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

Abstract

The invention relates to a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopic three-dimensional detection system based on a metasurface cylindrical lens and a working method, and belongs to the field of optical measurement. Comprising a first laser, a second laser, a first reflecting mirror, a first non-polarized beam splitting prism, a first half-wave plate, a beam expander, a polarized beam splitting 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-polarized beam splitting prism and a first optical filter. The device comprises a first optical filter, a first CCD detector, a second optical filter, a second CCD detector and a computer. A metasurface cylindrical lens, a dual-wavelength polarization phase fusion interference detection method and a full-aperture aberration elimination filtering back projection refractive index three-dimensional reconstruction method are adopted, and the three-dimensional distribution detection precision and efficiency of the refractive index and welding defects of the high-power optical fiber device are further improved.

Description

Technical Field

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

[0002] With the continuous development and progress of high-power fiber lasers, their application fields 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 the laser processing processes such as the manufacture, improvement, and upgrading of other weapons and equipment. They also have important and extensive application value in fields such as civilian laser processing. 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 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 welding process, and the quality of the welding point will also directly affect the output performance of the laser and the stability of long-term operation. High-precision detection of the refractive index and welding defects of high-power fiber devices is an important auxiliary means to improve the output characteristics of high-power fiber lasers.

[0003] At present, the detection of optical fiber fusion defects mainly adopts the method of optical microscopy imaging technology. This method can only obtain the projection position of two-dimensional fusion defects, but cannot obtain the three-dimensional distribution of fusion defects, which is blind for the guidance of the processing and fusion process of optical fiber devices. Digital holographic micro-tomography technology can quantitatively measure the three-dimensional distribution of optical fiber refractive index, but the current digital holographic micro-tomography technology generally uses microscope objective pairs to improve the lateral resolution, focuses and diverges the light beam through the microscope objective pair, and uses the focus to perform point scanning on the optical fiber sample to obtain high-precision optical fiber three-dimensional refractive index distribution information, but the point scanning detection process leads to 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, and are limited by the detection principle and have problems such as insufficient lateral resolution, small refractive index gradient detection range, large system error, and poor versatility, which cannot 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, slow detection efficiency, etc. existing in the high-precision three-dimensional detection of refractive index and fusion 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 three-dimensional distribution detection accuracy and efficiency of the refractive index and fusion defects of high-power optical fiber devices, reduce the complexity of the refractive index detection operation process, and improve the versatility.

[0005] The invention adopts the following technical solution:

[0006] A high-power optical fiber device refractive index dual-wavelength polarization holographic microscopic three-dimensional detection system based on a super-surface cylindrical lens, comprising a first laser, a second laser, a first reflector, a first non-polarization beam splitter prism, a first half-wave plate, a beam expander, a polarization beam splitter prism, a second reflector, a first super-surface cylindrical lens pair, a Wollaston prism, a second half-wave plate, a third reflector, a second super-surface cylindrical lens pair, a sample optical fiber, a second non-polarization 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 used to emit linear polarized light respectively. After being reflected by the first reflector, the linear polarized light emitted by the first laser is combined with the linear polarized light emitted by the second laser at the first non-polarizing beam splitter prism. The combined linear polarized light passes through the first half-wave plate and the beam expander in sequence and is divided into two light beams at the polarizing beam splitter prism, one of which is used as a reference light beam in the light path, and the other is used as an object light beam in the light path.

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

[0009] 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 super-surface cylindrical lens pair. After passing through the second super-surface 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 information of the sample optical fiber 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 divided into two beams. One beam passes through the first filter and enters the first CCD detector, interfering with the reference beam entering the first CCD detector. The other beam passes through the second filter and enters the second CCD detector, interfering 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 accordance with the reference light, satisfying the interference condition. Both the first super-surface cylindrical lens pair and the second super-surface cylindrical lens pair use dual-wavelength achromatic super-surface 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, and then diverge into parallel light and perform achromatic processing on the light beam.

[0010] The present invention utilizes a super-surface cylindrical lens pair to perform line scanning on a sample optical fiber in a digital holographic micro-tomography technique, thereby realizing rapid detection of the refractive index and fusion defects of a high-power optical fiber device. The super-surface cylindrical lens pair has the characteristics of a planar structure, a large numerical aperture NA, and a flexible achromatic design.

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

[0012] Preferably, a second rotating stage and a translation stage are provided on the sample optical fiber, and the second rotating stage is used to realize the rotation 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, so as to obtain a large axial measurement range of the sample optical fiber. The sample optical fiber is fixed at a certain angle by the second rotating stage and the translation stage at the focal line of the focusing of the second metasurface cylindrical lens; the first filter and the second filter can transmit light with wavelengths of 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 pattern patterns.

[0014] A working method of the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopic 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, and the beams are combined and then split into a reference beam and an object beam;

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

[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. After passing through the second metasurface cylindrical lens pair, the beam is amplified and a line scan is performed on the sample optical fiber to carry the information of the sample optical fiber.

[0018] (4) The object beam carrying the sample optical fiber information continues to propagate through the second non-polarizing beam splitter prism, where the reflected and transmitted beams are split into two beams, one of which passes through the first filter and enters the first CCD detector, thereby interfering with the reference beam entering the first CCD detector; the other passes through the second filter and enters the second CCD detector, thereby interfering 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 interference 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 fusion defects of the sample optical fiber using the full-aperture aberration-free filtered back-projection refractive index three-dimensional reconstruction method.

[0021] The dual-wavelength holographic interference detection of the present invention adopts the measurement principle of equivalent wavelength, which can expand the detection range of traditional interference detection instruments and effectively avoid phase mutation errors introduced by large refractive index change gradients. Polarization phase fusion technology is an emerging phase imaging technology in the field of polarization imaging. By fusing two orthogonal polarization phase images, the problem of phase singularity points of a single phase image can be solved, and the accuracy of phase extraction can be effectively improved. Combining the two for phase detection can increase the detection range of the refractive index gradient and the accuracy of phase extraction, and avoid the use of refractive index matching liquid 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 with 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 fiber refractive index digital holographic micro-tomography detection system. Metasurface lenses have received extensive attention from the academic community in recent years due to their planar structure, lightweight, and integrated features. Since metasurface lenses have the characteristics of planar structure, large numerical aperture NA, and flexible achromatic design, they can be applied to the field of optical ultra-microscopy to achieve ultra-high resolution detection that breaks through the diffraction limit of sub-wavelength optics. The ultra-surface cylindrical lens that combines the characteristics of the two can not only realize ultra-microscopy to increase the resolution of the system, but also further improve the detection efficiency of the system, and better realize high-precision and rapid detection of 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] Firstly, the two interference patterns collected by the first CCD detector and the second CCD detector are respectively 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 respectively subjected to Fourier transformation to obtain eight groups of Fourier distribution patterns, that is, their spectrum distribution is obtained.

[0025] Secondly, the eight groups of Fourier distribution diagrams 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 diagrams, and the phase distributions of the equivalent wavelengths are obtained as follows:

[0026]

[0027] in, and are the phase distributions of equivalent wavelengths in the first and second groups, respectively. and They are the phase distributions at wavelengths λ1 and λ2 in the first group, and 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 sets of equivalent wavelengths:

[0029]

[0030] Then, using components such as the 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 pattern background intensity of s light and p light, b s (x,y) and b p (x, y) are the fringe amplitude intensities of the interference pattern of s-light and p-light respectively, and The interference pattern fringe phase distributions of s-light and p-light respectively;

[0033] Then the phase distribution in two orthogonal directions is calculated by the interference pattern demodulation algorithm:

[0034]

[0035] Finally, the phase singularities in the two orthogonal phase images are extracted respectively, and the position differences of the phase singularities 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 value method. The specific method is to select The largest value among them is used to form the fused image.

[0038] Preferably, when comparing the position difference of the phase singularity, 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 the area with the phase singularity in the s direction is replaced with the smooth phase of the corresponding area in the p direction through comparison through the phase map. Similarly, the area with the phase singularity in the p direction is replaced with the smooth phase of the corresponding area in the s direction. The phase singularity is caused by error, and the phase singularity is removed by image fusion to reduce the measurement error and improve the phase extraction accuracy.

[0039] Preferably, in step (6), the process of the full-aperture aberration-free 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 elimination result under a single measurement angle, and then it is superimposed with the SL (Shepp-Logan) filter function to form the aberration elimination SL filter function;

[0041] Secondly, the one-dimensional refractive index projection function is obtained by 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, and the Fourier transform of the modified 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-eliminating SL filter function;

[0047] Finally, the Fourier transform of the modified projection function is back-projected to obtain the two-dimensional distribution of the refractive index of a single layer. After calculating the two-dimensional distribution of the refractive index of each layer in turn, 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 aberration, SL filter function, and Radon transform are all existing conventional technologies and will not be described in detail here.

[0051] For any details not provided in the present invention, please refer to the prior art.

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

[0053] 1. The present invention adopts a super-surface cylindrical lens pair to realize three-dimensional ultra-microscopic holographic imaging of the refractive index of the optical fiber for line scanning, breaking through the limitations of single-point detection of traditional microscopes and sub-wavelength optical microscopes, 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 welding 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-free filtered back-projection refractive index three-dimensional reconstruction technology to achieve full-aperture system aberration elimination and aberration-free 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 the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0058] Figure 1 Schematic diagram of the dual-wavelength polarization holographic microscopic three-dimensional detection system for the refractive index of high-power optical fiber devices based on metasurface cylindrical lenses;

[0059] Figure 2 This is the structural diagram of the high-power fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional 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 the metasurface cylindrical lens, where (a) is a top view and (b) is a front view;

[0062] Figure 5 The figures are comparison diagrams 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 Flow chart 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] Fig. 9 It is a flow chart of the dual-wavelength polarization phase fusion interference detection method;

[0067] Fig.10 This is a flow chart of the full-aperture aberration-free 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 prism, 5-first half-wave plate, 6-first rotating stage, 7-beam expander, 8-polarizing beam splitter prism, 9-second reflector, 10-first supersurface cylindrical lens pair, 11-Wollaston prism, 12-second half-wave plate, 13-third reflector, 14-second supersurface cylindrical lens pair, 15-sample optical fiber, 16-second rotating stage, 17-translation stage, 18-second non-polarizing beam splitter prism, 19-first filter, 20-first CCD detector, 21-second filter, 22-second CCD detector, 23-computer. DETAILED DESCRIPTION

[0069] In order to enable those skilled in the art 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 the art.

[0070] Example 1

[0071] A high-power fiber 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 super-surface cylindrical lens pair 10, a Wollaston prism 11, a second half-wave plate 12, a third reflector 13, a second super-surface 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 used to emit linear polarized light respectively. After being reflected by the first reflector 3, the linear polarized light emitted by the first laser 1 is combined with the linear polarized light emitted by the second laser 2 at the first non-polarizing beam splitter prism 4. The combined linear polarized light passes through the first half-wave plate 5 and the beam expander 7 in sequence, and is divided into two light beams at the polarizing beam splitter prism 8, one of which is used as a reference beam in the optical path, and the other is used as an object beam in the optical path;

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

[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 information of the sample optical fiber 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 light beams are divided into two light beams. One light beam passes through the first filter 19 and enters the first CCD detector 20, where it interferes with the reference light beam entering the first CCD detector. The other light beam passes through the second filter 21 and enters the second CCD detector 22, where it interferes with the reference light 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 super-surface cylindrical lens pair to perform line scanning on a sample optical fiber in a digital holographic micro-tomography technique, thereby realizing rapid detection of the refractive index and fusion defects of a high-power optical fiber device. The super-surface cylindrical lens pair has the characteristics of a planar structure, a large numerical aperture NA, and a flexible achromatic design.

[0076] Example 2

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

[0078] The sample optical fiber 15 is provided with a second rotating stage 16 and a translation stage 17. The second rotating stage 16 is used to realize the rotation positioning of the sample optical fiber at various angles, so that the computer 23 can collect holograms of the sample optical fiber at various angles; the translation stage 17 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. The sample optical fiber 15 is fixed at a certain angle by the second rotating stage and the translation stage and is located at the focal line of the focusing of the second metasurface cylindrical lens; the first filter and the second filter can transmit light with wavelengths of 632.8nm and 532nm respectively.

[0079] To measure the three-dimensional refractive index of 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 working method of a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopic 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=632.8nm and λ2=532nm. The beams are combined and then split into a reference beam and an object beam.

[0083] (2) The reference light beam is reflected by the second reflector 9 to the first metasurface cylindrical lens pair 10, and the light beam is amplified after passing through the first metasurface cylindrical lens pair 10. The amplified light beam passes through the Wollaston prism 11 and the second non-polarizing beam splitter prism 18 in turn, and is divided into two light beams due to reflection and projection in the second non-polarizing beam splitter prism 18. One light beam passes through the first filter 19 and enters the first CCD detector 20; the other light 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, thereby interfering 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, thereby interfering 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 fusion defects of the sample optical fiber using the full-aperture aberration-free filtered back-projection refractive index three-dimensional reconstruction method.

[0088] The dual-wavelength holographic interference detection of the present invention adopts the measurement principle of equivalent wavelength, which can expand the detection range of traditional interference detection instruments and effectively avoid phase mutation errors introduced by large refractive index change gradients. Polarization phase fusion technology is an emerging phase imaging technology in the field of polarization imaging. By fusing two orthogonal polarization phase images, the problem of phase singularity points of a single phase image can be solved, and the accuracy of phase extraction can be effectively improved. Combining the two for phase detection can increase the detection range of the refractive index gradient and the accuracy of phase extraction, and avoid the use of refractive index matching liquid 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 with 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 fiber refractive index digital holographic micro-tomography detection system. Metasurface lenses have received extensive attention from the academic community in recent years due to their planar structure, lightweight, and integrated features. Since metasurface lenses have the characteristics of planar structure, large numerical aperture NA, and flexible achromatic design, they can be applied to the field of optical ultra-microscopy to achieve ultra-high resolution detection that breaks through the diffraction limit of sub-wavelength optics. The ultra-surface cylindrical lens that combines the characteristics of the two can not only realize ultra-microscopy to increase the resolution of the system, but also further improve the detection efficiency of the system, and better realize high-precision and rapid detection of refractive index and welding defects of high-power optical fiber devices.

[0090] like Figure 3 , 4 As shown in Figure 5, the metasurface spherical lens focuses the light beam into a point, while the metasurface cylindrical lens focuses the light beam into a line, so that the sample optical fiber can be line scanned. Compared with point scanning, line scanning expands the axial range of the optical fiber for a single measurement, greatly improving the efficiency of high-precision detection of refractive index and fusion defects of high-power optical 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 of a super surface cylindrical lens is as described in Example 3, except that Figure 7 , 8 As shown in , 9, in step (5), the process of the dual-wavelength polarization phase fusion interference detection method is:

[0093] First, the two interference patterns collected by the first CCD detector 20 and the second CCD detector 22 are respectively shifted by 10 pixels in four directions, vertically up and down and horizontally left and right, to generate eight interference pattern sequences, and then the eight interference patterns are respectively Fourier transformed to obtain eight groups of Fourier distribution diagrams, that is, their spectrum distribution is obtained;

[0094] Secondly, the eight groups of Fourier distribution diagrams 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 diagrams, and the phase distributions of the equivalent wavelengths are obtained as follows:

[0095]

[0096] in, and are the phase distributions of equivalent wavelengths in the first and second groups, respectively. and They are the phase distributions at wavelengths λ1 and λ2 in the first group, and 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 sets of equivalent wavelengths:

[0098]

[0099] Then, using components such as the 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 pattern background intensity of s light and p light, b s (x,y) and b p (x, y) are the fringe amplitude intensities of the interference pattern of s-light and p-light respectively, and The interference pattern fringe phase distributions 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 singularities in the two orthogonal phase images are extracted respectively, and the position differences of the phase singularities 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 value method. The specific method is to select The largest value among them is used to form the fused image.

[0108] 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 the area with phase singularity in the s direction is replaced with the smooth phase of the corresponding area in the p direction through phase diagram comparison. Similarly, the area with phase singularity in the p direction is replaced with the smooth phase of the corresponding area in the s direction. Phase singularity is caused by error. Phase singularity is removed by image fusion to reduce measurement error and improve phase extraction accuracy.

[0109] Example 5

[0110] A working method of a high-power optical fiber device refractive index dual-wavelength polarization holographic microscopic three-dimensional detection system of a super surface cylindrical lens is as described in Example 3, except that Fig.10 As shown, in step (6), the process of the full-aperture aberration-free filtering back-projection refractive index three-dimensional reconstruction method is:

[0111] Firstly, the aberration is eliminated by phase aberration fitting technology to obtain the aberration elimination result under a single measurement angle, and then it is superimposed with the SL (Shepp-Logan) filter function to form the aberration elimination SL filter function;

[0112] Secondly, the one-dimensional refractive index projection function is obtained by 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, and the Fourier transform of the modified 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-eliminating SL filter function;

[0118] Finally, the Fourier transform of the modified projection function is back-projected to obtain the two-dimensional distribution of the refractive index of a single layer. After calculating the two-dimensional distribution of the refractive index of each layer in turn, 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 aberration, SL filter function, and 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 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 a metasurface cylindrical lens, characterized in that: It includes a first laser, a second laser, a first reflector, a first non-polarized beam splitter prism, a first half-wave plate, a beam expander, a polarized beam splitter prism, a second reflector, a first super-surface cylindrical lens pair, a Wollaston prism, a second half-wave plate, a third reflector, a second super-surface cylindrical lens pair, a sample optical fiber, a second non-polarized 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; The first laser and the second laser are used to emit linear polarized light respectively. After being reflected by the first reflector, the linear polarized light emitted by the first laser is combined with the linear polarized light emitted by the second laser at the first non-polarizing beam splitter prism. The combined linear polarized light passes through the first half-wave plate and the beam expander in sequence and is divided into two light beams at the polarizing beam splitter prism, one of which is used as a reference light beam in the light path, and the other is used as an object light beam in the light path. The reference beam is reflected to the first super-surface cylindrical lens pair after passing through the second reflector in sequence, and the beam is amplified after passing through the first super-surface cylindrical lens pair. The amplified beam passes through the Wollaston prism and the second non-polarizing beam splitter prism in sequence, and is divided into two beams due to reflection and projection in the second non-polarizing beam splitter prism, one beam enters the first CCD detector through the first filter; the other beam enters the second CCD detector through the second filter; The object light beam passes through the second half-wave plate and reaches the third reflector, and then reaches the second super-surface cylindrical lens pair after being reflected by the third reflector. After passing through the second super-surface cylindrical lens pair and the sample optical fiber, the light beam is amplified and carries the information of the sample optical fiber. The object light 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 divided into two light beams due to the reflected and transmitted light beams. One light beam passes through the first filter and enters the first CCD detector, where it interferes with the reference light beam entering the first CCD detector. The other light beam passes through the second filter and enters the second CCD detector, where it interferes with the reference light 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 super-surface 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 beam into a one-dimensional focal line and then perform a large-scale line scanning measurement on the sample optical fiber.

3. The high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on super-surface 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 light beam and the reference light beam.

4. The high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on super-surface cylindrical lens 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 super-surface cylindrical lens according to claim 4 is characterized in that: To measure the three-dimensional refractive index of 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 working method of the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional 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, and the beams are combined and then split into a reference beam and an object beam; (2) The reference light beam is reflected by the second reflector to the first metasurface cylindrical lens pair, and the light beam is amplified after passing through the first metasurface cylindrical lens pair. The amplified light beam passes through the Wollaston prism and the second non-polarizing beam splitter prism in turn, and is divided into two light beams due to reflection and projection in the second non-polarizing beam splitter prism, one of which enters the first CCD detector through the first filter; and the other enters the second CCD detector through the second filter; (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. After passing through the second metasurface cylindrical lens pair, the beam is amplified and a line scan is performed on the sample optical fiber to carry the information of the sample optical fiber. (4) The object beam carrying the sample optical fiber information continues to propagate through the second non-polarizing beam splitter prism, where the reflected and transmitted beams are split into two beams, one of which passes through the first filter and enters the first CCD detector, thereby interfering with the reference beam entering the first CCD detector; the other passes through the second filter and enters the second CCD detector, thereby interfering 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 interference 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 fusion defects of the sample optical fiber using the full-aperture aberration-free filtered back-projection refractive index three-dimensional reconstruction method.

7. The working method of the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on super-surface cylindrical lens according to claim 6 is characterized in that: In step (5), the process of the dual-wavelength polarization phase fusion interference detection method is as follows: Firstly, the two interference patterns collected by the first CCD detector and the second CCD detector are respectively 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 respectively subjected to Fourier transformation to obtain eight groups of Fourier distribution patterns, that is, their spectrum distribution is obtained. Secondly, the eight groups of Fourier distribution diagrams 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 diagrams, and the phase distributions of the equivalent wavelengths are obtained as follows: in, and are the phase distributions of equivalent wavelengths in the first and second groups, respectively. and They are the phase distributions at wavelengths λ1 and λ2 in the first group, and 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 sets of equivalent wavelengths: Then, using the 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 pattern background intensity of s light and p light, b s (x,y) and b p (x, y) are the fringe amplitude intensities of the interference pattern of s-light and p-light respectively, and The interference pattern fringe phase distributions 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 singularities in the two orthogonal phase images are extracted respectively, and the position differences of the phase singularities 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 working method of the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on super-surface cylindrical lens according to claim 7 is 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 singularities in the s direction is replaced with the smooth phase of the corresponding area in the p direction. Similarly, the area with phase singularities in the p direction is replaced with the smooth phase of the corresponding area in the s direction.

9. The working method of the high-power optical fiber device refractive index dual-wavelength polarization holographic microscopy three-dimensional detection system based on super-surface cylindrical lens according to claim 8 is characterized in that: In step (6), the process of the full-aperture aberration-free 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 elimination result under a single measurement angle, and then it is superimposed with the SL (Shepp-Logan) filter function to form the aberration elimination SL filter function; Secondly, the one-dimensional refractive index projection function is obtained by 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, and the Fourier transform of the modified 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-eliminating SL filter function; Finally, the Fourier transform of the modified projection function is back-projected to obtain the two-dimensional distribution of the refractive index of a single layer. After calculating the two-dimensional distribution of the refractive index of each layer in turn, 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.

Images