A polarization spectrum imaging lidar system

Abstract

The present invention belongs to the field of imaging laser radar, and more specifically, relates to a polarization spectrum imaging laser radar system. A broadband light source generates laser light, which passes through a collimator and a first focusing lens and then irradiates a two-dimensional scanning galvanometer. The laser is then reflected by the two-dimensional scanning galvanometer and irradiates an imaging object. The light reflected by the imaging object is collected by a telescope and enters a fiber collimator. It is then transmitted through an optical fiber to an electric polarization controller, and after polarization state modulation by the electric polarization controller, it enters a tilted fiber grating. The tilted fiber grating diffracts into free space. A second focusing lens focuses the wavelength diffracted light in free space, and the focused diffracted light is detected by an array detector. The present invention simplifies the structure of traditional polarization spectrum imaging systems and improves system integration.

Description

Technical Field

[0001] The present invention belongs to the field of imaging laser radar, and more specifically, relates to a polarization spectrum imaging laser radar system. Background Art

[0002] Target detection and recognition technologies play a vital role in remote sensing, telemetry, security monitoring, and other fields. Improving target recognition rates is crucial for target detection research. Rapidly changing natural backgrounds and increasingly sophisticated camouflage methods are making detection increasingly difficult. Traditional intensity imaging detection is subject to numerous limitations due to significant environmental influences and limited information content.

[0003] In recent years, with the continuous advancement and development of optoelectronic technology, many advanced target information detection technologies have emerged (such as the Chinese invention patent "Spatial Self-focusing Laser Differential Confocal Raman Spectroscopic Imaging Detection Method and Device" application number 201711464498.7). For example, spectral imaging technology can be used to obtain spectral information of the object being measured, and thus its chemical composition characteristics; polarization imaging technology can be used to obtain polarization information of the object being measured, and thus physical properties related to surface texture, roughness, material dielectric constant, etc. Polarization spectral imaging technology is the product of the effective combination of polarization imaging technology and spectral imaging technology. Generally speaking, it can be achieved by adding a dispersion element to the polarization imager or a polarization element to the spectral imager. However, such polarization spectral imaging systems contain a large number of optical components, and their structure is too complex and large, which limits their application. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a polarization spectrum imaging lidar system. The present invention simplifies the structure of the traditional polarization spectrum imaging system and improves the system integration.

[0005] The technical solution of the present invention is: a polarization spectrum imaging laser radar system, including a broadband light source, a collimator, a first focusing lens, a two-dimensional scanning galvanometer, an imaging object, a telescope, a fiber collimator, an optical fiber, an electric polarization controller, a tilted fiber grating, a second focusing lens, and an array detector, characterized in that: the broadband light source generates laser light, which passes through the collimator and the first focusing lens and then irradiates the two-dimensional scanning galvanometer, which is then reflected by the two-dimensional scanning galvanometer and irradiates the imaging object, the light reflected by the imaging object is collected by the telescope and enters the fiber collimator, is transmitted to the electric polarization controller through the optical fiber, and enters the tilted fiber grating after polarization state modulation by the electric polarization controller, and the tilted fiber grating is diffracted into free space; the second focusing lens focuses the wavelength diffracted light in the free space and the focused diffracted light is detected by the array detector.

[0006] According to the polarization spectrum imaging laser radar system as described above, it is characterized by: it also includes a packaging shell, a broadband light source, a collimating mirror, and a first focusing lens placed in parallel on the rear side of the interior of the packaging shell, the collimating mirror is located 5 cm to the left of the broadband light source outlet, the first focusing lens is located 5 cm to the left of the collimating mirror, the two-dimensional scanning galvanometer is located 20 cm to the left of the first focusing lens, the telescope, the fiber collimator, the optical fiber, and the electric polarization controller are placed in parallel in the middle of the packaging shell, the fiber collimator is located 10 cm to the left of the telescope, and the electric polarization controller is located 10 cm to the left of the fiber collimator, and are connected by optical fiber; the tilted fiber grating is fixed on the left side of the packaging shell, the second focusing lens and the array detector are placed parallel to the front side of the interior of the packaging shell, the second focusing lens is located 20 cm to the right of the tilted fiber grating, and the array detector is located 20 cm to the right of the second focusing lens.

[0007] According to the polarization spectrum imaging laser radar system as described above, it is characterized in that after the array detector receives the light signal, it performs spectrum calculation and average power calculation to obtain spectrum information. and average power .

[0008] According to the polarization spectrum imaging laser radar system as described above, it is characterized in that: the average power calculated after each polarization modulation is subjected to Fourier analysis to obtain the four coefficients ABCD, and the Stokes parameters are then calculated. ,

[0009]

[0010] According to the polarization spectrum imaging lidar system as described above, it is characterized in that after the broadband light source generates the laser, the scanning galvanometer is driven to make the echo signal of a certain imaging point of the imaging object enter the optical fiber transmission, and then the polarization modulation is performed by driving the electric polarization controller to rotate it by θ degrees.

[0011] According to the polarization spectrum imaging laser radar system as described above, it is characterized by: further including a polarization adjustment and calibration device, which includes a broadband light source, an electric polarization controller, a tilted fiber grating, a second focusing lens, an array detector, a coupler and a polarization analyzer. After the broadband light source generates laser light, the polarization state is modulated by the electric polarization controller and then divided into two paths by the coupler, one path inputs the polarization analyzer and the other path inputs the tilted fiber grating, which diffracts into free space; the second focusing lens focuses the wavelength diffracted light in the free space and the focused diffracted light is detected by the array detector.

[0012] According to the polarization spectrum imaging laser radar system as described above, it is characterized in that the calibration device draws a polarization adjustment calibration curve, and the generated polarization adjustment calibration curve is used to correct the rotation angle of polarization modulation to obtain the correct θ.

[0013] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0014] (1) The present invention uses an electric polarization controller and a tilted fiber Bragg grating to replace the polarization modulation module and the dispersion module in the traditional polarization spectrum imaging system. The polarization modulation characteristics of the electric polarization controller and the single polarization characteristics of the tilted fiber Bragg grating can realize the measurement of polarization information, while the dispersion characteristics of the tilted fiber Bragg grating can realize the measurement of spectral information alone.

[0015] (2) The entire polarization spectrum imaging lidar system of the present invention has a small system size and a simple structure.

[0016] In summary, the polarization spectrum imaging laser radar system of the present invention has a small size, simple composition, is not easily disturbed by external vibrations and other factors, and is convenient for large-scale production and integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural diagram of a polarization spectrum imaging lidar system described in the present invention.

[0018] Figure 2 This is an imaging flow chart of a polarization spectrum imaging lidar system described in the present invention.

[0019] Figure 3 This is a diagram of a polarization adjustment and calibration system of a polarization spectrum imaging laser radar system described in the present invention.

[0020] Figure 4 This is a diagram of an example of a polarization spectrum imaging lidar system described in the present invention.

[0021] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0022] Broadband light source 1, collimating mirror 2, first focusing lens 3, two-dimensional scanning galvanometer 4, imaging object 5, telescope 6, fiber collimator 7, optical fiber 8, electric polarization controller 9, tilted fiber Bragg grating 10, second focusing lens 11, array detector 12, coupler 13, polarization analyzer 14, packaging shell 15. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0024] like Figure 1 and Figure 4 As shown, the polarization spectrum imaging lidar system proposed in the present invention includes a broadband light source 1, a collimating mirror 2, a first focusing lens 3, a two-dimensional scanning galvanometer 4, an imaging object 5, a telescope 6, a fiber collimator 7, an optical fiber 8, a motorized polarization controller 9, a tilted fiber Bragg grating 10, a second focusing lens 11, and an array detector 12. The present invention uses the motorized polarization controller 9 and the tilted fiber Bragg grating 10 to replace the polarization modulation module and dispersion module in traditional polarization spectrum imaging systems. In comparison, the entire device is small in size, simple in composition, and is not easily disturbed by external factors such as vibration, making it easy to mass-produce and integrate. The broadband light source 1 generates laser light, which passes through the collimator 2 and the first focusing lens 3 and then irradiates the two-dimensional scanning galvanometer 4. The laser light is then reflected by the two-dimensional scanning galvanometer 4 and irradiates the imaging object 5. The light reflected by the imaging object 5 is collected by the telescope 6 and enters the fiber collimator 7. The light is transmitted to the electric polarization controller 9 through the optical fiber 8. After the polarization state is modulated by the electric polarization controller 9, the light enters the tilted fiber grating 10. The tilted fiber grating 10 diffracts into the free space. The second focusing lens 11 focuses the wavelength diffracted light in the free space and the focused diffracted light is detected by the array detector 12.

[0025] The broadband light source 1 is used to generate broadband laser.

[0026] The collimator 2 is used to collimate the input light generated by the broadband light source in free space.

[0027] The first focusing lens 3 is used to focus the collimated input light.

[0028] The two-dimensional scanning galvanometer 4 is used to reflect the input light onto the imaging object in a two-dimensional direction.

[0029] Imaging object 5, used for measured imaging.

[0030] The telescope 6 is used to focus the light reflected by the imaging object onto the fiber collimator.

[0031] The optical fiber collimator 7 is used to couple the light focused by the telescope into the optical fiber for transmission.

[0032] The optical fiber 8 is used to transmit the single-point echo light signal of the imaging object.

[0033] The electric polarization controller 9 is used to modulate the polarization state of the signal light transmitted in the optical fiber and measure the Stokes parameters of the echo light signal.

[0034] The tilted fiber Bragg grating 10 is used to diffract the input light into the free space at a wavelength-dependent diffraction angle; the second focusing lens 11 is used to focus the wavelength-dependent diffracted light in the free space and input the focused diffracted light into the array detector; the array detector 12 is used to detect the focused diffracted light and perform spectral and polarization calculations.

[0035] After the broadband light source 1 emits a broadband laser into free space, it is collimated and focused in free space by the collimator 2 and the first focusing lens 3, and then incident on the two-dimensional scanning galvanometer 4. The two-dimensional scanning galvanometer reflects the focused beam to the surface of the imaging object 5, and then generates an echo signal, which is received by the telescope 6 and focused to the fiber collimator 7. The fiber collimator 7 couples the echo signal light in the free space into the optical fiber 8 for transmission. The echo signal light is polarization modulated by the electric polarization controller 9, and then diffracted into the free space at a wavelength-related diffraction angle by the tilted fiber grating 10. The diffracted light of different wavelengths is then focused onto the array detector 12 by the second focusing lens 11.

[0036] like Figure 4 The figure shows an example of a polarization spectrum imaging lidar system according to the present invention, comprising a broadband light source 1, a collimator 2, a first focusing lens 3, a two-dimensional scanning galvanometer 4, an imaging object 5, a telescope 6, a fiber collimator 7, an optical fiber 8, a motorized polarization controller 9, a tilted fiber Bragg grating 10, a second focusing lens 11, an array detector 12, and a housing 15. The black arrows represent signal light. For clarity, the six directions of the housing 15 are used for description: front, back, left, right, top, and bottom. The broadband light source 1, collimator 2, and first focusing lens 3 are placed parallel to each other at the rear of the housing 15. The collimator 2 is located 5 cm to the left of the light outlet of the broadband light source 1, the first focusing lens 3 is located 5 cm to the left of the collimator 2, and the two-dimensional scanning galvanometer 4 is located 20 cm to the left of the first focusing lens 3. The telescope 6, fiber collimator 7, optical fiber 8, and electric polarization controller 9 are placed parallel to each other in the center of the housing 15. The fiber collimator 7 is located 10 cm to the left of the telescope 6, and the electric polarization controller 9 is located 10 cm to the left of the fiber collimator 7. They are connected by optical fibers. A tilted fiber Bragg grating (FBG) 10 is fixed to the left side of the housing 15. A second focusing lens 11 and an array detector 12 are placed parallel to each other at the front side of the housing 15. The second focusing lens 11 is located 20 cm to the right of the tilted fiber Bragg grating 10, and the array detector 12 is located 20 cm to the right of the second focusing lens 11. The final assembled dimensions of the present invention do not exceed 50 cm × 50 cm × 30 cm (length, width, and height), making the system compact.

[0037] like Figure 2 The figure shows the imaging flow chart of a polarization spectrum imaging lidar system proposed by the present invention. After the broadband light source generates laser light, the scanning galvanometer is driven to make the echo signal of a certain imaging point of the imaging object enter the optical fiber transmission. The coordinates of the imaging point are recorded as , then the polarization is modulated by driving the electric polarization controller to rotate it by θ degrees. In order to calculate the Stokes parameter, it is necessary to select at least eight angles with the same interval from 0° to 180° to measure the power to ensure the accuracy of the calculation. Therefore, the value of θ should satisfy: θ<22.5°. The smaller the value of θ, the more total rotations are required, and the higher the calculation accuracy. The polarization modulated optical signal is diffracted into free space by the tilted fiber grating and received by the array detector. The spectral information and average power are then calculated. , determine whether the current deflection modulation number n is greater than the total modulation number N. If it does not reach the total modulation number, change the rotation angle of the electric polarization controller to perform polarization modulation until n>N. Then calculate the Stokes parameter of the scanning galvanometer at the imaging point of the imaging object based on the average power of N modulations. The calculation formula is as follows:

[0038]

[0039] in 、 、 、 Represent the first, second, third, and third Fourier coefficients, respectively, which are used to calculate the Stokes parameters; 、 、 、 There are four Stokes parameters that can be used to fully describe the polarization state of light, representing the total light intensity, the difference between the horizontally polarized light intensity and the vertically polarized light intensity, the difference between the +45° polarized light intensity and the -45° polarized light intensity, and the difference between the right-handed circularly polarized light intensity and the left-handed circularly polarized light intensity.

[0040] The system then determines whether the entire object has been scanned. If not, it returns to step 2, driving the scanning mirror to continue analyzing the spectral information and Stokes parameters of the echo signal at the next imaging point. If the entire object has been scanned, polarization spectral imaging is performed based on the obtained two-dimensional intensity, spectral, and polarization information.

[0041] like Figure 3As shown, the present invention also includes a polarization adjustment and calibration device for a polarization spectrum imaging laser radar system. The calibration device is used to calibrate and correct the electric polarization controller of the imaging laser radar system. The polarization adjustment and calibration device includes a broadband light source 1, an electric polarization controller 9, a tilted fiber Bragg grating 10, a second focusing lens 11, an array detector 12, a coupler 13, and a polarization analyzer 14. After the broadband light source 1 generates laser light, the polarization state is modulated by the electric polarization controller 9 and then divided into two paths by the coupler 13. One path is input to the polarization analyzer 14, and the other path is input to the tilted fiber Bragg grating 10. The tilted fiber Bragg grating 10 diffracts into free space. The second focusing lens 11 focuses the wavelength diffracted light in free space, and the focused diffracted light is detected by the array detector 12.

[0042] The working process of the calibration device of the utility invention is as follows: the broadband light source 1 emits broadband laser, which is polarized by the electric polarization controller 9 and then divided into two equal power paths by the coupler. Each time the polarization modulation is performed, the electric polarization controller rotates a step angle. Observe the polarization change on the polarization analyzer until a cycle of change is observed. Record the step angle of each rotation The degree of polarization change after Finally, is the vertical axis, As the horizontal axis, a curve is fitted to draw the polarization adjustment calibration curve. The generated polarization adjustment calibration curve is used to correct the rotation angle of the polarization modulation of the upper lidar system to obtain the correct θ. For example, assuming that the target rotation angle θ is determined to be 22.5°, the corresponding polarization change degree should be , find the y-axis value according to the polarization adjustment calibration curve Assuming the corresponding x-axis value is 23°, the actual rotation angle of the motorized polarization controller in a polarization spectral imaging lidar system should be 23°. The purpose of this calibration system step is to ensure that the polarization change degree of the motorized polarization controller is consistent during each polarization modulation during the imaging process. After calibration, the polarization measurement error can be reduced to less than 1%.

Claims

1. A polarization spectrum imaging laser radar system, comprising a broadband light source, a collimating mirror, a first focusing lens, a two-dimensional scanning galvanometer, an imaging object, a telescope, a fiber collimator, an optical fiber, a motorized polarization controller, a tilted fiber Bragg grating, a second focusing lens, and an array detector, characterized in that: The broadband light source generates laser light that passes through a collimating mirror and a first focusing lens and then irradiates a two-dimensional scanning galvanometer. The laser light is then reflected by the two-dimensional scanning galvanometer and irradiates an imaging object. The light reflected by the imaging object is collected by a telescope and enters a fiber collimator. The light is then transmitted to an electric polarization controller through an optical fiber. After the electric polarization controller modulates the polarization state, the light enters a tilted fiber grating (FBG), which diffracts the light into free space. The second focusing lens focuses the wavelength diffracted light in free space and detects the focused diffracted light through an array detector. After the laser light is generated by the broadband light source, the scanning galvanometer is driven to cause an echo signal from a certain imaging point of the imaging object to enter the optical fiber for transmission. The polarization is then modulated by driving the electric polarization controller, causing the light to rotate by θ degrees. The device also includes a polarization adjustment calibration device, which includes a broadband light source, an electric polarization controller, a tilted fiber Bragg grating, a second focusing lens, an array detector, a coupler, and a polarization analyzer. After the broadband light source generates laser light, the polarization state is modulated by the electric polarization controller and then divided into two paths by the coupler. One path is input into the polarization analyzer, and the other path is input into the tilted fiber Bragg grating. The tilted fiber Bragg grating is diffracted into free space. The second focusing lens focuses the wavelength diffracted light in the free space and the array detector detects the focused diffracted light. The working process of the polarization adjustment calibration device is as follows: the broadband light source emits signal light, which is polarization modulated by the electric polarization controller and then divided into two equal power paths by the coupler. Each time the polarization modulation is performed, the electric polarization controller rotates a step angle. Observe the polarization change on the polarization analyzer and observe a change cycle; record the step angle of each rotation The degree of polarization change after ;by is the vertical axis, The horizontal coordinate is fitted with a curve to draw the polarization adjustment calibration curve. The generated polarization adjustment calibration curve is used to correct the rotation angle of the polarization modulation of the lidar system to obtain the correct θ.

2. The polarization spectrum imaging laser radar system according to claim 1, characterized in that: It also includes a packaging shell, a broadband light source, a collimator, and a first focusing lens are placed in parallel on the rear side of the interior of the packaging shell, the collimator is located 5 cm to the left of the broadband light source, the first focusing lens is located 5 cm to the left of the collimator, the two-dimensional scanning galvanometer is located 20 cm to the left of the first focusing lens, the telescope, the fiber collimator, the optical fiber, and the electric polarization controller are placed in parallel in the middle of the packaging shell, the fiber collimator is located 10 cm to the left of the telescope, and the electric polarization controller is located 10 cm to the left of the fiber collimator, and are connected by optical fiber; the tilted fiber Bragg grating is fixed on the left side of the packaging shell, the second focusing lens and the array detector are placed parallel to the front side of the interior of the packaging shell, the second focusing lens is located 20 cm to the right of the tilted fiber Bragg grating, and the array detector is located 20 cm to the right of the second focusing lens.

3. A polarization spectral imaging laser radar system according to claim 1 or 2, characterized in that: After the array detector receives the light signal, it performs spectrum calculation and average power calculation to obtain the spectrum information. and average power .

4. A polarization spectral imaging laser radar system according to claim 1 or 2, characterized in that: Perform Fourier analysis on the average power calculated after each polarization modulation to obtain the four coefficients ABCD, from which the Stokes parameters are calculated. , Where N is the total number of modulations, n is the current deflection modulation number, The rotation angle for the current deflection modulation times.

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