A continuous-wave lidar ranging device, system and working method combining coherent heterodyne with linear frequency modulation of laser intensity

Abstract

The present invention relates to the field of lidar ranging, and discloses a continuous-wave lidar ranging device, system and working method combining coherent heterodyne with linear frequency modulation of laser intensity. Circuit amplifier I and circuit amplifier II are both connected to a signal generator; a bias controller is connected to electro-optic modulator II, and electro-optic modulator II is connected to an optical fiber amplifier; electro-optic modulator I is respectively connected to an attenuator and a broadband linear frequency modulation source, and the broadband linear frequency modulation source is connected to electro-optic modulator II; the optical fiber amplifier is connected to transmitting and receiving lens I, and a dual-channel balanced detector is respectively connected to transmitting and receiving lens II and an AD acquisition card. It improves the all-weather adaptability of the system and at the same time improves the applicability of the payload platform. The coherent heterodyne combined working mode enables the system to measure the relative speed between the target and the system while measuring the distance, so as to predict the target position and improve the applicability of the system.

Description

Technical Field

[0001] The present invention relates to the field of lidar ranging, and specifically relates to a continuous wave lidar ranging device, system and working method combining coherent heterodyne with linear frequency modulation of laser intensity. Background Technique

[0002] An unmanned aerial vehicle is a powered, unmanned aerial vehicle that can carry a variety of mission equipment, can be remotely controlled or autonomously navigated, and can be reused, abbreviated as UAV (Unmanned Aerial Vehicle). The main guidance methods of UAVs are lidar, microwave radar, visible light cameras, etc., among which lidar is the mainstream solution.

[0003] As an extension of the radar concept, lidar uses laser for target detection and obtains information such as target distance, speed, and azimuth from the reflected light. Compared with microwave radar, lidar uses an optical signal with a shorter wavelength and has the advantages of good directivity, high spatial resolution, strong anti-interference ability, small size, and light weight. According to the different transmitted signals, lidar can be divided into two categories: pulsed lidar and continuous wave lidar. Pulsed lidar uses pulsed optical signals as detection signals and obtains target distance information by accurately measuring the flight time of reflected light pulses. The resolution of pulsed lidar is relatively reduced. To improve the range resolution, short pulses with low time delay jitter and ultrafast optoelectronic devices are required. At the same time, pulsed lidar generally uses direct detection to obtain echo signals and cannot perform Doppler velocity measurement; the relatively high pulsed power also poses requirements on device performance and eye safety.

[0004] Continuous wave lidar uses continuous optical signals as detection signals and has the characteristics of low peak power and high resolution. Specifically, continuous wave lidar can be further divided into phase lidar and frequency modulated continuous wave lidar. The former is based on phase laser ranging technology, uses a single-frequency signal to modulate the laser, and obtains the target distance information by phase discrimination of the reflected light signal. The disadvantage of this method is the existence of ambiguous distances, and the ranging range is limited by the modulation frequency. Frequency modulated continuous wave (FMCW) lidar combines the frequency modulated continuous wave ranging in modern radar technology with laser detection technology. This technology uses a linearly frequency modulated signal to modulate the laser and obtains the target distance information by comparing the instantaneous frequency difference between the reflected light signal and the local oscillator light signal. Frequency modulated continuous wave lidar has the following technical advantages: large ranging range; high range resolution; Doppler velocity measurement can be achieved; and it is conducive to on-chip integration.

[0005] There are two forms of loading linear frequency information into a laser, namely, a continuous-wave lidar with linear laser frequency modulation and a continuous-wave lidar with linear laser amplitude modulation. The continuous-wave lidar with linear laser amplitude modulation has advantages such as good linearity and simple structure, and can be applied to unmanned aircraft guidance. However, the current problem is that the amplitude modulation lidar can detect the speed of the target but cannot distinguish the moving direction of the target. In the case of an unmanned aircraft guiding to select and destroy a target, the transmission of the laser and the flight of the single unit require time, and the unmanned aircraft and the target are in a relative motion state. If the moving state of the target cannot be clearly known, it will have an error impact on the measurement of the current position of the target. Therefore, it is very important to be able to measure the position and moving state of the target in real time. Summary of the Invention

[0006] The present invention provides a continuous-wave lidar ranging device, system and its working method that combines coherent heterodyne with linear frequency modulation of laser intensity, which improves the all-weather adaptability of the system and at the same time improves the applicability of the payload platform.

[0007] The present invention is realized through the following technical solutions:

[0008] A continuous-wave lidar ranging device that combines coherent heterodyne with linear frequency modulation of laser intensity, the continuous-wave lidar ranging device includes a laser 1, an optical fiber beam splitter 2, an electro-optic frequency shifter 3, an electro-optic modulator 4, a bias controller 5, a circuit amplifier 6, a signal generator 7, an attenuator 8, a broadband linear frequency modulation source 9, an optical fiber amplifier 10, a transmitting and receiving lens 11, a dual-channel balanced detector 12, a beam combiner 13, an AD acquisition card 14 and a host computer 15;

[0009] The laser 1 is respectively connected to the optical fiber beam splitter 2 and the host computer 15, the optical fiber beam splitter 2 is respectively connected to the electro-optic frequency shifter 3 and the electro-optic modulator I4-1, the electro-optic frequency shifter 3 is respectively connected to the bias controller 5, the circuit amplifier I6-1 and the circuit amplifier II6-2, and both the circuit amplifier I6-1 and the circuit amplifier II6-2 are connected to the signal generator 7;

[0010] The bias controller 5 is connected to the electro-optic modulator II4-2, and the electro-optic modulator II4-2 is connected to the optical fiber amplifier 10;

[0011] The electro-optic modulator I4-1 is respectively connected to the attenuator 8 and the broadband linear frequency modulation source 9, the broadband linear frequency modulation source 9 is connected to the electro-optic modulator II4-2, and the attenuator 8 is connected to the dual-channel balanced detector 12;

[0012] The optical fiber amplifier 10 is connected to the transmitting and receiving lens I11-1, and the dual-channel balanced detector 12 is respectively connected to the transmitting and receiving lens II11-2 and the AD acquisition card 14;

[0013] The AD acquisition card 14 is connected to the host computer 15.

[0014] A continuous wave lidar ranging system that combines coherent heterodyning with linear frequency modulation of laser intensity. The continuous wave lidar ranging system includes a laser 1, an optical fiber beam splitter 2, an electro-optic frequency shifter 3, an electro-optic modulator 4, a bias controller 5, a circuit amplifier 6, a signal generator 7, an attenuator 8, a broadband linear frequency modulation source 9, an optical fiber amplifier 10, a transmitting and receiving lens 11, a dual-channel balanced detector 12, a beam combiner 13, an AD acquisition card 14, and a host computer 15;

[0015] The laser 1; serves as a laser seed source for emitting laser light;

[0016] The optical fiber beam splitter 2; is used to divide the laser into two paths to achieve separate modulation;

[0017] The electro-optic frequency shifter 3: is used to modulate an optical frequency; requires two radio frequency source signals, which are emitted by the signal generator 7, connected to drive the circuit amplifier 6 and then given to the electro-optic frequency shifter;

[0018] The electro-optic modulator 4; is used to achieve linear frequency modulation of laser intensity;

[0019] The bias controller 5 is used to control the DC bias current of the electro-optic frequency shifter; the laser passes through the controller and then outputs to the electro-optic modulator;

[0020] The circuit amplifier 6; is used to amplify the peak voltage of the radio frequency signal;

[0021] The signal generator 7; is used to generate radio frequency signals;

[0022] The attenuator 8; is used to attenuate the intensity amplitude of one path of laser light;

[0023] The broadband linear frequency modulation source 9; is used to generate a radio frequency signal with linear frequency modulation, and outputs it to the electro-optic modulator to modulate the laser intensity;

[0024] The optical fiber amplifier 10; is used to amplify the laser power;

[0025] The transmitting and receiving lens 11; the transmitting lens is used to emit laser light and adjust the laser emission beam divergence angle, and the receiving lens is used to receive the echo beam;

[0026] The dual-channel balanced detector 12; is used to detect optical signals and convert the optical signals into electrical signals,

[0027] The beam combiner 13 is used to combine two paths of laser light;

[0028] The AD acquisition card 14 is used to acquire electrical signals;

[0029] The host computer 15 is used to control the output of the laser on the one hand and process the acquired data on the other hand.

[0030] A continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity. The laser 1 is a 20 mW laser, a 1550 nm laser seed source; the electro-optic frequency shifter 3 is 100 MHz.

[0031] A continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity. The electrical signal transmission line of the continuous wave lidar ranging system includes an electro-optic frequency shifter, an electro-optic modulator I, an electro-optic modulator II, a radio frequency driver, a broadband linear frequency modulation source, a dual-channel balanced detector, and a data acquisition and processing unit;

[0032] The broadband linear frequency modulation source transmits electrical signals to the electro-optic modulator I and the electro-optic modulator II respectively,

[0033] The radio frequency driver transmits electrical signals to the electro-optic frequency shifter;

[0034] The dual-channel balanced detector transmits electrical signals to the data acquisition and processing unit.

[0035] A continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity. The optical fiber transmission line of the continuous wave lidar ranging system includes a laser seed source, an optical fiber beam splitter, an electro-optic frequency shifter, an electro-optic modulator I, an electro-optic modulator II, an optical fiber amplifier, a collimator I, a collimator II, a beam combiner, a beam expander I, a beam expander II, and a dual-channel balanced detector;

[0036] The laser seed source transmits optical signals to the electro-optic frequency shifter and the electro-optic modulator I respectively through the optical fiber beam splitter. The electro-optic frequency shifter transmits the optical signal to the electro-optic modulator II. The electro-optic modulator II transmits the optical fiber signal to the optical fiber amplifier. The optical fiber amplifier transmits the optical signal to the target through the collimator I and the beam expander I,

[0037] The beam expander II receives the optical signal returned by the target and transmits it to the dual-channel balanced detector through the collimator II and the beam combiner. The electro-optic modulator I transmits the optical signal to the dual-channel balanced detector through the beam combiner.

[0038] A continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity. Both the beam expander I and the beam expander II are 20-fold near-infrared broadband beam expander lenses of Edmond, with a field of view angle of 0.038° and a receiving aperture diameter of 33 mm;

[0039] The dual-channel balanced detector is a Thorlabs dual-channel balanced detector, model PDB480C-AC.

[0040] A working method of a continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity. The seed source outputs the master oscillator light and the local oscillator light. After modulation and amplification, the master oscillator light is irradiated onto the target through a circulator and a transmitting optical system. The echo signal is coupled into the circulator through the original path, and then coupled with the local oscillator light through a coupler. After the intermediate frequency signal is detected by a dual-channel balanced detector that can improve the signal-to-noise ratio, data acquisition is performed using an AD sampling card. Finally, the upper computer processes the data.

[0041] A working method of a continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity

[0042] The detectable intermediate frequency signal formula after demodulation is as follows.

[0043]

[0044]

[0045]

[0046]

[0047] In the formula, A L and A S respectively represent the amplitudes of the master and local oscillator light fields, m represents the modulation depth of the electro-optic modulator, f0 represents the initial frequency of the amplitude linear frequency modulation, τ represents the time required for the master oscillator light to travel from hitting the target to mixing with the local oscillator light, B represents the bandwidth of the amplitude linear frequency modulation, T represents the time of the linear frequency modulation, f represents the optical frequency, f d represents the frequency shift value of the electro-optic frequency shifter, and Δf d is the frequency shift value caused by the relative motion speed;

[0048] It can be seen from formula (4) that after adding a frequency shift device, there are three frequency components in the detected signal, which are respectively and (f d +Δf d ), where the frequency of the intermediate frequency signal is

[0049]

[0050] A working method of a continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity. According to the time-of-flight principle, the expression of the intermediate frequency signal corresponding to the distance R is:

[0051] R = c × τ (5)

[0052] where c is the speed of light; and the time τ is equal to:

[0053]

[0054] Therefore, the expression for the distance is represented as:

[0055]

[0056] As can be seen from the above, the relative motion speed between the target and the platform can be obtained by analyzing the signal frequency value:

[0057] v1 = λ × Δf d (8)

[0058] where λ is the wavelength of the light source, and the platform speed is known, denoted as v2. Therefore, the target speed v3 is obtained from v1 - v2.

[0059] A working method of a continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity. Assuming the moving speed of the projectile is v3 and the distance between the target and the platform is known as R, the position error at this time is expressed as:

[0060]

[0061] It can be deduced from the above formula (9) that by demodulating the distance information and speed information in the echo, the target position judgment error caused by the relative speed between the target and the platform can be eliminated;

[0062] It can be known from formula (7) that the ranging accuracy is expressed as:

[0063]

[0064] The beneficial effects of the present invention are:

[0065] Under the constraint of miniaturized volume, the spatial position arrangement and corresponding structural relationship of components such as the seed source, electro-optic modulator, electro-optic frequency shifter, fiber amplifier, circulator, coupler, transceiver optical system, detector, AD acquisition card, secondary power supply, etc. are the key to optimizing the space of the system.

[0066] In the laser intensity amplitude linear frequency modulation system of the present invention, a light frequency shifting device is added, so that an average operation is performed in one measurement, which can effectively reduce the influence of the "fence effect".

[0067] In the system of the present invention, a frequency shifting device is added, which can judge the relative motion state between the target and the platform, thereby eliminating the position information deviation caused by the target motion and realizing real-time calibration of the target information.

[0068] The present invention uses modern spectral analysis methods to analyze data spectral information, improve the frequency discrimination accuracy, and thus effectively increase the range resolution.

[0069] The present invention uses a scheme combining a narrow linewidth laser and an amplifier, effectively improving the detection range.

[0070] The optical effective calibration and maintaining the optical and mechanical stability of the present invention are the prerequisites for the efficient and stable detection of the coherent detection system. The three-pull and three-top structure and the mechanical tensioning bracket are used in cooperation to achieve optical calibration and structural stability.

[0071] The present invention adopts a scheme of heterodyne coherence combined with linear frequency modulation of laser intensity amplitude, and selects a short-wave infrared wavelength, which improves the all-weather adaptability of the system; it has high detection sensitivity, small volume, improves the applicability of the payload platform, and has the ability to be equipped on moving platforms such as unmanned aerial vehicles; combined with modern spectral analysis methods, it can effectively improve the range resolution and judge the target motion state, providing reliable information for target recognition, scene registration, etc. Description of the Drawings

[0072] Figure 1 is a schematic diagram of the system structure of the present invention.

[0073] Figure 2 is the mechanical model installation drawing of the present invention.

[0074] Figure 3 is the usage scenario diagram of the present invention, where Figure 3 -(a) Equipment scenario diagram, Figure 3 -(b) Target position diagram. Detailed Embodiments

[0075] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0076] A continuous wave lidar ranging device combining heterodyne coherence and linear frequency modulation of laser intensity, the continuous wave lidar ranging device includes a laser 1, an optical fiber beam splitter 2, an electro-optic frequency shifter 3, an electro-optic modulator 4, a bias controller 5, a circuit amplifier 6, a signal generator 7, an attenuator 8, a broadband linear frequency modulation source 9, an optical fiber amplifier 10, a transmitting and receiving lens 11, a dual-channel balanced detector 12, a beam combiner 13, an AD acquisition card 14, and a host computer 15;

[0077] The laser 1 is respectively connected to the optical fiber splitter 2 and the host computer 15. The optical fiber splitter 2 is respectively connected to the electro-optic frequency shifter 3 and the electro-optic modulator I 4-1. The electro-optic frequency shifter 3 is respectively connected to the bias controller 5, the circuit amplifier I 6-1 and the circuit amplifier II 6-2. Both the circuit amplifier I 6-1 and the circuit amplifier II 6-2 are connected to the signal generator 7;

[0078] The bias controller 5 is connected to the electro-optic modulator II 4-2, and the electro-optic modulator II 4-2 is connected to the optical fiber amplifier 10;

[0079] The electro-optic modulator I 4-1 is respectively connected to the attenuator 8 and the broadband chirp source 9. The broadband chirp source 9 is connected to the electro-optic modulator II 4-2. The attenuator 8 is connected to the dual-channel balanced detector 12;

[0080] The optical fiber amplifier 10 is connected to the transmitting and receiving lens I 11-1. The dual-channel balanced detector 12 is respectively connected to the transmitting and receiving lens II 11-2 and the AD acquisition card 14;

[0081] The AD acquisition card 14 is connected to the host computer 15.

[0082] A continuous wave lidar ranging system combining coherent heterodyne and laser intensity linear frequency modulation. The continuous wave lidar ranging system includes a laser 1, an optical fiber splitter 2, an electro-optic frequency shifter 3, an electro-optic modulator 4, a bias controller 5, a circuit amplifier 6, a signal generator 7, an attenuator 8, a broadband chirp source 9, an optical fiber amplifier 10, a transmitting and receiving lens 11, a dual-channel balanced detector 12, a beam combiner 13, an AD acquisition card 14, and a host computer 15;

[0083] The laser 1; serves as a laser seed source for emitting laser;

[0084] The optical fiber splitter 2; is used to divide the laser into two paths to achieve separate modulation;

[0085] The electro-optic frequency shifter 3: is used to modulate an optical frequency; requires two RF source signals, which are emitted by the signal generator 7, connected to drive the circuit amplifier 6 and then given to the electro-optic frequency shifter;

[0086] The electro-optic modulator 4; is used to achieve laser intensity linear frequency modulation;

[0087] The bias controller 5, is used to control the DC bias current of the electro-optic frequency shifter; the laser outputs to the electro-optic modulator after passing through the controller;

[0088] The circuit amplifier 6; is used to amplify the peak voltage of the RF signal;

[0089] The signal generator 7; for generating radio frequency signals;

[0090] The attenuator 8; for attenuating the intensity amplitude of a laser beam;

[0091] The broadband linear frequency modulation source 9; for generating radio frequency signals with linearly frequency - modulated output to an electro - optic modulator to modulate the laser intensity;

[0092] The fiber amplifier 10; for amplifying the laser power;

[0093] The transmitting and receiving lens 11; the transmitting lens is for transmitting the laser and adjusting the divergence angle of the laser beam, and the receiving lens is for receiving the echo beam;

[0094] The dual - path balanced detector 12; for detecting optical signals and converting optical signals into electrical signals,

[0095] The beam combiner 13, for combining two laser beams;

[0096] The AD acquisition card 14; for acquiring electrical signals;

[0097] The host computer 15; on the one hand, for controlling the output of the laser, and on the other hand, for processing the acquired data.

[0098] A continuous - wave lidar ranging system combining coherent heterodyne and linear frequency - modulation of laser intensity, the laser 1 is a 20mW laser, a 1550nm laser seed source; the electro - optic frequency shifter 3 is 100MHz.

[0099] A continuous - wave lidar ranging system combining coherent heterodyne and linear frequency - modulation of laser intensity, the electrical signal transmission line of the continuous - wave lidar ranging system includes an electro - optic frequency shifter, an electro - optic modulator I, an electro - optic modulator II, a radio - frequency driver, a broadband linear frequency - modulation source, a dual - path balanced detector, and a data acquisition and processing unit;

[0100] The broadband linear frequency - modulation source transmits electrical signals to the electro - optic modulator I and the electro - optic modulator II respectively,

[0101] The radio - frequency driver transmits electrical signals to the electro - optic frequency shifter;

[0102] The dual - path balanced detector transmits electrical signals to the data acquisition and processing unit.

[0103] A continuous-wave lidar ranging system that combines coherent heterodyning with linear frequency modulation of laser intensity. The fiber-optic transmission line of the continuous-wave lidar ranging system includes a laser seed source, an optical fiber beam splitter, an electro-optic frequency shifter, an electro-optic modulator I, an electro-optic modulator II, an optical fiber amplifier, a collimator I, a collimator II, a beam combiner, a beam expander I, a beam expander II, and a dual-channel balanced detector.

[0104] The laser seed source transmits optical signals to the electro-optic frequency shifter and the electro-optic modulator I respectively through the optical fiber beam splitter. The electro-optic frequency shifter transmits the optical signal to the electro-optic modulator II. The electro-optic modulator II transmits the fiber-optic signal to the optical fiber amplifier. The optical fiber amplifier transmits the optical signal to the target through the collimator I and the beam expander I.

[0105] The beam expander II receives the optical signal returned from the target and transmits it to the dual-channel balanced detector through the collimator II and the beam combiner. The electro-optic modulator I transmits the optical signal to the dual-channel balanced detector through the beam combiner.

[0106] A continuous-wave lidar ranging system that combines coherent heterodyning with linear frequency modulation of laser intensity. Both the beam expander I and the beam expander II are Edmond's 20x near-infrared broadband beam expander lenses, with a field of view of 0.038° and a receiving aperture diameter of 33 mm.

[0107] The dual-channel balanced detector is a Thorlabs dual-channel balanced detector, model number PDB480C-AC.

[0108] A working method of a continuous-wave lidar ranging system that combines coherent heterodyning with linear frequency modulation of laser intensity. The seed source outputs a master oscillator light and a local oscillator light. The master oscillator light is modulated and amplified, and then irradiates the target through a circulator and a transmitting optical system. The echo signal is coupled into the circulator through the original path, and then coupled with the local oscillator light through a coupler. The intermediate-frequency signal is detected by a dual-channel balanced detector that can improve the signal-to-noise ratio, and data is collected using an AD sampling card. Finally, the upper computer processes the data.

[0109] A working method of a continuous-wave lidar ranging system that combines coherent heterodyning with linear frequency modulation of laser intensity.

[0110] The formula for the detectable intermediate-frequency signal after demodulation is as follows.

[0111]

[0112]

[0113]

[0114]

[0115] In the formula, A L and A S respectively represent the amplitude magnitudes of the master local oscillator optical field, m represents the modulation depth of the electro-optic modulator, f0 represents the initial frequency of the amplitude linear frequency modulation, τ represents the time required for the master oscillator light to reach the target and mix with the local oscillator light, B represents the bandwidth of the amplitude linear frequency modulation, T represents the time of the linear frequency modulation, f represents the optical frequency, and f d represents the frequency shift value of the electro-optic frequency shifter, and Δf d is the frequency shift value caused by the relative motion speed;

[0116] Formula (1) and formula (2) are respectively the field amplitude expressions of the master oscillator light and the local oscillator optical field, formula (3) is the square-law formula for the mixing of the master local oscillator light, and formula (4) is the field amplitude expression of the detected intermediate frequency signal after mixing;

[0117] It can be seen from formula (4) that after adding the frequency shift device, there are three frequency components in the detected signal, which are respectively and (f d +Δf d ). Among them, the frequency of the intermediate frequency signal is

[0118] A working method of a continuous wave lidar ranging system combining coherent heterodyne and laser intensity linear frequency modulation. According to the time-of-flight principle, the expression of the intermediate frequency signal corresponding to the distance R is:

[0119] R = c×τ (5)

[0120] where c is the speed of light; and the time τ is equal to:

[0121]

[0122] Therefore, the expression of the distance is:

[0123]

[0124] As can be seen from the above, the relative motion speed between the target and the platform can be obtained by analyzing the signal frequency value:

[0125] v1 = λ×Δf d (8)

[0126] where λ is the wavelength of the light source, and the platform speed is known, set as v2. Therefore, the target speed v3 is obtained from v1 - v2.

[0127] A working method of a continuous wave lidar ranging system combining coherent heterodyne with linear frequency modulation of laser intensity. Assume the moving speed of the projectile is v3, the distance between the target and the platform is known as R, and the position error at this time can be expressed as:

[0128]

[0129] It can be deduced from the above formula (9) that by demodulating the distance information and speed information in the echo, the target position judgment error caused by the relative speed between the target and the platform can be eliminated;

[0130] It can be known from formula (7) that the ranging accuracy is expressed as:

[0131]

[0132] As can be seen from the above, one way to improve the ranging accuracy is to increase the frequency modulation bandwidth B; another way is to improve the frequency discrimination accuracy δf IF . Compared with the classical spectral analysis method, the modern spectral analysis method can effectively improve the frequency discrimination accuracy because it is not restricted by the data window. Therefore, the modern spectral analysis method is used for processing in data analysis. To meet the requirement of long-distance detection, the output power of the fiber amplifier is 1 - 10 W, the line width of the laser is 5 kHz, the linear frequency modulation source has a bandwidth of 300 MHz, and the frequency modulation time is 1 ms.

[0133] According to Figure 1 the principle block diagram, the structure design of the FMCW lidar is completed. The specific module installation diagram is shown in Figure 2 as shown. Some devices in the whole system are integrated into a box with dimensions of 800 mm × 500 mm × 200 mm. Among them, the amplifier, signal generator, and upper computer are placed outside the system and are connected to the equipment outside the equipment mold during measurement.

[0134] FMCW lidar ranging results

[0135] Using this set of lidar ranging devices, an indoor ranging experiment was completed. The device diagram of the ranging system is shown in Figure (a) of the following figure, and the target position diagram is shown in Figure (b) of the following figure.

[0136] The actual distance of the target is calculated by the following formula,

[0137] L = R - Δσ (11)

[0138] where L is the standard distance value of the target, R is the ranging value, and Δσ is the standard error.

[0139] The distance value was measured using a ruler, and 5 measurement values are shown in the above table. The mean value represents the initial distance, and the standard error can be calculated as,

[0140]

[0141] where x i (where i = 1, 2, …, 5) represents the distance measured each time, is the mean value of the measurement.

[0142] Table 1 Distance Measured with a Ruler

[0143]

[0144] First, use a meter ruler to measure the target distance. Table 1 shows the distance measured with a ruler indoors. Substitute the data in the above table into formula (12), and it can be calculated that the standard error is 0.1 cm. The target moves 10 cm each time. Therefore, the several distances to be measured are 7.800 m, 7.899 m, 7.999 m, 8.099 m, 8.199 m, and 8.299 m. Analyze the data using the modern spectral analysis Burg method and the fast Fourier transform method respectively. It can be seen from formula (4) that the intermediate frequency signal will have three frequency components, and the frequency components related to the distance are half of the difference between the frequency values on the left and right sides of the frequency shift frequency value in the spectrum, that is, one average operation is performed in one measurement, which can effectively reduce the influence of the "fence effect". Combining with the method of modern spectral analysis, the ranging accuracy is effectively improved.

[0145] Process the data using the above method. Take 10 groups of data for each distance value, take the average value of the calculated distance values, compare with the standard distance, and calculate the root mean square error of the two methods. The analysis results of the fast Fourier transform are shown in Table 2 below, and the analysis results of the modern spectral analysis are shown in Table 3 below:

[0146] Table 2 Results of Processing Data by Fast Fourier Transform

[0147]

[0148]

[0149] It can be seen from the above two tables that under a 300 MHz bandwidth, using the fast Fourier transform method can only resolve the distance of about 49 cm of the target movement, and using the modern spectral analysis method can effectively resolve the 10 cm of the target movement. Compared with the standard distance, its maximum error is about 1.6 cm, the minimum error is 0.4 cm, and the root mean square error is 1.024 cm. In summary, after adding a frequency shift device to the system, the modern spectral analysis method can effectively improve the ranging accuracy by 5 times.

[0150] Table 3 Results of Processing Data by Modern Spectral Analysis Method

[0151]

Claims

1. A continuous-wave lidar ranging system combining coherent heterodyne with linear frequency modulation of laser intensity, characterized in that, The continuous-wave lidar ranging system includes a laser (1), an optical fiber beam splitter (2), an electro-optic frequency shifter (3), an electro-optic modulator (4), a bias controller (5), a circuit amplifier (6), a signal generator (7), an attenuator (8), a broadband chirp source (9), an optical fiber amplifier (10), a transmitting and receiving lens (11), a dual-channel balanced detector (12), a beam combiner (13), an AD acquisition card (14), and a host computer (15); The laser (1); serves as a laser seed source for emitting laser; The optical fiber beam splitter (2); is used to divide the laser into two paths for separate modulation; The electro-optic frequency shifter (3): is used to modulate an optical frequency; two RF source signals are required, and the RF source signals are emitted by the signal generator (7), connected to drive the circuit amplifier (6) and then given to the electro-optic frequency shifter; The electro-optic modulator (4); is used to achieve linear chirp modulation of the laser intensity; The bias controller (5), which is used to control the DC bias current of the electro-optic frequency shifter; the laser outputs to the electro-optic modulator after passing through the controller; The circuit amplifier (6); is used to amplify the peak voltage of the RF signal; The signal generator (7); is used to generate RF signals; The attenuator (8); is used to attenuate the intensity amplitude of one path of the laser; The broadband chirp source (9); is used to generate an RF signal with linearly modulated frequency, and outputs it to the electro-optic modulator to modulate the laser intensity; The optical fiber amplifier (10); is used to amplify the laser power; The transmitting and receiving lens (11); the transmitting lens is used to emit laser and adjust the beam divergence angle of the laser emission, and the receiving lens is used to receive the echo beam; The dual-channel balanced detector (12); is used to detect optical signals and convert the optical signals into electrical signals, The beam combiner (13), which is used to combine two paths of laser; The AD acquisition card (14); is used to acquire electrical signals; The host computer (15); on the one hand, it is used to control the output of the laser, and on the other hand, it is used to process the acquired data; The laser (1) is respectively connected to the optical fiber beam splitter (2) and the host computer (15), the optical fiber beam splitter (2) is respectively connected to the electro-optic frequency shifter (3) and the electro-optic modulator I (4-1), the electro-optic frequency shifter (3) is respectively connected to the bias controller (5), the circuit amplifier I (6-1) and the circuit amplifier II (6-2), and both the circuit amplifier I (6-1) and the circuit amplifier II (6-2) are connected to the signal generator (7); The bias controller (5) is connected to the electro-optic modulator II (4-2), and the electro-optic modulator II (4-2) is connected to the optical fiber amplifier (10); The electro-optic modulator I (4-1) is respectively connected to the attenuator (8) and the broadband chirp source (9), the broadband chirp source (9) is connected to the electro-optic modulator II (4-2), and the attenuator (8) is connected to the dual-channel balanced detector (12); The fiber optic amplifier (10) is connected to the transmitting and receiving lens I (11-1), and the dual-channel balanced detector (12) is respectively connected to the transmitting and receiving lens II (11-2) and the AD acquisition card (14); The AD acquisition card (14) is connected to the host computer (15).

2. The continuous wave lidar ranging system according to claim 1, wherein The laser (1) is a 20mW laser, a 1550nm laser seed source; the electro-optic frequency shifter (3) is 100MHz.

3. The continuous wave lidar ranging system according to claim 1, wherein The electrical signal transmission line of the continuous wave lidar ranging system includes an electro-optic frequency shifter, an electro-optic modulator I, an electro-optic modulator II, a radio frequency driver, a broadband linear frequency modulation source, a dual-channel balanced detector, and a data acquisition and processing unit; The broadband linear frequency modulation source transmits electrical signals to the electro-optic modulator I and the electro-optic modulator II respectively, The radio frequency driver transmits electrical signals to the electro-optic frequency shifter; The dual-channel balanced detector transmits electrical signals to the data acquisition and processing unit.

4. The continuous wave lidar ranging system according to claim 1, characterized in that, The fiber optic transmission line of the continuous wave lidar ranging system includes a laser seed source, a fiber optic beam splitter, an electro-optic frequency shifter, an electro-optic modulator I, an electro-optic modulator II, a fiber optic amplifier, a collimator I, a collimator II, a beam combiner, a beam expander I, a beam expander II, and a dual-channel balanced detector; The laser seed source transmits optical signals to the electro-optic frequency shifter and the electro-optic modulator I respectively through the fiber optic beam splitter, the electro-optic frequency shifter transmits the optical signal to the electro-optic modulator II, the electro-optic modulator II transmits the fiber optic signal to the fiber optic amplifier, and the fiber optic amplifier transmits the optical signal to the target through the collimator I and the beam expander I, The beam expander II receives the optical signal returned by the target and transmits it to the dual-channel balanced detector through the collimator II and the beam combiner, and the electro-optic modulator I transmits the optical signal to the dual-channel balanced detector through the beam combiner.

5. The continuous wave lidar ranging system according to claim 4, characterized in that, Both the beam expander I and the beam expander II are 20-fold near-infrared broadband beam expander lenses of Edmond, with a field of view angle of 0.038° and a receiving aperture diameter of 33mm; The dual-channel balanced detector is a Thorlabs dual-channel balanced detector, model PDB480C-AC.

6. The working method of a continuous wave lidar ranging system combining coherent heterodyne with linear frequency modulation of laser intensity according to claim 1, characterized in that, The seed source outputs the local oscillator light and the main oscillator light; the main oscillator light is modulated and amplified, and then irradiates the target through the circulator and the transmitting optical system; the echo signal is coupled into the circulator through the original path, and then coupled with the local oscillator light through the coupler; after the intermediate frequency signal is detected by the dual-channel balanced detector that can improve the signal-to-noise ratio, data acquisition is performed using an AD sampling card; finally, the host computer processes the data.

7. According to the working method of the continuous wave lidar ranging system described in claim 6, it is characterized in that The formula for the detectable intermediate frequency signal after demodulation is as follows: （1） （2） （3） （4） In the formula, A L and A S respectively represent the amplitude magnitudes of the master local oscillator optical field, m represents the modulation depth of the electro-optic modulator, f 0 represents the initial frequency of the amplitude linear frequency modulation, τ represents the time required for the master oscillator light to travel from hitting the target to mixing with the local oscillator light, B represents the bandwidth of the amplitude linear frequency modulation, T represents the time of the linear frequency modulation, f represents the optical frequency, f d represents the frequency shift value of the electro-optic frequency shifter, is the frequency shift value caused by the relative motion speed; As can be seen from Equation (4), after adding the frequency shift device, there are three frequency components in the detected signal, namely , and . Among them, the frequency of the intermediate frequency signal is .

8. The working method of the continuous wave lidar ranging system according to claim 7, characterized in that, According to the time-of-flight principle, the distance R The expression of the corresponding intermediate-frequency signal is as follows: （5） wherein c is the speed of light; and time τ is further equal to: （6） Therefore, the expression of the distance is: （7） As can be seen from the above, the relative motion speed between the target and the platform can be obtained by analyzing the signal frequency value: （8） Among them is the wavelength of the light source, and the platform speed is known, denoted as v 2. Therefore, the target speed v 3 is obtained from v 1 - v 2.

9. The working method of the continuous wave lidar ranging system according to claim 8, characterized in that, Suppose the moving speed of the projectile is v 3, and the distance between the target and the platform is known to be R , and the position error at this time can be expressed as: （9） It can be deduced from the above formula (9) that by demodulating the distance information and speed information in the echo, the target position judgment error caused by the relative speed between the target and the platform can be eliminated; It can be known from formula (7) that the ranging accuracy is expressed as: （10）。

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