Pure solid-state scanning type absolute distance measurement system and target detection method thereof

Abstract

The invention provides a pure solid-state scanning type absolute ranging system and a target detection method thereof. The pure solid-state scanning type absolute ranging system comprises a light source, an optical fiber amplifier, a spatial light polarization controller, a pure solid-state light beam scanning and interference module, a spectrum acquisition module and a control and calculation module, the pure solid-state light beam scanning and interference module is based on the wavefront regulation and control principle, dynamic modulation of incident light wavefront is achieved by loading a two-dimensional programmable grating phase on a spatial light modulator, and therefore light beams are controlled to complete pure solid-state scanning in space according to a set path. When a scanning light beam irradiates a target pyramid, a strong return light signal is generated, the spectrum acquisition module captures two-dimensional spectrum resolution and two-dimensional spectrum image imaging of an interference signal, and the control and calculation module performs high-precision distance calculation of a target absolute distance through phase extraction and interference fringe analysis based on a dispersion interference principle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precise length measurement, in particular to a high-precision absolute distance measurement based on a femtosecond optical frequency comb and a dispersion interference principle, and specifically relates to a pure solid-state scanning absolute distance measurement system and a target detection method thereof. BACKGROUND

[0002] With the continuous evolution of high-end manufacturing towards complexity and intelligence, the structure of manufacturing devices is increasingly precise, and the scale and geometric complexity of measurement objects are constantly improving, which puts forward higher requirements for measurement systems in terms of the number of measurement points, measurement accuracy, response speed, and system integration. The traditional single-point or single-channel distance measurement method has been difficult to meet the efficient measurement needs of large-size and high-complexity structures. Currently, absolute distance measurement is developing in the direction of large-scale coverage, multi-target synchronization, high spatial resolution, high measurement rate, and system miniaturization. Under this background, developing high-precision laser absolute distance measurement technology with high flexible configuration capability and high-speed sampling capability has become a key technical direction that needs to be broken through.

[0003] Currently, femtosecond optical frequency combs are gradually being applied in the field of absolute distance measurement due to their high stability, wide bandwidth, and the ability to achieve spectral segmentation. Multi-channel distance measurement schemes using optical frequency combs as light sources mainly adopt the "splitting frequency" strategy as shown in CN117516385A and the "splitting light intensity" strategy as described in CN115031630B. CN117516385A discloses a system that uses a wavelength division multiplexer to allocate different wavelength regions to multiple distance measurement channels to achieve multi-channel synchronous distance measurement. The interference distance measurement system described in CN115031630B uses a beam splitter group composed of multiple beam splitters in cascade to guide light to multiple distance measurement channels, achieving multi-channel distance measurement. Although the above two methods have certain applicability in some distance measurement applications, their channel configuration is highly dependent on the pre-assignment of optical spectrum and light intensity, and the angle and spatial position of the outgoing light are limited by the hardware structure of the system, making it difficult to achieve dynamic configuration and flexible measurement, and lacking adaptability when facing changes in the number or position of targets.

[0004] To improve system flexibility, a common alternative solution is to introduce mechanical scanning means such as galvanometer mirrors to achieve dynamic pointing of the light beam in space, thereby covering multiple measurement targets. For example, CN111708004B discloses a distance measurement device that uses a galvanometer structure to achieve spatial deflection of a laser beam, which can perform point-by-point scanning measurement on multiple targets. This type of method has strong flexibility, but it relies on the dynamic driving of precise mechanical components and the tracking control of closed-loop algorithms, which has problems such as complex structure, difficult debugging, and low system integration.

[0005] In addition, the interferometric distance measurement system disclosed in CN115031630B uses a single-grating light splitting structure to collect spectral signals, and the obtained spectral resolution is limited. CN119413280A uses a rotating mirror structure with grating light splitting function to obtain a spectral pattern with higher resolution. However, the sampling rate of this structure is limited by the grating motion mechanism, and there is a constraint relationship between high sampling rate and high spectral resolution, thereby limiting its signal analysis capability in high-speed acquisition application scenarios. SUMMARY

[0006] In order to overcome the defects of the prior art, the present application provides a pure solid-state scanning absolute distance measurement system and a target detection method thereof. The pure solid-state scanning absolute distance measurement system is based on the principle of wavefront control, and by loading a two-dimensional programmable grating phase on a spatial light modulator, dynamic modulation of the incident light wavefront is realized, so as to control the light beam to complete pure solid-state scanning along a set path in space. Moreover, flexible control of the deflection angle of the light beam is realized by pure solid-state means, and a high-speed high-resolution spectrometer is designed to realize the cooperative matching between spatial light beam deflection and high-speed spectral sampling, thereby meeting the requirements of measurement efficiency and accuracy.

[0007] The object of the present application is achieved by the following technical solutions:

[0008] The first aspect of the present application is to provide a pure solid-state scanning absolute distance measurement system, comprising a light source, a fiber amplifier, a spatial light polarization controller, a pure solid-state light beam scanning and interference module, a spectral acquisition module and a control and calculation module connected in sequence.

[0009] The light source is used to generate femtosecond pulse laser.

[0010] The spatial light polarization controller is used to adjust the light signal so that the polarization state of the output light matches the required polarization state of the spatial light modulator.

[0011] The pure solid-state light beam scanning and interference module comprises a measurement arm, a reference arm, a first corner cube prism, a plurality of second corner cube prisms, a non-polarization beam splitting cube and a spatial light modulator.

[0012] The spatial light modulator controls the spatial deflection of the light beam in a pure solid-state manner, and is used for dynamic control of the direction of the outgoing light.

[0013] The first corner cube prism is arranged on the reference arm, and the second corner cube prisms are randomly placed in the scanning field of view of the spatial light modulator.

[0014] The incident end of the pure solid light beam scanning and interference module receives the outgoing light signal of the spatial light polarization controller and is orthogonally split by a non-polarization beam splitting cube, one way of which is reflected back along the original path after passing through a first corner prism; the other way is to realize the modulation of the incident light wavefront by loading a two-dimensional programmable grating phase on the spatial light modulator; a plurality of second corner prism targets in the scanning field of view are scanned, and the back light generated by the second corner prism and the reference light beam are reflected back through their respective light paths and then superimposed again in the non-polarization beam splitting cube to generate an interference signal at the output end; and the spatial light modulator 8 is electrically connected to the control and calculation module;

[0015] The spectral acquisition module is located at the outgoing end of the pure solid light beam scanning and interference module; it is used for linear focusing of the incident interference light from the pure solid light beam scanning and interference module, high-resolution spectral spreading in the longitudinal direction, and then secondary splitting of the signal after the longitudinal spectral spreading in the transverse direction, so as to realize two-dimensional spectral resolution and two-dimensional spectral image imaging of the interference signal, and high-speed two-dimensional spectral acquisition of each frequency in the interference image;

[0016] The control and calculation module is used for setting the scanning points and loading the phase diagram to the liquid crystal surface of the spatial light modulator, controlling the light beam to complete the pure solid scanning in the space along the set path, and receiving the two-dimensional spectral image from the spectral acquisition module, based on the dispersion interference principle, through phase extraction and interference fringe analysis, to perform high-precision distance calculation of the target absolute distance.

[0017] Further, a collimator is arranged between the optical fiber amplifier and the spatial light polarization controller.

[0018] Further, the spatial light polarization controller comprises a thin film linear polarizer and a 1 / 2 wave plate, the thin film linear polarizer receives the light signal from the collimator and generates linearly polarized light, and the 1 / 2 wave plate is used to adjust the polarization direction of the linearly polarized light.

[0019] Further, the spectral acquisition module is integrally installed in a constant-temperature vibration isolation dark box.

[0020] Further, the spectral acquisition module comprises a cylindrical lens, a VIPA, a grating, a convex lens and a CMOS camera; the cylindrical lens linearly focuses the light from the pure solid light beam scanning and interference module, and then the light sequentially passes through the orthogonally arranged VIPA and grating elements for two-dimensional dispersion processing, and finally is focused to the CMOS camera through the convex lens, realizing high-speed imaging acquisition of each comb interference signal; the CMOS camera converts the light signal into an electrical signal to form a two-dimensional spectral image.

[0021] Further, the spectral acquisition module and the spatial light modulator are matched in sampling rate, and the spatial light modulator is arranged at an angle of 45° between its normal direction and the incident light beam.

[0022] Further, the number of the second corner cube prisms is at least one. In a preferred embodiment, the number of the second corner cube prisms is 1-5.

[0023] The target detection method of the pure solid-state scanning absolute distance measurement system based on light wave front regulation and orthogonal light splitting includes:

[0024] Step one: pre-set a first corner cube prism and a plurality of second corner cube prisms; the first corner cube prism is on a reference arm, and the second corner cube prisms are randomly placed in a scanning field of view of a spatial light modulator; adjust the postures of all the corner cube prisms to ensure that a light beam can return to the original path after being incident on the corner cube prisms;

[0025] Step two: generate a femtosecond laser through a light source, and then sequentially pass through a fiber amplifier, a collimator, and a spatial light polarization controller to be incident on a non-polarization beam splitting cube; then the light is split into two parts, one part is a reference light beam, which is incident on the reference arm and returns to the original path after passing through the first corner cube prism; the other part is a measurement light beam, which is incident on a measurement arm;

[0026] Step three: the measurement light beam is incident on the surface of the spatial light modulator (SLM), and the host computer sets scanning points and sequentially loads single-frame phase maps to the liquid crystal surface of the spatial light modulator, so that the measurement light scans all points in the entire field of view according to a preset S-shaped spatial scanning track in the far field, to realize pure solid-state point-by-point scanning;

[0027] Step four: monitor the interference images returned by the CMOS camera during the scanning process, and judge in real time whether there is an additional interference signal except the longitudinal mode signal generated by the reference arm; if yes, it means that the measurement arm receives the target reflection signal at the current scanning position, and step five is executed;

[0028] Otherwise, only the background interference fringes formed by the fixed return light of the reference arm are presented in the interference image, and it is considered that there is no effective target at the current scanning position, and the new phase map is loaded in step three;

[0029] Step five: the return light generated by the second corner cube prism in the measurement arm and the reference light beam return after passing through their respective light paths, and then are superimposed in the non-polarization beam splitting cube to generate an interference signal at the output end, and form a two-dimensional spectrum image in the incident spectrum acquisition module;

[0030] Step six: receive the two-dimensional spectrum image, and based on the dispersion interference principle, perform high-precision distance calculation of the target absolute distance through phase extraction and interference fringe analysis;

[0031] Step seven: judge whether the current scanning process has covered all scanning points in the field of view, if yes, end the target detection process; otherwise, return to step three to continue the point-by-point scanning operation on the field of view until all scanning points are traversed or a preset termination condition is reached.

[0032] Further, the step of forming a two-dimensional spectral image in the spectral acquisition module in step five specifically comprises: the incident interference signal is linearly focused by a cylindrical lens, longitudinally dispersed by a VIPA, further dispersed by a grating, and then focused by a convex lens to form a two-dimensional spectral image on the back focal plane of a CMOS camera.

[0033] Further, the step six comprises:

[0034] The one-dimensional mapping data of the intensity of the interference signal-frequency is obtained by reconstructing all the fringe lines in a single free spectral range in the two-dimensional spectral image through an image processing algorithm, and the corresponding relationship between the interference fringe intensity and the frequency The cosine curve fitting is performed, the slope of the change of the phase with the frequency is extracted through the fitting, so that the optical path difference between the reference arm and the measurement arm, which is equivalent to the measured absolute distance, is obtained, and high-precision calculation of the absolute distance is obtained.

[0035] The pure solid-state scanning absolute distance measurement system based on the light wavefront regulation and orthogonal dispersion has the following beneficial effects:

[0036] Based on the wavefront regulation principle, the two-dimensional programmable grating phase is loaded on the spatial light modulator to realize flexible control of the deflection angle of the light beam, so that the light beam completes pure solid-state scanning according to the set path in space.

[0037] Based on the orthogonal dispersion principle, a high-speed high-resolution spectrometer is designed to collect the spectrum at high speed, which realizes the collaborative matching between the high dynamic deflection of the spatial light beam and the high-speed sampling of the spectrum, and meets the requirements of measurement efficiency and accuracy.

[0038] The pure solid-state scanning absolute distance measurement system is designed, the scanning points are set by the upper computer and the phase diagram is loaded to the liquid crystal surface of the spatial light modulator, so that the measurement light scans all points in the entire field of view according to the preset S-shaped spatial scanning track in the far field, when the scanning light beam irradiates to the target angle cone, a strong back light signal is generated and forms an interference signal with the reference light, and is captured at the spectrometer module. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a schematic diagram of the pure solid-state scanning absolute distance measurement system;

[0040] Figure 2 is a flowchart of the target detection method of the pure solid-state scanning absolute distance measurement system.

[0041] Among them, 1: femtosecond optical frequency comb light source; 2: fiber amplifier; 3: collimator; 4: thin film linear polarizer; 5: half wave plate; 6: unpolarized beam splitter cube; 71: first corner cube prism; 72: second corner cube prism; 8: spatial light modulator; 9: host computer; 10: cylindrical lens; 11: VIPA; 12: grating; 13: convex lens; 14: CMOS camera. Detailed Implementation

[0042] To make the objectives, technical solutions, beneficial effects, and significant advancements of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings provided in the examples of the present invention. Obviously, all the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort and in accordance with the content, implementation methods, and drawings of the present invention are within the scope of protection of the present invention.

[0043] It should be noted that the terms "first," "second," "third," etc., in the specification and claims of this invention are only used to distinguish different objects, and not to describe a specific order.

[0044] It should also be noted that the following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0045] like Figure 1 As shown, a pure solid-state scanning absolute ranging system includes a light source 1, an optical fiber amplifier 2, a collimator 3, a spatial light polarization controller, a pure solid-state beam scanning and interferometry module, a control and calculation module, and a spectrum acquisition module, which are connected in sequence via optical fibers.

[0046] The light source 1 uses a femtosecond optical frequency comb as the light source to generate broadband femtosecond pulsed laser.

[0047] The fiber amplifier 2 is an erbium-doped fiber amplifier, used to amplify the power of the output signal of the light source 1 and provide the required optical gain.

[0048] The collimator 3 receives the optical signal from the fiber amplifier 2 and couples the light into the spatial optical polarization controller with maximum efficiency.

[0049] The spatial light polarization controller includes a thin-film linear polarizer 4 and a half-wave plate 5. The thin-film linear polarizer 4 receives the optical signal from the collimator 3 and generates linearly polarized light, while the half-wave plate is used to adjust the polarization direction of the linearly polarized light. The relative angle of the two plates is pre-rotated to match the polarization state of the output light with the polarization state required by the spatial light modulator (SLM).

[0050] The pure solid-state light beam scanning and interference module includes a non-polarization beam splitting cube 6, a measurement arm, a reference arm, a first corner cube prism 71, a plurality of second corner cube prisms 72, and a spatial light modulator 8. The non-polarization beam splitting cube 6 is used to orthogonally split the light beam from the spatial light polarization controller to form a reference light beam and a measurement light beam. The light beam on the reference arm is the reference light beam, which is back-reflected by the first corner cube prism 71. The light beam on the measurement arm is the measurement light beam, which is deflected based on wavefront control by the spatial light modulator 9 to scan and cover a plurality of second corner cube prism targets in the field of view. The plurality of second corner cube prisms are randomly arranged in the scanning field of view of the spatial light modulator and are used to reflect the measurement light beam back to the interference region. The back light generated by the second corner cube prisms 72 and the reference light beam are re-overlapped in the non-polarization beam splitting cube 6 after being back-reflected through respective light paths, and an interference signal is generated at the output end of the non-polarization beam splitting cube 6, which is then emitted to the spectral acquisition module. The spatial light modulator 8 is electrically connected to the upper computer 9. The spatial light modulator is arranged at an angle of 45° between its normal direction and the incident light beam. The liquid crystal surface of the spatial light modulator loads a programmable phase pattern at a refresh rate of 100 Hz to control the spatial deflection of the light beam in a pure solid-state manner, dynamically control the direction of the emitted light, and realize scanning of different angle lines covering the entire field of view in a short time.

[0051] The spectral acquisition module is arranged at the exit end of the pure solid-state light beam scanning and interference module and is used for high-speed two-dimensional spectral acquisition. Moreover, the spectral acquisition module is integrally installed in a constant-temperature vibration isolation dark box to reduce the influence of environmental disturbance on imaging accuracy. The spectral acquisition module is arranged at the exit end of the pure solid-state light beam scanning and interference module and is installed in the constant-temperature vibration isolation dark box. The spectral acquisition module includes a cylindrical lens 10, a VIPA 11, a grating 12, a convex lens 13, and a CMOS camera 14. The cylindrical lens 10 performs line focusing on the incident interference light from the pure solid-state light beam scanning and interference module. The VIPA is used to perform high-resolution spectral spreading on the interference signal in the longitudinal direction. The spectral splitting function of the VIPA is only effective in the longitudinal direction, and the output light does not provide effective wavelength resolution capability in the transverse direction. The grating is arranged at the exit end of the VIPA. The grating 12 is arranged in a direction orthogonal to the spectral splitting direction of the VIPA and is used to perform transverse secondary spectral splitting on the signal after longitudinal spectral spreading, thereby realizing two-dimensional spectral resolution of the interference signal. The convex lens is arranged after the spectral splitting element and is used to image the two-dimensional spectral image to the back focal plane. The CMOS camera is arranged at the imaging plane and is used to perform high-speed acquisition on each frequency component in the interference image. The grating and the CMOS camera are arranged at the front focal plane and the back focal plane of the convex lens, respectively, to ensure imaging quality and dispersion accuracy.

[0052] The control and calculation module includes a host computer 9 receiving electrical signals from a CMOS camera 14, controlling the spatial light modulator to load a phase pattern to achieve fast programmable light beam pure solid-state scanning; at the same time, the two-dimensional spectral images collected by the CMOS camera are processed, based on the dispersion interference principle, through phase extraction and interference fringe analysis, to realize high-precision distance calculation of the target absolute distance.

[0053] As shown in Figure 2 , the target detection method of the pure solid-state scanning absolute distance measurement system based on light wavefront regulation and orthogonal light splitting comprises the following steps:

[0054] Step one: the first corner cube mirror 71 and a plurality of second corner cube prisms 72 are set in advance; the first corner cube mirror 71 constructs a reference target on the reference arm, and the second corner cube prisms 72 are randomly placed in the scanning field of view of the spatial light modulator to construct a measurement target; the poses of all the corner cube mirrors are adjusted to ensure that the light beam can return to the original path after being incident to the corner cube mirror;

[0055] The light source 1 generates femtosecond laser, which is sequentially amplified in optical fiber amplifier 2, exits as collimated laser through collimator 3, and adjusts the polarization state of the output light through spatial light polarization controller, so as to match the polarization state of the spatial light modulator 8, and then is incident to the pure solid-state light beam scanning and interference module.

[0056] Step two: the light beam incident to the pure solid-state light beam scanning and interference module is divided into two parts by the non-polarization beam splitting cube 6, one part is the reference light beam, which is incident to the reference arm and returns to the original path after the first corner cube prism 71; the other part is the measurement light beam, which is incident to the measurement arm;

[0057] Step three: the measurement light beam hits the liquid crystal surface of the spatial light modulator 8, and the host computer presets the scanning starting point and the phase pattern sequence, so that the measurement light scans all points in the entire field of view in S-shaped space scanning trajectory according to column priority order, to realize pure solid-state point-by-point scanning. Specifically, it includes:

[0058] S31: assuming that the spatial light modulator 8 (hereinafter referred to as SLM) far field imaging plane has a spatial resolution of , a two-dimensional rectangular coordinate system is established with the lower left corner as the origin, and is taken as the scanning starting point, and the first column point is scanned from top to bottom according to column priority order, then the second column point is scanned from bottom to top, and so on to scan all columns, forming an S-shaped space scanning trajectory;

[0059] In the first frame scanning process, if the target far field coordinate is , a magnitude mask matrix is constructed.wherein The amplitude mask matrix is input as the expected far-field intensity distribution, and the host computer control and calculation module iteratively generates the corresponding phase hologram using the Gerchberg-Saxton (GS) algorithm ;

[0060] All the single-frame phase holograms are arranged in an S-shaped scanning sequence as a priori determined hologram sequence to be loaded, denoted as:

[0061] .

[0062] S32: Determine whether the measurement system is in the initial state for the first time, i.e., whether the value is 1, if so, take the initial scanning starting point as the initial value, load the first phase image, and execute step S33; Otherwise, load the first phase image according to the S-shaped scanning sequence, and execute step S33.

[0063] Otherwise, load the first phase image according to the S-shaped scanning sequence, and execute step S33.

[0064] S33: Load the hologram to the SLM liquid crystal surface for subsequent acquisition and analysis.

[0065] To improve scanning efficiency, a suitable spatial step, i.e., spatial resolution, can be selected according to the target size to avoid pixel-by-pixel scanning, and the SLM has high frame rate response capability, so the overall scanning process theoretically takes a short time.

[0066] Step four: Real-time monitoring of the intensity distribution of the interference image returned by the CMOS camera in the spectral acquisition module. Determine whether there is an additional interference signal in the scanning process in addition to the longitudinal mode signal generated by the reference arm; if so, it means that the second corner cube prism 72 randomly placed in space has been detected, i.e., the measurement arm receives the target reflection signal at the current scanning position, causing a local concentrated bright spot in the far field at the corresponding position, and executing step five.

[0067] Otherwise, only the background interference fringes formed by the fixed return light of the reference arm are presented in the CMOS image, and there is no additional signal change, so it is considered that the current scanning position has no effective target, and the new phase image is loaded in step three.

[0068] Step five: In the scanning process, the bright spot coordinates in the field of view change constantly and move in an s-shaped manner, realizing pure solid-state point-by-point scanning based on the SLM; after scanning, the return light generated by the second corner cube prism 72 and the reference light beam are re-overlapped in the non-polarization beam splitting cube 6 after being reflected through their respective optical paths, generating an interference signal at the output end and sending it to the spectral acquisition module. ​​​​

[0069] Step six: the incident interference signal is linearly focused by the cylindrical lens 10, and then longitudinally dispersed by the VIPA 11. The VIPA 11 uses its interference structure to angularly separate different wavelengths of light in a direction perpendicular to the incident plane, and its spectral dispersion behavior can be described by the following relationship:

[0070]

[0071] wherein

[0072]

[0073] is the phase difference, is the wavelength of light, are the reflectivities of the front and back surfaces of the VIPA respectively, is the wave number, is the radius of the collimated light beam before entering the cylindrical lens, is the focal length of the cylindrical lens, is the focal length of the convex lens. is the longitudinal distance of the imaging point on the screen from the origin, and it can be seen that the dispersion of the VIPA is only effective in the longitudinal direction, and the output appears as a narrow and thin vertical light beam. Different wavelengths of light will overlap at the same longitudinal position and cannot be distinguished. Therefore, the output light of the VIPA needs to be incident on the grating 12 placed orthogonally to the VIPA, which further disperses light according to the grating equation

[0074]

[0075] wherein is the grating constant, i.e. the distance between two adjacent lines; and are the incident angle and the diffraction angle respectively; integer is the diffraction order, which is usually 1.

[0076] The grating 12 functions as a "wavelength-dependent transverse dispersion" that expands the wavelength information of different orders compressed in the same longitudinal line in the transverse direction to generate a two-dimensional high-resolution spectral image. The grating 12 can perform a second wavelength expansion in the transverse direction on the output light beam of the VIPA 11 to separate the originally longitudinally overlapping signals by wavelength.

[0077] Finally, after focusing by the convex lens 13, a two-dimensional spectral image is formed on the back focal plane of the CMOS camera 14, and the CMOS camera 14 completes high-speed spectral imaging and acquisition. Since the VIPA and grating dispersion processes are almost synchronous, the system can achieve high spectral resolution while maintaining high temporal resolution.

[0078] Step seven: the host computer 9 receives the two-dimensional spectral image captured by the CMOS camera and performs high-precision distance calculation. Specifically, it includes:

[0079] S71: Because the free spectral range of the VIPA element in the spectral acquisition module is limited in the vertical direction, each image vertical line can only record a limited number of frequency patterns. To completely recover the spectral structure, the host computer first reconstructs all vertical lines within a single free spectral range in the two-dimensional spectral image through an image stitching algorithm to obtain the mapping data of the interference signal intensity-frequency, that is,

[0080]

[0081] wherein, is the frequency component of the optical frequency comb, is the corresponding relationship of the reconstructed interference fringe intensity with frequency, represents the relationship between the interference signal amplitude and the frequency under ideal conditions. In addition, the phase can be expressed as , wherein represents the optical path difference between the reference arm and the measurement arm in the pure solid-state light beam scanning and interference module, which is equivalent to the measured absolute distance, is the refractive index of the atmosphere, is the speed of light in vacuum.

[0082] S72: the corresponding relationship of the interference fringe intensity with frequency is fitted with a cosine curve, and the change slope of the phase with respect to the frequency is extracted through the fitting, and finally the absolute distance is calculated according to

[0083] (5)

[0084] to realize high-precision calculation of the absolute distance.

[0085] Step eight: judge whether the current scanning process has covered all scanning points in the field of view, that is, is , if so, end the target detection process; otherwise, return to S32 and continue to perform the point-by-point scanning operation on the field of view until all scanning points are traversed or the preset termination condition is reached.

[0086] The present application breaks away from the dependence on the number of second corner cube prisms, and even if there is only one second corner cube prism, as long as the measurement light performs a point-by-point scanning operation on the field of view according to the set S-shaped scanning path.

[0087] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing examples, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing examples can be modified, or some or all of the technical features can be replaced equivalently, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application. The non-essential improvements, adjustments or replacements made by those skilled in the art according to the content of the present application are within the scope of the present application.

Claims

1. A pure solid-state scanning absolute ranging system, characterized in that, It includes a light source (1), an optical fiber amplifier (2), a spatial light polarization controller, a pure solid-state beam scanning and interference module, a spectrum acquisition module, and a control and calculation module connected in sequence; The light source (1) is used to generate femtosecond pulsed laser; The spatial light polarization controller is used to adjust the optical signal so that the polarization state of the output light matches the polarization state required by the spatial light modulator (8); The solid-state beam scanning and interference module includes a measuring arm, a reference arm, a first corner cube prism (71), multiple second corner cube prisms (72), a non-polarizing beam splitter cube (6), and a spatial light modulator (8). The spatial light modulator (8) controls the spatial deflection of the beam in a purely solid-state manner, and is used for dynamic control of the direction of the outgoing light. The first corner bevel prism (71) is arranged on the reference arm, and the second corner bevel prism (72) is randomly placed in the scanning field of view of the spatial light modulator (8); The pure solid-state beam scanning and interference module receives the light signal emitted from the spatial light polarization controller at its incident end and orthogonally splits it through the non-polarized beam splitting cube (6). One path is reflected back along the reference arm through the first corner bevel prism (71) and then back along the original path. The other path modulates the incident light wavefront by loading a two-dimensional programmable grating phase onto the spatial light modulator (8). Multiple second corner bevel prism targets are scanned in the field of view. The backlight generated by the second corner bevel prism (72) and the reference beam are reflected back through their respective optical paths and then superimposed in the non-polarized beam splitting cube (6), generating an interference signal at its output end. Moreover, the spatial light modulator (8) is electrically connected to the control and calculation module. The spectral acquisition module is located at the output end of the pure solid-state beam scanning and interference module; it is used to perform line focusing on the incident interference light from the pure solid-state beam scanning and interference module, perform high-resolution spectral expansion in the longitudinal direction, and then perform secondary spectral splitting on the signal after longitudinal spectral expansion, thereby realizing two-dimensional spectral resolution and two-dimensional spectral image imaging of the interference signal, and performing high-speed two-dimensional spectral acquisition on each frequency in the interference image. The control and calculation module is used to set the scanning points and sequentially load the phase map onto the liquid crystal surface of the spatial light modulator (8), control the beam to complete the pure solid-state scanning in space according to the set path, and receive the two-dimensional spectrum image from the spectrum acquisition module. Based on the principle of dispersive interference, the module performs high-precision distance calculation of the target absolute distance through phase extraction and interference fringe analysis.

2. The pure solid-state scanning absolute ranging system according to claim 1, characterized in that, A collimator (3) is also provided between the fiber amplifier (2) and the spatial polarization controller.

3. The pure solid-state scanning absolute ranging system according to claim 1, characterized in that, The spatial light polarization controller includes a thin-film linear polarizer (4) and a half-wave plate (5). The thin-film linear polarizer (4) receives light signals from the collimator (3) and generates linearly polarized light, while the half-wave plate (5) is used to adjust the polarization direction of the linearly polarized light.

4. The pure solid-state scanning absolute ranging system according to claim 1, characterized in that, The entire spectral acquisition module is installed in a constant temperature and vibration isolation dark box.

5. The pure solid-state scanning absolute ranging system according to claim 1, characterized in that, The spectral acquisition module includes a cylindrical lens (10), a VIPA (11), a grating (12), a convex lens (13), and a CMOS camera (14). The cylindrical lens (10) performs line focusing on the light from the pure solid-state beam scanning and interference module. Then, the light passes through the orthogonally arranged VIPA (11) and grating (12) elements for two-dimensional dispersion processing. Finally, it is focused by the convex lens (13) onto the CMOS camera (14) to achieve high-speed imaging acquisition of the interference signals of each comb tooth. The CMOS camera (14) converts the optical signal into an electrical signal to form a two-dimensional spectral image.

6. The pure solid-state scanning absolute ranging system according to claim 1, characterized in that, The spectral acquisition module and the spatial light modulator (8) are matched in sampling rate, and the spatial light modulator (8) is arranged with its normal direction at a 45° angle to the incident beam.

7. The pure solid-state scanning absolute ranging system according to claim 1, characterized in that, The number of the second corner cube prism (72) is at least one.

8. The target detection method of the pure solid-state scanning absolute ranging system according to any one of claims 1 to 7, comprising: Step 1: Pre-set a first corner bevel (71) and multiple second corner bevel prisms (72); wherein the first corner bevel (71) is on the reference arm, and the second corner bevel prisms (72) are randomly placed in the scanning field of view of the spatial light modulator; adjust the attitude of all corner bevels to ensure that the beam can return along the same path after entering the corner bevel; Step 2: The femtosecond laser generated by the light source (1) passes through the fiber amplifier (2), collimator (3), and spatial polarization controller in sequence before being incident on the unpolarized beam splitter cube (6); then the light is split into two parts, one part is the reference beam, which is incident on the reference arm and returns along the original path after passing through the first corner bevel prism (71); the other part is the measurement beam, which is incident on the measurement arm. Step 3: The measurement beam hits the surface of the spatial light modulator (SLM). The host computer sets the scanning points and loads the single-frame phase map onto the liquid crystal surface of the spatial light modulator (8) in sequence, so that the measurement beam scans all points in the entire field of view in the far field according to the preset S-shaped spatial scanning trajectory, realizing pure solid-state point-by-point scanning. Step 4: During the scanning process, monitor the interference image returned by the CMOS camera and determine in real time whether there are any additional interference signals besides the longitudinal mode signal generated by the reference arm; If so, it means that the measuring arm has received the target reflection signal at the current scanning position, and proceed to step five; Otherwise, if the interferometric image only shows the background interference fringes formed by the fixed backlight of the reference arm, it is considered that there is no effective target at the current scanning position, and the process returns to step three to load a new phase image. Step 5: The reflected light from the second corner prism in the measuring arm and the reference beam are reflected back through their respective optical paths and then superimposed in the non-polarized beam splitter cube, generating an interference signal at its output end, which is then incident on the spectral acquisition module to form a two-dimensional spectral image. Step Six: Receive the two-dimensional spectral image, and based on the principle of dispersive interference, perform high-precision distance calculation of the target's absolute distance through phase extraction and interference fringe analysis; Step 7: Determine whether the current scanning process has covered all scanning points within the field of view. If so, end the target detection process. Otherwise, return to step three and continue performing point-by-point scanning of the field of view until all scan points have been traversed or the preset termination condition has been met.

9. The target detection method according to claim 8, characterized in that, The steps in step five of forming a two-dimensional spectral image in the spectral acquisition module specifically include: the incident interference signal is linearly focused by the cylindrical lens (10), longitudinally dispersed by the VIPA (11), further split by the grating (12), and focused by the convex lens (13) to form a two-dimensional spectral image on the back focal plane of the CMOS camera (14).

10. The target detection method according to claim 8, characterized in that, Step six includes: By reconstructing all vertical lines within a single free spectral range in a two-dimensional spectral image using an image stitching algorithm, the intensity-frequency mapping data of the interference signal is obtained, and the correspondence between the intensity of the interference fringes and the frequency is determined. Cosine curve fitting is performed, and the slope of the phase change with respect to frequency is extracted through this fitting to obtain the optical path difference between the reference arm and the measuring arm, which is equivalent to the absolute distance being measured, thereby obtaining a high-precision solution for the absolute distance.

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