Ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping

Abstract

The invention provides an ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping, and the system comprises an ultrafast laser which is connected with a first coupler and is used for transmitting detection light, first reference light and second reference light; the two-dimensional frequency-space mapping module is used for converting the detection light into two-dimensional dispersion light, and the two-dimensional dispersion light detects a detected object and returns the detected object; the coherent detection light path module is used for performing interference on the first reference light and the returned two-dimensional dispersion light to obtain an interference spectrum; the dispersion Fourier transform-based measurement module is used for performing dispersion Fourier transform on the interference spectrum to obtain phase information of the measured object; and the distance measuring module is used for coupling the returned two-dimensional dispersion light with the second reference light to obtain the distance between the measured object and the ultrafast laser and the moving speed of the measured object. According to the invention, the detection refresh frame rate and the scanning rate are higher than those of a traditional laser radar, and the morphology information of the measured object is measured at the micron-dimension longitudinal resolution.

Description

Technical Field

[0001] The present application belongs to the field of laser radar technology, and more specifically, to an ultrafast laser radar system based on two-dimensional frequency-space mapping of ultrashort pulse lasers. Background Art

[0002] Light detection and ranging (LiDAR) is a type of optical three-dimensional sensor and is widely used in smart driving, augmented reality (AR) and virtual reality (VR). Therefore, the high detection refresh frame rate and high spatial resolution of LiDAR are the main development trends of this technology.

[0003] Current LiDARs use mechanical beam guides as scanning devices, such as rotating polygonal reflectors, reflector scanners, and prism deflector scanners. However, these solutions are unstable, bulky, and have low scanning speeds for mechanical scanning devices. Therefore, the introduction of a new type of scanning detection that combines ultrashort pulse lasers with two-dimensional light scanning is an important development direction in the field of LiDAR.

[0004] Spectral scanning is a solid-state beam steering method that is achieved by combining a swept laser source with a dispersive element. Typically, beam steering techniques based on spectral scanning are combined with other scanners to achieve faster scanning rates. Common dispersive modules use gratings for dispersion, however, gratings can only achieve one-dimensional beam steering, so another mechanical beam steering device is usually required to achieve two-dimensional beam steering, which increases system complexity and reduces scanning rates.

[0005] Ultrafast lasers have ultra-high pulse repetition frequencies and are widely used in the field of precision measurement. Ultrafast lasers can be used as pulse light sources with extremely high emission repetition frequencies. Based on the dispersion Fourier change, this feature can be used to perform real-time demodulation of a single spectrum. Therefore, two-dimensional optical scanning can be used to enable laser radars to achieve a MHz detection refresh frame rate.

[0006] How to achieve higher detection refresh frame rate and ultrafast measurement of three-dimensional imaging, increase the scanning rate of laser radar and reduce the complexity of the system is the technical problem to be solved by the present invention. Summary of the invention

[0007] To achieve the above-mentioned purpose, the technical solution adopted in this application is: to provide an ultrafast laser radar system based on two-dimensional frequency-space mapping of ultrashort pulse laser, including an ultrafast laser, a two-dimensional frequency-space mapping module, a coherent detection optical path module, a dispersion Fourier transform-based measurement module and a ranging module; The ultrafast laser is connected to a first coupler for emitting a detection light, a first reference light, and a second reference light; The two-dimensional frequency-space mapping module is used to convert the detection light into two-dimensional dispersion light, and the two-dimensional dispersion light detects the object to be measured and returns; The coherent detection optical path module is used to interfere the first reference light with the returned two-dimensional dispersed light to obtain an interference spectrum; The dispersion Fourier transform based measurement module is used to perform dispersion Fourier transform on the interference spectrum to obtain a single pulse spectrum, and then obtain the real-time phase of each spectrum through fast Fourier transform and inverse fast Fourier transform deconvolution, thereby obtaining the real-time phase of each spatial point; The distance measurement module is used to couple the returned two-dimensional dispersed light with the second reference light to obtain the distance between the measured object and the ultrafast laser and the moving speed of the measured object.

[0008] Optionally, the coherent detection optical path module includes a circulator, a second coupler, a third coupler, a single-mode optical fiber and an adjustable optical delay line, the input end of the first coupler is connected to the output end of the ultrafast laser, the first output end of the first coupler is connected to the first end of the circulator, the second end of the circulator is connected to the two-dimensional frequency-space mapping module, the third end of the circulator is connected to the input end of the second coupler, the first output end of the second coupler is connected to the first input end of the third coupler, and the second output end of the first coupler is connected to the second input end of the third coupler through the single-mode optical fiber and the adjustable optical delay line.

[0009] Optionally, the two-dimensional frequency-space mapping module includes a collimator, a two-dimensional dispersion module and a beam expander, the second end of the circulator is connected to the first end of the collimator, the second end of the collimator is aligned with the two-dimensional dispersion module, and the two-dimensional dispersion module is aligned with the beam expander.

[0010] Optionally, the dispersion Fourier transform-based measurement module includes a dispersion Fourier module and a first photodetector, the input end of the dispersion Fourier module is connected to the output end of the third coupler, and the input end of the dispersion Fourier module is connected to the input end of the first photodetector.

[0011] Optionally, the ranging module includes a fourth coupler and a second photodetector, the first input end of the fourth coupler is connected to the third output end of the first coupler, the second input end of the fourth coupler is connected to the second output end of the second coupler, and the output end of the fourth coupler is connected to the input end of the second photodetector.

[0012] Optionally, it also includes a real-time oscilloscope and a signal processing module, the output end of the first photodetector is connected to the first input end of the real-time oscilloscope, the output end of the second photodetector is connected to the second input end of the real-time oscilloscope, and the output end of the real-time oscilloscope is connected to the signal processing module.

[0013] The beneficial effects of the ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping provided by the present application are: 1. This application uses an ultrafast laser as a detection light source, performs surface scanning measurement of the object to be measured with a high-repetition-frequency pulse train and combines the dispersion Fourier transform to perform real-time demodulation of the single spectrum, thereby enabling the detection refresh frame rate and scanning rate to be higher than traditional lidar.

[0014] 2. This application uses the ToF (Time of Flight) principle for distance measurement. By calculating the pulse delay between the reference light path and the detection light path and multiplying it by the speed of light, the distance between the measured object and the detection light source is obtained. Using ToF distance measurement, distance measurement can be performed every 100 nanoseconds, and the moving speed of the object can be obtained by comparing the displacement of the same point.

[0015] 3. The present application utilizes the interference of two-dimensional scanning surface detection light and reference light, and then uses dispersive Fourier transform to demodulate the real-time single-frame interference spectrum, and then obtains the fine shape of the object being measured by the phase solution method. Through this method, the morphological information of the object being measured is measured with a longitudinal resolution of the micron level. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 A schematic diagram of the structure of an ultrafast laser radar system based on two-dimensional frequency-space mapping of ultrashort pulse lasers provided in an embodiment of the present application; Figure 2 A schematic diagram of the principle of the ranging module provided in the embodiment of the present application; Figure 3 The principle diagram of phase solution for coherent detection in this application; Figure 4 This is a diagram illustrating an example of coherent detection phase solution in this application. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0019] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0020] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0021] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0022] Please also read Figure 1-Figure 4 , the ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping provided in an embodiment of the present application is now described.

[0023] An ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping, comprising an ultrafast laser, a two-dimensional frequency-space mapping module, a coherent detection optical path module, a dispersion Fourier transform-based measurement module and a distance measurement module; The ultrafast laser is used to emit the detection light, the first reference light and the second reference light; The two-dimensional frequency-space mapping module is used to convert the detection light into two-dimensional dispersion light, and the two-dimensional dispersion light detects the object to be measured and returns; The coherent detection optical path module is used to interfere the first reference light with the returned two-dimensional dispersed light to obtain an interference spectrum; The dispersion Fourier transform-based measurement module is used to perform dispersion Fourier transform on the interference spectrum to obtain a single pulse spectrum, and then obtain the real-time phase of each spectrum through fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) deconvolution, thereby obtaining the real-time phase of each spatial point (real-time instantaneous phase of each spectrum); The distance measurement module is used to couple the returned two-dimensional dispersed light with the second reference light to obtain the distance between the measured object and the ultrafast laser and the moving speed of the measured object.

[0024] The present application uses an ultrafast laser as a detection light source, and the emitted light beam is divided into a detection light, a first reference light, and a second reference light through a first coupler. The detection light is converted into a two-dimensional dispersed light through a two-dimensional frequency-space mapping module, and the object to be measured is detected and returned along the original path. The first reference light and the returned two-dimensional dispersed light are input into the coherent detection optical path module for interference to obtain an interference spectrum. The interference spectrum is subjected to a dispersion Fourier transform based on a dispersion Fourier transform measurement module to obtain a single pulse spectrum, and then the real-time phase of each spectrum is obtained through fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) deconvolution, thereby obtaining the real-time instantaneous phase of each spectrum. The real-time phase information can be demodulated to restore the fine morphology of the object to be measured. The two-dimensional dispersed light returned by the ranging module is coupled with the second reference light, and the ToF principle is used to obtain the distance between the object to be measured and the ultrafast laser and the moving speed of the object to be measured. Since ultrashort pulse lasers have a light pulse repetition frequency of more than MHz and can demodulate the real-time spectrum of a single pulse based on the principle of dispersion Fourier transform, a two-dimensional mobile platform or scanning galvanometer can be used to achieve ultrafast frame rate scanning of the object being measured with the light pulse repetition period as the scanning frame rate.

[0025] In some embodiments of the present application, see Figure 1 The coherent detection optical path module includes a first coupler, a circulator, a second coupler, a third coupler, a single-mode optical fiber (SMF) and an adjustable optical delay line. The input end of the first coupler is connected to the output end of the ultrafast laser, the first output end of the first coupler is connected to the first end of the circulator, the second end of the circulator is connected to the two-dimensional frequency-space mapping module, the third end of the circulator is connected to the input end of the second coupler, the first output end of the second coupler is connected to the first input end of the third coupler, and the second output end of the first coupler is connected to the second input end of the third coupler through the single-mode optical fiber and the adjustable optical delay line.

[0026] The detection light output by the first coupler is input from the first end of the circulator, output from the second end of the circulator to the two-dimensional frequency-space mapping module, detects the object to be measured and returns, inputs from the second end of the circulator, and then outputs from the third end of the circulator to the second coupler, and is split into the third coupler and the fourth coupler through the second coupler. The first reference light output by the first coupler is sequentially input into the third coupler through the single-mode optical fiber and the adjustable optical delay line to interfere with the detection light to obtain an interference spectrum.

[0027] In some embodiments of the present application, see Figure 1 The two-dimensional frequency-space mapping module includes a collimator, a two-dimensional dispersion module and a beam expander. The second end of the circulator is connected to the first end of the collimator, the second end of the collimator is aligned with the two-dimensional dispersion module, and the two-dimensional dispersion module is aligned with the beam expander.

[0028] Collimators are used to make the incident light beam parallel and prevent the light beam from diverging. Two-dimensional dispersion modules are used to disperse light of different wavelengths so that they can be processed or measured separately. Beam expanders are used to expand the diameter of a parallel input light beam to a larger parallel output beam.

[0029] In some embodiments of the present application, see Figure 1 The dispersion Fourier transform measurement module includes a dispersion Fourier module and a first photodetector, the input end of the dispersion Fourier module is connected to the output end of the third coupler, and the input end of the dispersion Fourier module is connected to the input end of the first photodetector.

[0030] The interference spectrum output by the third coupler is Fourier transformed by the dispersion Fourier module to obtain the phase information of the object under test. The first photoelectric detector can demodulate the fine morphological features of the object under test according to the phase information of the object under test.

[0031] In some embodiments of the present application, see Figure 1 The ranging module includes a fourth coupler and a second photodetector, the first input end of the fourth coupler is connected to the third output end of the first coupler, the second input end of the fourth coupler is connected to the second output end of the second coupler, and the output end of the fourth coupler is connected to the input end of the second photodetector.

[0032] By coupling the detection light and the second reference light in the fourth coupler to obtain the pulse delay, the second photodetector can calculate the distance between the object under test and the detection light source. Because the ultrafast laser used can achieve a refresh rate of MHz, that is, refresh once every hundred nanoseconds, the object's moving speed can be calculated based on the relative moving distance of the scanning point.

[0033] In some embodiments of the present application, see Figure 1, also includes a real-time oscilloscope and a signal processing module, the output end of the first photodetector is connected to the first input end of the real-time oscilloscope, the output end of the second photodetector is connected to the second input end of the real-time oscilloscope, and the output end of the real-time oscilloscope is connected to the signal processing module.

[0034] Working principle: In this application, a beam of light from an ultrashort pulse laser is connected to the first coupler to obtain highly coherent light; after passing through the first coupler, it is divided into three beams, namely, detection light, first reference light and second reference light. The detection light is input into the circulator, and after passing through the collimator, two-dimensional dispersion module and beam expander, two-dimensional dispersion light is formed. After detecting the object to be measured, the light returns to the circulator and inputs the second coupler. Through the second coupler, it is split into the third coupler and the fourth coupler, and acts with two different reference beams respectively. After the second reference light is output through the first coupler, it is coupled with the beam output by the second coupler in the fourth coupler, and the ToF ranging principle is used to calculate the distance and movement rate between the light source and the object to be measured according to the round-trip time of the light beam. Because this application uses an ultrafast laser, it can reach a detection refresh frame rate of MHz level, that is, it detects once every hundred nanoseconds, so the object movement rate can be calculated according to the displacement of the scanning point. The ToF ranging principle is to obtain the distance between the object to be measured and the detection light source by multiplying the delay time of the returned pulse light by the speed of light. The first reference light is output by the first coupler and then coupled with the light beam output by the second coupler through a single-mode fiber (SMF) and an adjustable optical delay line. The phase information of the object can be obtained by interfering the first reference light with the detection light and then performing a dispersive Fourier transform. The fine morphology of the object under test can be restored by demodulating the phase information. Since the ultrashort pulse laser has a light pulse repetition frequency of more than MHz and the real-time spectrum of a single pulse can be demodulated based on the principle of dispersive Fourier transform, a two-dimensional mobile platform or a scanning galvanometer can be used to achieve ultra-fast frame rate scanning of the object under test with the light pulse repetition period as the scanning frame rate.

[0035] Figure 2 Figure 1 is a schematic diagram of the working principle of the ranging module. Figure 2 (a) It can be seen that the pulse width of each optical pulse is in the order of ps, and the interval between each pulse is in the order of ns. Figure 2 (a) shows a pulse from the transmitter that does not reach the detection object. Figure 2 (b) shows the pulse that returns after reaching the detection surface. By measuring the pulse delay τ, the distance from the object to the detector can be obtained by calculation, and the moving speed of the object can also be calculated.

[0036] Figure 3The schematic diagram of the coherent detection phase solution principle. After the interference between the first reference light and the detection light, the dispersion Fourier transform is performed, and then the inverse Fourier transform is performed to demodulate the phase information. The depth information of the object under test will be loaded on the phase of the interference spectrum. The FSR (free spectral range) and phase change are obtained by dispersive Fourier transform, inverse Fourier transform, and phase solution of the interference spectrum, thereby obtaining the depth information of the object under test. Figure 4 The "CYL" in the figure represents a three-dimensional object placed on a plane, simulating the difference in depth; the red arrows point to points A and C in the figure. The pixel coordinates of the two points are the same, but the phases are different. The height of the point can be indirectly obtained by calculating the phase difference under the same coordinates. Based on this principle, the phase information of the entire image can be obtained, and the information of the entire image can be demodulated.

[0037] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An ultrafast laser radar system based on two-dimensional frequency-space mapping of ultrashort pulse lasers, characterized in that: It includes ultrafast laser, two-dimensional frequency-space mapping module, coherent detection optical path module, dispersion Fourier transform-based measurement module and distance measurement module; The ultrafast laser is connected to a first coupler for emitting a detection light, a first reference light, and a second reference light; The two-dimensional frequency-space mapping module is used to convert the detection light into two-dimensional dispersion light, and the two-dimensional dispersion light detects the object to be measured and returns; The coherent detection optical path module is used to interfere the first reference light with the returned two-dimensional dispersed light to obtain an interference spectrum; The dispersion Fourier transform based measurement module is used to perform dispersion Fourier transform on the interference spectrum to obtain a single pulse spectrum, and then obtain the real-time phase of each spectrum through fast Fourier transform and inverse fast Fourier transform deconvolution, thereby obtaining the real-time phase of each spatial point; The distance measurement module is used to couple the returned two-dimensional dispersed light with the second reference light to obtain the distance between the measured object and the ultrafast laser and the moving speed of the measured object.

2. The ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping as claimed in claim 1, characterized in that: The coherent detection optical path module includes a circulator, a second coupler, a third coupler, a single-mode optical fiber and an adjustable optical delay line. The input end of the first coupler is connected to the output end of the ultrafast laser, the first output end of the first coupler is connected to the first end of the circulator, the second end of the circulator is connected to the two-dimensional frequency-space mapping module, the third end of the circulator is connected to the input end of the second coupler, the first output end of the second coupler is connected to the first input end of the third coupler, and the second output end of the first coupler is connected to the second input end of the third coupler through the single-mode optical fiber and the adjustable optical delay line.

3. The ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping as claimed in claim 2, characterized in that: The two-dimensional frequency-space mapping module includes a collimator, a two-dimensional dispersion module and a beam expander. The second end of the circulator is connected to the first end of the collimator, the second end of the collimator is aligned with the two-dimensional dispersion module, and the two-dimensional dispersion module is aligned with the beam expander.

4. The ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping as claimed in claim 2, characterized in that: The dispersion Fourier transform-based measurement module includes a dispersion Fourier module and a first photodetector, wherein the input end of the dispersion Fourier module is connected to the output end of the third coupler, and the input end of the dispersion Fourier module is connected to the input end of the first photodetector.

5. The ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping as claimed in claim 4, characterized in that: The ranging module includes a fourth coupler and a second photodetector, wherein the first input end of the fourth coupler is connected to the third output end of the first coupler, the second input end of the fourth coupler is connected to the second output end of the second coupler, and the output end of the fourth coupler is connected to the input end of the second photodetector.

6. The ultrafast laser radar system based on ultrashort pulse laser two-dimensional frequency-space mapping as claimed in claim 5, characterized in that: It also includes a real-time oscilloscope and a signal processing module, wherein the output end of the first photodetector is connected to the first input end of the real-time oscilloscope, the output end of the second photodetector is connected to the second input end of the real-time oscilloscope, and the output end of the real-time oscilloscope is connected to the signal processing module.

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