CN115097478A - Continuous wave laser radar ranging device and system combining coherent heterodyne with laser intensity linear frequency modulation and working method thereof - Google Patents

Abstract

The invention relates to the field of laser radar ranging, and discloses a continuous wave laser radar ranging device and system combining coherent heterodyne with laser intensity linear frequency modulation and a working method thereof. The circuit amplifier I and the circuit amplifier II are both connected with the signal generator; the bias controller is connected with an electro-optical modulator II, and the electro-optical modulator II is connected with the optical fiber amplifier; the electro-optical modulator I is respectively connected with the attenuator and the broadband linear frequency modulation source, and the broadband linear frequency modulation source is connected with the electro-optical modulator II; the optical fiber amplifier is connected with the transmitting and receiving lens I, and the double-path balance detector is respectively connected with the transmitting and receiving lens II and the AD acquisition card. The all-weather adaptability of the system is improved, and the applicability of the load platform is improved. The working mode of coherent heterodyne combination is adopted, so that the system can measure the relative speed between the target and the system while measuring the distance, thereby predicting the position of the target and improving the applicability of the system.

Description

A Continuous Wave Lidar Based on Coherent Heterodyne Combined with Laser Intensity Chirp Modulation Distance measuring device, system and working method thereof

technical field

The invention relates to the field of laser radar ranging, and in particular relates to a continuous wave laser radar ranging device, system and working method using coherent heterodyne combined with laser intensity linear frequency modulation modulation.

Background technique

In many application areas, autonomy is gradually replacing human labor to complete a variety of tasks. For example, autonomous machines in the military can perform some dangerous tasks, and autonomous devices in civilians can perform monotonous tasks such as surveillance and reconnaissance. These needs to replace human operation have promoted the development of autonomous system technology, and drones have emerged as the backbone of autonomous systems in the air. Unmanned aerial vehicle (UAV) is an unmanned aerial vehicle that is powered, can carry various mission equipment, can be controlled by remote control or autonomous navigation, and can be reused. The main methods of UAV guidance are lidar, microwave radar, visible light camera, etc., of which lidar is the mainstream solution.

As an extension of the radar concept, lidar uses lasers to detect targets and obtain target distance, speed, orientation and other information from reflected light. Compared with microwave radar, lidar uses optical signals with shorter wavelengths, which has the advantages of good directionality, high spatial resolution, strong anti-interference ability, small size and light weight. Depending on the transmitted signal, lidar can be divided into two categories: pulsed lidar and continuous wave lidar. Pulsed laser radar uses pulsed light 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 low. In order to improve the range resolution, short pulses with low 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; higher pulse power also puts forward requirements for device performance and human eye safety.

Continuous wave lidar uses continuous optical signal as detection signal, which has the characteristics of low peak power and high resolution. Specifically, continuous wave lidar can be divided into phased lidar and frequency-modulated continuous wave lidar. The former is based on the phase laser ranging technology, modulates the laser with a single frequency signal, and finally obtains the target distance information by performing phase discrimination on the reflected light signal. The disadvantage of this method is that there is an ambiguous distance, and the ranging range is limited by the modulation frequency. Frequency Modulated Continuous Wave (FMCW) LiDAR is a combination of FMCW ranging in modern radar technology and laser detection technology. The technology uses a chirp signal to modulate the laser, and obtains 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 speed measurement can be achieved; it is conducive to on-chip integration.

There are two forms of loading linear frequency information into the laser, which are divided into laser frequency linear modulation continuous wave lidar and laser amplitude linear modulation continuous wave lidar. Laser amplitude linear modulation continuous wave lidar has the advantages of good linearity and simple structure, and can be used in UAV guidance, but the current problem is that amplitude modulation lidar can detect the speed of the target, but cannot distinguish the target In the direction of movement, when the UAV guidance chooses to destroy the target, the transmission of the laser and the flight of the monomer take time, and the UAV and the target are in a state of relative motion. If the motion state of the target cannot be clearly known, it will cause an error in the measurement of the current position of the target. Therefore, it is very important to be able to measure the position and motion state of the target in real time.

SUMMARY OF THE INVENTION

The invention provides a continuous wave laser radar ranging device, system and working method with coherent heterodyne combined with laser intensity linear frequency modulation modulation, which improves the all-weather adaptability of the system and the applicability of the load platform.

The present invention is achieved through the following technical solutions:

A continuous wave laser radar ranging device with coherent heterodyne combined with laser intensity linear frequency modulation modulation, the continuous wave laser radar ranging device comprises a laser 1, an optical fiber beam splitter 2, an electro-optical frequency shifter 3, an electro-optical modulator 4, Bias voltage controller 5, circuit amplifier 6, signal generator 7, attenuator 8, broadband chirp source 9, fiber amplifier 10, transmitting and receiving lens 11, dual balanced detector 12, beam combiner 13, AD acquisition card 14 and the host computer 15;

The laser 1 is respectively connected with the optical fiber beam splitter 2 and the host computer 15, and the optical fiber beam splitter 2 is respectively connected with the electro-optical frequency shifter 3 and the electro-optical modulator 14-1, and the electro-optical frequency shifter 3 is respectively connected with the electro-optical frequency shifter 3. It is connected with the bias controller 5, the circuit amplifier I6-1 and the circuit amplifier II6-2, and the circuit amplifier I6-1 and the circuit amplifier II6-2 are both connected with the signal generator 7;

The bias controller 5 is connected with the electro-optical modulator II4-2, and the electro-optical modulator II4-2 is connected with the fiber amplifier 10;

The electro-optical modulator I4-1 is respectively connected with the attenuator 8 and the broadband chirp source 9, the broadband chirp source 9 is connected with the electro-optical modulator II4-2, and the attenuator 8 is connected with the two-way balanced detector. 12 connected;

The optical fiber amplifier 10 is connected with the transmitting and receiving lens I11-1, and the two-way balanced detector 12 is respectively connected with the transmitting and receiving lens II11-2 and the AD acquisition card 14;

The AD acquisition card 14 is connected with the host computer 15 .

A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity linear frequency modulation modulation, the continuous wave laser radar ranging system comprises a laser 1, an optical fiber beam splitter 2, an electro-optical frequency shifter 3, an electro-optical modulator 4, Bias voltage controller 5, circuit amplifier 6, signal generator 7, attenuator 8, broadband chirp source 9, fiber amplifier 10, transmitting and receiving lens 11, dual balanced detector 12, beam combiner 13, AD acquisition card 14 , host computer 15;

The laser 1; as a laser seed source, used for emitting laser light;

The optical fiber beam splitter 2 is used to divide the laser into two paths to realize separate modulation;

Described electro-optical frequency shifter 3: used to modulate one optical frequency; Two radio frequency source signals are required, and the radio frequency source signal is emitted by the signal generator 7, and is connected to the drive circuit amplifier 6 and then given to the electro-optical frequency shifter;

The electro-optical modulator 4; used to realize linear frequency modulation of laser intensity;

The bias voltage controller 5 is used to control the DC bias current of the electro-optical frequency shifter; the laser is output to the electro-optical modulator after passing through the controller;

The circuit amplifier 6; used to amplify the peak voltage of the radio frequency signal;

the signal generator 7; for generating radio frequency signals;

The attenuator 8; used to attenuate the intensity amplitude of one laser;

the broadband linear frequency modulation source 9; used to generate a frequency linearly modulated radio frequency signal, and output it to the electro-optical modulator, thereby modulating the laser intensity;

the fiber amplifier 10; used for amplifying laser power;

The transmitting and receiving lens 11; the transmitting lens is used for emitting laser light and adjusting the divergence angle of the laser beam, and the receiving lens is used for receiving the echo beam;

The two-way balanced detector 12 is used for detecting optical signals, converting the optical signals into electrical signals,

The beam combiner 13 is used to combine two laser beams;

The AD acquisition card 14; for acquiring electrical signals;

The upper computer 15 is used to control the laser output on the one hand, and to process the collected data on the other hand.

A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity chirp modulation, the laser 1 is a 20mW laser, a 1550nm laser seed source; the electro-optical frequency shifter 3 is 100MHz.

A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity linear frequency modulation modulation, the electrical signal transmission line of the continuous wave laser radar ranging system comprises an electro-optical frequency shifter, an electro-optical modulator I, an electro-optical modulator II, RF driver, broadband chirp source, dual balanced detector and data acquisition and processing unit;

The broadband chirp source transmits electrical signals to the electro-optical modulator I and the electro-optical modulator II, respectively,

the radio frequency driver transmits the electrical signal to the electro-optical frequency shifter;

The two-way balanced detector transmits electrical signals to the data acquisition and processing unit.

A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity linear frequency modulation modulation, the optical fiber transmission line of the continuous wave laser radar ranging system includes a laser seed source, a fiber beam splitter, an electro-optical frequency shifter, Electro-optical modulator I, electro-optical modulator II, fiber amplifier, collimator I, collimator II, beam combiner, beam expander I, beam expander II and dual balanced detectors;

The laser seed source transmits the optical signal to the electro-optical frequency shifter and the electro-optical modulator I respectively through the fiber beam splitter, the electro-optical frequency shifter transmits the optical signal to the electro-optical modulator II, and the electro-optical modulator II transmits the optical fiber to the optical fiber. The signal is transmitted to the fiber amplifier, which transmits the optical signal to the target through the collimator 1 and the beam expander 1,

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

A continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity, the beam expander I and beam expander II are Edmond's 20 times near-infrared broadband beam expander lenses, and the field of view is 0.038 °, the diameter of the receiving aperture is 33mm;

The dual-channel balanced detector is Thorlabs dual-channel balanced detector, the model is PDB480C-AC.

A working method of a continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity linear frequency modulation modulation, wherein the seed source outputs main oscillation light and local oscillation light; after the main oscillation light is modulated and amplified, it passes through a circulator and transmits The optical system illuminates the target; 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 a dual-channel balanced detector that can improve the signal-to-noise ratio, AD sampling is used The card is used for data collection; finally, the data is processed by the host computer.

A working method of a continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity chirp modulation,

The demodulated and detectable IF signal formula is shown below.

In the formula, A _L and A _S represent the amplitude of the main local oscillator light field, m represents the modulation depth of the electro-optical modulator, f ₀ represents the initial frequency of the amplitude chirp modulation, and τ represents the main vibration light from hitting the target to the The time required for local oscillator optical mixing, B is the bandwidth of amplitude chirp modulation, T is the time of chirp modulation, f is the optical frequency, f _d is the frequency shift value of the electro-optical frequency shifter, Δf _d is the relative motion speed The resulting frequency shift value;

和(f_d+Δf_d)，其中，中频信号的频率为It can be seen from formula (4) that after adding the frequency shifting device, the detected signal has 3 frequency components, which are

and (f _d +Δf _d ), where the frequency of the IF signal is

A working method of a continuous wave lidar ranging system with coherent heterodyne combined with laser intensity chirp modulation. According to the time-of-flight principle, the expression of the intermediate frequency signal corresponding to the distance R is:

R=c×τ (5)

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

So the expression for distance is expressed as:

It can be seen from the above that the relative motion speed of the target and the platform can be obtained by analyzing the signal frequency value:

v ₁ =λ×Δf _d (8)

Where λ is the wavelength of the light source, and the speed of the platform is known, which is set as v ₂ , so the target speed v ₃ is obtained from v ₁ -v ₂ .

A working method of continuous wave lidar ranging system with coherent heterodyne combined with laser intensity chirp modulation, assuming that the moving speed of the projectile is v ₃ , the distance between the target and the platform can be known as R, and the position error at this time can be expressed as :

It can be seen from the derivation of the above formula (9) that by demodulating the distance information and velocity information in the echo, the target position judgment error caused by the relative velocity between the target and the platform can be eliminated;

From formula (7), it can be known that the ranging accuracy is expressed as:

The beneficial effects of the present invention are:

Under the constraints of miniaturized volume, the present invention can arrange the spatial positions of components such as seed source, electro-optic modulator, electro-optic frequency shifter, optical fiber amplifier, circulator, coupler, transceiver optical system, detector, AD acquisition card, secondary power supply, etc. The layout and the corresponding structural relationship are the key to composing the optimal space of the system.

The laser intensity amplitude linear frequency modulation modulation system of the present invention adds an optical frequency shift device, so that an average operation is performed in one measurement, which can effectively reduce the influence of the "fence effect".

The frequency shifting device is added to the system of the present invention, 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.

The present invention uses the modern spectrum analysis method to analyze the data spectrum information, improves the frequency discrimination precision, and thus effectively increases the distance resolution.

The scheme of using the combination of the narrow linewidth laser and the amplifier of the present invention can effectively improve the detection distance.

Effective optical calibration and maintaining optical and mechanical stability of the present invention are the premise of efficient and stable detection of the coherent detection system.

The invention adopts the scheme of heterodyne coherence combined with laser intensity amplitude linear frequency modulation modulation, and selects short-wave infrared wavelength, which improves the all-weather adaptability of the system; the detection sensitivity is high, the volume is small, the applicability of the load platform is improved, and it is equipped with a straight UAV. It can effectively improve the distance resolution, judge the motion state of the target, and provide reliable information for target recognition and scene registration.

Description of drawings

FIG. 1 is a schematic diagram of the system structure of the present invention.

FIG. 2 is a drawing of the die assembly of the present invention.

Fig. 3 is a usage scene diagram of the present invention, wherein Fig. 3-(a) is a device scene diagram, and Fig. 3-(b) is a target position diagram.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of 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.

A continuous wave laser radar ranging device with coherent heterodyne combined with laser intensity linear frequency modulation modulation, the continuous wave laser radar ranging device comprises a laser 1, an optical fiber beam splitter 2, an electro-optical frequency shifter 3, an electro-optical modulator 4, Bias voltage controller 5, circuit amplifier 6, signal generator 7, attenuator 8, broadband chirp source 9, fiber amplifier 10, transmitting and receiving lens 11, dual balanced detector 12, beam combiner 13, AD acquisition card 14 and the host computer 15;

The laser 1 is respectively connected with the optical fiber beam splitter 2 and the host computer 15, and the optical fiber beam splitter 2 is respectively connected with the electro-optical frequency shifter 3 and the electro-optical modulator 14-1, and the electro-optical frequency shifter 3 is respectively connected with the electro-optical frequency shifter 3. It is connected with the bias controller 5, the circuit amplifier I6-1 and the circuit amplifier II6-2, and the circuit amplifier I6-1 and the circuit amplifier II6-2 are both connected with the signal generator 7;

The bias controller 5 is connected with the electro-optical modulator II4-2, and the electro-optical modulator II4-2 is connected with the fiber amplifier 10;

The electro-optical modulator I4-1 is respectively connected with the attenuator 8 and the broadband chirp source 9, the broadband chirp source 9 is connected with the electro-optical modulator II4-2, and the attenuator 8 is connected with the two-way balanced detector. 12 connected;

The optical fiber amplifier 10 is connected with the transmitting and receiving lens I11-1, and the two-way balanced detector 12 is respectively connected with the transmitting and receiving lens II11-2 and the AD acquisition card 14;

The AD acquisition card 14 is connected with the host computer 15 .

A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity linear frequency modulation modulation, the continuous wave laser radar ranging system comprises a laser 1, an optical fiber beam splitter 2, an electro-optical frequency shifter 3, an electro-optical modulator 4, Bias voltage controller 5, circuit amplifier 6, signal generator 7, attenuator 8, broadband chirp source 9, fiber amplifier 10, transmitting and receiving lens 11, dual balanced detector 12, beam combiner 13, AD acquisition card 14 , host computer 15;

The laser 1; as a laser seed source, used for emitting laser light;

The optical fiber beam splitter 2 is used to divide the laser into two paths to realize separate modulation;

Described electro-optical frequency shifter 3: used to modulate one optical frequency; Two radio frequency source signals are required, and the radio frequency source signal is emitted by the signal generator 7, and is connected to the drive circuit amplifier 6 and then given to the electro-optical frequency shifter;

The electro-optical modulator 4; used to realize linear frequency modulation of laser intensity;

The bias voltage controller 5 is used to control the DC bias current of the electro-optical frequency shifter; the laser is output to the electro-optical modulator after passing through the controller;

The circuit amplifier 6; used to amplify the peak voltage of the radio frequency signal;

the signal generator 7; for generating radio frequency signals;

The attenuator 8; used to attenuate the intensity amplitude of one laser;

the broadband linear frequency modulation source 9; used to generate a frequency linearly modulated radio frequency signal, and output it to the electro-optical modulator, thereby modulating the laser intensity;

the fiber amplifier 10; used for amplifying laser power;

The transmitting and receiving lens 11; the transmitting lens is used for emitting laser light and adjusting the divergence angle of the laser beam, and the receiving lens is used for receiving the echo beam;

The two-way balanced detector 12 is used for detecting optical signals, converting the optical signals into electrical signals,

The beam combiner 13 is used to combine two laser beams;

The AD acquisition card 14; for acquiring electrical signals;

The upper computer 15 is used to control the laser output on the one hand, and to process the collected data on the other hand.

A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity chirp modulation, the laser 1 is a 20mW laser, a 1550nm laser seed source; the electro-optical frequency shifter 3 is 100MHz.

A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity linear frequency modulation modulation, the electrical signal transmission line of the continuous wave laser radar ranging system comprises an electro-optical frequency shifter, an electro-optical modulator I, an electro-optical modulator II, RF driver, broadband chirp source, dual balanced detector and data acquisition and processing unit;

The broadband chirp source transmits electrical signals to the electro-optical modulator I and the electro-optical modulator II, respectively,

the radio frequency driver transmits the electrical signal to the electro-optical frequency shifter;

The two-way balanced detector transmits electrical signals to the data acquisition and processing unit.

A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity linear frequency modulation modulation, the optical fiber transmission line of the continuous wave laser radar ranging system includes a laser seed source, a fiber beam splitter, an electro-optical frequency shifter, Electro-optical modulator I, electro-optical modulator II, fiber amplifier, collimator I, collimator II, beam combiner, beam expander I, beam expander II and dual balanced detectors;

The laser seed source transmits the optical signal to the electro-optical frequency shifter and the electro-optical modulator I respectively through the fiber beam splitter, the electro-optical frequency shifter transmits the optical signal to the electro-optical modulator II, and the electro-optical modulator II transmits the optical fiber to the optical fiber. The signal is transmitted to the fiber amplifier, which transmits the optical signal to the target through the collimator 1 and the beam expander 1,

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

A continuous wave lidar ranging system combining coherent heterodyne and linear frequency modulation of laser intensity, the beam expander I and beam expander II are Edmond's 20 times near-infrared broadband beam expander lenses, and the field of view is 0.038 °, the diameter of the receiving aperture is 33mm;

The dual-channel balanced detector is Thorlabs dual-channel balanced detector, the model is PDB480C-AC.

A working method of a continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity linear frequency modulation modulation, wherein the seed source outputs main oscillation light and local oscillation light; after the main oscillation light is modulated and amplified, it passes through a circulator and transmits The optical system illuminates the target; 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 a dual-channel balanced detector that can improve the signal-to-noise ratio, AD sampling is used The card is used for data collection; finally, the data is processed by the host computer.

A working method of a continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity chirp modulation,

The demodulated and detectable IF signal formula is shown below.

In the formula, A _L and A _S represent the amplitude of the main local oscillator light field, m represents the modulation depth of the electro-optical modulator, f ₀ represents the initial frequency of the amplitude chirp modulation, and τ represents the main vibration light from hitting the target to the The time required for local oscillator optical mixing, B is the bandwidth of amplitude chirp modulation, T is the time of chirp modulation, f is the optical frequency, f _d is the frequency shift value of the electro-optical frequency shifter, Δf _d is the relative motion speed The resulting frequency shift value;

Formula (1) and formula (2) are the field amplitude expressions of the main oscillator light and the local oscillator light field, respectively. The field amplitude expression of the detected IF signal;

和(f_d+Δf_d)，其中，中频信号的频率为

It can be seen from formula (4) that after adding the frequency shifting device, the detected signal has 3 frequency components, which are

and (f _d +Δf _d ), where the frequency of the IF signal is

A working method of a continuous wave lidar ranging system with coherent heterodyne combined with laser intensity chirp modulation. According to the time-of-flight principle, the expression of the intermediate frequency signal corresponding to the distance R is:

R=c×τ (5)

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

So the expression for distance is expressed as:

It can be seen from the above that the relative motion speed of the target and the platform can be obtained by analyzing the signal frequency value:

v ₁ =λ×Δf _d (8)

Where λ is the wavelength of the light source, and the speed of the platform is known, which is set as v ₂ , so the target speed v ₃ is obtained from v ₁ -v ₂ .

A working method of continuous wave lidar ranging system with coherent heterodyne combined with laser intensity chirp modulation, assuming that the moving speed of the projectile is v ₃ , the distance between the target and the platform can be known as R, and the position error at this time can be expressed as :

It can be seen from the derivation of the above formula (9) that by demodulating the distance information and velocity information in the echo, the target position judgment error caused by the relative velocity between the target and the platform can be eliminated;

From formula (7), it can be known that the ranging accuracy is expressed as:

It can be seen from the above that one of the methods to improve the ranging accuracy is to increase the frequency modulation bandwidth B; the other method 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 limited by the data window. Therefore, modern spectral analysis methods are used in data analysis. In order to achieve long-distance detection requirements, the output power of the fiber amplifier is 1-10W, the laser linewidth is 5kHz, the bandwidth of the linear frequency modulation source is 300MHz, and the frequency modulation time is 1ms.

According to the principle block diagram in Figure 1, the structural design of the FMCW lidar is completed, and the specific mold assembly diagram is shown in Figure 2. Part of the equipment in the whole system is integrated into a box of 800mm×500mm×200mm. Among them, the amplifier, signal generator, and upper computer are placed outside the system. When measuring, they are connected to the equipment from outside the equipment mold.

FMCW lidar ranging results

Using this set of lidar ranging device, the indoor ranging experiment was completed. The installation diagram of the ranging system is shown in figure (a) in the following figure, and the target position figure is shown in figure (b) in the figure below.

The target actual distance is calculated by the following formula,

L=R-Δσ (11)

Where L is the standard distance value of the target, R is the range value, and Δσ is the standard error.

Use a ruler to measure the distance value, and get 5 measurements as shown in the above table, the mean value represents the initial distance, and the standard error can be calculated as,

为测量的均值。where x _i (where i=1,2...5) represents the distance of each measurement,

is the mean value of the measurement.

Table 1 feet measure distance

First, use the meter ruler to measure the target distance. Table 1 is the indoor distance measuring ruler. Substitute the data in the above table into formula (12), and the calculation shows that the standard error is 0.1cm. The target moves 10cm each time, so it can be seen that the distances to be measured are 7.800m, 7.899m, 7.999m, 8.099m, 8.199m, and 8.299m. The data were analyzed 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 3 frequency components, and the frequency component related to the distance is half of the difference between the frequency values on the left and right sides of the frequency shift frequency value in the frequency spectrum, that is, an average operation is performed in one measurement. , which can effectively reduce the impact of the "fence effect". Combined with modern spectral analysis methods, the ranging accuracy can be effectively improved.

The above method was used to process the data, 10 groups of data were taken for each distance value, the calculated distance value was averaged, compared with the standard distance, and the root mean square error of the two methods was calculated. The fast Fourier transform analysis results are shown in Table 2 below, and the modern spectrum analysis results are shown in Table 3 below:

Table 2 Fast Fourier Transform processing data results

It can be seen from the above two tables that under the bandwidth of 300MHz, the fast Fourier transform method can only distinguish the distance of the target moving about 49cm, and the modern spectral analysis method can effectively distinguish the target moving 10cm. Compared with the standard distance, the maximum error is about 1.6cm, the minimum error is 0.4cm, and the root mean square error is 1.024cm. To sum up, after adding the frequency shifting device to the system, the modern spectrum analysis method can effectively improve the ranging accuracy by 5 times.

Table 3 Results of data processing by modern spectral analysis methods

Claims (10)

1. A continuous wave laser radar ranging device of coherent heterodyne combined with laser intensity linear frequency modulation modulation, it is characterized in that, described continuous wave laser radar ranging device comprises laser (1), optical fiber beam splitter (2), electro-optical Frequency shifter (3), electro-optical modulator (4), bias voltage controller (5), circuit amplifier (6), signal generator (7), attenuator (8), broadband chirp source (9), optical fiber an amplifier (10), a transmitting and receiving lens (11), a two-way balanced detector (12), a beam combiner (13), an AD acquisition card (14) and a host computer (15); The laser (1) is respectively connected with an optical fiber beam splitter (2) and a host computer (15), and the optical fiber beam splitter (2) is respectively connected with an electro-optical frequency shifter (3) and an electro-optical modulator I (4- 1) are connected, the electro-optical frequency shifter (3) is respectively connected with the bias controller (5), the circuit amplifier I (6-1) and the circuit amplifier II (6-2), the circuit amplifier I ( 6-1) and circuit amplifier II (6-2) are connected to the signal generator (7); The bias voltage controller (5) is connected with the electro-optical modulator II (4-2), and the electro-optical modulator II (4-2) is connected with the optical fiber amplifier (10); The electro-optical modulator I (4-1) is respectively connected with the attenuator (8) and the broadband chirp source (9), and the broadband chirp source (9) is connected with the electro-optical modulator II (4-2) , the attenuator (8) is connected with the dual-way balanced detector (12); The optical fiber amplifier (10) is connected with the transmitting and receiving lens I (11-1), and the two-way balanced detector (12) is respectively connected with the transmitting and receiving lens II (11-2) and the AD acquisition card (14) ; The AD acquisition card (14) is connected with the upper computer (15). 2. A continuous wave laser radar ranging system with coherent heterodyne combined with laser intensity chirp modulation, it is characterized in that, described continuous wave laser radar ranging system comprises laser (1), optical fiber beam splitter (2), electro-optical Frequency shifter (3), electro-optical modulator (4), bias voltage controller (5), circuit amplifier (6), signal generator (7), attenuator (8), broadband chirp source (9), optical fiber an amplifier (10), a transmitting and receiving lens (11), a two-way balanced detector (12), a beam combiner (13), an AD acquisition card (14), and a host computer (15); the laser (1); as a laser seed source, used for emitting laser light; The optical fiber beam splitter (2); used for dividing the laser into two paths to realize separate modulation; The electro-optical frequency shifter (3) is used to modulate one optical frequency; two radio frequency source signals are required, and the radio frequency source signals are emitted by the signal generator (7), which is connected to the drive circuit amplifier (6) and then supplied to the electro-optical frequency shifter; the electro-optic modulator (4); used for realizing laser intensity chirp modulation; The bias voltage controller (5) is used to control the DC bias current of the electro-optical frequency shifter; the laser is output to the electro-optical modulator after passing through the controller; the circuit amplifier (6); used for amplifying the peak voltage of the radio frequency signal; the signal generator (7); for generating radio frequency signals; the attenuator (8); used to attenuate the intensity amplitude of one laser; the broadband linear frequency modulation source (9); used for generating a frequency linearly modulated radio frequency signal, and outputting it to an electro-optical modulator, thereby modulating the laser intensity; the optical fiber amplifier (10); used for amplifying laser power; The transmitting and receiving lens (11); the transmitting lens is used for emitting laser light and adjusting the divergence angle of the laser beam, and the receiving lens is used for receiving the echo beam; The two-way balanced detector (12); used for detecting optical signals, converting the optical signals into electrical signals, The beam combiner (13) is used to combine two laser beams; the AD acquisition card (14); for acquiring electrical signals; The upper computer (15) is used to control the output of the laser on the one hand, and to process the collected data on the other hand. 3 . The continuous wave laser radar ranging system according to claim 2 , wherein the laser ( 1 ) is a 20 mW laser, a 1550 nm laser seed source; and the electro-optical frequency shifter ( 3 ) is 100 MHz. 4 . 4. The continuous wave laser radar ranging system according to claim 2, wherein the electrical signal transmission line of the continuous wave laser radar ranging system comprises an electro-optical frequency shifter, an electro-optical modulator I, and an electro-optical modulator II , RF driver, broadband chirp source, dual balanced detector and data acquisition and processing unit; The broadband chirp source transmits electrical signals to the electro-optical modulator I and the electro-optical modulator II, respectively, the radio frequency driver transmits the electrical signal to the electro-optical frequency shifter; The two-way balanced detector transmits electrical signals to the data acquisition and processing unit. 5. The continuous wave laser radar ranging system according to claim 2, wherein the optical fiber transmission line of the continuous wave laser radar ranging system comprises a laser seed source, a fiber beam splitter, an electro-optical frequency shifter , electro-optic modulator I, electro-optic modulator II, fiber amplifier, collimator I, collimator II, beam combiner, beam expander I, beam expander II and dual balanced detectors; The laser seed source transmits the optical signal to the electro-optical frequency shifter and the electro-optical modulator I respectively through the optical fiber beam splitter, the electro-optical frequency shifter transmits the optical signal to the electro-optical modulator II, and the electro-optical modulator II transmits the optical fiber to the optical fiber. The signal is transmitted to the fiber amplifier, which 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 two-way balanced detector through the collimator II and the beam combiner, and the electro-optical modulator I transmits the optical signal to the two-way balanced detector through the beam combiner device. 6. The continuous wave laser radar ranging system according to claim 5, wherein the beam expander I and the beam expander II are Edmond's 20 times near-infrared broadband beam expander lenses, and the field of view is 0.038°, the diameter of the receiving aperture is 33mm; The dual-channel balanced detector is Thorlabs dual-channel balanced detector, the model is PDB480C-AC. 7. the working method of the continuous wave laser radar ranging system of a kind of coherent heterodyne combined with laser intensity linear frequency modulation modulation according to claim 2, is characterized in that, described seed source outputs main oscillation light and local oscillation light; After the light is modulated and amplified, it is irradiated on the target through the circulator and the emission 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; the intermediate frequency signal can improve the signal-to-noise ratio After detection by the dual-channel balanced detector, AD sampling card is used for data acquisition; finally, the data is processed by the host computer. 8. The working method of the continuous wave lidar ranging system according to claim 7, wherein, The demodulated and detectable IF signal formula is shown below.

In the formula, A _L and A _S represent the amplitude of the main local oscillator light field, m represents the modulation depth of the electro-optical modulator, f ₀ represents the initial frequency of the amplitude chirp modulation, and τ represents the main vibration light from hitting the target to the The time required for local oscillator optical mixing, B is the bandwidth of amplitude chirp modulation, T is the time of chirp modulation, f is the optical frequency, f _d is the frequency shift value of the electro-optical frequency shifter, Δf _d is the relative motion speed The resulting frequency shift value; It can be seen from formula (4) that after adding the frequency shifting device, the detected signal has 3 frequency components, which are

and (f _d +Δf _d ), where the frequency of the IF signal is

9. The working method of the continuous wave laser radar ranging system according to claim 8, characterized in that, as can be seen from the time-of-flight principle, the expression of the intermediate frequency signal corresponding to the distance R is: R=c×τ (5) where c is the speed of light; and time τ is equal to:

So the expression for distance is expressed as:

It can be seen from the above that the relative motion speed of the target and the platform can be obtained by analyzing the signal frequency value: v ₁ =λ×Δf _d (8) Where λ is the wavelength of the light source, and the speed of the platform is known, which is set as v ₂ , so the target speed v ₃ is obtained from v ₁ -v ₂ . 10. The working method of the continuous wave lidar ranging system according to claim 9, characterized in that, assuming that the moving speed of the projectile body is v ₃ , the distance between the target and the platform can be known as R, and it can be known that the position error at this time is expressed as: for:

It can be seen from the derivation of the above formula (9) that by demodulating the distance information and velocity information in the echo, the target position judgment error caused by the relative velocity between the target and the platform can be eliminated; From formula (7), it can be known that the ranging accuracy is expressed as:

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