High-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system and working method based on metasurface cylindrical lens

Abstract

The present invention relates to a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopic three-dimensional detection system and working method based on a metasurface cylindrical lens, belonging to the field of optical measurement. It comprises a first laser, a second laser, a first reflector, a first non-polarizing beam splitter prism, a first half-wave plate, a beam expander, a polarizing beam splitter prism, a second reflector, a first metasurface cylindrical lens pair, a Wollaston prism, a second half-wave plate, a third reflector, a second metasurface cylindrical lens pair, a sample optical fiber, a second non-polarizing beam splitter prism, a first filter, a first CCD detector, a second filter, a second CCD detector and a computer. The present invention adopts a metasurface cylindrical lens, a dual-wavelength polarization phase fusion interferometric detection method and a full-aperture aberration-corrected filtered back-projection refractive index three-dimensional reconstruction method to further improve the three-dimensional distribution detection accuracy and efficiency of the refractive index and fusion defects of high-power optical fiber devices.

Description

Technical Field

[0001] The present invention relates to a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopic three-dimensional detection system based on a supersurface cylindrical lens and a working method, belonging to the technical field of optical measurement. Background Art

[0002] With the continuous development and progress of high-power fiber lasers, their application areas are becoming more and more extensive. In the field of laser weapons, high-power fiber lasers are an important component of laser weapons and can provide irreplaceable laser light sources for laser processing processes such as the manufacture, improvement, and upgrade of other weapons and equipment. They also have important and extensive application value in civilian laser processing and other fields. Therefore, they are one of the core technologies that major countries in the world are competing to develop. High-power fiber lasers are connected by optical fiber devices, such as large mode field gain fibers, high-power combiners, fiber Bragg gratings, etc. The refractive index uniformity of these devices will directly affect the performance of the laser, and these devices need to be connected together through a fusion process. The quality of the fusion point will also directly affect the output performance and long-term stability of the laser. High-precision detection of the refractive index and fusion defects of high-power fiber devices is an important auxiliary means to improve the output characteristics of high-power fiber lasers.

[0003] Currently, the main method used to detect fiber fusion defects is optical microscopy. This method can only obtain the projection position of two-dimensional fusion defects, but cannot obtain the three-dimensional distribution of fusion defects. It is blind to the guidance of the processing and fusion process of optical fiber devices. Digital holographic microtomography technology can quantitatively measure the three-dimensional distribution of the refractive index of optical fibers. However, the current digital holographic microtomography technology generally uses a microscope objective to improve the lateral resolution. The microscope objective is used to focus and diverge the light beam, and the focus is used to perform point scanning on the optical fiber sample to obtain high-precision three-dimensional refractive index distribution information of the optical fiber. However, the point scanning detection process results in low overall detection efficiency of the system. In addition, the existing methods usually use refractive index matching liquid to assist in measuring the refractive index of the optical fiber. However, due to the limitations of the detection principle, there are problems such as insufficient lateral resolution, small refractive index gradient detection range, large system error, and poor versatility. Therefore, it is impossible to achieve high-precision and rapid three-dimensional refractive index detection of high-power optical fiber devices. Summary of the Invention

[0004] In order to solve the problems of small refractive index gradient detection range, low lateral resolution, and slow detection efficiency in the current high-precision three-dimensional detection of refractive index and welding defects of high-power optical fiber devices, the present invention provides a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system and working method based on metasurface cylindrical lenses, aiming to further improve the accuracy and efficiency of three-dimensional distribution detection of refractive index and welding defects of high-power optical fiber devices, reduce the complexity of the refractive index detection operation process, and improve versatility.

[0005] The invention adopts the following technical solutions:

[0006] A high-power optical fiber device refractive index dual-wavelength polarization holographic microscopic three-dimensional detection system based on a metasurface cylindrical lens comprises a first laser, a second laser, a first reflector, a first non-polarizing beam splitter prism, a first half-wave plate, a beam expander, a polarizing beam splitter prism, a second reflector, a first metasurface cylindrical lens pair, a Wollaston prism, a second half-wave plate, a third reflector, a second metasurface cylindrical lens pair, a sample optical fiber, a second non-polarizing beam splitter prism, a first filter, a first CCD detector, a second filter, a second CCD detector, and a computer; the first CCD detector and the second CCD detector are both connected to the computer, and the computer is used to obtain a corrected interference pattern;

[0007] The first laser and the second laser are respectively used to emit linearly polarized light. After being reflected by the first reflector, the linearly polarized light emitted by the first laser is combined with the linearly polarized light emitted by the second laser at a first non-polarizing beam splitter prism. The combined linearly polarized light passes through a first half-wave plate and a beam expander in sequence and is split into two light beams at the polarizing beam splitter prism, one of which serves as a reference beam in the optical path, and the other serves as an object beam in the optical path.

[0008] The reference beam is reflected by the second reflector to the first metasurface cylindrical lens pair, and the beam is amplified by the first metasurface cylindrical lens pair. The amplified beam passes through the Wollaston prism and the second non-polarizing beam splitter prism in sequence, and is split into two beams due to reflection and projection in the second non-polarizing beam splitter prism. One beam passes through the first filter and enters the first CCD detector; the other beam passes through the second filter and enters the second CCD detector.

[0009] After passing through the second half-wave plate, the object beam reaches the third reflector. After being reflected by the third reflector, it reaches the second metasurface cylindrical lens pair. After passing through the second metasurface cylindrical lens pair and the sample fiber, the beam is amplified and carries the information of the sample fiber. The object beam carrying the sample fiber information continues to propagate through the second non-polarizing beam splitter prism. In the second non-polarizing beam splitter prism, the reflected and transmitted beams are split into two beams. One beam passes through the first filter and enters the first CCD detector, where it interferes with the reference beam entering the first CCD detector. The other beam passes through the second filter and enters the second CCD detector, where it interferes with the reference beam entering the second CCD detector. The second half-wave plate can rotate the polarization direction of the object light to keep it consistent with the reference light, satisfying the interference condition. Both the first and second metasurface cylindrical lens pairs use dual-wavelength achromatic metasurface cylindrical lens pairs, which can converge parallel light beams into a one-dimensional focal line, perform line scanning on the sample fiber, and then diverge into parallel light and perform achromatic processing on the beams.

[0010] The present invention utilizes a metasurface cylindrical lens pair to perform line scanning of a sample optical fiber in digital holographic microtomography, thereby enabling rapid detection of refractive index and splice defects in high-power optical fiber devices. The metasurface cylindrical lens pair features a planar structure, a large numerical aperture (NA), and flexible achromatic design.

[0011] Preferably, the first half-wave plate is disposed on a first rotating stage. By adjusting the rotation angle of the first rotating stage, the first half-wave plate cooperates with the polarization beam splitter prism to adjust the intensity ratio between the object beam and the reference beam. The first rotating stage can rotate 360 ​​degrees about the light propagation direction as an axis. Rotating a certain angle allows the first half-wave plate to cooperate with the polarization beam splitter prism to adjust the intensity ratio between the object beam path and the reference beam path.

[0012] Preferably, a second rotation stage and a translation stage are provided on the sample fiber. The second rotation stage is used to achieve rotational positioning of the sample fiber at various angles, allowing the computer to capture holograms of the sample fiber at various angles. The translation stage is used to achieve axial movement of the measured position of the sample fiber, thereby obtaining a large axial measurement range of the sample fiber. The sample fiber is fixed at a certain angle by the second rotation stage and the translation stage at the focal line of the second metasurface cylindrical lens. The first filter and the second filter can transmit light of wavelengths λ1 and λ2, respectively.

[0013] Preferably, to perform three-dimensional refractive index measurement on the sample optical fiber, it is necessary to collect 0-180° with a step length of 1 degree, and obtain a total of 180 interference patterns.

[0014] A method for operating the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on the above-mentioned metasurface cylindrical lens comprises the following steps:

[0015] (1) The first laser and the second laser emit linearly polarized light with wavelengths of λ1 and λ2, respectively. The beams are combined and then split into a reference beam and an object beam.

[0016] (2) The reference beam is reflected by the second reflector to the first metasurface cylindrical lens pair, and the beam is amplified after passing through the first metasurface cylindrical lens pair. The amplified beam passes through the Wollaston prism and the second non-polarizing beam splitter prism in turn, and is split into two beams due to reflection and projection in the second non-polarizing beam splitter prism. One beam passes through the first filter and enters the first CCD detector; the other beam passes through the second filter and enters the second CCD detector;

[0017] (3) The object beam passes through the second half-wave plate and reaches the third reflector. After being reflected by the third reflector, it reaches the second metasurface cylindrical lens pair. The beam is amplified by the second metasurface cylindrical lens pair and the sample fiber is line-scanned to carry the information of the sample fiber.

[0018] (4) The object beam carrying the sample optical fiber information continues to propagate through the second non-polarizing beam splitter prism. In the second non-polarizing beam splitter prism, the reflected and transmitted beams are split into two beams. One beam passes through the first filter and enters the first CCD detector, where it interferes with the reference beam entering the first CCD detector. The other beam passes through the second filter and enters the second CCD detector, where it interferes with the reference beam entering the second CCD detector.

[0019] (5) The interference pattern transmitted to the computer is subjected to a dual-wavelength polarization phase fusion interferometry detection method to obtain a corrected interference pattern;

[0020] (6) The corrected interference pattern is used to reconstruct the three-dimensional distribution of the refractive index and welding defects of the sample optical fiber using the full-aperture aberration-corrected filtered back-projection refractive index three-dimensional reconstruction method.

[0021] The dual-wavelength holographic interferometry detection of the present invention adopts the measurement principle of equivalent wavelengths, which can expand the detection range of traditional interferometry detection instruments and effectively avoid phase mutation errors introduced by large refractive index gradient changes. Polarization phase fusion technology is an emerging phase imaging technology in the field of polarization imaging. By fusing two orthogonal polarization phase images, it solves the problem of phase singularities in a single phase image and can effectively improve the accuracy of phase extraction. Combining the two for phase detection can increase the detection range of the refractive index gradient and the accuracy of phase extraction, avoiding the use of refractive index matching fluid during the detection process.

[0022] Cylindrical lenses are widely used in beam shaping, scanning equipment, and holographic displays because of their one-dimensional focusing function. Compared to spherical lenses that focus the light beam into a point, cylindrical lenses focus the light beam into a line, which can improve the efficiency of the entire optical fiber refractive index digital holographic micro-tomography detection system. Metasurface lenses have received widespread attention from the academic community in recent years due to their planar structure, lightweight, and integrated features. Since metasurface lenses have the characteristics of a planar structure, a large numerical aperture NA, and flexible achromatic design, they can be applied to the field of optical ultramicroscopy to achieve ultra-high-resolution detection that breaks through the diffraction limit of subwavelength optics. The metasurface cylindrical lens that combines the characteristics of the two can not only realize ultramicroscopy to increase the resolution of the system, but also further improve the detection efficiency of the system, and better achieve high-precision and rapid detection of the refractive index and welding defects of high-power optical fiber devices.

[0023] Preferably, in step (5), the process of the dual-wavelength polarization phase fusion interference detection method is:

[0024] First, the two interference patterns collected by the first and second CCD detectors are shifted by 10 pixels in the four directions of vertical and horizontal, respectively, to generate a sequence of eight interference patterns. Then, the eight interference patterns are Fourier transformed to obtain eight sets of Fourier distribution maps, that is, their spectral distribution.

[0025] Secondly, the eight groups of Fourier distribution maps are divided into two groups according to the horizontal and vertical orthogonal translation directions. The spectrum translation interpolation processing is performed on each group of four Fourier distribution maps to obtain the phase distribution of the equivalent wavelength:

[0026]

[0027] in, and are the phase distributions of equivalent wavelengths in the first and second groups, respectively. and are the phase distributions at wavelengths λ1 and λ2 in the first group, and They are the phase distributions at wavelengths λ1 and λ2 in the second group, h is the optical path difference, n s is the refractive index of the optical fiber, n0 is the refractive index of the surrounding medium, Λ is the equivalent wavelength, and its size is

[0028] The phase calculation result of the equivalent wavelength is considered to be the mean of the phase distribution of the two groups of equivalent wavelengths:

[0029]

[0030] Then, using components such as a Wollaston prism, an interference pattern containing two orthogonal directions is obtained:

[0031]

[0032] Among them I s (x,y) and I p (x, y) are the interference pattern intensities of s-light and p-light, respectively. s (x,y) and a p (x, y) are the interference patterns of s-light and p-light respectively, and b is the background light intensity. s (x,y) and b p (x, y) are the interference pattern fringe amplitude intensities of s-light and p-light respectively, and The phase distributions of the interference pattern fringes of s-light and p-light respectively;

[0033] The phase distribution in two orthogonal directions is then calculated using the interferogram demodulation algorithm:

[0034]

[0035] Finally, the phase singular points in the two orthogonal phase images are extracted respectively, and the position differences of the phase singular points are compared. The image fusion is performed by solving the maximum value of the reliability factor using the two polarization phase images:

[0036]

[0037] Among them, F(x,y) is the fused image. The phase image after removing the singular point is fused by the maximum method. The specific method is to select The maximum value among them is used to form the fused image.

[0038] Preferably, when comparing the positional differences of phase singularities, the region where the phase is distorted is the phase singularity. Phase singularities can be extracted by extracting regions where the phase is not smooth. Phase maps are then compared, and regions with phase singularities in the s direction are replaced with the smoothed phases of the corresponding regions in the p direction. Similarly, regions with phase singularities in the p direction are replaced with the smoothed phases of the corresponding regions in the s direction. Phase singularities are caused by errors, and image fusion is used to remove them, reducing measurement errors and improving phase extraction accuracy.

[0039] Preferably, in step (6), the process of the full-aperture aberration-corrected filtered back-projection refractive index three-dimensional reconstruction method is:

[0040] Firstly, the aberration is eliminated by phase aberration fitting technology to obtain the aberration-eliminating result at a single measurement angle, which is then superimposed with the SL (Shepp-Logan) filter function to form the aberration-eliminating SL filter function.

[0041] Secondly, the one-dimensional refractive index projection function is obtained using Radon transform at a certain projection angle:

[0042]

[0043] Where R(θ,p) is the one-dimensional refractive index projection function, f(x,y) is the image function, θ is the projection angle, p is the distance between the projection line and the origin, and δ(x) is the Dirac function;

[0044] Then, the one-dimensional refractive index projection function is Fourier transformed to obtain R(ω,α), which is multiplied by the aberration-eliminating SL filter function for filtering. The Fourier transform of the corrected projection function is obtained as follows:

[0045] F(ω,α)=R(ω,α)H(ω)(10)

[0046] Where F(ω,α) is the Fourier transform of the corrected projection function, R(ω,α) is the Fourier transform of the uncorrected one-dimensional refractive index projection function, and H(ω) is the aberration-correcting SL filter function;

[0047] Finally, the Fourier transform of the corrected projection function is back-projected to obtain the two-dimensional distribution of the refractive index of a single layer. The two-dimensional distribution of the refractive index of each layer is calculated in turn, and the three-dimensional distribution of the refractive index is obtained by superposition:

[0048]

[0049] Where n(x, y, z) is the three-dimensional refractive index of the optical fiber, ω is the angular frequency, and α is the projection angle.

[0050] It is worth noting that the phase aberration fitting technology to eliminate aberrations, the SL filter function, and the Radon transform are all existing conventional technologies and will not be described in detail here.

[0051] Where the present invention is not exhaustive, please refer to the prior art.

[0052] The beneficial effects of the present invention are:

[0053] 1. The present invention uses a metasurface cylindrical lens pair to achieve three-dimensional ultramicroscopic holographic imaging of the refractive index for line scanning of optical fibers, breaking through the limitations of single-point detection with traditional microscopes and subwavelength optical microscopy, expanding the axial range of the optical fiber for a single measurement, and greatly improving the efficiency of high-precision detection of the refractive index and fusion defects of high-power optical fiber devices.

[0054] 2. The present invention adopts dual-wavelength interference pattern phase extraction technology, which can expand the detection range of traditional interference detection instruments and avoid the use of matching liquid.

[0055] 3. The present invention adopts a phase singularity removal technology based on polarization phase fusion, which can remove the influence of phase singularities on the three-dimensional detection results of the optical fiber refractive index.

[0056] 4. The present invention adopts full-aperture aberration-corrected filtered back-projection refractive index three-dimensional reconstruction technology to achieve full-aperture system aberration elimination and aberration-corrected three-dimensional reconstruction in the refractive index measurement of optical fiber devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The drawings in the specification, which constitute a part of this application, are used to provide further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute improper limitations on this application.

[0058] Figure 1 Schematic diagram of a high-power fiber device refractive index dual-wavelength polarization holographic microscopy 3D detection system based on metasurface cylindrical lenses;

[0059] Figure 2 This is a structural diagram of the high-power fiber device refractive index dual-wavelength polarization holographic microscopy 3D detection system based on metasurface cylindrical lenses;

[0060] Figure 3 Schematic diagram of beam focusing of the metasurface spherical lens, where (a) is a top view and (b) is a front view;

[0061] Figure 4 Schematic diagram of beam focusing of metasurface cylindrical lens, where (a) is a top view and (b) is a front view;

[0062] Figure 5 Comparison diagram of the metasurface spherical lens pair and the metasurface cylindrical lens pair scanning the sample optical fiber, wherein (a) is a top view of the metasurface spherical lens pair scanning the sample optical fiber point, (b) is a top view of the metasurface cylindrical lens pair scanning the sample optical fiber line, (c) is a front view of the metasurface spherical lens pair scanning the sample optical fiber point, and (d) is a front view of the metasurface cylindrical lens pair scanning the sample optical fiber point;

[0063] Figure 6 Flowchart for line scanning of a paired fiber for a metasurface cylindrical lens;

[0064] Figure 7 Schematic diagram of dual-wavelength phase extraction;

[0065] Figure 8 Schematic diagram of the generation of interference patterns in two orthogonal polarization directions and the phase singularities appearing at different spatial positions in the corresponding phase diagram;

[0066] Figure 9 This is a flow chart of the dual-wavelength polarization phase fusion interferometry detection method;

[0067] Figure 10 This is a flow chart of the full-aperture aberration-corrected filtered back-projection refractive index 3D reconstruction technology;

[0068] In the figure, 1-first laser, 2-second laser, 3-first reflector, 4-first non-polarizing beam splitter, 5-first half-wave plate, 6-first rotating stage, 7-beam expander, 8-polarizing beam splitter, 9-second reflector, 10-first metasurface cylindrical lens pair, 11-Wollaston prism, 12-second half-wave plate, 13-third reflector, 14-second metasurface cylindrical lens pair, 15-sample optical fiber, 16-second rotating stage, 17-translation stage, 18-second non-polarizing beam splitter, 19-first filter, 20-first CCD detector, 21-second filter, 22-second CCD detector, 23-computer. DETAILED DESCRIPTION

[0069] In order to enable people in this technical field to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the implementation of this specification, but are not limited to this. Anything not fully described in the present invention shall be based on the conventional technology in this field.

[0070] Example 1

[0071] A high-power fiber optic device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on metasurface cylindrical lenses, such as Figure 1 、 2 As shown, it includes a first laser 1, a second laser 2, a first reflector 3, a first non-polarizing beam splitter prism 4, a first half-wave plate 5, a beam expander 7, a polarizing beam splitter prism 8, a second reflector 9, a first metasurface cylindrical lens pair 10, a Wollaston prism 11, a second half-wave plate 12, a third reflector 13, a second metasurface cylindrical lens pair 14, a sample optical fiber 15, a second non-polarizing beam splitter prism 18, a first filter 19, a first CCD detector 20, a second filter 21, a second CCD detector 22 and a computer 23; the first CCD detector 20 and the second CCD detector 22 are both connected to the computer 23, and the computer 23 is used to obtain a corrected interference pattern;

[0072] The first laser 1 and the second laser 2 are respectively used to emit linearly polarized light. The linearly polarized light emitted by the first laser 1 is reflected by the first reflector 3 and then combined with the linearly polarized light emitted by the second laser 2 at the first non-polarizing beam splitter prism 4. The combined linearly polarized light passes through the first half-wave plate 5 and the beam expander 7 in sequence and is split into two light beams at the polarizing beam splitter prism 8, one of which serves as a reference beam in the optical path and the other as an object beam in the optical path.

[0073] The reference beam is reflected by the second reflector 9 and then to the first metasurface cylindrical lens pair 10. The reference beam is amplified by the first metasurface cylindrical lens pair 10. The amplified reference beam passes through the Wollaston prism 11 and the second non-polarizing beam splitter prism 18 in sequence. In the second non-polarizing beam splitter prism 18, the reference beam is split into two beams due to reflection and projection. One beam passes through the first filter 19 and enters the first CCD detector 20. The other beam passes through the second filter 21 and enters the second CCD detector 22.

[0074] The object light beam passes through the second half-wave plate 12 and reaches the third reflector 13. After being reflected by the third reflector 13, it reaches the second metasurface cylindrical lens pair 14. After passing through the second metasurface cylindrical lens pair 14 and the sample optical fiber 15, the light beam is amplified and carries the information of the sample optical fiber 15. The object light beam carrying the sample optical fiber information continues to propagate through the second non-polarizing beam splitter 18. In the second non-polarizing beam splitter 18, the reflected and transmitted light beams are divided into two beams. One beam passes through the first filter 19 and enters the first CCD detector 20, where it interferes with the reference beam entering the first CCD detector. The other beam passes through the second filter 21 and enters the second CCD detector 22, where it interferes with the reference beam entering the second CCD detector. The second half-wave plate can make the polarization direction of the object light rotate in the same direction as the reference light, satisfying the interference condition. Both the first metasurface cylindrical lens pair and the second metasurface cylindrical lens pair use dual-wavelength achromatic metasurface cylindrical lens pairs, which can converge parallel light beams into a one-dimensional focal line and then perform line scanning on the sample optical fiber, such as Figure 5 As shown, the light is then diverged into parallel light and the light beam is achromatized.

[0075] The present invention utilizes a metasurface cylindrical lens pair to perform line scanning of a sample optical fiber in digital holographic microtomography, thereby enabling rapid detection of refractive index and splice defects in high-power optical fiber devices. The metasurface cylindrical lens pair features a planar structure, a large numerical aperture (NA), and flexible achromatic design.

[0076] Example 2

[0077] A high-power fiber optic device refractive index dual-wavelength polarization holographic microscopy 3D detection system based on a metasurface cylindrical lens is as described in Example 1, except that a first half-wave plate 5 is disposed on a first rotating stage 6. By adjusting the rotation angle of the first rotating stage 6, the first half-wave plate 5 cooperates with a polarization beam splitter prism to adjust the intensity ratio between the object beam and the reference beam. The first rotating stage 6 can rotate 360 ​​degrees about the light propagation direction as an axis. Rotating a certain angle allows the first half-wave plate 5 to cooperate with the polarization beam splitter prism to adjust the intensity ratio between the object beam path and the reference beam path.

[0078] A second rotation stage 16 and a translation stage 17 are mounted on the sample fiber 15. The second rotation stage 16 is used to rotate and position the sample fiber at various angles, allowing the computer 23 to capture holograms of the sample fiber at various angles. The translation stage 17 is used to axially move the sample fiber at the measured position, thereby achieving a large axial measurement range for the sample fiber. The sample fiber 15 is fixed at a specific angle by the second rotation and translation stages at the focal line of the second metasurface cylindrical lens. The first and second filters transmit light with wavelengths of 632.8 nm and 532 nm, respectively.

[0079] To perform three-dimensional refractive index measurement on the sample optical fiber, it is necessary to collect 0-180°, with a step size of 1 degree, and obtain a total of 180 interference patterns.

[0080] Example 3

[0081] A method for operating a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on the metasurface cylindrical lens of Example 2 comprises the following steps:

[0082] (1) The first laser 1 and the second laser 2 emit linearly polarized light with wavelengths λ1 and λ2, respectively. In this embodiment, λ1 = 632.8 nm and λ2 = 532 nm. After combining the beams, they are split into a reference beam and an object beam.

[0083] (2) The reference beam is reflected by the second reflector 9 to the first metasurface cylindrical lens pair 10, and the beam is amplified after passing through the first metasurface cylindrical lens pair 10. The amplified beam passes through the Wollaston prism 11 and the second non-polarizing beam splitter prism 18 in sequence, and is split into two beams due to reflection and projection in the second non-polarizing beam splitter prism 18. One beam passes through the first filter 19 and enters the first CCD detector 20; the other beam passes through the second filter 221 and enters the second CCD detector 22.

[0084] (3) The object beam passes through the second half-wave plate 12 and reaches the third reflector 13. After being reflected by the third reflector 13, it reaches the second metasurface cylindrical lens pair 14. After passing through the second metasurface cylindrical lens pair 14, the beam is amplified and a line scan is performed on the sample optical fiber to carry the information of the sample optical fiber.

[0085] (4) The object beam carrying the sample optical fiber information continues to propagate through the second non-polarizing beam splitter prism 18. In the second non-polarizing beam splitter prism 18, the reflected and transmitted beams are split into two beams. One beam passes through the first filter 19 and enters the first CCD detector 20, where it interferes with the reference beam entering the first CCD detector. The other beam passes through the second filter 21 and enters the second CCD detector 22, where it interferes with the reference beam entering the second CCD detector.

[0086] (5) The interference pattern transmitted to the computer 23 is subjected to a dual-wavelength polarization phase fusion interference detection method to obtain a corrected interference pattern;

[0087] (6) The corrected interference pattern is used to reconstruct the three-dimensional distribution of the refractive index and welding defects of the sample optical fiber using the full-aperture aberration-corrected filtered back-projection refractive index three-dimensional reconstruction method.

[0088] The dual-wavelength holographic interferometry detection of the present invention adopts the measurement principle of equivalent wavelengths, which can expand the detection range of traditional interferometry detection instruments and effectively avoid phase mutation errors introduced by large refractive index gradient changes. Polarization phase fusion technology is an emerging phase imaging technology in the field of polarization imaging. By fusing two orthogonal polarization phase images, it solves the problem of phase singularities in a single phase image and can effectively improve the accuracy of phase extraction. Combining the two for phase detection can increase the detection range of the refractive index gradient and the accuracy of phase extraction, avoiding the use of refractive index matching fluid during the detection process.

[0089] Cylindrical lenses are widely used in beam shaping, scanning equipment, and holographic displays because of their one-dimensional focusing function. Compared to spherical lenses that focus the light beam into a point, cylindrical lenses focus the light beam into a line, which can improve the efficiency of the entire optical fiber refractive index digital holographic micro-tomography detection system. Metasurface lenses have received widespread attention from the academic community in recent years due to their planar structure, lightweight, and integrated features. Since metasurface lenses have the characteristics of a planar structure, a large numerical aperture NA, and flexible achromatic design, they can be applied to the field of optical ultramicroscopy to achieve ultra-high-resolution detection that breaks through the diffraction limit of subwavelength optics. The metasurface cylindrical lens that combines the characteristics of the two can not only realize ultramicroscopy to increase the resolution of the system, but also further improve the detection efficiency of the system, and better achieve high-precision and rapid detection of the refractive index and welding defects of high-power optical fiber devices.

[0090] like Figure 3 、 4 As shown in Figures 5 and 6, the metasurface spherical lens focuses the beam into a point, while the metasurface cylindrical lens focuses the beam into a line, enabling line scanning of the sample fiber. Compared to point scanning, line scanning extends the axial range of the fiber for a single measurement, greatly improving the efficiency of high-precision inspection of refractive index and splice defects in high-power fiber devices.

[0091] Example 4

[0092] A working method of a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system with a metasurface cylindrical lens is as described in Example 3, except that, Figure 7 、 8 As shown in FIG9 , in step (5), the process of the dual-wavelength polarization phase fusion interference detection method is as follows:

[0093] First, the two interference patterns collected by the first CCD detector 20 and the second CCD detector 22 are shifted by 10 pixels in four directions, vertically up and down and horizontally left and right, to generate a sequence of eight interference patterns. Then, the eight interference patterns are Fourier transformed to obtain eight sets of Fourier distribution patterns, that is, their spectral distribution is obtained.

[0094] Secondly, the eight groups of Fourier distribution maps are divided into two groups according to the horizontal and vertical orthogonal translation directions. The spectrum translation interpolation processing is performed on each group of four Fourier distribution maps to obtain the phase distribution of the equivalent wavelength:

[0095]

[0096] in, and are the phase distributions of equivalent wavelengths in the first and second groups, respectively. and are the phase distributions at wavelengths λ1 and λ2 in the first group, and They are the phase distributions at wavelengths λ1 and λ2 in the second group, h is the optical path difference, n s is the refractive index of the optical fiber, n0 is the refractive index of the surrounding medium, Λ is the equivalent wavelength, and its size is

[0097] The phase calculation result of the equivalent wavelength is considered to be the mean of the phase distribution of the two groups of equivalent wavelengths:

[0098]

[0099] Then, using components such as a Wollaston prism, an interference pattern containing two orthogonal directions is obtained:

[0100]

[0101]

[0102] Among them I s (x,y) and I p (x, y) are the interference pattern intensities of s-light and p-light, respectively. s (x,y) and a p (x, y) are the interference patterns of s-light and p-light respectively, and b is the background light intensity. s (x,y) and b p (x, y) are the interference pattern fringe amplitude intensities of s-light and p-light respectively, and The phase distributions of the interference pattern fringes of s-light and p-light respectively;

[0103] The phase distribution in two orthogonal directions is then calculated using the interferogram demodulation algorithm:

[0104]

[0105] Finally, the phase singular points in the two orthogonal phase images are extracted respectively, and the position differences of the phase singular points are compared. The image fusion is performed by solving the maximum value of the reliability factor using the two polarization phase images:

[0106]

[0107] Among them, F(x,y) is the fused image. The phase image after removing the singular point is fused by the maximum method. The specific method is to select The maximum value among them is used to form the fused image.

[0108] When comparing the positional differences of phase singularities, areas of phase distortion are identified as phase singularities. Phase singularities can be extracted by extracting areas with uneven phases. Comparing these areas through phase maps, the areas with phase singularities in the s direction are then replaced with the smoothed phases of the corresponding areas in the p direction. Similarly, areas with phase singularities in the p direction are replaced with the smoothed phases of the corresponding areas in the s direction. Phase singularities are caused by errors, and image fusion can be used to remove them, reducing measurement errors and improving phase extraction accuracy.

[0109] Example 5

[0110] A working method of a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system with a metasurface cylindrical lens is as described in Example 3, except that, Figure 10 As shown, in step (6), the process of the full-aperture aberration-corrected filtered back-projection refractive index three-dimensional reconstruction method is:

[0111] Firstly, the aberration is eliminated by phase aberration fitting technology to obtain the aberration-eliminating result at a single measurement angle, which is then superimposed with the SL (Shepp-Logan) filter function to form the aberration-eliminating SL filter function.

[0112] Secondly, the one-dimensional refractive index projection function is obtained using Radon transform at a certain projection angle:

[0113]

[0114] Where R(θ,p) is the one-dimensional refractive index projection function, f(x,y) is the image function, θ is the projection angle, p is the distance between the projection line and the origin, and δ(x) is the Dirac function;

[0115] Then, the one-dimensional refractive index projection function is Fourier transformed to obtain R(ω,α), which is multiplied by the aberration-eliminating SL filter function for filtering. The Fourier transform of the corrected projection function is obtained as follows:

[0116] F(ω,α)=R(ω,α)H(ω)(10)

[0117] Where F(ω,α) is the Fourier transform of the corrected projection function, R(ω,α) is the Fourier transform of the uncorrected one-dimensional refractive index projection function, and H(ω) is the aberration-correcting SL filter function;

[0118] Finally, the Fourier transform of the corrected projection function is back-projected to obtain the two-dimensional distribution of the refractive index of a single layer. The two-dimensional distribution of the refractive index of each layer is calculated in turn, and the three-dimensional distribution of the refractive index is obtained by superposition:

[0119]

[0120] Where n(x, y, z) is the three-dimensional refractive index of the optical fiber, ω is the angular frequency, and α is the projection angle.

[0121] It is worth noting that the phase aberration fitting technology to eliminate aberrations, the SL filter function, and the Radon transform are all existing conventional technologies and will not be described in detail here.

[0122] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on metasurface cylindrical lenses, characterized by: The invention comprises a first laser, a second laser, a first reflecting mirror, a first non-polarizing beam splitter prism, a first half-wave plate, a beam expander, a polarizing beam splitter prism, a second reflecting mirror, a first metasurface cylindrical lens pair, a Wollaston prism, a second half-wave plate, a third reflecting mirror, a second metasurface cylindrical lens pair, a sample optical fiber, a second non-polarizing beam splitter prism, a first optical filter, a first CCD detector, a second optical filter, a second CCD detector and a computer; the first CCD detector and the second CCD detector are both connected to the computer, and the computer is used to obtain a corrected interference pattern; The first laser and the second laser are respectively used to emit linearly polarized light. After being reflected by the first reflector, the linearly polarized light emitted by the first laser is combined with the linearly polarized light emitted by the second laser at a first non-polarizing beam splitter prism. The combined linearly polarized light passes through a first half-wave plate and a beam expander in sequence and is split into two light beams at the polarizing beam splitter prism, one of which serves as a reference beam in the optical path, and the other serves as an object beam in the optical path. The reference beam is reflected by the second reflector to the first metasurface cylindrical lens pair, and the beam is amplified by the first metasurface cylindrical lens pair. The amplified beam passes through the Wollaston prism and the second non-polarizing beam splitter prism in sequence, and is split into two beams due to reflection and projection in the second non-polarizing beam splitter prism. One beam passes through the first filter and enters the first CCD detector; the other beam passes through the second filter and enters the second CCD detector. After passing through the second half-wave plate, the object beam reaches the third reflector, and after being reflected by the third reflector, it reaches the second metasurface cylindrical lens pair. After passing through the second metasurface cylindrical lens pair and the sample optical fiber, the beam is amplified and carries the information of the sample optical fiber; the object beam carrying the sample optical fiber information continues to propagate through the second non-polarizing beam splitter prism, and in the second non-polarizing beam splitter prism, it is split into two beams due to the reflected and transmitted beams. One beam passes through the first filter and enters the first CCD detector, where it interferes with the reference beam entering the first CCD detector; the other beam passes through the second filter and enters the second CCD detector, where it interferes with the reference beam entering the second CCD detector.

2. The high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on metasurface cylindrical lens according to claim 1 is characterized in that: A dual-wavelength achromatic metasurface cylindrical lens pair is used to converge the parallel light beams into a one-dimensional focal line, and then a large-scale line scanning measurement of the sample optical fiber is performed.

3. The high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on metasurface cylindrical lens according to claim 1 is characterized in that: The first half-wave plate is arranged on the first rotating platform. By adjusting the rotation angle of the first rotating platform, the first half-wave plate cooperates with the polarization beam splitter prism to adjust the light intensity ratio between the object beam and the reference beam.

4. The high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on metasurface cylindrical lenses according to claim 3 is characterized in that: A second rotating stage and a translation stage are provided on the sample optical fiber. The second rotating stage is used to realize the rotational positioning of the sample optical fiber at various angles, so that the computer can collect holograms of the sample optical fiber at various angles; the translation stage is used to realize the axial movement of the measured position of the sample optical fiber to obtain a large axial measurement range of the sample optical fiber.

5. The high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on metasurface cylindrical lenses according to claim 4 is characterized in that: To perform three-dimensional refractive index measurement on the sample optical fiber, it is necessary to collect 0-180°, with a step size of 1 degree, and obtain a total of 180 interference patterns.

6. A method for operating the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy 3D detection system based on the metasurface cylindrical lens according to claim 5, characterized in that: The steps include: (1) The first laser and the second laser emit linearly polarized light with wavelengths of λ1 and λ2, respectively. The beams are combined and then split into a reference beam and an object beam. (2) The reference beam is reflected by the second reflector to the first metasurface cylindrical lens pair, and the beam is amplified after passing through the first metasurface cylindrical lens pair. The amplified beam passes through the Wollaston prism and the second non-polarizing beam splitter prism in turn, and is split into two beams due to reflection and projection in the second non-polarizing beam splitter prism. One beam passes through the first filter and enters the first CCD detector; the other beam passes through the second filter and enters the second CCD detector; (3) The object beam passes through the second half-wave plate and reaches the third reflector. After being reflected by the third reflector, it reaches the second metasurface cylindrical lens pair. The beam is amplified by the second metasurface cylindrical lens pair and the sample fiber is line-scanned to carry the information of the sample fiber. (4) The object beam carrying the sample optical fiber information continues to propagate through the second non-polarizing beam splitter prism. In the second non-polarizing beam splitter prism, the reflected and transmitted beams are split into two beams. One beam passes through the first filter and enters the first CCD detector, where it interferes with the reference beam entering the first CCD detector. The other beam passes through the second filter and enters the second CCD detector, where it interferes with the reference beam entering the second CCD detector. (5) The interference pattern transmitted to the computer is subjected to a dual-wavelength polarization phase fusion interferometry detection method to obtain a corrected interference pattern; (6) The corrected interference pattern is used to reconstruct the three-dimensional distribution of the refractive index and welding defects of the sample optical fiber using the full-aperture aberration-corrected filtered back-projection refractive index three-dimensional reconstruction method.

7. The operating method of the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy 3D detection system based on metasurface cylindrical lenses according to claim 6, characterized in that: In step (5), the process of the dual-wavelength polarization phase fusion interference detection method is as follows: First, the two interference patterns collected by the first and second CCD detectors are shifted by 10 pixels in the four directions of vertical and horizontal, respectively, to generate a sequence of eight interference patterns. Then, the eight interference patterns are Fourier transformed to obtain eight sets of Fourier distribution maps, that is, their spectral distribution. Secondly, the eight groups of Fourier distribution maps are divided into two groups according to the horizontal and vertical orthogonal translation directions. The spectrum translation interpolation processing is performed on each group of four Fourier distribution maps to obtain the phase distribution of the equivalent wavelength: in, and are the phase distributions of equivalent wavelengths in the first and second groups, respectively. and are the phase distributions at wavelengths λ1 and λ2 in the first group, and They are the phase distributions at wavelengths λ1 and λ2 in the second group, h is the optical path difference, n s is the refractive index of the optical fiber, n0 is the refractive index of the surrounding medium, Λ is the equivalent wavelength, and its size is The phase calculation result of the equivalent wavelength is considered to be the mean of the phase distribution of the two groups of equivalent wavelengths: Then, using a Wollaston prism element, an interference pattern containing two orthogonal directions is obtained: Among them I s (x,y) and I p (x, y) are the interference pattern intensities of s-light and p-light, respectively. s (x,y) and a p (x, y) are the interference patterns of s-light and p-light respectively, and b is the background light intensity. s (x,y) and b p (x, y) are the interference pattern fringe amplitude intensities of s-light and p-light respectively, and The phase distributions of the interference pattern fringes of s-light and p-light respectively; The phase distribution in two orthogonal directions is then calculated using the interferogram demodulation algorithm: Finally, the phase singular points in the two orthogonal phase images are extracted respectively, and the position differences of the phase singular points are compared. The image fusion is performed by solving the maximum value of the reliability factor using the two polarization phase images: Among them, F(x,y) is the fused image.

8. The operating method of the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy 3D detection system based on metasurface cylindrical lenses according to claim 7, characterized in that: When comparing the position differences of phase singularities, the area where the phase is distorted is the phase singularity. The phase singularity can be extracted by extracting the area where the phase is not smooth, and then compared through the phase diagram. Then, the area with phase singularity in the s direction is replaced with the smooth phase of the corresponding area in the p direction. Similarly, the area with phase singularity in the p direction is replaced with the smooth phase of the corresponding area in the s direction.

9. The operating method of the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy 3D detection system based on metasurface cylindrical lenses according to claim 8, characterized in that: In step (6), the process of the full-aperture aberration-corrected filtered back-projection refractive index three-dimensional reconstruction method is as follows: Firstly, the aberration is eliminated by phase aberration fitting technology to obtain the aberration-eliminating result at a single measurement angle, which is then superimposed with the SL (Shepp-Logan) filter function to form the aberration-eliminating SL filter function. Secondly, the one-dimensional refractive index projection function is obtained using Radon transform at a certain projection angle: Where R(θ,p) is the one-dimensional refractive index projection function, f(x,y) is the image function, θ is the projection angle, p is the distance between the projection line and the origin, and δ(x) is the Dirac function; Then, the one-dimensional refractive index projection function is Fourier transformed to obtain R(ω,α), which is multiplied by the aberration-eliminating SL filter function for filtering. The Fourier transform of the corrected projection function is obtained as follows: F(ω,α)=R(ω,α)H(ω)(10) Where F(ω,α) is the Fourier transform of the corrected projection function, R(ω,α) is the Fourier transform of the uncorrected one-dimensional refractive index projection function, and H(ω) is the aberration-correcting SL filter function; Finally, the Fourier transform of the corrected projection function is back-projected to obtain the two-dimensional distribution of the refractive index of a single layer. The two-dimensional distribution of the refractive index of each layer is calculated in turn, and the three-dimensional distribution of the refractive index is obtained by superposition: Where n(x, y, z) is the three-dimensional refractive index of the optical fiber, ω is the angular frequency, and α is the projection angle.

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