprises a transmission type structure composed of an objective lens and an eyepiece, the incident divergent laser is expanded by the eyepiece and then collimated by the objective lens to be emitted.

[0012] The balanced detector comprises a fiber coupler, two pairs of PIN diodes and a transimpedance amplifier, when the optical signal and the local oscillator (LO) signal enter the fiber coupler to be frequency-mixed, two signals with a phase difference of 180° are output, enter the light-sensitive surfaces of two parallel PIN diodes respectively, two current signals with opposite phases are generated, the two current signals are processed by difference, and finally a voltage signal is obtained through current-voltage output conversion by the transimpedance amplifier.

[0013] The third telescope comprises a Cassegrain optical telescope, the front end of the Cassegrain optical telescope is a secondary mirror, and the rear end is a primary mirror, when the returned light beam is incident into the telescope barrel, the light beam is reflected and converged by the primary mirror at the rear end to the secondary mirror, the secondary mirror reflects and converges the light beam again, a pinhole diaphragm is installed at the focal point position, a convex lens is arranged at the rear of the diaphragm, the divergent light beam is collimated through the convex lens, other wavelengths of light are filtered out through the interference filter, and then the light is incident into the photomultiplier tube.

[0014] The application has the advantages that the miniaturized three-dimensional dual-wavelength multifunctional laser radar device can provide efficient and accurate wind field environment and aerosol concentration data for an aircraft, and provides important guidance and protection for the take-off and landing and flight safety of the aircraft, and has the characteristics of high space-time resolution, lightness and small blind area. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of the application;

[0016] Figure 2 It is a structural schematic diagram of the balanced detector;

[0017] Figure 3 It is a structural schematic diagram of the third telescope. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme of the embodiments of the application will be described clearly and completely below in combination with the drawings in the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, not all the embodiments. The components of the embodiments of the application described and shown in the drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the application provided in combination with the drawings is not intended to limit the protection scope of the claimed application, but only represents selected embodiments of the application. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the application. The application will be further described below in combination with the drawings.

[0019] As Figure 1 shown, the application specifically relates to a miniaturized three-dimensional dual-wavelength multifunctional laser radar device, which comprises a host computer (PC), a digital signal processor, a servo system, a laser, a balanced detector, a telescope, a frequency doubler and a photomultiplier tube (PMT) and the like, and completes the receiving and transmitting work of optical signals.

[0020] The laser radar takes an optical fiber as a gain medium, can produce narrow linewidth and high-power pulsed laser, and the 1550nm laser is divided into two paths by an optical coupler, one path generates 775nm laser through frequency doubling, the wavelength laser is emitted into the atmosphere after beam expansion and collimation, acts on aerosol particles in the air to cause Mie scattering, and part of the scattered light signal enters the telescope 3, the light beam enters the photomultiplier tube (PMT) after focusing and collimation, completes the photoelectric conversion process, and the electrical signal is collected by the digital signal processor and uploaded to the host computer (PC) to calculate the backscattering coefficient, extinction coefficient and optical thickness and the like.

[0021] Another path is 1550nm wavelength, which is injected into the telescope 1 through the optical circulator, the telescope 1 emits the light beam to the atmosphere after expanding and collimating, due to the movement of aerosol particles, the light signal acting on the aerosol particles is superimposed with a Doppler shift, part of the backscattered light signal is mixed with the local oscillator signal after passing through the telescope 1 and the optical circulator, two paths of light signals are introduced with a phase difference of 180°, 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 by fast Fourier transform (FFT), and then the radial wind speed of the aerosol particles is extracted. Because the aerosol particles are small in volume and light in mass, their movement in space reflects the atmospheric wind field. At the same time, the servo system can receive the instructions issued by the host computer (PC) to realize the rotation in the azimuth and elevation directions, change the pointing of the transmitting and receiving beams, and thus complete the space scanning.

[0022] Further, the optical circulator is a common port for receiving and transmitting, which can replace the transceiver switch to realize time-sharing application, reduce the switching time, effectively reduce the detection blind area, and has the characteristics of low insertion loss and high channel isolation.

[0023] Further, the telescope 1 adopts a transmission structure composed of an objective lens and an eyepiece, which can expand the divergent light beam through the eyepiece and then emit it after collimation by the objective lens. The receiving is the same.

[0024] Further, as shown in Figure 2 The laser radar balanced detector functions to perform frequency mixing and photoelectric conversion of the returned light signal, and internally includes 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.

[0025] When the optical signal and the local oscillator signal (LO) enter the fiber coupler for frequency mixing, two paths of signals with a phase difference of 180° are output, which are incident on the light-sensitive surfaces of the two parallel PIN diodes to generate two paths of current signals with opposite phases. Then, the two paths of current signals are processed by difference to greatly improve the amplitude of the output signal and suppress noise. Finally, the transimpedance amplifier (TIA) performs current-to-voltage output conversion to obtain a voltage signal, greatly improving the sensitivity of the detector.

[0026] Further, the telescope 2 adopts a Galilean structure to expand and collimate the light signal and then emit it to the air, which has the advantages of low loss and small divergence angle.

[0027] Further, as shown in Figure 3As shown, the telescope 3 functions to receive the light signal emitted by the telescope into the air and scattered back, the telescope 3 is a Cassegrain optical telescope, the front end is a secondary mirror, and the rear end is a primary mirror. When the returned light beam is incident into the telescope barrel, the light beam is reflected and converged by the rear end primary mirror to the secondary mirror. The secondary mirror reflects and converges the light beam again. In order to reduce the interference light in the environment from entering the photomultiplier tube, a small aperture diaphragm is installed at the focal point position. The diaphragm has a small light transmission hole as much as possible to ensure that the signal light can pass through completely and to block the interference light in the environment to the maximum extent. The rear stage of the diaphragm is a convex lens, which is used to collimate the divergent light beam. The collimated light beam passes through an interference filter to filter out light of other wavelengths. The light signal of the desired wavelength is incident into the photomultiplier tube.

[0028] Further, the interference filter is coated with multiple layers of film on the surface by a special process, so that the light of different wavelengths is reflected and interfered. The light of the desired 775nm wavelength is interfered and enhanced, and the light of the remaining wavelengths is noise or interference signal, which is reflected into the atmosphere.

[0029] Further, the photomultiplier tube has high sensitivity and noise, and can realize single-photon-level reception, so that the signal-to-noise ratio and sensitivity of the radar application can be effectively improved. The photomultiplier tube mainly uses photoelectric effect. When a photon passes through the incident window and is incident on the cathode, the cathode is excited to generate electrons. The electrons enter the electron multiplication electrode under the attraction of the focusing electrode, realize multi-stage electron multiplication, and finally are collected by the anode to form a current. The output current is further amplified by a transimpedance amplifier and outputs a voltage signal which is collected by a digital signal processor.

[0030] Further, the laser radar laser adopts an all-fiber laser. The laser 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. The laser source is divided into two paths by a 1*2 optical fiber coupler. One path is a local oscillator signal for receiving frequency mixing, and the other path is an excitation signal which is pulse-modulated by an acousto-optic modulator (AOM) and is subjected to 80MHz frequency shift processing. The frequency-shifted signal is then power amplified by an EDFA. The amplified laser signal is again divided into two paths by an optical fiber coupler. One path is subjected to frequency doubling processing, and the other path is emitted into the atmosphere by the telescope 1.

[0031] The laser control mode is serial port control. The host computer transmits instructions through the signal processor and then transmits them to the laser through the serial port. The control information such as pulse output energy and pulse width can be controlled. At the same time, the laser has an external trigger interface. The signal processor generates a 10KHz repetition frequency TTL level to realize pulse repetition frequency control and synchronization.

[0032] Further, the servo system is composed of a motor, a reducer, an encoder, a power supply system and a communication control board, and can provide low-ripple direct current power supply for the optical transceiver assembly, and the servo system adopts a two-dimensional structure design and can rotate in the azimuth and elevation directions. The servo system has multiple observation modes including PPI, RPI, RHI, DBS, LOS, VAD and self-defined scanning.

[0033] The servo motor has the advantages of large torque and high precision, can ensure that the servo system is not affected in severe weather such as strong wind, and can withstand a maximum gust of 50 m / s. The servo system has a safety design, and the rotating brake is applied after power failure to prevent rotation due to gravity during transportation or maintenance and to avoid safety hazards. The servo system can be manually controlled by a host computer or an external handle, which is convenient for maintenance.

[0034] Further, the digital signal processor is responsible for collecting and processing the intermediate frequency signals output by the balance detector and the voltage signals output by the photomultiplier tube, and outputs the processed data. The laser radar digital signal processor has a dual-channel signal acquisition capability, the channel sampling bit number is 14, and the sampling frequency can reach 1GHz. The main algorithm is fast Fourier transform, which can convert the echo message to the frequency domain for Doppler frequency analysis, and supports large overlap operation. The digital signal processor has a spectrum accumulation operation function for the same position distance library under multiple working periods, and the maximum accumulation number can reach more than 6000. After completing the spectrum processing, the processing result is transmitted to the host computer through the gigabit Ethernet.

[0035] The signal processor has RS422 / RS232 / TTL serial communication function, and the communication interface supports the communication protocol of the servo turntable, the laser and other auxiliary equipment. The azimuth angle and elevation angle positioning, azimuth angle uniform speed scanning, azimuth angle fan scanning, elevation angle fan scanning and azimuth body scanning functions can be sent to the servo turntable, and the azimuth angle, elevation angle and other sensor information of the servo turntable can be obtained from the servo turntable, and the return period interval is 20ms.

[0036] The above only describes the preferred embodiments of the present application, and it should be understood that the present application is not limited to the forms disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and improvements, and can be modified by the above-mentioned teaching or related technical or knowledge within the scope of the concept described herein. The modification and change made by the person skilled in the art without departing from the spirit and scope of the present application shall be within the protection scope of the appended claims of the present application.

Claims

1. A miniaturized three-dimensional dual-wavelength multi-functional lidar device, characterized by: 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 paths of laser into the first optical path module and the second optical path module respectively, the second optical path module emits the input laser into the atmosphere after frequency doubling and beam expansion collimation, Mie scattering occurs to aerosol particles in the air, the scattered light collection module collects the scattered light signal and completes photoelectric conversion to input into the digital signal processor, and the digital signal processor uploads to the host computer for product calculation; The first optical path module emits the input laser into the atmosphere after beam expansion collimation, simultaneously collects the backscattering light signal superimposed with Doppler shift, performs mixing and signal photoelectric conversion, then the signal is subjected to fast Fourier transform by the digital signal processor to obtain power spectrum data, and then the radial wind speed of the aerosol particles is extracted to reflect the atmospheric wind field.

2. The miniaturized three-dimensional dual-wavelength multi-functional lidar device according to claim 1, characterized in that: The device further comprises a servo system which receives the instructions issued by the host computer to realize rotation in the azimuth and elevation directions, changes the pointing of the transmitting and receiving beams, and thus completes spatial scanning.

3. The miniaturized three-dimensional dual-wavelength multi-functional lidar device according to claim 1, characterized in that: The second optical path module comprises a frequency doubling device, a second telescope and two mirrors, one path of laser is halved in wavelength after passing through the frequency doubling device, then is expanded and collimated by the second telescope, and is emitted into the atmosphere through the two mirrors to cause Mie scattering to aerosol particles in the air.

4. The miniaturized three-dimensional dual-wavelength multi-functional lidar device according to claim 1, characterized in that: The scattered light collection module comprises a third telescope, an interference filter and a photomultiplier tube, part of the scattered light signal enters the third telescope to be focused and collimated, then passes through the interference filter to be incident into the photomultiplier tube to complete signal photoelectric conversion, the electric signal is collected by the digital signal processor and uploaded to the host computer for product calculation of backscattering coefficient, extinction coefficient and optical thickness.

5. The miniaturized three-dimensional dual-wavelength multi-functional lidar device according to claim 1, characterized in that: The first optical path module comprises an optical circulator, a balanced detector and a first telescope, laser is injected into the first telescope through the optical circulator, the first telescope expands and collimates the light beam to emit into the atmosphere, due to the movement of aerosol particles, the light signal acting on the aerosol particles is superimposed with Doppler shift, part of the backscattering light signal is mixed with the local oscillator (LO) signal after passing through the first telescope and the optical circulator, two paths of light signals with a phase difference of 180° are output, an intermediate frequency electric signal is output after signal photoelectric conversion by the balanced detector, the power spectrum data is obtained by fast Fourier transform by the digital signal processor, and then the radial wind speed of the aerosol particles is extracted to reflect the atmospheric wind field.

6. The miniaturized three-dimensional dual-wavelength multi-functional lidar device according to claim 5, characterized in that: The first telescope comprises a transmission structure composed of an objective lens and an eyepiece, the incident divergent laser is expanded by the eyepiece and then collimated by the objective lens to be emitted.

7. The miniaturized three-dimensional dual-wavelength multi-functional lidar device according to claim 5, characterized in that: The balanced detector comprises a fiber coupler, two pairs of PIN diodes and a transimpedance amplifier; when the optical signal and the local oscillator (LO) signal enter the fiber coupler to be frequency-mixed, two paths of signals with a phase difference of 180° are output, enter the light-sensitive surfaces of two parallel PIN diodes respectively, two paths of current signals with opposite phases are generated, the two paths of current signals are processed by difference, and finally a voltage signal is obtained by output conversion of current and voltage by the transimpedance amplifier.

8. The miniaturized three-dimensional dual-wavelength multi-functional lidar 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 of which is a primary mirror, when the returned light beam is incident to the telescope barrel, the light beam is reflected and converged by the rear end primary mirror to the secondary mirror, the secondary mirror reflects and converges the light beam again, a pinhole diaphragm is installed at the focal point position, a convex lens is arranged at the rear stage position of the diaphragm, the divergent light beam is collimated through the convex lens, other wavelength light is filtered through an interference filter, and then the light beam is incident into a photomultiplier tube.

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