Geometric dimension detection device and method

Abstract

The application provides a geometric size detection device and method, wherein the detection device comprises a light source assembly, an interference figure forming assembly and an image processing system; the light source assembly is arranged on one side of a to-be-detected optical fiber preform and is used for providing polarized light so that the polarized light is projected on the to-be-detected optical fiber preform; the interference figure forming assembly is arranged on the other side of the to-be-detected optical fiber preform, and the interference figure forming assembly forms an interference image based on ordinary light and very light generated by birefringence; and the image processing system is used for collecting the interference image and detecting the geometric size of the to-be-detected optical fiber preform based on the collected image. The geometric size detection device and method provided by the application can directly, completely and non-destructively detect the geometric size of a polygonal optical fiber preform, without the need of pre-drawing the optical fiber preform into an optical fiber or slicing, thereby improving the research and production efficiency and realizing the control of the geometric size of the polygonal optical fiber preform from the source.

Description

Technical Field

[0001] This invention relates to the field of optical fiber testing technology, and in particular to a geometric dimension detection device and method. Background Technology

[0002] Geometric dimensions are a crucial aspect of fiber optic quality inspection and a key parameter characterizing the coupling efficiency between the fiber and the light source, influencing factors such as connection loss and bending loss. Polygonal fiber preforms, used in the fabrication of double-clad gain fibers, determine the overall internal and external structure of the fiber. Therefore, assessing the geometric dimensions of polygonal fiber preforms is an essential part of fiber preform quality inspection.

[0003] Currently, there are three main approaches to inspecting the geometric dimensions of polygonal optical fiber preforms. The first is to draw the polygonal preform into an optical fiber, then flatten the fiber's end face and inspect its geometry under a microscope. This process, from preform preparation and drawing to testing, is lengthy and slow, significantly impacting R&D and production efficiency. The second approach involves longitudinally slicing the polygonal preform into individual pieces, then grinding and polishing the end faces before inspecting their geometry. This method damages the integrity of the polygonal preform; even if the geometry is correct, it cannot be drawn into an optical fiber and must be re-prepared, greatly increasing R&D and production costs. The third approach uses an optical fiber preform inspection device manufactured in the United States. This device can only inspect the geometric dimensions of circular optical fiber preforms and cannot inspect the geometry of polygonal preforms.

[0004] Therefore, how to achieve non-destructive testing of the geometric dimensions of optical fiber preforms while ensuring production efficiency remains an urgent problem to be solved in the field of optical fiber testing. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a geometric dimension detection device and method that can directly, completely and non-destructively detect the geometric dimensions of polygonal optical fiber preforms while ensuring production efficiency.

[0006] This invention provides a geometric dimension detection device, comprising:

[0007] A light source assembly is disposed on one side of the fiber preform under test, and the light source assembly is used to provide polarized light so that the polarized light is projected onto the fiber preform under test;

[0008] An interferogram forming component is disposed on the other side of the fiber preform under test, and the interferogram forming component forms an interference image based on ordinary light and extraordinary light generated by birefringence;

[0009] An image processing system is used to acquire the interference image and detect the geometric dimensions of the fiber preform under test based on the acquired image.

[0010] According to a geometric dimension detection device provided by the present invention, the image processing system includes:

[0011] An optical system is used to scale the interference image to obtain a first image;

[0012] An imaging system is used to acquire the first image, obtain a second image, and detect the geometric dimensions of the optical fiber preform under test based on the second image.

[0013] According to a geometric dimension detection device provided by the present invention, the optical system includes:

[0014] A first optical subsystem is used to reduce the interference image based on a first magnification to obtain a first reduced image;

[0015] A second optical subsystem is used to magnify the first reduced image based on a second magnification to obtain a second magnified image, and to use the second magnified image as the first image.

[0016] According to a geometric dimension detection device provided by the present invention, the light source assembly includes:

[0017] A light source used to emit a beam of light;

[0018] A focusing lens is used to focus the light beam to emit focused plane light;

[0019] A polarizer is used to convert the focused plane light into the polarized light;

[0020] The interferogram forming component includes a polarizer;

[0021] The focusing lens, the polarizing lens, the analyzer, and the optical system are located in the same optical path, and their centers are located on the same horizontal line.

[0022] According to a geometric dimension detection device provided by the present invention, the light source is disposed inside the lens barrel of the focusing lens, and the position of the light source on the horizontal and vertical planes inside the lens barrel is adjustable.

[0023] According to a geometric dimension detection device provided by the present invention, the light source assembly further includes:

[0024] A full-wave mirror is used to increase the optical path difference of the polarized light;

[0025] The polarizer, the full-wave mirror, and the analyzer are mounted on an adjustable bracket, and the centers of the polarizer, the full-wave mirror, and the analyzer are located on the same horizontal line.

[0026] According to a geometric dimension detection device provided by the present invention, the detection device further includes:

[0027] The displacement platform is used to move the fiber preform under test on a horizontal plane.

[0028] According to a geometric dimension detection device provided by the present invention, the displacement platform is specifically used for:

[0029] The fiber preform under test is moved in the X and / or Y directions on the horizontal plane.

[0030] The X direction is perpendicular to the optical path of the polarized light, and the Y direction is perpendicular to the X direction.

[0031] The present invention also provides a method for detecting geometric dimensions, comprising:

[0032] The interference image is acquired, which is formed by the ordinary light and the extraordinary light obtained by birefringence of polarized light on the fiber preform under test;

[0033] Based on the acquired images, the geometric dimensions of the optical fiber preform under test are detected.

[0034] According to a geometric dimension detection method provided by the present invention, the step of detecting the geometric dimensions of the optical fiber preform under test based on the acquired image includes:

[0035] Based on the acquired image, the geometric dimensions of the fiber preform under test at the measured position are detected. The measured position is the longitudinal position on the fiber preform under test where birefringence occurs.

[0036] Based on the acquired image, the geometric dimensions of the optical fiber preform under test are detected, and then the process further includes:

[0037] The control displacement platform moves the fiber preform under test to adjust the measured position, and the interference image is acquired after the adjustment is completed.

[0038] This invention provides a geometric dimension detection device and method. The device provides polarized light through a light source assembly and projects it onto a fiber optic preform under test, generating birefringence within the preform. An interferogram forming assembly forms an interference image based on the ordinary and extraordinary rays generated by the birefringence. An image processing system acquires the interference image and detects the geometric dimensions of the preform based on the acquired image. The geometric dimension detection device and method provided by this invention eliminate the need to pre-draw the fiber optic preform into an optical fiber or to slice it, enabling direct, complete, and non-destructive detection of the geometric dimensions of polygonal fiber optic preforms. This improves R&D and production efficiency and reduces R&D and production costs. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is one of the structural schematic diagrams of the geometric dimension detection device provided by the present invention;

[0041] Figure 2 This is a schematic diagram of the image processing system of the geometric dimension detection device provided by the present invention;

[0042] Figure 3 This is a schematic diagram of the optical system of the geometric dimension detection device provided by the present invention;

[0043] Figure 4 This is a schematic diagram of the structure of the light source assembly of the geometric dimension detection device provided by the present invention;

[0044] Figure 5 This is the second schematic diagram of the geometric dimension detection device provided by the present invention;

[0045] Figure 6 This is one of the flowcharts illustrating the geometric dimension detection method provided by the present invention;

[0046] Figure 7 This is the second flowchart of the geometric dimension detection method provided by the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0048] Double-clad gain fiber, as the gain medium of fiber lasers, absorbs pump light to generate excitation and emission, converting the pump light into signal light of a different wavelength or producing signal light with higher power. The inner cladding structure of double-clad gain fiber used in fiber lasers is generally polygonal. This is to break rotational symmetry, prevent the pump light from forming a spiral beam in the inner cladding, and improve the absorption efficiency of the pump light. The fiber preform is a material prefabrication used to draw the fiber. Double-clad gain fiber is generally formed by grinding the fiber preform into a polygonal shape and drawing it. The prepared polygonal fiber preform is then heated at high temperature and drawn at a certain traction speed to form the double-clad gain fiber. Therefore, the internal and external structures of the fiber preform determine the internal and external structures of the double-clad gain fiber.

[0049] The outer diameter of polygonal optical fiber preforms is typically a few millimeters to tens of millimeters. When light is shone on the preform from the side, the polygonal shape causes varying degrees of refraction or reflection of the light, preventing it from focusing on the fiber core and making it invisible. Therefore, measuring the geometric dimensions of polygonal optical fiber preforms is a challenge. To address this, this invention provides a geometric dimension inspection device that can perform non-destructive testing of the geometric dimensions of optical fiber preforms while maintaining production efficiency.

[0050] Figure 1 This is one of the structural schematic diagrams of the geometric dimension detection device provided in the embodiments of the present invention, such as... Figure 1 As shown, the detection device includes:

[0051] A light source assembly 110 is disposed on one side of the fiber preform 120 to be tested. The light source assembly 110 is used to provide polarized light so that the polarized light is projected onto the fiber preform 120 to be tested.

[0052] Interference pattern forming component 130 is disposed on the other side of the fiber preform 120 under test. Interference pattern forming component 130 forms an interference image based on ordinary light and extraordinary light generated by birefringence.

[0053] Image processing system 140 is used to acquire interference images and detect the geometric dimensions of the fiber preform 120 under test based on the acquired images.

[0054] It should be noted that polarized light refers to light waves whose light vector vibration direction remains unchanged or changes in a certain regular pattern. According to its properties, polarized light can be further classified into plane-polarized light (also known as linearly polarized light), circularly polarized light, elliptically polarized light, and partially polarized light. Generally, if the vibration direction of the electric vector of a light wave is confined to a specific plane, this type of polarized light is called plane-polarized light. Because the vibration direction of this type of polarized light is a straight line during propagation, it is also called linearly polarized light.

[0055] The light source assembly 110 in this embodiment of the invention can be an optical element capable of providing or generating polarized light, or a group of optical elements capable of providing or generating polarized light composed of multiple optical elements. This embodiment of the invention does not limit this.

[0056] Understandably, birefringence refers to the phenomenon where a single incident ray produces two refracted rays. When light propagates in an inhomogeneous body, its propagation speed and refractive index change with the direction of vibration, and it has more than one refractive index value. When a light wave is incident on an inhomogeneous body, except in special directions, it will undergo birefringence, decomposing into two polarized rays with mutually perpendicular vibration directions, different propagation speeds, and unequal refractive indices. This phenomenon is birefringence.

[0057] For example, in this embodiment of the invention, the polarized light provided by the light source assembly 110 can be plane-polarized light, and the fiber preform under test 120 can be a polygonal fiber preform. The light source assembly 110 is placed on one side of the fiber preform under test 120, so that the optical path of the plane-polarized light it provides is perpendicular to the axial direction of the fiber preform under test 120. After the plane-polarized light is projected onto the fiber preform under test 120, birefringence will occur inside it. At this time, the plane-polarized light will be split into two beams with mutually perpendicular polarization directions and different propagation speeds, namely ordinary light and extraordinary light. After the two beams pass through the fiber preform under test 120, an optical path difference will be generated.

[0058] It should be noted that both ordinary and extraordinary rays are plane-polarized light. The vibration of the ordinary ray is perpendicular to its principal plane, while the vibration of the extraordinary ray lies within its principal plane. Interference is a phenomenon where two (or more) beams of light, under certain conditions, superimpose and exhibit stable mutual reinforcement or weakening at different locations in the overlapping region. Normally, two independent light sources or two different parts of the same light source do not produce interference. However, by using methods such as reflection or refraction, light emitted from the same source can be split into two beams. These two beams travel along different paths in space, producing a fixed optical path difference. When they converge again, interference occurs.

[0059] Specifically, the interferogram forming component 130 is disposed on the other side of the fiber preform 120 under test, such that the ordinary and extraordinary beams transmitted from the fiber preform 120 under test illuminate the interferogram forming component 130. After passing through the interferogram forming component 130, an interference image with geometric features is obtained, generated by the ordinary and extraordinary beams in the same plane. It should be noted that the interference image with geometric features generated in this embodiment corresponds to the geometric dimensions of the polygonal cladding structure and core structure of the fiber preform 120 under test.

[0060] The image processing system 140 is located after the interferogram forming component 130. It receives the interference image generated by the interferogram forming component 130. After analysis and processing by the image processing system 140, the interference image is imaged. The geometric dimensions of the optical fiber preform 120 under test can be obtained by performing geometric dimension detection on the image image generated by the image processing system 140 through the host software. The geometric dimension parameters of the polygonal optical fiber preform mainly include the core diameter and cladding diameter.

[0061] The geometric dimension detection device provided in this embodiment of the invention provides polarized light through a light source assembly 110, which is projected onto the fiber preform 120 under test. This generates birefringence within the fiber preform 120. An interferogram forming assembly 130 forms an interference image based on the ordinary and extraordinary rays generated by the birefringence. An image processing system 140 acquires the interference image and detects the geometric dimensions of the fiber preform 120 based on the acquired image. This method eliminates the need to pre-draw the fiber preform into an optical fiber or to slice it, enabling direct, complete, and non-destructive detection of the geometric dimensions of polygonal fiber preforms. Compared to existing fiber geometric dimension detection devices, the geometric dimension detection device provided in this embodiment of the invention improves R&D and production efficiency, reduces R&D and production costs, simplifies the setup of the experimental device, and is easy to operate, enabling control of the geometric dimensions of polygonal fiber preforms from the source.

[0062] Figure 2 A schematic diagram of the image processing system of the geometric dimension detection device provided in an embodiment of the present invention. Based on the above embodiments, as follows... Figure 2 As shown, the image processing system includes:

[0063] Optical system 141 is used to scale the interference image to obtain a first image;

[0064] The imaging system 142 is used to acquire a first image, obtain a second image, and detect the geometric dimensions of the fiber preform 120 under test based on the second image.

[0065] It should be noted that image scaling refers to the process of adjusting the size of a digital image. Image scaling is a non-trivial process that requires a trade-off between processing efficiency and the smoothness and sharpness of the result.

[0066] Specifically, the optical system 141 is located after the interferogram forming component 130. It receives the interferogram and scales the interferogram so that the obtained first image can be completely imaged on the imaging system 142, thereby enabling direct and complete detection of the geometric dimensions of the polygonal fiber preform and ensuring the accuracy of the detection results.

[0067] The imaging system 142 is located after the optical system 141. It receives and acquires the first image after scaling. The first image is imaged by the imaging system 142. The geometric dimensions of the image of the imaging system 142 are detected by the host software to obtain the geometric dimensions of the optical fiber preform 120 to be tested.

[0068] It should be noted that the geometric dimension detection of the imaging system 142 through the host software specifically includes: importing the acquired second image into the host software (e.g., MATLAB), obtaining the maximum gray value of the second image, determining the cladding boundary coordinates and core boundary coordinates based on the maximum gray value, filtering the cladding boundary coordinates and core boundary coordinates, and performing polynomial fitting on the filtered cladding boundary coordinates and core boundary coordinates to calculate the geometric dimensions of the prefabricated fiber rod 120 to be tested.

[0069] Figure 3 This is a schematic diagram of the optical system of the geometric dimension detection device provided in an embodiment of the present invention. Based on any of the above embodiments, such as... Figure 3 As shown, the optical system 141 includes:

[0070] The first optical subsystem 1411 is used to reduce the interference image based on a first magnification to obtain a first reduced image;

[0071] The second optical subsystem 1412 is used to magnify the first reduced image based on a second magnification to obtain a second magnified image, and to use the second magnified image as the first image.

[0072] Specifically, in this embodiment of the invention, the camera target surface size of the first optical subsystem 1411 can be 4 / 3 inches, the working distance can be 50-100 mm, and the first magnification can be 0.01-0.1X. After receiving the interference image, the first optical subsystem 1411 reduces the interference image based on the first magnification, so that the first reduced image conforms to the size of the display area, ensuring that the image can be completely imaged on the imaging system 142.

[0073] In this embodiment of the invention, the second optical subsystem 1412 can be a CCD camera, and the second magnification can be 40 to 100X. After receiving the first reduced image, the second optical subsystem 1412 magnifies the first reduced image based on the second magnification, so that the image can be imaged on the imaging system 142 with a higher resolution, which facilitates the imaging system 142 to detect and calculate the geometric dimensions of the fiber preform 120 under test.

[0074] It should be noted that the optical system 141 in this embodiment of the invention includes a first optical subsystem 1411 and a second optical subsystem 1412. The two optical subsystems work together to magnify the pixel units of the camera chip to the pixel units of the liquid crystal display, achieving a one-to-one or many-to-one magnification and display of the camera units. In this embodiment of the invention, the outer diameter of the fiber preform 120 under test can be 1 to 100 mm. The magnification of the first optical subsystem 1411 and the second optical subsystem 1412 can be selected according to the size of the fiber preform 120 under test, with the specific magnification taking the specific diameter of the fiber preform 120 under test as a reference.

[0075] Figure 4 This is a schematic diagram of the light source assembly of the geometric dimension detection device provided in an embodiment of the present invention. Based on any of the above embodiments, such as... Figure 4 As shown, the light source assembly 110 includes:

[0076] Light source 111 is used to emit a beam of light;

[0077] Focusing lens 112 is used to focus the light beam to emit focused plane light;

[0078] Polarizer 113 is used to convert focused plane light into polarized light;

[0079] Interferogram forming component 130 includes analyzer 131;

[0080] The focusing lens 112, polarizer 113, analyzer 131 and optical system 141 are located in the same optical path and their centers are located at the same horizontal position.

[0081] Specifically, light source 111 refers to an object that can emit electromagnetic waves (including visible light and invisible light such as ultraviolet, infrared, and X-rays) within a certain wavelength range, and usually refers to an object that can emit visible light. In the embodiments of the present invention, light source 111 can be an LED (Light Emitting Diode) light source. LED light sources are light-emitting diode light sources, which have advantages such as small size, long lifespan, and high efficiency.

[0082] It should be noted that focusing is the process of controlling a beam of light or a stream of particles to converge to a single point as much as possible. In this embodiment of the invention, the focusing lens 112 is used to focus the light beam emitted by the light source 111, obtaining focused plane light which is then projected onto the polarizer 113. The polarizer 113 is a filter that allows light of a specific polarization to pass through while blocking other polarized light waves. It can convert undefined or mixed-polarized beams into clearly defined polarized beams, i.e., polarized light. Therefore, the focused plane light emitted from the focusing lens 112 is converted into plane-polarized light after passing through the polarizer 113.

[0083] In practical applications, the aforementioned plane-polarized light can be generated through reflection, multiple refractions, birefringence, and selective absorption. For example, it can be generated using polarizing filters, polarizing mirrors, polarizers, or modulators. This embodiment of the invention uses a polarizer 112 to generate plane-polarized light; the device has a simple structure and is easy to operate.

[0084] When the polarizer 113 is used to check whether a certain beam is linearly polarized, it becomes the analyzer 131. After the plane-polarized light is projected onto the fiber preform 120 under test, since the fiber preform 120 can be a polygonal fiber preform, the plane-polarized light will undergo birefringence inside the fiber preform 120 under test, and will be split into two beams with mutually perpendicular polarization directions and different propagation speeds, namely the ordinary beam and the extraordinary beam. After these two beams pass through the fiber preform 120 under test, they will produce an optical path difference. After passing through the analyzer 131, an interference image with geometric characteristics produced by the ordinary beam and the extraordinary beam in the same plane is obtained.

[0085] By placing the focusing lens 112, polarizer 113, analyzer 131, and optical system 141 on the same optical path and with their centers at the same horizontal position, the accuracy of the detection results can be guaranteed and the possible errors during the detection process can be reduced.

[0086] Furthermore, the light source 111 is disposed inside the barrel of the focusing lens 112, and the position of the light source 111 on the horizontal and vertical planes inside the barrel is adjustable. Installing the light source 111 inside the barrel of the focusing lens 112 not only provides some protection for the light source 111, but also ensures that the light emission center of the light source 111 is aligned with the center of the focusing lens 112, further improving the focusing effect of the focusing lens 112 on the light beam.

[0087] Furthermore, the light source assembly 110 also includes:

[0088] Full-wave mirror 114 is used to increase the optical path difference of polarized light;

[0089] The polarizer 113, the full-wave mirror 114 and the analyzer 131 are mounted on an adjustable bracket, and the centers of the polarizer 113, the full-wave mirror 114 and the analyzer 131 are located on the same horizontal line.

[0090] Specifically, the main function of the full-wave mirror 114 is to increase the optical path difference of polarized light, acting as a sensitive filter. Designed according to a specific wavelength of light, the full-wave mirror 114 allows linearly polarized light of that wavelength to pass through without attenuation, while converting light of nearby wavelengths into elliptically polarized light, thus achieving filtering. In this embodiment of the invention, the additional optical path of the full-wave mirror 114 can be greater than or equal to 500 μm, enhancing the filtering effect, facilitating imaging by the subsequent imaging system and the detection of geometric dimensions, and ensuring the accuracy of the detection results.

[0091] The positions of the polarizer 113, the full-wave mirror 114, and the analyzer 131 can be adjusted using the adjustable bracket, so that the centers of the polarizer 113, the full-wave mirror 114, and the analyzer 131 are on the same horizontal line, further ensuring the accuracy of the test results and reducing possible errors during the test process.

[0092] Figure 5 This is a second structural schematic diagram of the geometric dimension detection device provided in an embodiment of the present invention. Based on any of the above embodiments, such as... Figure 5 As shown, the detection device also includes:

[0093] The displacement platform 150 is used to move the fiber preform 120 to be tested on the horizontal plane.

[0094] Specifically, the fiber preform 120 to be tested is placed horizontally on the displacement platform 150. By moving the displacement platform 150, the fiber preform 120 to be tested can be moved, thereby adjusting the longitudinal position of the fiber preform 120 to be tested.

[0095] The displacement platform 150 in this embodiment of the invention can use components such as stepper motors and ball screws to significantly reduce vibration and noise, achieve high positioning accuracy, and effectively ensure the straightness, flatness and other indicators of the displacement platform 150.

[0096] Based on the above embodiments, the displacement platform 150 is specifically used for:

[0097] Drive the fiber preform 120 to be tested to move in the X and / or Y directions on the horizontal plane;

[0098] The X direction is perpendicular to the optical path of the polarized light, and the Y direction is perpendicular to the X direction.

[0099] Specifically, during the initial adjustment, by adjusting the position of the displacement platform 150 along the X and / or Y directions, plane-polarized light can be projected onto the measured position on the fiber preform 120 under test. Simultaneously, focusing control can be achieved for image imaging on the imaging system 142. After obtaining the geometric dimensions of the first measured position of the fiber preform 120, the displacement platform 150 can be adjusted along the Y direction, moving the fiber preform 120 along its longitudinal direction to obtain the geometric dimensions of different measured positions across the entire fiber preform 120. In this embodiment of the invention, the displacement platform 150 can move within a range of 0–300 mm along the X direction and 0–300 mm along the Y direction.

[0100] Figure 6 This is one of the flowcharts illustrating a geometric dimension detection method provided in an embodiment of the present invention. Based on any of the above embodiments, such as... Figure 6 As shown, the detection method includes:

[0101] Step 610: Acquire the interference image. The interference image is formed by the ordinary light and extraordinary light obtained by birefringence of polarized light on the fiber preform 120 under test.

[0102] It should be noted that polarized light refers to light waves whose light vector vibration direction remains unchanged or changes in a certain regular pattern. According to its properties, polarized light can be further classified into plane-polarized light (also known as linearly polarized light), circularly polarized light, elliptically polarized light, and partially polarized light. The polarized light in this embodiment of the invention can be plane-polarized light. Plane-polarized light can be generated through reflection, multiple refractions, birefringence, and selective absorption, for example, using polarizing filters, polarizing mirrors, polarizers, or modulators. This embodiment of the invention does not impose any limitations on this.

[0103] It should be understood that when light waves are incident on a non-homogeneous body, they will decompose into two polarized beams with mutually perpendicular vibration directions, different propagation speeds, and different refractive indices. This phenomenon is called birefringence. In this embodiment of the invention, the fiber preform 120 under test can be a polygonal fiber preform. When plane-polarized light is projected onto the fiber preform 120 under test, birefringence will occur within it, splitting into two beams with mutually perpendicular polarization directions and different propagation speeds, namely, the ordinary beam and the extraordinary beam. After these two beams pass through the fiber preform 120 under test, an optical path difference will be generated. When the ordinary beam and the extraordinary beam are superimposed under certain conditions, they exhibit a stable phenomenon of mutual reinforcement or weakening at different locations in the overlap region, thereby producing an interference pattern.

[0104] Specifically, image acquisition is the process of obtaining signal distribution information of an image through an imaging device. When polarized light is projected onto the fiber preform 120 under test, birefringence is generated inside it. Based on the ordinary and extraordinary rays obtained by birefringence, an interference image is formed. The interference image can be acquired and imaged by an imaging device to obtain an image with certain geometric features that can be used for geometric dimension detection.

[0105] Step 620: Based on the acquired image, detect the geometric dimensions of the optical fiber preform 120 to be tested.

[0106] Specifically, after acquiring the image, the acquired image can be imported into the host software (e.g., MATLAB) to obtain the maximum gray value of the acquired image. Based on the maximum gray value, the cladding boundary coordinates and core boundary coordinates are determined. The cladding boundary coordinates and core boundary coordinates are then filtered. Polynomial fitting is performed on the filtered cladding boundary coordinates and core boundary coordinates to calculate the geometric dimensions of the prefabricated fiber rod 120 to be tested.

[0107] The geometric dimension detection method provided in this embodiment of the invention projects polarized light onto the fiber preform 120 under test, generating birefringence inside the fiber preform 120. An interference image formed by the ordinary and extraordinary rays obtained from the birefringence is acquired, and the geometric dimensions of the fiber preform 120 are detected based on the acquired image. This method eliminates the need to pre-draw the fiber preform 120 into an optical fiber or to slice it. It allows for direct, complete, and non-destructive detection of the geometric dimensions of the polygonal fiber preform. Compared with existing detection methods, the geometric dimension detection method provided in this embodiment of the invention improves R&D and production efficiency, reduces R&D and production costs, is easy to operate, and enables control of the geometric dimensions of the polygonal fiber preform from the source.

[0108] Figure 7 This is a second schematic flowchart illustrating the geometric dimension detection method provided in this embodiment of the invention. Based on the above embodiments, as... Figure 7 As shown, step 620 specifically includes:

[0109] Step 621: Based on the acquired image, detect the geometric dimensions of the fiber preform 120 under test at the measured position, which is the longitudinal position on the fiber preform 120 under test where birefringence occurs.

[0110] Specifically, the outer diameter of a polygonal optical fiber preform is typically a few millimeters to tens of millimeters. When inspecting the geometric dimensions of a polygonal optical fiber preform, light is projected from one side of the preform. For example, if polarized light is projected onto the preform 120 under test from one side, the polygonal shape will cause the light to refract or reflect to varying degrees. Since the light is projected from one side of the preform 120, the measured position is the longitudinal position on the preform 120 where birefringence occurs.

[0111] Furthermore, the fiber preform 120 under test usually has a certain length. For example, in this embodiment of the invention, the length of the fiber preform 120 under test can be greater than or equal to 0.1m. The cladding structure and core structure of the fiber preform 120 under test are not uniform along its longitudinal direction. Therefore, it is necessary to detect the geometric dimensions at different longitudinal positions of the fiber preform 120 under test.

[0112] Accordingly, after step 621, the detection method further includes:

[0113] Step 630: Control the displacement platform 150 to move the fiber preform 120 to be tested in order to adjust the position to be tested, and acquire the interference image after the adjustment is completed.

[0114] It should be noted that the displacement platform 150 in this embodiment of the invention can be controlled to move automatically using components such as stepper motors and ball screws. After completing the geometric dimension detection of the first longitudinal position of the optical fiber preform 120 under test, the displacement platform 150 can be controlled to move, thereby moving the optical fiber preform 120 under test, and thus detecting the geometric dimensions of the optical fiber preform 120 under test at different longitudinal positions.

[0115] Based on any of the above embodiments, this invention provides a geometric dimension detection method applied to a geometric dimension detection device, wherein the detection device includes a light source 111, a focusing lens 112, a polarizer 113, a full-wave mirror 114, a displacement platform 150, an analyzer 131, an optical system 141, and an imaging system 142. Accordingly, the detection method specifically includes:

[0116] A complete fiber preform 120 to be tested is horizontally placed in the displacement platform 150. The displacement platform 150 is moved to adjust the longitudinal test position of the fiber preform 120, which is denoted as L1. The centers of the focusing lens 112, polarizer 113, analyzer 131, and optical system 141 are aligned at the same horizontal level using an adjustable bracket. The light source 111, optical system 141, and imaging system 142 are turned on sequentially. The light emitted from the light source 111 is focused by the focusing lens 112 to obtain a focused plane light. The focused plane light is then converted into plane-polarized light by the polarizer 113. This plane-polarized light is projected onto the fiber preform 120. At position L1 on the fiber preform 120, birefringence is generated inside the fiber preform 120. At this point, the plane-polarized light will split into ordinary and extraordinary rays with mutually perpendicular polarization directions and different propagation speeds. After passing through the fiber preform 120, the ordinary and extraordinary rays will produce an optical path difference. An interference image with geometric characteristics generated by the ordinary and extraordinary rays in the same plane can be obtained through the analyzer 131. The interference image is scaled by the optical system 141, and the scaled image is imaged by the imaging system 142. The image is then detected and calculated to obtain the geometric dimensions at L1 on the fiber preform 120. The displacement platform 150 moves the fiber preform 120 to adjust its longitudinal test position, denoted as L2. After adjustment, the light source 111, optical system 141, and imaging system 142 are turned on again to detect and obtain the geometric dimensions at L2 on the fiber preform 120. In this way, the geometric dimensions of the entire fiber preform 120 at different longitudinal positions can be obtained.

[0117] The geometric dimension detection device and method provided in this invention can directly and completely detect the geometric dimensions of polygonal optical fiber preforms without damage, without having to draw the optical fiber preforms into optical fibers in advance or cut them, thereby improving R&D and production efficiency and reducing R&D and production costs.

[0118] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0119] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A geometric dimension detecting device, characterized by, The application relates to a fiber preform testing device and a testing method thereof. The device comprises: a light source assembly arranged on one side of a fiber preform to be tested, the fiber preform to be tested being a polygonal fiber preform, the light source assembly being used to provide polarized light so that the polarized light is projected on the fiber preform to be tested; an interference figure forming assembly arranged on the other side of the fiber preform to be tested, the interference figure forming assembly being used to form an interference figure based on ordinary light and extraordinary light generated by birefringence, the birefringence being generated by the polarized light in the interior of the fiber preform to be tested, the geometric features of the interference figure corresponding to the core and cladding structure of the fiber preform to be tested; an image processing system used to acquire the interference figure and detect the geometric size of the core and / or cladding of the fiber preform to be tested based on the acquired image. The image processing system comprises: an optical system used to scale the interference figure to obtain a first image; an imaging system used to acquire the first image to obtain a second image and detect the geometric size of the core and / or cladding of the fiber preform to be tested based on the second image. The optical system comprises: a first optical subsystem used to scale down the interference figure based on a first magnification to obtain a first scaled-down image; 2. The geometric dimension detecting apparatus according to claim 1, wherein a second optical subsystem used to scale up the first scaled-down image based on a second magnification to obtain a second scaled-up image, the second scaled-up image being used as the first image. The light source assembly comprises: a light source used to emit a light beam; a focusing mirror used to focus the light beam to emit focused plane light; a polarizing mirror used to convert the focused plane light into the polarized light; The interference figure forming assembly comprises an analyzer; 3. The geometric dimension detecting apparatus according to claim 2, wherein The focusing mirror, the polarizing mirror, the analyzer and the optical system are located on the same optical path and have the same horizontal center.

4. The geometric dimension detecting apparatus according to claim 2, wherein The light source is arranged in a mirror barrel of the focusing mirror, and the horizontal and vertical positions of the light source in the mirror barrel are adjustable. The light source assembly further comprises: a full-wave mirror used to increase the optical path difference of the polarized light; 5. The geometric dimension detecting apparatus according to any one of claims 1 to 4, characterized by The polarizing mirror, the full-wave mirror and the analyzer are arranged on an adjustable support, and the centers of the polarizing mirror, the full-wave mirror and the analyzer are located on the same horizontal line. Further comprising:

6. The geometric dimension detecting apparatus according to claim 5, wherein a displacement platform used to drive the fiber preform to be tested to move in a horizontal plane. The displacement platform is specifically used to: drive the fiber preform to be tested to move in an X direction and / or a Y direction in the horizontal plane; 7. A geometric dimension detection method applied to the geometric dimension detection device according to any one of claims 1 to 6, characterized in that, The X direction is perpendicular to the optical path of the polarized light, and the Y direction is perpendicular to the X direction. The method comprises: acquiring an interference figure, the interference figure being formed by ordinary light and extraordinary light generated by birefringence of polarized light on a fiber preform to be tested; 8. The geometric dimension detecting method according to claim 7, wherein detecting the geometric size of the fiber preform to be tested based on the acquired image. The step of detecting the geometric size of the fiber preform to be tested based on the acquired image comprises: detecting the geometric size of the fiber preform to be tested at a measured position, the measured position being a longitudinal position where birefringence is generated on the fiber preform to be tested. The method further comprises, after detecting the geometric size of the optical fiber preform based on the collected image, adjusting the measured position by moving the displacement platform to drive the optical fiber preform to be measured, and collecting the interference image after the adjustment is completed. The method further comprises, after detecting the geometric size of the optical fiber preform based on the collected image, adjusting the measured position by moving the displacement platform to drive the optical fiber preform to be measured, and collecting the interference image after the adjustment is completed.

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