Long-distance high-precision laser positioning system and method based on tunnel environment

Abstract

The invention discloses a long-distance high-precision laser positioning system and method based on a tunnel environment, and the system comprises a laser emission unit which emits a fundamental mode Gaussian beam, and a beam expanding and collimating unit which is disposed at the downstream of a light path of the laser emission unit, carries out the beam expanding and collimating processing of the beam, and compresses the far-field divergence angle of the output beam; the adaptive optical control unit comprises a wavefront correction device and a control processor. The beam expanding and collimating unit has a thermal stability structure, and the optical material combination adopted by the lens is configured as follows: based on a thermal drift model, the influence of the thermal expansion coefficient and the refractive index temperature coefficient of the lens material on the focal length is mutually compensated; the control processor operates a stochastic parallel gradient descent algorithm, applies stochastic disturbance voltage to the wavefront correction device, and performs iterative optimization by taking the Strill ratio of the far-field light spot as an evaluation function, so as to adjust the wavefront phase of the output light beam in real time. According to the invention, the precision of long-distance laser positioning in a complex tunnel environment can be improved.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction equipment and laser technology, and specifically relates to a long-distance high-precision laser positioning system and method based on the tunnel environment. Background Technology

[0002] In the field of tunnel construction technology, the precise control of the tunneling axis and the positioning and installation of construction equipment are highly dependent on high-precision optical reference lines. Establishing a long-distance, highly stable laser reference line is a prerequisite for realizing the automation and intelligence of tunnel construction.

[0003] Chinese invention patent application CN114577188A discloses a laser collimation and guidance device and system for tunnel construction, comprising: a base; a calibration plate, one side of which is equipped with a laser emitter, and the other side of which is used to receive laser signals from the initial end of the tunnel or from laser emitters of other calibration plates; a calibration bracket connected to the calibration plate via a crossbar, the crossbar serving as the rotation axis of the calibration plate; a height adjustment structure mounted on the calibration bracket for adjusting the height of the calibration plate; a rotation structure connected to the calibration bracket for adjusting the angle of the calibration plate; and a horizontal displacement structure connected to the calibration bracket for adjusting the horizontal displacement of the calibration plate. Coordinate positioning is achieved through the calibration plate, ensuring that the laser beams emitted by the laser emitter are aligned end-to-end, guaranteeing the clarity of long-distance laser beam transmission, and overcoming the problem of low accuracy in measuring distant tunnel construction processes using a total station in low light conditions.

[0004] The above solutions still face significant technical bottlenecks when dealing with high-precision construction requirements, mainly in the following aspects: Existing technologies primarily focus on adjusting the displacement and angle of mechanical structures, without optimizing the physical transmission characteristics of the laser beam itself. Due to the physical diffraction effect of light, ordinary laser beams inevitably diverge during long-distance transmission (e.g., 50 meters and above). At a distance of 50 meters, the spot width of conventional laser line projectors often far exceeds the engineering requirement of 1 centimeter, resulting in a blurred spot on the calibration plate and difficulty in identifying the center, severely affecting the positioning accuracy of the baseline.

[0005] The working conditions inside the tunnel are extremely complex, with significant dust scattering, airflow disturbances caused by temperature and humidity changes, and vibrations from heavy machinery operations. Existing mechanical adjustment structures can only perform static geometric alignment and cannot address beam jitter and wavefront distortion caused by air turbulence in real time, leading to drift and morphological degradation of the far-field beam on the calibration plate. Dust interference manifests primarily as: laser energy attenuation, decreased signal-to-noise ratio, and reduced far-field beam contrast; alteration of beam propagation direction, causing non-fixed-mode wavefront distortion; and particularly strong scattering effects on dust particles with wavelengths similar to the laser wavelength.

[0006] Variations in tunnel ambient temperature cause optical components to expand and contract with temperature changes, altering the refractive index and radius of curvature of lenses. Current technologies do not address the thermal stability design of optical systems. Under prolonged operation, thermal drift of optical parameters can further exacerbate beam divergence and pointing errors, making it difficult to meet the demands of all-weather, high-precision, automated construction. Summary of the Invention

[0007] This invention provides a long-distance high-precision laser positioning system and method based on tunnel environments, aiming to solve the problem of insufficient positioning accuracy in the field of long-distance laser positioning in tunnel environments.

[0008] To address the aforementioned technical problems, this invention proposes a long-range, high-precision laser positioning system based on a tunnel environment, comprising a laser emitting unit for emitting a fundamental Gaussian beam, and: A beam expanding and collimating unit is located downstream of the optical path of the laser emitting unit. It is used to expand and collimate the fundamental mode Gaussian beam and compress the far-field divergence angle of the output beam. Adaptive optics control unit, including wavefront correction device and control processor; The beam expanding and collimating unit has a thermally stable structure, and the combination of optical materials used in the lens is configured such that, based on the thermal drift model, the influence of the thermal expansion coefficient and the temperature coefficient of refractive index of the lens material on the focal length is mutually compensated, so as to suppress beam divergence caused by changes in ambient temperature. The adaptive optics control unit is configured to perform dynamic compensation: the control processor runs a stochastic parallel gradient descent algorithm, applies a random perturbation voltage to the wavefront correction device, and iteratively optimizes the wavefront phase of the output beam in real time using the Strell ratio of the far-field spot as the evaluation function to compensate for dynamic aberrations caused by environmental turbulence or vibration.

[0009] Preferably, the beam expanding and collimating unit adopts a Kepler telescope structure, including a focal length of... The eyepiece and focal length are Objective lens; The system beam expansion ratio M is defined as:

[0010] The system beam expansion ratio M is configured to satisfy the following condition: the initial divergence angle output by the laser emitting unit is such that... After beam expansion, the far-field divergence angle of the output beam Less than 0.1 mrad.

[0011] Preferably, the lens curvature and thickness parameters in the beam expanding and collimating unit are optimized based on a wavefront aberration model established by Zernike polynomials. The objective function of the optimization is to minimize the root mean square value of the wavefront error in order to eliminate static aberrations introduced by lens manufacturing and assembly.

[0012] Preferably, in the thermal stability structure, the thermal expansion coefficient α and the refractive index temperature coefficient β of the lens material satisfy the following: the focal length drift caused by the change in lens geometry due to temperature change is opposite in direction and equal in value to the focal length drift caused by the change in refractive index, thus maintaining the stability of the system output divergence angle under temperature change.

[0013] Preferably, the wavefront correction device is a deformable mirror, and the control processor is configured to execute a stochastic parallel gradient descent algorithm according to the following steps: A set of random perturbation voltage vectors is generated and applied to the deformable mirror; Collect performance index values ​​after applying perturbation and Among them, performance indicators The Strelby ratio of the far-field light spot; Calculate the gradient of the performance index change, and update the control voltage vector according to the direction of gradient descent or ascent:

[0014] in, This is the updated control voltage vector at the next time step after the (n+1)th iteration. Let be the set of control voltages applied to each actuator of the wavefront correction device at the current moment of the nth iteration. This is the gain coefficient. The change in performance indicators A random perturbation vector with dimension k is artificially applied, and k controls the number of channels. During iteration, a random perturbation vector with dimension k is generated. .

[0015] Preferably, the laser emitting unit emits a fundamental mode Gaussian beam, and the beam expanding and collimating unit is configured to: adjust the beam waist radius This makes the Rayleigh distance of the beam... Increase, thus increasing the propagation distance At a distance of meters, the diameter of the beam is Keep it below 1 cm.

[0016] Preferably, the system further includes: The far-field spot detection unit is located at the far-field end of the beam propagation path or coupled to the optical path through a beam splitter, and is used to acquire far-field spot images of the laser beam in real time. The far-field spot detection unit is communicatively connected to the control processor, and transmits the acquired spot image to the control processor. The control processor calculates the ratio of the peak light intensity of the actual spot to the peak light intensity of the ideal diffraction-limited system to obtain the Strell ratio.

[0017] Preferably, the system further includes a temperature monitoring and control module; The temperature monitoring and control module is configured to: continuously detect the tunnel ambient temperature T, and predict the change in lens focal length based on a preset thermal drift model; based on passive thermal compensation using lens materials, further perform active temperature adjustment on the beam expander and collimator unit to maintain the optical devices operating within a preset constant temperature range.

[0018] Preferably, the laser emitting unit is configured to emit laser light in the near-infrared band, wherein the center wavelength of the laser light in the near-infrared band is in the range of 1500–1600 nm.

[0019] Preferably, the control processor is further configured to perform system initialization before laser emission: Received input laser wavelength Initial waist radius and target projection distance ; Based on the Gaussian beam transmission model, calculate the target projection distance. The required Rayleigh distance for the required spot width ; According to the Rayleigh distance Calculate the minimum beam expansion ratio required for the beam expanding and collimating unit. And adjust or verify the combination parameters of the objective and eyepiece based on the minimum beam expansion ratio.

[0020] On the other hand, the present invention also proposes a long-distance high-precision laser positioning method based on a tunnel environment, the method being based on the system described in the first aspect of the present invention, and comprising the following steps: A fundamental Gaussian beam is emitted, and the beam is expanded and collimated using a beam expanding and collimating unit to compress the far-field divergence angle of the output beam. During beam transmission, passive thermal drift compensation is performed using the beam expanding and collimating unit. The beam expanding and collimating unit is equipped with a lens with a specific combination of optical materials. The mutual cancellation of the influence of the thermal expansion coefficient and the temperature coefficient of refractive index of the lens material on the focal length is utilized to suppress beam divergence caused by changes in ambient temperature. Perform real-time dynamic compensation based on adaptive optics: run a stochastic parallel gradient descent algorithm, apply random perturbation voltage to the wavefront correction device in the optical path, use the Strell ratio of the far-field spot as the evaluation function for iterative optimization, and adjust the wavefront phase of the output beam in real time to compensate for dynamic aberrations caused by environmental turbulence or vibration.

[0021] Compared with the prior art, the present invention has the following technical effects: 1. The laser positioning system proposed in this invention establishes a precise mathematical model based on Gaussian beam propagation theory, accurately translating the engineering requirement of a beam width ≤ 1 cm at 50 meters into an optical design specification of a divergence angle < 0.1 mrad. By employing a Kepler-structured beam expansion and collimation system, and combining Zernike polynomials to optimize the lens surface shape for static aberrations, beam divergence is suppressed at the source of physical optics, ensuring the energy concentration of the reference beam during long-distance transmission and solving the problems of severe beam divergence and blurred edges in traditional equipment.

[0022] 2. The laser positioning system proposed in this invention addresses the optical parameter drift caused by diurnal and seasonal temperature differences within tunnels by establishing a thermal drift model for the lens focal length. By employing a material matching strategy, a combination of lens materials whose thermal expansion coefficients and refractive index temperature coefficients can mutually compensate are selected. Utilizing the offsetting effect of geometric deformation and refractive index changes, passive thermal stabilization of the optical system is achieved. This design maintains focal length stability without the need for complex temperature control equipment, significantly improving the system's reliability in variable temperature environments.

[0023] 3. The laser positioning system proposed in this invention introduces adaptive optics technology to address the unavoidable random dynamic interferences such as dust, air turbulence, and mechanical vibration during tunnel construction. The system utilizes a stochastic parallel gradient descent algorithm, with the Strell ratio of the far-field beam as the evaluation core, to dynamically compensate the wavefront phase of the output beam in real time using a wavefront correction device. This enables the system to possess active beam correction capability, allowing it to compensate for beam jitter and distortion caused by environmental disturbances in real time, ensuring that the baseline remains clear and stable.

[0024] 4. The laser positioning system proposed in this invention solves the problem that a single technical means cannot simultaneously address diffraction, thermal effects, and turbulence. It also provides a high-precision visual reference for the automatic guidance of tunnel boring machines that far exceeds conventional methods, and has important practical engineering value for improving the quality, efficiency, and intelligence level of tunnel construction.

[0025] 5. The laser positioning system proposed in this invention is equipped with a near-infrared laser emitting unit, which significantly reduces the scattering loss of laser in dusty media from a physical level. Combined with polarization filtering technology, it effectively suppresses background scattering noise, enabling the system to maintain high contrast and center positioning accuracy of the far-field spot even in dusty environments. This reduces the dependence on the dynamic compensation range of the adaptive optics system and significantly improves the system's environmental adaptability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the laser positioning system described in this invention; Figure 2 This is a schematic diagram of the adaptive optics control unit described in an embodiment of the present invention; Figure 3 This is a schematic diagram of the laser positioning method described in this invention.

[0027] Reference numerals: 1. Laser emitting unit; 2. Beam expanding and collimating unit; 21. Eyepiece; 22. Objective lens; 3. Laser beam. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present application and with reference to the accompanying drawings.

[0029] The beam width described in this embodiment refers to twice the beam radius w(z), i.e., the beam diameter. The technical specification is: at a distance of 50 meters, the beam diameter does not exceed 1 centimeter (i.e., radius w(50) ≤ 0.005m).

[0030] Example 1 This embodiment describes a long-range, high-precision laser positioning system based on a tunnel environment, such as... Figure 1 As shown, it includes a laser emitting unit 1 for emitting a fundamental Gaussian beam, and: The beam expanding and collimating unit 2 is located downstream of the optical path of the laser emitting unit 1 and is used to expand and collimate the fundamental mode Gaussian beam to compress the far-field divergence angle of the output beam. The adaptive optics control unit (not shown in the figure) includes a wavefront correction device and a control processor.

[0031] In this embodiment, the parameter design of the laser emitting unit 1 takes into account the spectral characteristics of high-concentration dust in the tunnel. Dust with different chemical compositions (such as silicates and calcium carbonate) and particle sizes has significantly different scattering cross-sections and absorption coefficients for lasers of different wavelengths. To reduce environmental interference at the source, this system preferably uses a 1550nm laser as the light source, specifically with a wavelength range of 1500–1600nm. Compared to the visible light bands commonly used in tunnel construction (such as 635nm red light or 532nm green light), the 1550nm laser has a longer wavelength, which can significantly reduce the Rayleigh scattering effect caused by tiny dust particles. This band is located in the low-absorption atmospheric window of typical tunnel mineral dust, resulting in minimal energy attenuation of the beam during transmission, thus ensuring the brightness of the light spot after transmission over a distance of 50 meters. The 1550nm laser is in the eye-safe band, allowing for the use of higher emission power while meeting safety standards; at the same time, this band avoids spectral interference from visible light illumination equipment, and combined with polarization filtering technology at the receiving end, it can significantly improve the signal-to-noise ratio of the system. Specific polarization filtering technology includes a polarization filtering module disposed at the optical path receiver; the polarization filtering module is configured to filter out depolarized light noise generated by dust scattering and only allow signal light that maintains a specific polarization state to pass through, so as to improve the signal-to-noise ratio of the far-field light spot.

[0032] Because the fundamental mode Gaussian beam possesses ideal diffraction-limited characteristics, its optical field distribution and propagation behavior can be predicted and controlled through precise mathematical models. Therefore, to ensure the accuracy of subsequent long-distance positioning, laser emitting unit 1 is configured to output a fundamental mode Gaussian beam. Specifically, the propagation characteristics of the fundamental mode Gaussian beam are mainly determined by the laser wavelength λ and the beam waist radius. The laser beam waist radius refers to the position of the minimum beam radius during laser beam propagation, which determines the focusing ability and application effect of the beam. In this embodiment, z=0 is defined as the beam waist position (i.e., the narrowest point of the beam), and r is the vertical distance from a point on the beam cross-section to the beam's central axis.

[0033] At the waist position (z=0), the amplitude distribution of the light field satisfies the following mathematical model:

[0034] in, The peak amplitude at the center of the beam is denoted as z, and the beam propagation distance is denoted as z, which represents the distance propagated along the optical axis with the beam waist position as the origin (z=0). This represents the distribution of the light field amplitude at the waist position, varying with radial distance r. This represents the maximum electric field amplitude at the center of the beam (r=0), i.e., the peak intensity at the center of the beam.

[0035] when At this point, the beam exhibits a perfectly concentrated spot at the beam waist radius. After the beam leaves laser emitting unit 1 and propagates into free space, it gradually diverges due to physical diffraction. To overcome this problem, this embodiment optimizes the system design based on the propagation model of a Gaussian beam in free space. The beam radius after propagation distance z is... The evolutionary pattern is as follows:

[0036]

[0037] in, Rayleigh distance, defined as the beam radius. Increase to waist radius of The distance the beam travels is a key parameter characterizing the divergence characteristics of a beam. It represents the transition zone from near-perfect to significant divergence. By manufacturing a larger beam waist radius, the longer the Rayleigh distance is controlled, the smaller the divergence angle of the beam in the far field becomes, thus obtaining a beam with a very small divergence angle and extremely long propagation distance.

[0038] Based on the above model, it can be seen that to reduce the far-field divergence angle, the Rayleigh distance must be increased, and the Rayleigh distance is related to the waist radius. It is proportional to the square of the equation. Therefore, the beam expanding and collimating unit 2 in this embodiment is configured to shape the beam according to the above model.

[0039] Specifically, the beam expander and collimator 2 increases the beam waist radius through optical transformation, thereby significantly extending the Rayleigh distance. By creating a sufficiently large beam waist radius, the divergence angle of the beam in the far field is minimized. In the specific configuration of this embodiment, by adjusting parameters such as the beam expansion ratio, the system meets the following engineering specifications: at a propagation distance z = 50 meters, the beam diameter... It remains within 1 centimeter (0.01 meters). This enables the system to meet the stringent requirements of long-distance, high-precision positioning in tunnel environments.

[0040] Furthermore, to ensure beam quality, this embodiment fully considers the variation in wavefront curvature when designing the optical system. The wavefront curvature radius of the beam during transmission... satisfy:

[0041] This means that the wavefront of the beam is not always planar. Therefore, in the selection and assembly of the beam expander and collimator unit 2 and subsequent optical elements, the curvature of the lens is precisely calculated to match the radius of curvature of the incident beam's wavefront. This matching design effectively avoids the introduction of optical aberrations such as spherical aberration and astigmatism, ensuring that the laser beam maintains good collimation characteristics after passing through the lens group.

[0042] In this embodiment, the beam expanding and collimating unit 2, located downstream of the laser emitting unit 1, adopts a Keplerian telescope structure. This structure mainly consists of two lenses: an eyepiece 21 near the laser emitting unit 1 (focal length of...). ) and objective lens 22 (focal length is) near the output end ).

[0043] To achieve a beam diameter of no more than 1 centimeter (i.e., beam radius) at a transmission distance of 50 meters. To meet the engineering requirements of (meters), this embodiment employs a precise parameter design method based on optical theory. The control processor is also configured to perform system initialization before laser emission. Received input laser wavelength Initial waist radius and target projection distance ; Based on the Gaussian beam transmission model, calculate the target projection distance. The required Rayleigh distance for the required spot width ; According to the Rayleigh distance Calculate the minimum beam expansion ratio required for the beam expanding and collimating unit 2. And adjust or verify the combination parameters of objective lens 22 and eyepiece 21 based on the minimum beam expansion ratio.

[0044] First, define the beam expansion ratio M of the system. The beam expansion ratio is determined by the ratio of the focal lengths of the two lenses, that is:

[0045] According to the Gaussian beam transform theory, the beam waist radius of the output beam after passing through this beam expander system is... Beam waist radius of the input beam (i.e., the laser output beam) Satisfies the linear amplification relationship:

[0046] At the same time, the far-field divergence angle of the output beam divergence angle with the input beam They are inversely proportional, meaning the larger the beam expansion ratio, the smaller the output divergence angle:

[0047] Where λ is the laser wavelength.

[0048] To facilitate the calculation of optical parameters, this embodiment converts the spatial requirement of a light spot radius of no more than 5mm at 50 meters into optical angular parameters. Based on the far-field approximation:

[0049] To meet the above engineering requirements, the system's output divergence angle... It must be compressed to an extremely small range. After calculation, this constraint was determined to be:

[0050] That is, the beam expansion ratio M of the system is configured to satisfy the following: such that the initial divergence angle output by the laser emitting unit 1 is... After beam expansion, the far-field divergence angle of the output beam Less than 0.1 mrad. This index serves as the core constraint for all subsequent calculations and optimizations of optical parameters.

[0051] Based on the above constraints, the minimum beam expansion ratio required to satisfy the divergence angle requirement is first calculated. :

[0052] Based on the calculated minimum beam expansion ratio Based on the availability of actual optical components, the abstract magnification parameter is transformed into specific physical parameters, that is, a suitable focal length combination is selected for the eyepiece 21 and the objective lens 22. and ), making Satisfy the above Requirements.

[0053] After initially determining the lens parameters, this embodiment further verifies the design results using the precise Gaussian beam propagation equation, rather than relying solely on the far-field approximation. At the propagation distance L, the precise beam radius w(L) is calculated using the following formula:

[0054] The equation is solved using an optimized algorithm, ensuring that at L=50 meters, the calculated w(L) is strictly less than or equal to... Meters. If the beam is required to be nearly ideally collimated in the far field (i.e., the spot size increases linearly and slowly with distance), then the design must ensure that... much smaller To optimize the objective, the optimal lens focal length combination for the beam expander and collimator unit 2 was ultimately determined.

[0055] In an ideal beam-expanding and collimating system, the light wave output after beam expansion should be a perfect plane wave, meaning its wavefront (the surface formed by points with the same phase during light wave propagation) is completely flat. Theoretically, such a plane wave has the smallest divergence angle when propagating over long distances.

[0056] However, this embodiment fully considers non-ideal factors in actual engineering manufacturing. In the actual manufacturing and assembly process, lens curvature errors, refractive index inhomogeneities, thickness deviations, and mechanical assembly errors can all cause distortion of the wavefront of the emitted light wave, making it no longer an ideal plane. This distortion is called optical aberration. If it is not controlled, it will cause the far-field spot to become blurred and widened, failing to meet the accuracy requirement of a spot width of ≤1 cm at 50 meters.

[0057] Therefore, in this embodiment, the beam expander and collimator unit 2 incorporates a wavefront aberration correction model based on Zernike polynomials during the design phase to perform in-depth system optimization. The lens curvature and thickness parameters in the beam expander and collimator unit 2 are optimized based on the wavefront aberration model established using Zernike polynomials. The objective function of the optimization is to minimize the root mean square value of the wavefront error, thereby eliminating static aberrations introduced by lens manufacturing and assembly. The specific method is as follows: Wavefront aberration of a beam using Zernike polynomials Mathematical decomposition and modeling are performed, and the model expression is as follows:

[0058] in, These are Zernike polynomials, representing different types of aberrations; For the corresponding coefficients, ρ and θ are the normalized radial and angular coordinates at the pupil, respectively.

[0059] Based on the above model, this system uses the root mean square (RMS) value of minimizing the wavefront error as the core evaluation index to iteratively optimize the optical parameters. The formula for calculating the RMS value is as follows:

[0060] Where A represents the integration region. During the optimization process, the calculated RMS value is brought close to zero by adjusting the radius of curvature of the lens, the center thickness, and the refractive index distribution of the lens assembly.

[0061] Through the aforementioned aberration correction methods, this embodiment can control the wavefront of the output beam at an extremely high level of flatness. Only when the RMS value is sufficiently small (i.e., the wavefront is sufficiently flat) can the energy of the laser beam be physically ensured to remain highly concentrated throughout the 50-meter propagation path, overcoming the adverse effects of lens manufacturing defects and ultimately achieving the stringent technical specification of a spot diameter not exceeding 1 centimeter.

[0062] Furthermore, considering the complexity of the tunnel construction environment, ambient temperature variation ΔT is a significant disturbance. Temperature fluctuations not only cause thermal expansion and contraction of optical lenses (changing their radius of curvature and thickness) but also alter the refractive index of the lens material. These changes in physical properties directly lead to a drift in the effective focal length of the lenses in the beam expander and collimator system, resulting in an increase in the divergence angle of the output beam. If left uncontrolled, the system may fail to meet the accuracy requirement of a beam width ≤1 cm at 50 meters after prolonged operation.

[0063] To this end, this embodiment establishes a thermal drift mathematical model and adopts a material matching strategy based on the model to construct a thermally stable optical system.

[0064] First, we quantify the effect of temperature change on the focal length of a single lens. If only geometric thermal expansion is considered, the change in focal length Δf approximately linearly correlates with the focal length f, the coefficient of thermal expansion α, and the temperature difference ΔT.

[0065] Output divergence angle of beam expanding and collimating system Depends on the input divergence angle and system beam expansion ratio (i.e., focal length ratio) ):

[0066] When the ambient temperature changes, the focal length of eyepiece 21 changes. The focal length of objective lens 22 becomes At this point, the new output divergence angle for:

[0067] To assess the severity of the thermal effect, this embodiment measures the change in the divergence angle. Partial differential estimation was performed:

[0068] Geometric thermal drift formula and Substituting into the above partial differential equation (where (where the coefficients of thermal expansion are the materials of eyepiece 21 and objective lens 22, respectively). Simplification yields:

[0069] The above model analysis shows that the thermal instability of the output beam divergence angle The difference in thermal expansion coefficients between eyepiece 21 and objective lens 22 It is directly proportional. Based on this conclusion, this embodiment adopts two thermal compensation measures: geometric dimension matching and comprehensive thermal effect optimization.

[0070] Geometric size matching: When selecting lenses, prioritize materials with similar coefficients of thermal expansion (i.e., Through this matching, the thermal drift caused by geometrical changes cancels each other out in the denominator and numerator of the expansion ratio, thereby significantly reducing... .

[0071] Comprehensive thermal effect optimization: In addition to the geometric thermal expansion analysis described above, this embodiment further considers the lens refractive index temperature coefficient β ( The effect of temperature change on the refractive index. Since the refractive index also significantly alters the focal length with temperature, to achieve optimal thermal stability, the lens material combination selected for this system is configured such that its coefficient of thermal expansion α is proportional to the temperature coefficient of refractive index β. The combined effects of these properties compensate for each other. This is achieved by selecting physical properties (α and α). By using lens material combinations that are similar or satisfy specific compensation relationships, the focal length ratio of the system remains constant under tunnel day-night or seasonal temperature differences, thus maintaining high accuracy of the baseline. Specifically, the thermal expansion coefficient α and refractive index temperature coefficient β of the lens material satisfy the following: the focal length drift caused by changes in lens geometry due to temperature changes is opposite in direction and equal in value to the focal length drift caused by changes in refractive index, maintaining the stability of the system's output divergence angle under temperature variations.

[0072] Although the aforementioned beam expander and collimator 2 effectively corrects the system's static aberrations through initial optical design and thermal stabilization measures, unavoidable dynamic interference factors still exist in the actual tunnel construction environment. These mainly include mechanical vibrations generated by large machinery operations and air turbulence caused by temperature differences in airflow. These interferences are characterized by strong randomness and rapid changes in frequency, resulting in wavefront distortion. It is a function of time and cannot be eliminated by a fixed combination of lenses.

[0073] To address this issue, in this embodiment, the adaptive optics control unit is configured to perform dynamic compensation for real-time closed-loop control: the control processor runs a Stochastic Parallel Gradient Descent (SPGD) algorithm, applying random perturbation voltages to the wavefront correction device and iteratively optimizing using the Strell ratio of the far-field spot as the evaluation function to adjust the wavefront phase of the output beam in real time, thereby compensating for dynamic aberrations caused by environmental turbulence or vibration. In this embodiment, the wavefront correction device is a deformable mirror.

[0074] like Figure 2 As shown, Figure 2This is a schematic diagram of the adaptive optics control unit provided in one embodiment of the present invention. The unit mainly consists of a wavefront correction device (such as a microlens array or deformable mirror), an SPGD algorithm processor, and a far-field detection module. The SPGD algorithm processor, as the core control element, is communicatively connected to the wavefront correction device and is used to calculate and output the control voltage.

[0075] The core logic lies in establishing a performance index that accurately reflects beam quality and compensating for random aberrations through continuous iterative optimization. Specifically, this embodiment selects the Strell ratio S of the far-field spot as the performance index J. The Strell ratio is defined as the ratio of the peak light intensity of a real optical system to the peak light intensity of an ideal diffraction-limited system, and its mathematical expression is:

[0076] in, This represents the actual peak intensity of the light spot. The peak intensity of the ideal diffraction-limited spot when there is no aberration; It is the pupil function. It is the total wavefront phase that includes environmental distortion and system correction.

[0077] By adjusting the control voltage vector V of the deformable mirror in real time, the J value is maximized, thereby maintaining the optimal beam quality. When S=1, it indicates that the beam quality has reached the diffraction limit (optimal state); when S<1, it indicates the presence of aberrations, and the smaller the value, the more diffuse the beam quality. The control objective of this system is to maximize performance indicators through real-time adjustment. value.

[0078] In this embodiment, the control processor is configured to execute a stochastic parallel gradient descent algorithm according to the following steps: A set of random perturbation voltage vectors is generated and applied to the deformable mirror; Collect performance index values ​​after applying perturbation and Among them, performance indicators The Strelby ratio of the far-field light spot; Calculate the gradient of the performance index change and update the control voltage vector according to the direction of gradient descent or rise.

[0079] Specifically, the processor in the adaptive optics control unit is configured to repeatedly execute the SPGD algorithm according to the following steps to update the control voltage vector V of the wavefront correction device in real time: First, generate a random perturbation vector of dimension k (corresponding to the number of control channels). All elements in the vector are randomly assigned values, for example, ±1. Then, a small voltage perturbation is synchronously applied to all control channels. First, a positive perturbation voltage is applied. Then a negative perturbation voltage is applied. :

[0080]

[0081] in, This is the reference control voltage for the current nth iteration.

[0082] Next, using far-field spot detection, the applied light is rapidly measured. and The corresponding performance index values ​​are denoted as follows: and Then, the change in performance metrics (approximate gradient) is calculated. ):

[0083] Finally, based on the calculated changes in performance indicators According to the gradient optimization direction (even if (The direction of increasing value) updates the control voltage, resulting in the voltage vector for the (n+1)th iteration. :

[0084] in, This is the updated control voltage vector at the next time step after the (n+1)th iteration. Let be the set of control voltages applied to each actuator of the wavefront correction device at the current moment of the nth iteration. It is the gain coefficient (step size), used to control the convergence speed and stability.

[0085] In a preferred embodiment of the present invention, the system further includes: A far-field spot detection unit is disposed at the far-field end of the beam propagation path or coupled to the optical path through a beam splitter, for real-time acquisition of far-field spot images of the laser beam; the far-field spot detection unit is communicatively connected to the control processor, and transmits the acquired spot images to the control processor, which calculates the ratio of the peak light intensity of the actual spot to the peak light intensity of the ideal diffraction-limited system to obtain the Strell ratio.

[0086] In a preferred embodiment of the present invention, the system further includes a temperature monitoring and control module; the temperature monitoring and control module is configured to: continuously detect the tunnel ambient temperature T, and predict the change in lens focal length according to a preset thermal drift model; based on passive thermal compensation using lens material, further perform active temperature adjustment on the beam expanding and collimating unit 2 to maintain the optical device working within a preset constant temperature range.

[0087] Example 2 This embodiment presents a long-range, high-precision laser positioning method based on a tunnel environment. The method is based on the system described in Embodiment 1, such as... Figure 3 As shown, it includes the following steps: A fundamental Gaussian beam is emitted, and the beam enters the beam expanding and collimating unit 2. The beam is expanded and collimated by the beam expanding and collimating unit 2 to compress the far-field divergence angle of the output beam. During beam transmission, passive thermal drift compensation is performed using the beam expanding and collimating unit 2. The beam expanding and collimating unit 2 is equipped with a lens with a specific combination of optical materials. The beam divergence caused by changes in ambient temperature is suppressed by the mutual cancellation of the thermal expansion coefficient and refractive index temperature coefficient of the lens material on the focal length. Perform real-time dynamic compensation based on adaptive optics: run a stochastic parallel gradient descent algorithm, apply random perturbation voltage to the wavefront correction device in the optical path, use the Strell ratio of the far-field spot as the evaluation function for iterative optimization, and adjust the wavefront phase of the output beam in real time to compensate for dynamic aberrations caused by environmental turbulence or vibration.

[0088] Those skilled in the art will understand that before emitting the fundamental Gaussian beam, the system includes initialization and parameter setting steps: inputting the laser wavelength according to the Gaussian beam transmission model. With the initial waist radius It automatically calculates the Rayleigh distance and establishes a mathematical model for beam propagation. This is based on the target distance L = 50m and the beam width. Determine the required output divergence angle according to the requirements. And then through the formula Calculate the minimum beam expansion ratio.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A long-range, high-precision laser positioning system based on a tunnel environment, comprising a laser emitting unit for emitting a fundamental mode Gaussian beam, characterized in that, Also includes: A beam expanding and collimating unit is located downstream of the optical path of the laser emitting unit. It is used to expand and collimate the fundamental mode Gaussian beam and compress the far-field divergence angle of the output beam. as well as Adaptive optics control unit, including wavefront correction device and control processor; The beam expanding and collimating unit has a thermally stable structure, and the combination of optical materials used in the lens is configured such that, based on the thermal drift model, the influence of the thermal expansion coefficient and the temperature coefficient of refractive index of the lens material on the focal length is mutually compensated, so as to suppress beam divergence caused by changes in ambient temperature. The adaptive optics control unit is configured to perform dynamic compensation: the control processor runs a stochastic parallel gradient descent algorithm, applies a random perturbation voltage to the wavefront correction device, and iteratively optimizes the wavefront phase of the output beam in real time using the Strell ratio of the far-field spot as the evaluation function to compensate for dynamic aberrations caused by environmental turbulence or vibration.

2. The system according to claim 1, characterized in that, The beam expanding and collimating unit adopts a Kepler telescope structure, including a focal length of... The eyepiece and focal length are Objective lens; The system beam expansion ratio M is defined as: The system beam expansion ratio M is configured to satisfy the following condition: the initial divergence angle output by the laser emitting unit is such that... After beam expansion, the far-field divergence angle of the output beam Less than 0.1 mrad.

3. The system according to claim 1, characterized in that, The lens curvature and thickness parameters in the beam expanding and collimating unit are optimized based on a wavefront aberration model established by Zernike polynomials. The objective function of the optimization is to minimize the root mean square value of the wavefront error in order to eliminate static aberrations introduced by lens manufacturing and assembly.

4. The system according to claim 1, characterized in that, In the aforementioned thermal stability structure, the thermal expansion coefficient α and the refractive index temperature coefficient β of the lens material satisfy the following: the focal length drift caused by the change in lens geometry due to temperature change is opposite in direction and equal in value to the focal length drift caused by the change in refractive index, thus maintaining the stability of the system output divergence angle under temperature change.

5. The system according to claim 1, characterized in that, The wavefront correction device is a deformable mirror, and the control processor is configured to execute a stochastic parallel gradient descent algorithm according to the following steps: A set of random perturbation voltage vectors is generated and applied to the deformable mirror; Collect performance index values ​​after applying perturbation and Among them, performance indicators The Strelby ratio of the far-field light spot; Calculate the gradient of the performance index change, and update the control voltage vector according to the direction of gradient descent or ascent: in, This is the updated control voltage vector at the next time step after the (n+1)th iteration. Let be the set of control voltages applied to each actuator of the wavefront correction device at the current moment of the nth iteration. This is the gain coefficient. The change in performance indicators Let k be a randomly perturbation vector applied manually, and k be the number of control channels. During iteration, a random perturbation vector of dimension k is generated. .

6. The system according to claim 1, characterized in that, The beam expanding and collimating unit is configured to: adjust the beam waist radius This makes the Rayleigh distance of the beam... Increase, thus increasing the propagation distance At a distance of meters, the diameter of the beam is Keep it below 1 cm.

7. The system according to claim 1, characterized in that, The system also includes: The far-field spot detection unit is located at the far-field end of the beam propagation path or coupled to the optical path through a beam splitter, and is used to acquire far-field spot images of the laser beam in real time. The far-field spot detection unit is communicatively connected to the control processor, and transmits the acquired spot image to the control processor. The control processor calculates the ratio of the peak light intensity of the actual spot to the peak light intensity of the ideal diffraction-limited system to obtain the Strell ratio.

8. The system according to claim 1, characterized in that, The laser emitting unit is configured to emit laser light in the near-infrared band, wherein the center wavelength of the laser light in the near-infrared band is in the range of 1500–1600 nm.

9. The system according to claim 1, characterized in that, The control processor is also configured to perform system initialization before laser emission: Received input laser wavelength Initial waist radius and target projection distance ; Based on the Gaussian beam transmission model, calculate the target projection distance. The required Rayleigh distance for the required spot width ; According to the Rayleigh distance Calculate the minimum beam expansion ratio required for the beam expanding and collimating unit. And adjust or verify the combination parameters of the objective and eyepiece based on the minimum beam expansion ratio.

10. A long-range, high-precision laser positioning method based on a tunnel environment, characterized in that, The method, based on the system as described in claim 1, includes the following steps: A fundamental Gaussian beam is emitted, and the beam is expanded and collimated using a beam expanding and collimating unit to compress the far-field divergence angle of the output beam. During beam transmission, passive thermal drift compensation is performed using the beam expanding and collimating unit. The beam expanding and collimating unit is equipped with a lens with a specific combination of optical materials. The mutual cancellation of the influence of the thermal expansion coefficient and the temperature coefficient of refractive index of the lens material on the focal length is utilized to suppress beam divergence caused by changes in ambient temperature. Perform real-time dynamic compensation based on adaptive optics: run a stochastic parallel gradient descent algorithm, apply random perturbation voltage to the wavefront correction device in the optical path, use the Strell ratio of the far-field spot as the evaluation function for iterative optimization, and adjust the wavefront phase of the output beam in real time to compensate for dynamic aberrations caused by environmental turbulence or vibration.

Images