Coded Frequency Modulated Continuous Wave Ranging and Velocity Measuring Method Based on Focal Plane Switching Array

Abstract

The present invention discloses a coded frequency-modulated continuous wave ranging and velocity measurement method based on a focal plane switch array. The method of the present invention first applies frequency offsets with different shift amounts to the frequency-modulated continuous wave light source signal by means of an electro-optic modulator, and emits the coded frequency-modulated continuous wave light signals with different shift amounts as scanning light signals with different emission angles through the focal plane switch array. By coordinately controlling the one-to-one correspondence between the shift amount and the optical switch, the scanning angle information is encoded into the optical wave frequency parameter. The method of the present invention not only realizes the separation and asynchronous operation of the bistatic configuration of the receiver and the transmitter, thereby improving the flexibility, signal-to-noise ratio and detection speed of the system, but also can realize the high-precision measurement of multiple targets, and significantly improve the working efficiency and robustness of the lidar system in complex environments.

Description

Technical Field

[0001] The present invention relates to the technical field of lidar, and in particular to a ranging and velocity measurement method based on a focal plane switch array for frequency modulated continuous wave (FMCW). Background Art

[0002] Compared with microwave radar, lidar uses a laser with a shorter wavelength as the transmitted signal. The laser beam emitted by lidar has the advantages of a smaller divergence angle and better directivity, and can also achieve higher range resolution and angular resolution. Secondly, the laser has strong anti-interference ability, so the possibility of being interfered by external signals is extremely low. Based on these advantages of lidar, it can be applied in many fields. In the transportation field, lidar can be used as a speedometer, a locator, and an imager; in the field of atmospheric detection, lidar can be used to detect air quality and the thickness of the atmosphere; in the environment, lidar can be used to detect terrain and landforms; in driverless, lidar is called the "eyes of the car" and can replace humans to automatically identify routes. Compared with vision sensors, lidar has a long sensing distance, does not require depth algorithms, and is not affected by light, and is expected to become the mainstream application for L4 / L5 levels of intelligent driving.

[0003] Classified according to the scanning method, lidar can be divided into mechanical lidar, hybrid solid-state lidar, and all-solid-state lidar. Mechanical lidar is large in size, high in cost, and low in stability, and is gradually withdrawn from the mainstream market. Although the hybrid solid-state lidar reduces the cost to a certain extent, its reliability and scanning field of view still have certain limitations. The all-solid-state lidar based on a silicon-based optical chip is considered to be the ultimate solution for lidar, and the focal plane switch array (FPSA) uses a focal plane optical system similar to a camera to map each angle in the field of view to a pixel on the rear focal plane of the imaging lens, which is very conducive to large-scale integration.

[0004] According to the classification of ranging and velocity measurement methods, lidar can be divided into the time-of-flight measurement scheme and the frequency-modulated continuous-wave ranging scheme. The time-of-flight measurement scheme (Time of Flight, TOF) is one of the most widely used ranging methods in current lidar. Its working principle is to measure the time elapsed from the emission to the return of a laser pulse and calculate the distance to the target object in combination with the speed of light. The TOF scheme has the characteristics of simple implementation and wide application range, and performs excellently especially in medium and long-distance measurements. However, the TOF scheme has high requirements for time measurement accuracy, and in high-speed moving scenarios, the accuracy of distance measurement may be affected to a certain extent. In addition, the use of high-power pulsed lasers increases energy consumption and poses potential safety hazards to certain application scenarios. Compared with the TOF scheme, the frequency-modulated continuous-wave (FMCW) ranging scheme is a more advanced measurement method. It utilizes the frequency modulation characteristics of lasers and calculates the target distance by measuring the frequency difference between the reflected signal and the transmitted signal. At the same time, it can also accurately measure the target speed through the Doppler effect. The FMCW scheme has the advantages of high precision, high resolution, and low power consumption, and is particularly suitable for short-distance and high-precision application scenarios. In addition, the FMCW ranging scheme inherently has strong anti-interference ability and can avoid interference from ambient light or other lidar signals.

[0005] In the reported FPSA+FMCW lidar schemes, a single-base transceiver configuration is mostly adopted, where the transmitting end and the receiving end share the same optical path. During a single angle scanning cycle, this scheme must wait for the echo signal to be received and complete beat frequency extraction and signal demodulation before entering the next angle scanning cycle. There is still room for improvement in terms of detection speed and signal-to-noise ratio. Summary of the Invention

[0006] To solve the problems existing in the background technology, the object of the present invention is to provide a coded frequency-modulated continuous-wave ranging and velocity measurement method based on a focal plane switch array. This method synergistically controls the frequency shift amount of the frequency-modulated continuous-wave light source and the focal plane switch array, and encodes the scanning angle information of the emitted laser into the optical wave frequency parameters. At the receiving end of the lidar, three-dimensional space information and velocity information can be directly parsed from the frequency parameters of the echo signal through coherent detection, realizing 4D point cloud imaging. This technology allows for a bistatic configuration and asynchronous operation of the transmitting and receiving ends of the lidar, improving the flexibility, signal-to-noise ratio, and detection speed of the lidar system, and providing a new sensing solution for fields such as autonomous driving and intelligent robots.

[0007] The technical solution adopted by the present invention is:

[0008] I. A coded frequency-modulated continuous-wave ranging and velocity measurement method based on a focal plane switch array

[0009] The ranging and velocity measuring method includes the following steps:

[0010] S1) Split the frequency-modulated continuous-wave light source signal with a triangular-wave frequency-time function to obtain a local oscillator light signal and an original light signal; the original light signal refers to an uncoded light signal without frequency shift applied.

[0011] Preferably, a laser is used to generate a narrow-bandwidth laser signal, and a single-sideband modulator is used to linearly frequency-modulate the narrow-bandwidth laser signal to generate a frequency-modulated continuous-wave light source signal with a triangular-wave frequency-time function; the narrow-bandwidth laser signal is a single-wavelength laser signal with a bandwidth less than 100 kHz.

[0012] S2) Apply different frequency shifts to the original light signal to obtain coded frequency-modulated continuous-wave light signals with different frequency shift amounts, and use a focal plane switch array to emit the coded frequency-modulated continuous-wave light signal with a specific frequency shift amount as a scanning light signal with a corresponding emission angle.

[0013] Specifically, the focal plane switch array serves as the transmitting end of the lidar.

[0014] Specifically, the focal plane switch array includes multiple optical switches, and the emission angles of the scanning light signals emitted through each optical switch are different; each optical switch corresponds to a frequency shift amount, and the frequency shift amounts corresponding to each optical switch are different.

[0015] Specifically, in step S2, within each scanning period, an electro-optic modulator is used to apply a specific frequency shift amount to the original light signal according to a radio frequency signal to obtain a coded frequency-modulated continuous-wave light signal, and at the same time, keep the optical switch corresponding to the frequency shift amount in the on state. The coded frequency-modulated continuous-wave light signal is emitted through the corresponding optical switch as a scanning light signal with a corresponding emission angle.

[0016] Preferably, after the current scanning period ends, turn off the current optical switch and immediately turn on the next optical switch to enter the next scanning period. Since the present invention adopts bistatic reception, after the transmission ends, after turning off the current optical switch, the next optical switch can be directly turned on without delay in the middle, realizing continuous scanning.

[0017] Preferably, a unique position index is set for each optical switch, and the position indexes of the optical switches are arranged in sequence from 1 to N. The product of the position index number of the optical switch and a preset frequency shift step is set as the frequency shift amount corresponding to the optical switch, and the frequency shift step is 100 - 1000 MHz.

[0018] S3) Use a receiver to receive the echo light signal, mix the echo light signal with the local oscillator light signal to obtain a beat light signal;

[0019] Specifically, the receiver serves as the receiving end of the lidar.

[0020] Preferably, the receiver and the focal plane switch array are configured at different locations.

[0021] S4) Perform spectral analysis on the beat frequency optical signal to obtain the emission angle, the distance between the target object and the lidar, and the speed of the target object.

[0022] The specific steps of S4 are as follows:

[0023] S4.1) Obtain two beat frequency peaks of the beat frequency optical signal.

[0024] S4.2) Obtain the propagation delay time based on the two beat frequency peaks, and then obtain the distance between the target object and the lidar based on the propagation delay time.

[0025] Specifically, the following formula is used to process the two beat frequency peaks to obtain the propagation delay time:

[0026] t d =T(f b2 -f b1 ) / 4B

[0027] In the formula, t d is the propagation delay time, T is the modulation period of the frequency modulated continuous wave, f b1 is the beat frequency peak corresponding to the difference frequency at the rising edge of the triangular wave, f b2 is the beat frequency peak corresponding to the difference frequency at the falling edge of the triangular wave, and B is the modulation bandwidth of the frequency modulated continuous wave.

[0028] S4.3) Obtain the total frequency shift amount based on the two beat frequency peaks, and obtain the emission angle based on the total frequency shift amount; obtain the difference between the total frequency shift amount and the frequency shift amount to obtain the Doppler frequency shift, and obtain the speed of the target object based on the Doppler frequency shift.

[0029] Specifically, based on the two beat frequency peaks, the following formula is used to obtain the total frequency shift amount:

[0030] △f=(f b1 +f b2 ) / 2

[0031] In the formula, △f is the total frequency shift amount, f b1 is the beat frequency peak corresponding to the difference frequency at the rising edge of the triangular wave, f b2 is the beat frequency peak corresponding to the difference frequency at the falling edge of the triangular wave.

[0032] Specifically, the following formula is used to process the Doppler frequency shift to obtain the speed of the target object:

[0033] f d =2v / λ

[0034] where f d is the Doppler frequency shift caused by the velocity of the target object, v is the velocity of the target object, and λ is the wavelength of the optical signal emitted by the lidar.

[0035] In the process of obtaining the exit angle based on the total frequency shift amount, if the total frequency shift amount is between two adjacent frequency shift amounts of different magnitudes, the exit angle of the optical switch corresponding to the smaller frequency shift amount is used as the angle of the target object.

[0036] S4.4) Take each exit angle and the corresponding distance between the target object and the lidar and the velocity of the target object as a set of ranging and velocity measurement results.

[0037] Furthermore, the ranging and velocity measurement results can be used for lidar 4D point cloud imaging. Step S4 further includes: mapping each exit angle and the corresponding distance between the target object and the lidar and the velocity of the target object into a measurement point in 4D space, and the set of all measurement points forms a 4D lidar point cloud image.

[0038] II. A lidar applied to the above ranging and velocity measurement method

[0039] The lidar includes:

[0040] A frequency-modulated continuous wave generation module for generating a frequency-modulated continuous wave light source signal;

[0041] A radio frequency source for emitting a radio frequency signal;

[0042] A beam splitter for splitting the frequency-modulated continuous wave light source signal;

[0043] An electro-optic modulator for applying a frequency shift to the original optical signal according to the radio frequency signal to obtain a coded frequency-modulated continuous wave optical signal;

[0044] A focal plane switch array for acting as a transmitter to emit the coded frequency-modulated continuous wave optical signal with a specific frequency shift amount as a scanned optical signal with a corresponding exit angle;

[0045] A cooperative control module for cooperatively controlling the radio frequency signal and the power-on signal of the optical switch, so that within each scanning period, the radio frequency signal, the frequency shift amount of the coded frequency-modulated continuous wave optical signal, the optical switch, and the exit angle correspond one by one;

[0046] A receiver for acting as the receiving end of the lidar and receiving the backscattered optical signal; preferably configured at a different location from the focal plane switch array;

[0047] An optical coupler for mixing the backscattered optical signal and the local oscillator optical signal to obtain a beat optical signal;

[0048] A spectrum analysis module is used to perform spectrum analysis on the beat frequency optical signal to obtain the emission angle, the distance between the target object and the lidar, and the speed of the target object.

[0049] III. Application of a Lidar

[0050] The lidar can be used to generate a 4D lidar point cloud image.

[0051] The beneficial effects of the present invention are as follows:

[0052] 1. The present invention allows the transmitter and the receiver to be separated in a bistatic configuration, and can be flexibly arranged according to the needs of actual applications, enhancing the flexibility of the lidar system and being applicable to high-precision measurement scenarios such as autonomous driving, drone perception, and security monitoring.

[0053] 2. The present invention allows the operations of transmitting and receiving optical signals to be asynchronous. Angle, distance, and speed information can be extracted only through frequency-domain analysis of the signal at the receiving end, thereby realizing 4D point cloud imaging of the lidar, avoiding the complexity of synchronous operations in traditional systems, and improving the detection speed and signal-to-noise ratio of the lidar system.

[0054] 3. Since the present invention adopts bistatic reception, after the emission is completed, after closing the current optical switch, the next optical switch can be directly opened without delay in the middle, realizing continuous scanning. Description of the Drawings

[0055] Figure 1 is the framework diagram of the system of the present invention;

[0056] Figure 2 is the design schematic diagram of the one-dimensional focal plane switch array;

[0057] Figure 3 is the design schematic diagram of the two-dimensional focal plane switch array in the present invention;

[0058] Figure 4 is the schematic diagram of spectrum analysis in the method of the present invention; wherein, (a) is the frequency-time function of the frequency-modulated continuous-wave light source signal and the reflected light signal; (b) is the frequency-time function of the beat frequency signal;

[0059] Figure 5 is the simulation result of measurement point ① in the effect schematic diagram of the method of the present invention applied to the lidar system;

[0060] Figure 6 is the simulation result of measurement point ② in the effect schematic diagram of the method of the present invention applied to the lidar system;

[0061] Figure 7Schematic diagram of the effect of the method of the present invention applied to a lidar system; simulation result of measurement point ③

[0062] Figure 8 Schematic diagram of the principle of the method of the present invention applied to a lidar system Detailed implementation manners

[0063] The present invention will be further described below with reference to the accompanying drawings and embodiments

[0064] The method of the present invention applies different frequency offsets to the frequency-modulated continuous-wave light source signal by using an electro-optic modulator, performs frequency encoding on the optical signals emitted from each optical switch unit, and thus realizes frequency marking of the scanning angle of the emitted optical signal, that is, encodes the scanning angle information into the optical wave frequency parameters. The method of the present invention utilizes frequency-domain decoding technology to accurately extract the distance, speed, and angle information of the target from the received echo signal. At the same time, the present invention can realize the separation and asynchronous operation of the bistatic configuration of the receiver and the transmitter, thereby improving the flexibility, signal-to-noise ratio, and detection speed of the system. Generally speaking, the method of the present invention can realize 4D point cloud imaging of lidar and significantly improve the working efficiency and robustness of the lidar system in complex environments

[0065] The first aspect of the present invention provides a coded frequency-modulated continuous-wave ranging and velocity measurement method based on a focal plane switch array. The method of the present invention specifically includes the following steps

[0066] S1) Split a frequency-modulated continuous-wave light source signal with a frequency-time function of a triangular wave to obtain a local oscillator optical signal and an original optical signal

[0067] Optionally, using external modulation technology, a single-sideband modulator is used to linearly frequency-modulate a narrow-bandwidth laser signal generated by a laser to generate a frequency-modulated continuous-wave light source signal with a frequency-time function of a triangular wave

[0068] Preferably, the narrow-bandwidth laser signal is a single-wavelength laser signal with a bandwidth less than 100 kHz

[0069] Optionally, a beam splitter is used to split the frequency-modulated continuous-wave light source signal

[0070] Optionally, the frequency-modulated continuous-wave light source signal is split at a ratio of 1:99, 1% is used as the local oscillator optical signal for beat-frequency processing with the echo signal, and 99% is used as the original optical signal

[0071] S2) Apply frequency shifts of different frequencies to the original optical signal to obtain coded frequency-modulated continuous-wave optical signals with different frequency shift amounts, and use a focal plane switch array to emit the coded frequency-modulated continuous-wave optical signal with a specific frequency shift amount as a scanned optical signal with a corresponding emission angle. Specifically, the focal plane switch array is used as the transmitter of the lidar.

[0072] Specifically, the focal plane switch array and the receiver serve as the transmitting end and the receiving end of the lidar respectively, and the receiver is configured at a different location from the focal plane switch array.

[0073] Specifically, the emission angle is used to represent the emission direction of the scanned optical signal, and can be represented by the angle of the scanned optical signal relative to the principal optical axis of the convex lens in the focal plane switch array.

[0074] Specifically, the frequency shift amount refers to the frequency change amount when a frequency shift is applied to the original optical signal.

[0075] Specifically, the focal plane switch array includes a plurality of optical switches, and the emission angles of the scanned optical signals emitted by each optical switch are different from each other. Each optical switch corresponds to a frequency shift amount, and the frequency shift amounts corresponding to each optical switch are different from each other. Thus, by turning on the optical switch corresponding to the frequency shift amount of the coded frequency-modulated continuous-wave optical signal, the coded frequency-modulated continuous-wave optical signal can be emitted as a scanned optical signal with a corresponding emission angle through this optical switch. Furthermore, the present invention can combine the frequency offsets of different frequency shift amounts and the focal plane switch array to perform frequency coding on the scanned optical signals with different emission angles, realizing the frequency marking of the emission angle. It should be noted that the emission angles of the scanned optical signals of each optical switch unit are different from each other based on the structure of the optical switch array. The focal plane switch array usually includes a plurality of optical switch units arranged in an array. Each optical switch unit is mainly composed of an optical switch and a grating antenna. Each optical switch unit can be independently controlled to achieve energy concentration and angle scanning. When the optical switch is turned on, the incident light passes through the grating antenna and is emitted by the optical switch. Since the optical switch array is integrated on a silicon optical chip and placed at the rear focal plane of a convex lens, a scanned optical signal at a certain angle is necessarily generated every time an optical switch is turned on.

[0076] In step S2, the scanning process is usually continuous and can be divided into multiple scanning periods. During each scanning period, the focal plane switch array emits the coded frequency-modulated continuous-wave optical signal with a specific frequency shift amount as a scanned optical signal with a corresponding emission angle. Only one optical switch is turned on during each scanning period to output a scanned optical signal with a corresponding emission angle. For example, in the focal plane switch array, a unique position index i is set for each optical switch to represent its position in the array. In the current scanning period, the optical switch with the position index i is turned on, and a frequency shift of the frequency shift amount f i is applied to the original optical signal to obtain a coded frequency-modulated continuous-wave optical signal, and the coded frequency-modulated continuous-wave optical signal is emitted through this optical switch as a scanned optical signal with a corresponding emission angle θi The scanned optical signal. Each optical switch corresponds to a specific frequency shift amount f i , and the frequency shift amounts corresponding to each optical switch are different from each other. During the scanning process, the opening sequence of the optical switches is determined by an independent preset activation sequence, which stipulates the order in which the optical switches are activated in sequence. The position index of the optical switch is not necessarily the same as the opening sequence.

[0077] Preferably, within each scanning period, a radio frequency source is used to generate a radio frequency signal with a specific frequency, and an electro-optic modulator is used to apply a frequency shift to the original optical signal according to the frequency of the radio frequency signal to obtain a coded frequency-modulated continuous wave optical signal. The frequency shift amount of the coded frequency-modulated continuous wave optical signal is the same as the frequency of the radio frequency signal. At the same time, the optical switch corresponding to the frequency shift amount is kept in the open state, and the coded frequency-modulated continuous wave optical signal is emitted through the optical switch as a scanned optical signal with a corresponding emission angle.

[0078] Preferably, the time lengths of each scanning period are the same for easy overall control. After the current scanning period T t ends, the current optical switch is turned off, and the next optical switch is turned on according to the preset activation sequence to enter the next scanning period T t+1 . Since the present invention adopts bistatic reception, after the transmission ends, after turning off the current optical switch, the next optical switch can be directly turned on without delay in the middle.

[0079] Preferably, a position index is set for each optical switch, the position indexes of each optical switch are arranged in sequence from 1 to N, and the product of the position index number of the optical switch and the preset frequency shift step is set as the frequency shift amount corresponding to the optical switch. The step of the frequency shift amount is preferably 100~1000 MHz. The step of the frequency shift amount should be large enough to ensure that during the measurement of the Doppler frequency shift speed, the frequency shift generated due to the speed of the target object does not exceed the step range, thereby avoiding measurement errors. In a specific implementation, the value of the frequency shift step can be set according to the speed measurement range.

[0080] S3) Use a receiver to receive the backscattered optical signal, mix the backscattered optical signal and the local oscillator optical signal to obtain a beat optical signal.

[0081] Optionally, an optical coupler is used for mixing.

[0082] S4) Perform spectral analysis on the beat optical signal to obtain the emission angle, the distance between the target object and the lidar, and the speed of the target object corresponding thereto.

[0083] Optionally, a spectrometer or a Fast Fourier Transform (FFT) method is used for spectral analysis.

[0084] Step S4 is specifically:

[0085] S4.1) Obtain two beat frequency peaks of the beat frequency optical signal. Since the frequency-time function of the frequency-modulated continuous wave is a triangular wave signal, there are rising and falling edges, and the difference frequencies generated during these two processes are different, so two beat frequency peaks are generated.

[0086] S4.2) Obtain the propagation delay time based on the two beat frequency peaks, and then obtain the ranging result based on the propagation delay time. Process the two beat frequency peaks through the following formula to obtain the propagation delay time:

[0087] t d =T(f b2 -f b1 ) / 4B

[0088] In the formula, t d is the propagation delay time, T is the modulation period of the frequency-modulated continuous wave, f b1 is the beat frequency peak corresponding to the difference frequency of the rising edge of the triangular wave, f b2 is the beat frequency peak corresponding to the difference frequency of the falling edge of the triangular wave, and B is the modulation bandwidth of the frequency-modulated continuous wave;

[0089] Process the propagation delay time through the following formula to obtain the ranging result:

[0090] t d =2R / c

[0091] In the formula, t d is the propagation delay time, R is the distance between the target object and the lidar, and c is the speed of light.

[0092] S4.3) Obtain the total frequency shift amount based on the two beat frequency peaks, determine the corresponding optical switch according to the total frequency shift amount or the interval where the total frequency shift amount is located, and then obtain the emission angle corresponding to the optical switch, that is, the angle of the target object; obtain the difference between the total frequency shift amount and the frequency shift amount to obtain the Doppler frequency shift, and obtain the speed of the target object according to the Doppler frequency shift. If the total frequency shift amount is between two adjacent frequency shift amounts of different sizes, then use the emission angle of the optical switch corresponding to the smaller frequency shift amount as the angle of the target object.

[0093] S4.4) Take each emission angle analyzed from the beat frequency optical signal and the corresponding distance between the target object and the lidar and the speed of the target object as a set of ranging and velocity measurement results.

[0094] Furthermore, the ranging and velocity measurement results can be used for 4D point cloud imaging of the lidar. Step S4 also includes: mapping each emission angle and the corresponding distance between the target object and the lidar and the speed of the target object into a measurement point in 4D space, and the set of all measurement points forms a 4D lidar point cloud image.

[0095] The second aspect of the present invention provides a coded frequency modulated continuous wave lidar based on a focal plane switch array. As Figure 1 shown, the lidar of the present invention includes:

[0096] A frequency modulated continuous wave generation module for generating a frequency modulated continuous wave light source signal with a triangular wave as the frequency-time function;

[0097] A radio frequency source for emitting radio frequency signals of different frequencies; the output end outputs radio frequency signals;

[0098] A beam splitter for splitting the frequency modulated continuous wave light source signal to obtain a local oscillator light signal and an original light signal; the input end is connected to the light signal output end of the single sideband modulator through an optical fiber, the first output end outputs the original light signal, and the second output end outputs the local oscillator light signal;

[0099] An electro-optic modulator for applying a frequency shift to the original light signal according to radio frequency signals of different frequencies to obtain a coded frequency modulated continuous wave light signal with different frequency shift amounts; the optical signal input end is connected to the first output end of the beam splitter through an optical fiber, the radio frequency signal input end is communicatively connected to the output end of the radio frequency source through a radio frequency cable or a microstrip line, and the optical signal output end outputs the coded frequency modulated continuous wave light signal;

[0100] A focal plane switch array for acting as a transmitter to emit a coded frequency modulated continuous wave light signal with a specific frequency shift amount as a scanned light signal with a corresponding emission angle; the output end outputs a scanned light signal with an emission angle corresponding to the frequency shift amount of the coded frequency modulated continuous wave light signal;

[0101] A cooperative control module for cooperatively controlling the radio frequency signal of the electro-optic modulator and the power-on signal of the optical switch, so that within each scanning period, the frequency of the radio frequency signal, the frequency shift amount of the coded frequency modulated continuous wave light signal, the position index of the optical switch, and the emission angle of the scanned light signal correspond one by one; the output end is electrically connected to the control end of the radio frequency source and the control end of the focal plane switch array respectively;

[0102] A receiver for receiving the reflected light signal, which is configured remotely from the focal plane switch array; the input end receives the reflected light signal;

[0103] An optical coupler for mixing the reflected light signal and the local oscillator light signal to obtain a beat frequency light signal; the first input end is connected to the receiver through an optical fiber and receives the reflected light signal, the second input end is connected to the beam splitter of the beam splitter through an optical fiber and receives the local oscillator light signal, and the output end outputs the beat frequency light signal;

[0104] A spectrum analysis module is used to perform spectrum analysis on the beat frequency optical signal and analyze the angle information, so as to obtain the outgoing angle and the ranging and velocity measurement results corresponding to the outgoing angle; the input end is connected to the output end of the optical coupler through an optical fiber, and the output end outputs the ranging and velocity measurement results or visualizes the ranging and velocity measurement results.

[0105] Optionally, the frequency modulated continuous wave generation module mainly consists of a laser, a waveform generator, and a single sideband modulator. The laser is used to emit a narrow bandwidth laser signal, and the output end outputs the narrow bandwidth laser signal. The waveform generator is used to emit a frequency linearly modulated radio frequency signal, and the output end outputs the frequency linearly modulated radio frequency signal; the single sideband modulator is used to linearly frequency modulate the narrow bandwidth laser signal according to the frequency linearly modulated radio frequency signal to generate a frequency modulated continuous wave light source signal with a triangular wave as the frequency-time function; the optical signal input end is connected to the light output end of the laser through an optical fiber, the radio frequency signal input end is communicatively connected to the output end of the waveform generator through a radio frequency cable or a microstrip line, the output end outputs the frequency modulated continuous wave light source signal, and the output end is connected to the input end of the optical splitter through an optical fiber.

[0106] Optionally, the spectrum analysis module mainly consists of a photoelectric balanced detector, a spectrum analyzer, and a display and calculation unit. The input end of the photoelectric balanced detector is connected to the output end of the optical coupler through an optical fiber, the output end is electrically connected to the input end of the spectrum analyzer, the output end of the spectrum analyzer outputs the spectrum of the beat signal to the display and calculation unit, and after the display and calculation unit obtains the ranging and velocity measurement results according to the spectrum of the beat signal, it outputs the ranging and velocity measurement results or visualizes the ranging and velocity measurement results.

[0107] The third aspect of the present invention provides an application of a coded frequency modulated continuous wave lidar based on a focal plane switch array. The lidar can be used for 4D point cloud imaging of the lidar.

[0108] During the imaging process, the outgoing angle and the velocity of the target object at the point corresponding to the outgoing angle are obtained according to each group of ranging and velocity measurement results.

[0109] The specific embodiments of the present invention are as follows: Embodiment

[0110] The principle of the present invention will be further described below in conjunction with this embodiment.

[0111] The ranging and velocity measurement method of this embodiment is implemented by a lidar as shown in Figure 1 :

[0112] In the lidar of this embodiment, a frequency-modulated continuous wave generation module composed of a laser, a waveform generator, and a single-sideband modulator is adopted to generate a frequency-modulated continuous wave light source signal with a triangular wave as the frequency-time function. A beam splitter is used to split the frequency-modulated continuous wave light source signal. An electro-optic modulator is used to perform frequency encoding on the frequency-modulated continuous wave light source signal. A cooperative control module is used to cooperatively control the radio frequency signal of the electro-optic modulator and the power-on signal of the optical switch. A receiver configured remotely from the focal plane switch array is used to receive the backscattered light signal. An optical coupler is used to mix the backscattered light signal and the local oscillator light signal. A spectrum analysis module composed of a photoelectric balanced detector, a spectrometer, and a display calculation unit is used to perform spectrum analysis on the beat light signal. The spectrum of the beat light signal is obtained through the spectrometer, and then the spectrum is processed by the display calculation unit to obtain the ranging and velocity measurement results.

[0113] In the lidar of this embodiment, a focal plane switch array is used as the transmitter, that is, the scanning device of the lidar. The emission direction of the scanning light signal is controlled by the focal plane switch array, and each opened optical switch corresponds to an optical emission angle. When receiving an encoded frequency-modulated continuous wave light signal with a frequency shift of f i , the optical switch with position index i is opened, and the laser emission angle is θ i .

[0114] As Figure 2 shown, the focal plane switch array places the grating antenna array on the rear focal plane of the convex lens, and each grating antenna is connected to the input light source through an optical switch. The array composed of the grating antenna and the optical switch unit is integrated on a silicon-based optical chip. When the cooperative control module is used to control the corresponding optical switch in the focal plane switch array to open, the input light is routed to a certain antenna, and the light beam emitted from the antenna is collimated into a parallel light beam by the convex lens and emitted. It can be realized that when the optical switch with position index i is turned on, the collimated laser with an emission angle of θ i is emitted to achieve beam scanning. Specifically, the emission angle of the collimated light beam is related to the position of the optical switch relative to the convex lens and satisfies the following formula:

[0115] tanθ i =x i / f

[0116] In the formula, θ i is the angle between the emission direction of the emitted light beam and the principal optical axis of the convex lens when the i-th optical switch is turned on, x i is the coordinate of the i-th optical switch relative to the principal optical axis of the convex lens, and f is the focal length of the convex lens.

[0117] Figure 2 The one-dimensional FPSA beam steering principle demonstrated in

[0118] Figure 3 This is the schematic diagram of the design of the two-dimensional focal plane switch array in the present invention. By integrating an optical switch and a grating antenna unit on a silicon-based optical chip to form a two-dimensional array and placing it on the focal plane of a convex lens, two-dimensional beam steering can be achieved, and then two-dimensional beam scanning of the lidar can be realized.

[0119] Figure 4 The schematic diagram of the signal processing of the present invention is shown. Figure 4 In (a) of, the solid line represents the frequency-modulated continuous-wave light source signal generated based on the external modulation principle, and its frequency-time function is a triangular wave; the dotted line represents the frequency-time function of the echo light signal. After beam splitting, the part used as the light source signal is added with a frequency shift f through an electro-optic modulator i and then transmitted by the FPSA. After encountering the target, part of the signal is reflected back and received by the system. Since the signal propagation requires a certain time, the echo signal has a time delay t relative to the transmitted signal d , which will cause a frequency difference between the echo signal and the intrinsic signal. The propagation delay t d is directly related to the distance R of the target, and the expression is:

[0120] t d = 2R / c

[0121] In the formula, t d is the propagation delay time, R is the distance between the target object and the lidar, and c is the speed of light.

[0122] If the target object has a relative velocity v, the reflected signal will introduce an additional frequency shift due to the Doppler effect, which is called the Doppler frequency shift f d . The relationship between the Doppler frequency shift and the relative velocity of the target is:

[0123] f d = 2v / λ

[0124] In the formula, f d is the Doppler frequency shift caused by the velocity of the target object, v is the velocity of the target object, and λ is the wavelength of the light signal emitted by the lidar.

[0125] In summary, the offset between the received echo signal and the intrinsic signal is caused by three parts: the frequency shift f generated by the electro-optic modulator i , the time delay t caused by the distance d and the Doppler frequency shift f caused by the velocity d .

[0126] Figure 4 In (b) of, it represents the frequency-time function of the beat frequency signal, that is, the frequency difference between the echo signal and the intrinsic signal. This beat frequency signal will show f in the spectrum analyzerb1 and f b2 Two beat frequency peaks, corresponding to the difference frequencies corresponding to the rising edge and the falling edge of the triangular wave respectively. The time delay t can be calculated based on the two beat frequency peaks d and the total frequency shift amount △f:

[0127] t d =T(f b2 -f b1 ) / 4B

[0128] △f=(f b1 +f b2 ) / 2

[0129] In the formula, t d is the propagation delay time, T is the modulation period of the frequency-modulated continuous wave, f b1 is the beat frequency peak corresponding to the difference frequency at the rising edge of the triangular wave, f b2 is the beat frequency peak corresponding to the difference frequency at the falling edge of the triangular wave, B is the modulation bandwidth of the frequency-modulated continuous wave, and △f is the total frequency shift amount.

[0130] The total frequency shift amount △f includes two components, which are the frequency shift f i caused by the light source signal passing through the electro-optic modulator and the Doppler frequency shift f d caused by the target object velocity, that is:

[0131] △f=f i +f d

[0132] In the formula, △f is the total frequency shift amount, f i is the frequency shift caused by the electro-optic modulator, and f d is the Doppler frequency shift caused by the target object velocity.

[0133] For distinction, in this embodiment, through cooperative control, the frequency shift amount f i of the light source corresponding to the optical switch with position index i is:

[0134] f i =i×△f i

[0135] In the formula, △f i is the frequency shift step. In this embodiment, the frequency shift step is a fixed value and is applicable to all optical switches.

[0136] In the method of the present invention, the frequency shift step △f i is set to be large enough so as not to affect the measurement of f d .

[0137] Therefore, through f b1 and f b2After calculating the total frequency shift amount Δf, first determine the position index of the optical switch based on Δf or the interval where Δf is located to determine its emission angle. If the total frequency shift amount Δf is equal to f i , then confirm that the position index corresponding to this beam of light is i. If the total frequency shift amount Δf is in the interval (f i , f i +Δf i ), then confirm that the position index corresponding to this beam of light is i. Then, calculate the Doppler frequency shift from f d =Δf - f i , and further calculate the velocity of the target object.

[0138] In this embodiment, the process of ranging and velocity measurement using the above lidar is specifically as follows:

[0139] 1) Based on the external modulation technology, use a single-sideband modulator to linearly frequency-modulate a narrow-bandwidth laser signal to generate a frequency-modulated continuous-wave light source signal with a frequency-time function of a triangular wave ( Figure 4 as shown in (a));

[0140] 2) Use a splitter to split the frequency-modulated continuous-wave light source 1:99, where 1% is used as the intrinsic optical signal required for subsequent signal processing and is beat with the echo signal, and 99% is used as the original optical signal;

[0141] 3) Apply a frequency shift with a fixed frequency to the original optical signal through an electro-optic modulator, and then enter the focal plane switch array. The focal plane switch array serves as the transmitter of the lidar, controlling the emission direction of the coded frequency-modulated continuous-wave optical signal to achieve the emission of scanned laser light at different angles (emission angles);

[0142] In this embodiment, the method for controlling the emission direction of the coded frequency-modulated continuous-wave optical signal to achieve the emission of scanned laser light at different angles (emission angles) is specifically as follows: Each time a light switch in the focal plane switch array is opened, it corresponds to a light emission angle. When the light switch with position index i is opened, the corresponding laser emission angle is θ i ;

[0143] In this embodiment, the process of achieving a one-to-one correspondence between the frequency shift amount, the optical switch, and the emission angle is specifically as follows: Coordinate the control of the radio frequency signal of the electro-optic modulator and the power-on signal of the optical switch, so that within the scanning period of the light switch with position index i, the radio frequency source of the electro-optic modulator continuously generates a radio frequency signal, and the frequency of the radio frequency signal is f i , achieving a one-to-one correspondence between the frequency shift amount f i of the emitted light and the emission angle of θ i ;

[0144] 4) The emitted optical signal is reflected after hitting the target object and the echo signal is received by a receiver configured at a different location from the transmitter. After mixing with the eigen-optical signal in step 2, a beat optical signal is generated, which is converted into an electrical signal by a balanced photodetector;

[0145] 5) Perform spectral analysis on the electrical signal, calculate the frequency shift amount, signal time delay, and Doppler frequency shift through the beat frequency peak of the result, and then obtain information such as the angle, distance, and speed of the target. The result can be further used for 4D imaging.

[0146] Figures 5 - 7 The figure shows the frequency-domain simulation result of the beat signal in the method of the present invention. In the simulation, the modulation bandwidth B of the original frequency-modulated continuous-wave optical signal is set to 5 GHz, and the modulation period T is set to 100 μs; the frequency shift step size △f i is set to 100 MHz, and the index number of the optical switch is set according to the emission angle, that is, the emission angle corresponding to the optical switch with index i is i degrees. Then the corresponding relationship between the frequency shift amount and the angle is f i = 100 * θ i , that is, when the emission optical angle is 1°, the corresponding frequency shift amount is 100 MHz. In this embodiment, simulation calculations are performed on three measurement points with emission angles of 1°, 5°, and 10°. Assume that the distances of the target objects at the measurement points of 1° and 5° are 10 m and the speeds are 5 m / s, and the distance of the target object at the measurement point of 10° is 20 m and the speed is 20 m / s. Through simulation, the spectra of the beat signals at the three points are respectively presented as Figure 5 、 Figure 6 、 Figure 7 . Through the two peaks of the beat signal, the results of the emission angle, distance, and speed can be calculated according to the formula. The comparison between the theoretical values and the measured values is shown in the following table:

[0147]

[0148] 4D lidar point cloud imaging can be achieved based on a set of multiple measurement points.

[0149] Figure 8 The figure shows the ideal effect diagram of applying the method of the present invention to a lidar system. By opening the optical switches at different positions through a cooperative control system and performing signal processing, multiple sets of data on angles, distances, and speeds can be obtained, and finally a 4D lidar point cloud image containing distance and speed information can be presented.

[0150] In summary, compared with the solution using unencoded frequency-modulated continuous wave, the method of the present invention realizes complete imaging of an object in the frequency domain. Specifically, by performing frequency-domain analysis on the final echo signal, angle, distance, and velocity information can be resolved, and then lidar point cloud can be obtained. That is, for the point at the position with an angle of θ relative to the lidar, the distance and velocity of the target object at this point relative to the lidar are used for point cloud imaging.

[0151] The above specific embodiments are used to explain the present invention rather than limit the present invention. Any modification and change made to the present invention within the spirit and scope of the claims of the present invention fall within the protection scope of the present invention.

[0152] The above description is only a preferred embodiment of the present invention. Therefore, any equivalent changes or modifications made according to the structure, features, and principles described in the scope of the present invention patent application are included in the scope of the present invention patent application.

Claims

1. A coded frequency modulated continuous wave ranging and velocity measurement method based on a focal plane switch array, characterized in that, It includes the following steps: S1) Split the frequency-modulated continuous-wave light source signal with a triangular-wave frequency-time function to obtain a local oscillator light signal and an original light signal; S2) Apply frequency shifts of different frequencies to the original light signal to obtain coded frequency-modulated continuous-wave light signals with different frequency shift amounts. Use a focal plane switch array to emit the coded frequency-modulated continuous-wave light signal with a specific frequency shift amount as a scanning light signal with a corresponding emission angle; The focal plane switch array includes multiple optical switches, each optical switch corresponding to a different frequency shift amount, and the scanning light signals emitted by each optical switch have different emission angles; S3) Use a receiver to receive the backscattered light signal, mix the backscattered light signal with the local oscillator light signal to obtain a beat light signal; the receiver is configured at a different location from the focal plane switch array; S4) Perform spectral analysis on the beat light signal to obtain the emission angle, the distance between the target object and the lidar, and the speed of the target object.

2. The coded frequency modulated continuous wave ranging and velocity measurement method based on a focal plane switch array according to claim 1, characterized in that: In step S2, within each scanning period, use an electro-optic modulator to apply a specific frequency shift amount to the original light signal according to a radio frequency signal to obtain a coded frequency-modulated continuous-wave light signal, and at the same time keep the optical switch corresponding to the frequency shift amount in the on state. The coded frequency-modulated continuous-wave light signal is emitted by the optical switch as a scanning light signal with a corresponding emission angle; after the current scanning period ends, turn off the current optical switch and immediately turn on the next optical switch to enter the next scanning period.

3. The coded frequency modulated continuous wave ranging and velocity measuring method based on a focal plane switch array according to claim 1, characterized in that: The focal plane switch array and the receiver serve as the transmitting end and receiving end of the lidar respectively, and the receiver is configured at a different location from the focal plane switch array.

4. The coded frequency modulated continuous wave ranging and velocity measuring method based on a focal plane switch array according to claim 1, characterized in that: Set the product of the position index number of the optical switch and a preset frequency shift step size as the frequency shift amount corresponding to the optical switch, and the frequency shift step size is 100 - 1000 MHz.

5. The coded frequency modulated continuous wave ranging and velocity measurement method based on a focal plane switch array according to claim 1, characterized in that: Step S4 is specifically: S4.1) Obtain two beat frequency peaks of the beat light signal; S4.2) According to the two beat frequency peaks, obtain the propagation delay time through the following formula, and then obtain the distance between the target object and the lidar according to the propagation delay time: t d =T(f b2 -f b1 ) / 4B where t d is the propagation delay time, T is the modulation period of the frequency-modulated continuous wave, f b1 is the beat frequency peak corresponding to the rising edge of the triangular wave for the difference frequency, f b2 is the beat frequency peak corresponding to the falling edge of the triangular wave for the difference frequency, and B is the modulation bandwidth of the frequency-modulated continuous wave; S4.3) According to the two beat frequency peaks, obtain the total frequency shift amount through the following formula: △f=(f b1 +f b2 ) / 2 where Δf is the total frequency shift, and f b1 is the beat frequency peak corresponding to the difference frequency at the rising edge of the triangular wave, and f b2 is the beat frequency peak corresponding to the difference frequency at the falling edge of the triangular wave; Subsequently, obtain the emission angle according to the total frequency shift amount; Obtain the difference between the total frequency shift amount and the frequency shift amount to obtain the Doppler frequency shift, and according to the Doppler frequency shift, obtain the speed of the target object through the following formula: f d = 2v / λ where f d is the Doppler frequency shift caused by the velocity of the target object, v is the velocity of the target object, and λ is the wavelength of the optical signal emitted by the lidar; S4.4) Take each emission angle and the corresponding distance between the target object and the lidar and the speed of the target object as a set of ranging and velocity measurement results.

6. The coded frequency modulated continuous wave ranging and velocity measuring method based on a focal plane switch array according to claim 5, characterized in that: During the process of obtaining the emission angle according to the total frequency shift amount, if the total frequency shift amount is between two adjacent frequency shift amounts of different magnitudes, use the emission angle of the optical switch corresponding to the smaller frequency shift amount as the angle of the target object.

7. The coded frequency-modulated continuous wave ranging and velocity measurement method based on a focal plane switch array according to claim 1, wherein: In step S1, use a laser to generate a narrow-bandwidth laser signal, and use a single-sideband modulator to perform linear frequency modulation on the narrow-bandwidth laser signal to generate a frequency-modulated continuous-wave light source signal with a triangular-wave frequency-time function; the narrow-bandwidth laser signal is a single-wavelength laser signal with a bandwidth less than 100 kHz.

8. The coded frequency modulated continuous wave ranging and velocity measuring method based on a focal plane switch array according to claim 1, characterized in that: The step S4 further includes: mapping each emission angle, the corresponding distance between the target object and the lidar, and the speed of the target object into a measurement point in a 4D space, and the set of all measurement points forms a 4D lidar point cloud image.

9. A lidar applied to the ranging and velocity measurement method according to any one of claims 1 to 8, characterized in that, including: a frequency-modulated continuous wave generation module for generating a frequency-modulated continuous wave light source signal; a radio frequency source for emitting a radio frequency signal; a beam splitter for splitting the frequency-modulated continuous wave light source signal; an electro-optic modulator for applying a frequency shift to the original optical signal according to the radio frequency signal to obtain a coded frequency-modulated continuous wave optical signal; a focal plane switch array for serving as the transmitting end of the lidar and emitting the coded frequency-modulated continuous wave optical signal with a specific frequency shift amount as a scanned optical signal with a corresponding emission angle; a cooperative control module for cooperatively controlling the radio frequency signal and the power-on signal of the optical switch, so that within each scanning period, the radio frequency signal, the frequency shift amount of the coded frequency-modulated continuous wave optical signal, the optical switch, and the emission angle correspond one by one; a receiver for serving as the receiving end of the lidar and receiving the reflected optical signal; an optical coupler for mixing the reflected optical signal and the local oscillator optical signal to obtain a beat optical signal; a spectrum analysis module for performing spectrum analysis on the beat optical signal to obtain the emission angle, the corresponding distance between the target object and the lidar, and the speed of the target object.

10. An application of a lidar as described in claim 9, characterized in that: for generating a 4D lidar point cloud image.

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