Optical fiber preform defect detection device and method

Abstract

The invention discloses an optical fiber preform defect detection device and method, and relates to the technical field of optical information. The first laser emitting device is used for emitting first laser in the radial direction of the optical fiber preform to be measured; the first laser receiving device is used for receiving the first laser which is transmitted by the first laser transmitting device and penetrates through the circle center of the to-be-detected optical fiber preform so as to determine the axial position of the defect of the to-be-detected optical fiber preform; the optical fiber bearing device is used for bearing and rotating an optical fiber preform to be tested; the second laser emitting device is used for emitting second laser in the circumferential direction of the defect position of the optical fiber preform to be detected; the second laser receiving device is used for receiving the second laser which is transmitted by the second laser transmitting device and penetrates through the optical fiber preform to be detected so as to determine the radial position of the defect of the optical fiber preform to be detected; and the angle measuring device is used for measuring the rotation angle of the to-be-measured optical fiber preform so as to determine the angular position of the defect of the to-be-measured optical fiber preform in the circumferential direction.

Description

Technical Field

[0001] This application relates to the field of optical information technology, and in particular to a device and method for detecting defects in optical fiber preforms. Background Technology

[0002] Before being drawn into fibers, optical fibers exist in the form of optical fiber preforms. The performance of optical fibers depends on the quality of the optical fiber preforms. Even minor defects in the optical fiber preforms can affect the yield and transmission performance of the optical fibers. Therefore, it is essential to identify the defects in the optical fiber preforms.

[0003] Under current rod manufacturing processes, visible defects such as bubbles and opaque impurities are easily generated inside the rod. However, the current inspection process relies on manual visual inspection, which results in poor objectivity and makes it impossible to accurately measure the location of defects. Summary of the Invention

[0004] This application provides a device and method for detecting defects in optical fiber preforms, so as to locate the specific location of defects in the core rod.

[0005] In a first aspect, this application provides a defect detection device for optical fiber preforms, comprising: A first laser emitting device is used to radially emit a first laser onto the fiber preform under test; The first laser receiving device is used to receive the first laser emitted by the first laser emitting device that passes through the center of the optical fiber preform under test, so as to determine the axial position of the defect in the optical fiber preform under test. Fiber optic carrier device, used to carry and rotate the fiber optic preform to be tested; The second laser emitting device is used to emit a second laser in the circumferential direction at the defect location of the fiber preform under test; The second laser receiving device is used to receive the second laser emitted by the second laser emitting device that passes through the fiber preform under test, so as to determine the radial position of the defect in the fiber preform under test. An angle measuring device is used to measure the rotation angle of the optical fiber preform under test in order to determine the angular position of the defect in the optical fiber preform under test in the circumferential direction.

[0006] This application employs a first laser emitting device to radially emit a first laser beam across the fiber optic preform under test; a first laser receiving device receives the first laser beam emitted by the first laser emitting device, which passes through the center of the fiber optic preform under test, to determine the axial position of the defect in the fiber optic preform under test. A second laser emitting device emits a second laser beam circumferentially around the location of the defect in the fiber optic preform under test; a second laser receiving device receives the second laser beam emitted by the second laser emitting device, which passes through the fiber optic preform under test, to determine the radial position of the defect in the fiber optic preform under test; and an angle measuring device measures the rotation angle of the fiber optic preform under test to determine the angular position of the defect in the circumferential direction. This allows for the determination of the three-dimensional coordinates of the defect in the entire fiber optic preform under test, pinpointing its exact location.

[0007] It should be noted that before the first laser emitted by the first laser emitter passes through the center of the optical fiber preform under test and is received by the first laser receiver, the positions of the first laser emitter and the first laser receiver are calibrated so that when the laser signal emitted by the first laser emitter is received by the first laser receiver, the laser aperture areas are equal, the positions coincide, and the center positions coincide.

[0008] It should be noted that the second laser emitting device is placed on one side of the circumference of the fiber preform under test, and the second laser receiving device is placed on the other side of the circumference of the fiber preform under test at a relatively opposite position. The height position of the defect in the fiber preform under test can be located by ensuring that the center of the second laser signal emitted by the second laser emitting device and the center of the second laser signal received by the second laser receiving device are on the same horizontal line.

[0009] In some embodiments, the first laser emission point of the first laser emitting device, the first laser receiving point of the first laser receiving device, and the center of the fiber preform under test are aligned in a straight line. Typically, the fiber preform under test is laid flat along its axial direction on a fiber carrier. The first laser emitting device is located above the fiber carrier, and the first laser receiving device is located below the fiber preform under test on the fiber carrier. The fiber preform under test is supported by at least two horizontally placed rollers. The first laser receiving device is located at the exact center of the two horizontally placed rollers on the fiber carrier. This arrangement ensures that, on the cross-section of the fiber preform under test, the first laser emitted from the first laser emitting device passes through the center of the fiber preform and is received by the first laser receiving device below. This ensures that the center of the laser emission point of the first laser emitting device, the center of the fiber preform under test, and the center of the laser receiving point of the first laser receiving device are aligned in a straight line, improving measurement accuracy.

[0010] In some embodiments, the second laser emitting point of the second laser emitting device and the second laser receiving point of the second laser receiving device are set at the same height. Setting the second laser emitting point of the second laser emitting device and the second laser receiving point of the second laser receiving device at the same height ensures that the height of the second laser emitting point is the height of the defect in the fiber preform of the fiber core rod under test.

[0011] In some embodiments, the first laser emitting device and the first laser receiving device are movably arranged along the axial direction of the fiber preform under test, and the axial position of the defect in the fiber preform under test can be located by moving the first laser emitting device and the first laser receiving device; and / or, The second laser emitting device and the second laser receiving device are movably arranged along the radial and axial directions of the fiber preform under test. By moving the second laser emitting device and the second laser receiving device, the radial position of defects at different axial positions on the fiber preform under test can be located.

[0012] It should be noted that the angle measuring device can be installed on the handle of the fiber preform to be tested. A 0° mark, such as a downward or upward arrow, can be set on the handle of the fiber preform to be tested. The upward or downward arrow is the starting point of 0°. After rotating the fiber preform to be tested, the angle between the arrow position and the vertical direction can be regarded as the angle position of the defect.

[0013] Secondly, this application provides a method for detecting defects in optical fiber preforms, applied to the optical fiber preform defect detection device described in the first aspect, comprising the following steps: Starting from one end of the fiber preform to be tested, a first laser is emitted through the first laser emitting device and passes through the center of the fiber preform to be tested, and the first laser is received through the first laser receiving device. The first laser intensity received by the first laser receiving device at multiple radial angles of the optical fiber preform under test passes through the center of the optical fiber preform under test. The ratio of the first laser intensity received by the first laser receiving device passing through the center of the optical fiber preform under test to the preset first laser intensity is used to determine whether the current angular position is the defect position of the optical fiber preform under test. The first laser intensity passing through the center of the fiber preform under test is obtained by the first laser receiving device at multiple axial positions. The ratio of the first laser intensity passing through the center of the fiber preform under test received by the first laser receiving device to the preset first laser intensity is used to determine whether the current axial position is the defect position of the fiber preform under test. After determining the axial position and angle of the defect in the fiber preform under test, a second laser is emitted through the second laser emitting device and receives the second laser passing through the fiber preform under test. The radial height is then determined to be the location of the defect in the fiber preform under test based on the ratio of the intensity of the second laser passing through the fiber preform received by the second laser receiving device to the preset intensity of the second laser.

[0014] Typically, in the optical fiber preform under test, the laser signal loss has less than 0.1% impact on the overall laser signal intensity. The typical attenuation coefficients for air and SiO2 glass are around 10... -7 The optical path lengths are on the order of dB / m and 0.01 dB / m, respectively. In this method, the optical path lengths of both air and SiO2 are within 10 dB / m. -1 The laser signal loss is on the order of millimeter (m), so the total attenuation in air and glass is less than 0.1%. However, when bubbles or impurities are present in the fiber preform under test, the laser signal loss is significant, resulting in noticeable abrupt changes. Therefore, the ratio of the first laser intensity received by the first laser receiver passing through the center of the fiber preform under test to the preset first laser intensity can determine whether there is a defect at the current measurement location. Typically, this ratio can be between 0.89 and 0.94. That is, if the ratio is between 0.89 and 0.94, the fiber preform under test at the current location is considered defect-free. If the ratio is less than 0.89, the fiber preform under test at the current location is considered defective. At the same axial position, the entire fiber preform under test needs to be rotated 360° to ensure that radial points on every axial cross-section are measured, reducing omissions.

[0015] The ratio of the second laser intensity received by the second laser receiving device passing through the fiber optic preform under test to a preset second laser intensity can be used to determine whether there is a defect at the current measurement height. Specifically, if the ratio is within the preset range, the fiber optic preform at the current position is considered defect-free. Conversely, if the ratio is outside the preset range, the fiber optic preform at the current height is considered defective. Typically, the ratio of the second laser intensity to the preset second laser intensity is related to the incident angle of the second laser. For an incident angle of 60°, the range is 0.66-0.71; for 30°, it is 0.86-0.91; and for 0°, it is 0.89-0.94.

[0016] In some embodiments, the first laser receiving device, which acquires the radial direction of the optical fiber preform at multiple angles, receives the first laser intensity passing through the center of the optical fiber preform under test. Determining whether the current angular position is a defect location of the optical fiber preform under test based on the ratio of the first laser intensity received by the first laser receiving device passing through the center of the optical fiber preform under test to a preset first laser intensity includes: Rotate the fiber preform under test circumferentially at a first preset angle; The intensity of the first laser passing through the center of the fiber preform is obtained by a first laser receiving device at multiple radial angles of the fiber preform under test. If the ratio of the intensity of the first laser passing through the center of the fiber preform under test received by the first laser receiving device to the preset first laser intensity does not meet the first threshold, then the current angle is the circumferential position of the defect in the fiber preform under test.

[0017] The first preset angle can be 3~5°, meaning that after measuring one diameter of the fiber preform under test, the fiber preform is rotated 3~5°, and the point on the diameter of the next fiber preform under test is measured to check for defects. The first threshold can be 0.89~0.94, that is, when the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to the preset first laser intensity is in the range of 0.89~0.94, the fiber preform under test at the current radial position can be considered to be defect-free; when the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to the preset first laser intensity is less than 0.89, the fiber preform under test at the current radial position is considered to have a defect.

[0018] In some embodiments, the step of obtaining the first laser intensity passing through the center of the fiber preform under test received by the first laser receiving device at multiple axial positions, and determining whether the current axial position is a defect location of the fiber preform under test based on the ratio of the first laser intensity passing through the center of the fiber preform under test received by the first laser receiving device to a preset first laser intensity includes: A laser emitting device and a first laser receiving device are moved simultaneously along the axial direction of the optical fiber preform to be tested at a first preset rate. The intensity of the first laser passing through the center of the fiber preform under test is obtained by the first laser receiving device at multiple axial positions of the fiber preform under test. If the ratio of the intensity of the first laser passing through the center of the optical fiber preform to be tested, received by the first laser receiving device, to the preset first laser intensity does not meet the second threshold, it indicates that the current axial position is the axial defect position of the optical fiber preform to be tested.

[0019] Starting from one end of the fiber preform under test, the first preset speed can be 1~5mm. That is, after measuring all points of a complete circular cross-section of the fiber preform under test, the speed is moved 1~5mm to measure whether there is a defect at the test point of the circular cross-section at the next axial position. The second threshold can be 0.89~0.94. That is, when the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to the preset first laser intensity is in the range of 0.89~0.94, the fiber preform under test at the current radial position can be considered to be without defects. When the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to the preset first laser intensity is less than 0.89, the fiber preform under test at the current radial position is considered to have defects.

[0020] In some embodiments, after determining the axial position and angle of the defect in the fiber preform under test, a second laser is emitted through the fiber preform under test via a second laser emitting device, and a second laser receiving device receives the second laser passing through the fiber preform under test. Determining whether the current radial height is the location of the defect in the fiber preform under test based on the ratio of the intensity of the second laser passing through the fiber preform received by the second laser receiving device to a preset second laser intensity includes: After determining the axial position and angle of the defect in the fiber preform to be tested, the second laser emitting device and the second laser receiving device are moved at a second preset rate in the radial direction of the fiber preform to be tested, starting from the center of the fiber preform to be tested. A second laser is emitted through the fiber preform under test by a second laser emitting device, and the intensity of the second laser transmitted through the fiber preform under test is obtained by a second laser receiving device. If the ratio of the intensity of the second laser received by the second laser receiving device passing through the fiber preform under test to the preset second laser intensity does not meet the third threshold, then the current radial height is the radial defect location of the fiber preform under test.

[0021] Determining the axial position and angle of a defect in the fiber optic preform under test only determines the length and angle of the defect from the starting point, not its distance from the center. By moving the second laser emitting and receiving devices radially along the fiber optic preform at a second preset rate, starting from the center, the specific height of the defect can be determined based on the ratio of the second laser intensity received by the second laser receiver passing through the fiber optic preform to a preset second laser intensity. This ratio is typically related to the incident angle of the second laser. For an incident angle of 60°, the third threshold range is 0.66-0.71; for 30°, it is 0.86-0.91; and for 0°, it is 0.89-0.94. The second preset rate can be 1-2 mm / cycle in the vertical direction and 0.5-2° / cycle in the angular direction.

[0022] It should be noted that the height of the defect is only needed after the axial and angular positions of the defect have been determined. Once the circular cross-section is confirmed to be defect-free, there is no need to activate the second laser emitting device and the second laser receiving device; the next circular cross-section can be measured directly.

[0023] In some embodiments, the radial defect location of the fiber preform under test satisfies the following formula:

[0024] ; Where h is the distance from the radial position of the defect in the fiber preform to be tested to the center of the circle; n1 is the refractive index of air; n2 is the refractive index of the cladding of the optical fiber preform under test; θ1 is the incident angle of the second laser; θ2 is the refraction angle of the second laser beam; R O The radius at the measurement section of the fiber preform to be tested; α is the horizontal tilt angle of the incident laser.

[0025] In some embodiments, the preset laser intensity is corrected according to the following formula: ; Among them, P O The preset laser intensity; P i To increase the intensity of the laser emitted by the laser emitting device; R is the reflection coefficient of the fiber preform-air interface under test, which is the ratio of the reflected light intensity to the incident light intensity. k is the fitting correction coefficient; ε is the random noise constant. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of an optical fiber preform defect detection device according to an embodiment of this application.

[0028] Figure 2 This is a schematic diagram of the structure of the optical fiber preform under test according to an embodiment of this application.

[0029] Figure 3 This is a schematic diagram of the structure of a defect detection device for optical fiber preform under test according to an embodiment of this application.

[0030] Figure 4 This is a flowchart illustrating the defect detection process for optical fiber preforms according to an embodiment of this application.

[0031] Figure 5 This is a flowchart illustrating the defect detection process for optical fiber preforms according to an embodiment of this application.

[0032] Figure 6 This is a flowchart illustrating the defect detection process for optical fiber preforms according to an embodiment of this application.

[0033] Figure 7 This is a flowchart illustrating the defect detection process for optical fiber preforms according to an embodiment of this application.

[0034] Explanation of icon numbers: 100 Fiber optic preform defect detection device; 1 First laser emitting device; 2 First laser receiving device; 3 Fiber optic carrier device; 31 Roller; 4 Second laser emitting device; 5 Second laser receiving device; 200 Fiber optic preform to be tested. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] Before being drawn into fibers, optical fibers exist in the form of optical fiber preforms. The performance of optical fibers depends on the quality of the optical fiber preforms. Even minor defects in the optical fiber preforms can affect the yield and transmission performance of the optical fibers. Therefore, it is essential to identify the defects in the optical fiber preforms.

[0037] Under current rod manufacturing processes, visible defects such as bubbles and opaque impurities are easily generated inside the rod. However, the current inspection process relies on manual visual inspection, which results in poor objectivity and makes it impossible to accurately measure the location of defects.

[0038] In view of this, this application provides a device and method for detecting defects in optical fiber preforms, so as to locate the specific location of defects in the core rod.

[0039] Firstly, such as Figures 1 to 3 As shown, this application provides a fiber optic preform defect detection device 100, comprising: The first laser emitting device 1 is used to emit a first laser in the radial direction of the fiber preform 200 to be tested; The first laser receiving device 2 is used to receive the first laser emitted by the first laser emitting device 1 that passes through the center of the fiber preform 200 under test, so as to determine the axial position of the defect in the fiber preform 200 under test. Fiber optic carrier device 3 is used to carry and rotate the fiber optic preform 200 to be tested; The second laser emitting device 4 is used to emit a second laser in the circumferential direction at the defect position of the fiber preform 200 to be tested; The second laser receiving device 5 is used to receive the second laser emitted by the second laser emitting device 4 that passes through the fiber preform 200 under test, so as to determine the radial position of the defect in the fiber preform 200 under test. An angle measuring device is used to measure the rotation angle of the fiber preform 200 under test in order to determine the angular position of the defect in the fiber preform 200 under test in the circumferential direction.

[0040] This application employs a first laser emitting device 1 to radially emit a first laser beam from the fiber preform 200 under test; a first laser receiving device 2 receives the first laser beam emitted by the first laser emitting device 1, which passes through the center of the fiber preform 200 under test, to determine the axial position of the defect in the fiber preform 200 under test. A second laser emitting device 4 emits a second laser beam circumferentially from the location of the defect in the fiber preform 200 under test; a second laser receiving device 5 receives the second laser beam emitted by the second laser emitting device 4, which passes through the fiber preform 200 under test, to determine the radial position of the defect in the fiber preform 200 under test; and an angle measuring device measures the rotation angle of the fiber preform 200 under test to determine the angular position of the defect in the circumferential direction. Thus, the three-dimensional coordinates of the fiber preform defect within the entire fiber preform 200 under test can be determined, locating the specific position of the defect.

[0041] It should be noted that before the first laser emitted by the first laser emitting device 1, which passes through the center of the optical fiber preform 200 under test, is received by the first laser receiving device 2, the positions of the first laser emitting device 1 and the first laser receiving device 2 are calibrated so that when the laser signal emitted by the first laser emitting device 1 is received by the first laser receiving device 2, the laser aperture areas are equal, the positions coincide, and the center positions coincide.

[0042] It should be noted that the second laser emitting device 4 is placed on one side of the circumference of the fiber preform 200 to be tested, and the second laser receiving device 5 is placed on the other side of the circumference of the fiber preform 200 to be tested. The height position of the defect in the fiber preform 200 to be tested can be located when the center of the second laser signal emitted by the second laser emitting device 4 and the center of the second laser signal received by the second laser receiving device 5 are on the same horizontal line.

[0043] In conjunction with the first aspect, in some embodiments provided in this application, the first laser emitting point of the first laser emitting device 1, the first laser receiving point of the first laser receiving device 2, and the center of the optical fiber preform 200 to be tested are arranged in a straight line. Typically, the fiber preform 200 under test is laid flat along the axial direction on the fiber carrier 3. The first laser emitting device 1 is located above the fiber carrier 3, and the first laser receiving device 2 is located below the fiber preform 200 under test on the fiber carrier 3. The fiber preform 200 under test is supported by at least two horizontally placed rollers 31. The first laser receiving device 2 is located at the center of the two horizontally placed rollers 31 on the fiber carrier 3. This arrangement ensures that, on the cross-section of the fiber preform 200 under test, the first laser emitted from the first laser emitting device 1 passes through the center of the fiber preform 200 under test and is received by the first laser receiving device 2 below. This ensures that the center of the laser emission point of the first laser emitting device 1, the center of the fiber preform 200 under test, and the center of the laser receiving point of the first laser receiving device 2 are on the same straight line, reducing laser loss and improving measurement accuracy.

[0044] In conjunction with the first aspect, in some embodiments provided in this application, the second laser emitting point of the second laser emitting device 4 and the second laser receiving point of the second laser receiving device 5 are set at the same height. Setting the second laser emitting point of the second laser emitting device 4 and the second laser receiving point of the second laser receiving device 5 at the same height ensures that the height of the second laser emitting point is the height of the defect in the fiber preform 200 to be tested.

[0045] In conjunction with the first aspect, in some embodiments provided in this application, the first laser emitting device 1 and the first laser receiving device 2 are movably arranged along the axial direction of the fiber preform 200 to be tested. By moving the first laser emitting device 1 and the first laser receiving device 2, the axial position of the defect in the fiber preform 200 to be tested can be located.

[0046] In conjunction with the first aspect, in some embodiments provided in this application, the second laser emitting device 4 and the second laser receiving device 5 are movably arranged along the radial and axial directions of the fiber preform 200 under test. By moving the second laser emitting device 4 and the second laser receiving device 5, the radial position of defects at different axial positions in the fiber preform 200 under test can be located.

[0047] It should be noted that the angle measuring device can be installed on the handle of the fiber preform 200 to be tested. A 0° mark, such as a downward or upward arrow, can be set on the handle of the fiber preform 200 to be tested. The upward or downward arrow is the starting point of 0°. After rotating the fiber preform 200 to be tested, the angle between the arrow position and the vertical direction can be regarded as the angle position of the defect.

[0048] Secondly, such as Figure 4 As shown, this application provides a method for detecting defects in optical fiber preforms, applied to the optical fiber preform defect detection device described in the first aspect, comprising the following steps: S100. Starting from one end of the fiber preform to be tested, a first laser is emitted through the first laser emitting device and passes through the center of the fiber preform to be tested, and the first laser is received through the first laser receiving device. S200: Obtain the first laser intensity passing through the center of the optical fiber preform under test from the first laser receiving device at multiple radial angles of the optical fiber preform under test, and determine whether the current angular position is the defect position of the optical fiber preform under test based on the ratio of the first laser intensity passing through the center of the optical fiber preform under test received by the first laser receiving device to the preset first laser intensity. S300: Obtain the first laser intensity passing through the center of the optical fiber preform under test received by the first laser receiving device at multiple axial positions, and determine whether the current axial position is a defect position of the optical fiber preform under test based on the ratio of the first laser intensity passing through the center of the optical fiber preform under test received by the first laser receiving device to the preset first laser intensity. S400. After determining the axial position and angle of the defect in the fiber preform to be tested, a second laser is emitted through the second laser emitting device and passes through the fiber preform to be tested. The second laser receiving device receives the second laser passing through the fiber preform to be tested. Based on the ratio of the intensity of the second laser passing through the fiber preform to be tested received by the second laser receiving device to the preset intensity of the second laser, it is determined whether the current radial height is the defect position of the fiber preform to be tested.

[0049] Typically, in the optical fiber preform under test, the laser signal loss has less than 0.1% impact on the overall laser signal intensity. The typical attenuation coefficients for air and SiO2 glass are around 10... -7 The optical path lengths are on the order of dB / m and 0.01 dB / m, respectively. In this method, the optical path lengths of both air and SiO2 are within 10 dB / m. -1The laser signal loss is on the order of millimeter (m), so the total attenuation in air and glass is less than 0.1%. However, when bubbles or impurities are present in the fiber preform under test, the laser signal loss is significant, resulting in noticeable abrupt changes. Therefore, the ratio of the first laser intensity received by the first laser receiver passing through the center of the fiber preform under test to the preset first laser intensity can determine whether there is a defect at the current measurement location. Typically, this ratio can be between 0.89 and 0.94. That is, if the ratio is between 0.89 and 0.94, the fiber preform under test at the current location is considered defect-free. If the ratio is less than 0.89, the fiber preform under test at the current location is considered defective. At the same axial position, the entire fiber preform under test needs to be rotated 360° to ensure that radial points on every axial cross-section are measured, reducing omissions.

[0050] The ratio of the second laser intensity received by the second laser receiving device passing through the fiber optic preform under test to a preset second laser intensity can be used to determine whether there is a defect at the current measurement height. Specifically, if the ratio is within the preset range, the fiber optic preform at the current position is considered defect-free. Conversely, if the ratio is outside the preset range, the fiber optic preform at the current height is considered defective. Typically, the ratio of the second laser intensity to the preset second laser intensity is related to the incident angle of the second laser. For an incident angle of 60°, the range is 0.66-0.71; for 30°, it is 0.86-0.91; and for 0°, it is 0.89-0.94.

[0051] In conjunction with the second aspect, such as Figure 5 As shown, in some embodiments provided in this application, the first laser receiving device that receives the first laser intensity passing through the center of the fiber preform at multiple radial angles of the fiber preform under test, and determines whether the current angular position is a defect position of the fiber preform under test based on the ratio of the first laser intensity passing through the center of the fiber preform under test received by the first laser receiving device to a preset first laser intensity, includes: S201. Rotate the fiber preform to be tested circumferentially at a first preset angle. S202. Obtain the intensity of the first laser passing through the center of the fiber preform under test, received by the first laser receiving device at multiple radial angles of the fiber preform under test. S203. If the ratio of the intensity of the first laser passing through the center of the optical fiber preform to be tested, received by the first laser receiving device, to the preset first laser intensity does not meet the first threshold, then the current angle is the circumferential position of the defect in the optical fiber preform to be tested.

[0052] The first preset angle can be 3~5°, meaning that after measuring one diameter of the fiber preform under test, the fiber preform is rotated 3~5°, and the point on the diameter of the next fiber preform under test is measured to check for defects. The first threshold can be 0.89~0.94, that is, when the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to the preset first laser intensity is in the range of 0.89~0.94, the fiber preform under test at the current radial position can be considered to be defect-free; when the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to the preset first laser intensity is less than 0.89, the fiber preform under test at the current radial position is considered to have a defect.

[0053] In conjunction with the second aspect, such as Figure 6 As shown, in some embodiments provided in this application, the step of obtaining the first laser intensity passing through the center of the fiber preform under test received by the first laser receiving device at multiple axial positions, and determining whether the current axial position is a defect location of the fiber preform under test based on the ratio of the first laser intensity passing through the center of the fiber preform under test received by the first laser receiving device to a preset first laser intensity includes: S301. Simultaneously move a laser emitting device and a first laser receiving device along the axial direction of the optical fiber preform to be tested at a first preset speed. S302. Obtain the intensity of the first laser passing through the center of the fiber preform under test, received by the first laser receiving device at multiple axial positions. S303. If the ratio of the intensity of the first laser passing through the center of the optical fiber preform to be tested, received by the first laser receiving device, to the preset first laser intensity does not meet the second threshold, it indicates that the current axial position is the axial defect position of the optical fiber preform to be tested.

[0054] Starting from one end of the fiber preform under test, the first preset speed can be 1~5mm. That is, after measuring all points of a complete circular cross-section of the fiber preform under test, the speed is moved 1~5mm to measure whether there is a defect at the test point of the circular cross-section at the next axial position. The second threshold can be 0.89~0.94. That is, when the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to the preset first laser intensity is in the range of 0.89~0.94, the fiber preform under test at the current radial position can be considered to be without defects. When the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to the preset first laser intensity is less than 0.89, the fiber preform under test at the current radial position is considered to have defects.

[0055] In conjunction with the second aspect, such as Figure 7 As shown, in some embodiments provided in this application, after determining the axial position and angle of the defect in the fiber preform under test, a second laser is emitted through the fiber preform under test via a second laser emitting device, and a second laser receiving device receives the second laser passing through the fiber preform under test. Determining whether the current radial height is the location of the defect in the fiber preform under test based on the ratio of the intensity of the second laser passing through the fiber preform under test received by the second laser receiving device to a preset second laser intensity includes: S401. After determining the axial position and angle of the defect in the fiber preform to be tested, starting from the center of the fiber preform to be tested, move the angle of the second laser emitting device and the second laser receiving device in the radial direction of the fiber preform to be tested at a second preset rate. S402. A second laser is emitted through the second laser emitting device and passes through the fiber preform under test. The second laser receiving device receives the second laser passing through the fiber preform under test and obtains the intensity of the second laser passing through the fiber preform under test received by the second laser receiving device. S403. If the ratio of the intensity of the second laser received by the second laser receiving device passing through the fiber preform under test to the preset second laser intensity does not meet the third threshold, then the current radial height is the radial defect position of the fiber preform under test.

[0056] Determining the axial position and angle of a defect in the fiber optic preform under test only determines the length and angle of the defect from the starting point, not its distance from the center. By moving the second laser emitting and receiving devices radially along the fiber optic preform at a second preset rate, starting from the center, the specific height of the defect can be determined based on the ratio of the second laser intensity received by the second laser receiver passing through the fiber optic preform to a preset second laser intensity. This ratio is typically related to the incident angle of the second laser. For an incident angle of 60°, the third threshold range is 0.66-0.71; for 30°, it is 0.86-0.91; and for 0°, it is 0.89-0.94. The second preset rate can be 1-2 mm / cycle in the vertical direction and 0.5-2° / cycle in the angular direction.

[0057] It should be noted that the height of the defect is only needed after the axial and angular positions of the defect have been determined. Once the circular cross-section is confirmed to be defect-free, there is no need to activate the second laser emitting device and the second laser receiving device; the next circular cross-section can be measured directly.

[0058] In conjunction with the second aspect, in some embodiments provided in this application, the radial defect location of the optical fiber preform under test satisfies the following formula:

[0059] ; Where h is the distance from the radial position of the defect in the fiber preform to be tested to the center of the circle; n1 is the refractive index of air; n2 is the refractive index of the cladding of the optical fiber preform under test; θ1 is the incident angle of the second laser; θ2 is the refraction angle of the second laser beam; R O The radius at the measurement section of the fiber preform to be tested; α is the horizontal tilt angle of the incident laser.

[0060] In conjunction with the second aspect, in some embodiments provided in this application, the preset laser intensity is corrected according to the following formula: ; Among them, P O The preset laser intensity; P i To increase the intensity of the laser emitted by the laser emitting device; R is the reflection coefficient of the fiber preform-air interface under test, which is the ratio of the reflected light intensity to the incident light intensity. k is the fitting correction coefficient; ε is the random noise constant.

[0061] The technical solutions provided in this application will be described in detail below with reference to the embodiments.

[0062] Example 1 Embodiment 1 of this application provides a method for detecting defects in optical fiber preforms, including the following steps: The first and second laser emitting devices use highly collimated S-polarized lasers as light sources, with the following parameters: wavelength 532nm; beam diameter <1mm; divergence angle ≤0.3mrad; intensity 100mW.

[0063] A starting 0° is pre-set on the handle of the fiber preform under test, with the vertical arrow pointing downwards as 0° and clockwise rotation as the direction of rotation. The end of the fiber preform under test marked with the arrow is taken as the axial starting 0 point. A first laser emitting device emits a laser signal, which is received by a first laser receiving device after passing through the diameter of the fiber preform under test. The first laser emitting device and the first laser receiving device move synchronously along the axis of the fiber preform under test in steps of 1 mm / time through a control system. In each step, the robotic arm grips the fiber preform under test and drives it to rotate 360°. If the ratio of the first laser intensity received by the first laser receiving device during the rotation to the preset first laser intensity is within the range of 0.89 to 0.94, the next step is continued; if the ratio of the first laser intensity to the preset first laser intensity during the rotation is less than 0.89, it indicates that the axis position is incorrect. A defect exists. The data acquisition system records the angles φ1 and φ2 when the laser light intensity signal changes and returns to the normal range during this process, as well as the axial coordinates Z1 and Z2. At this time, the starting angle of the defect in the fiber preform under test is φ1, the ending angle is φ2, the starting axial distance is Z1 (0.2*n1mm, where n1 is the number of steps at the beginning of the defect) and Z2 (0.2*n2mm, where n1 is the number of steps at the end of the defect), the center angle of the defect is (φ1+φ2) / 2, and the axial distance from the center of the defect to the starting point is (Z1+Z2) / 2.

[0064] Since a starting 0° is defined, defects in the fiber preform under test may be located in the upper region of the fiber (0-90° and 270-360°) or the lower region (90-270°). Because the lower part of the fiber is supported by rollers, the second laser emitting device and the second laser receiving device are typically positioned in the upper region of the fiber (0-90° and 270-360°) to reduce the influence of the rollers on the laser signal. This ensures that the laser emitted by the second laser emitting device propagates only in the upper region of the fiber (0-90° and 270-360°), that is, moving only upwards from the center of the fiber preform. At this point, it is necessary to measure the radial direction of the defects in the fiber preform. When measuring the height from the center, if the defect angle of the fiber preform under test is between 0~90° and 270~360°, it can be measured directly. If the angle of the fiber preform under test is in the lower region of the fiber (90~270°), the fiber preform under test needs to be rotated 180° so that the defect is located in the upper part, facilitating the transmission of the second laser signal. Typically, the second laser emitting device and the second laser receiving device are horizontally positioned, parallel to the horizontal plane containing the axis of the fiber under test. The measured height is thus the height of the defect in the fiber under test. Specifically, the second laser emitted by the second laser emitting device is refracted twice at the fiber preform-air interface and received by the second laser receiving device. Using a PID control system, the height H of the laser source of the second laser emitting device from the platform and the angle α between the incident light and the horizontal plane (the platform plane is parallel to the horizontal plane, and the horizontal distances of the second laser receiving device and the second laser emitting device from the fiber preform under test are equal) are adjusted until the height of the laser spot on the second laser receiving device from the fiber carrier platform is consistent with the height H of the laser emitted by the second laser receiving device. At this point, the optical path within the fiber preform under test is parallel to the horizontal plane. Adjust H in 1mm increments until the upper and lower edges of the defect are determined. The positions of the upper and lower edges are determined based on the relative magnitude of the second laser intensity detected by the second laser receiver and the preset second laser intensity (the range is 0.66-0.71 when the incident angle is 60°, 0.86-0.91 when the incident angle is 30°, and 0.89-0.94 when the incident angle is 0°). Under this optical path, laser loss comes from Fresnel reflection at points B and C and attenuation in the optical paths AB, BC, and CD. The optical path BC < the rod diameter, generally below 200mm, and the optical paths AB and CD are approximately 300mm. Typical attenuation coefficients for air and SiO2 glass are around 10... -7 The values ​​are in the dB / m and 0.01 dB / m ranges, and calculations show that their impact on light intensity is negligible, less than 0.1%. Therefore, the preset P... O The main influence is the reflection coefficient R at the fiber preform-air interface. Model establishment:

[0065]

[0066] Where: P O The preset laser intensity received by the second laser receiving device; R is the reflection coefficient of the fiber preform-air interface under test, which is the ratio of the reflected light intensity to the incident light intensity. P i The intensity of the second laser emitted by the second laser emitting device; k is the fitting correction coefficient, which is obtained by fitting the measured value with the theoretical value; ε is random noise, obtained by fitting the measured value with the theoretical value.

[0067] The height of the optical fiber preform to be tested can be calculated using the following formula:

[0068] in: n1 is the refractive index of air; n2 is the refractive index of the cladding of the fiber preform under test; θ1 is the angle of incidence; θ2 is the angle of refraction; h is the distance from the center of the circle; R O The radius at the measurement section of the fiber preform to be tested; α is the horizontal tilt angle of the incident laser.

[0069] ; ; The starting height of the defect in the fiber preform under test is h1 from the center of the circle, and the ending height is h2 from the center of the circle. The center height of the defect in the fiber preform under test is (h1+h2) / 2. Therefore: The length of the defect rotation axis (i.e., the defect length) of the optical fiber preform under test is a = Z2 - Z1; The length of the defect equatorial axis (i.e., the defect width) of the fiber preform under test is b = h2 - h1; The coordinates of the defect center column (i.e. the defect location) of the fiber preform under test are ((h1+h2) / 2, (φ1+φ2) / 2, (Z1+Z2) / 2), which accurately locates the defect location and size of the fiber preform under test.

[0070] In summary, a first laser emitter emits a first laser radially along the fiber preform under test; a first laser receiver receives the first laser emitted by the first laser emitter, which passes through the center of the fiber preform under test, to determine the axial position of the defect in the fiber preform under test. A second laser emitter emits a second laser circumferentially around the defect location in the fiber preform under test; a second laser receiver receives the second laser emitted by the second laser emitter, which passes through the fiber preform under test, to determine the radial position of the defect in the fiber preform under test; an angle measuring device measures the rotation angle of the fiber preform under test to determine the angular position of the defect in the circumferential direction. Therefore, the three-dimensional coordinates of the defect in the entire fiber preform under test can be determined, pinpointing the specific location of the defect.

[0071] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0072] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0073] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0074] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A defect detection device for optical fiber preforms, characterized in that, include: A first laser emitting device is used to radially emit a first laser onto the fiber preform under test; The first laser receiving device is used to receive the first laser emitted by the first laser emitting device that passes through the center of the optical fiber preform under test, so as to determine the axial position of the defect in the optical fiber preform under test. Fiber optic carrier device, used to carry and rotate the fiber optic preform to be tested; The second laser emitting device is used to emit a second laser in the circumferential direction at the defect location of the fiber preform under test; The second laser receiving device is used to receive the second laser emitted by the second laser emitting device that passes through the fiber preform under test, so as to determine the radial position of the defect in the fiber preform under test. An angle measuring device is used to measure the rotation angle of the optical fiber preform under test in order to determine the angular position of the defect in the optical fiber preform under test in the circumferential direction.

2. The optical fiber preform defect detection device as described in claim 1, characterized in that, The first laser emission point of the first laser emission device, the first laser receiving point of the first laser receiving device, and the center of the optical fiber preform under test are arranged in a straight line.

3. The optical fiber preform defect detection device as described in claim 1, characterized in that, The second laser emitting point of the second laser emitting device and the second laser receiving point of the second laser receiving device are set at the same height.

4. The optical fiber preform defect detection device as described in claim 1, characterized in that: The first laser emitting device and the first laser receiving device are movably arranged along the axial direction of the optical fiber preform under test; and / or, The second laser emitting device and the second laser receiving device are movably arranged along the radial and axial directions of the optical fiber preform under test.

5. A method for detecting defects in optical fiber preforms, characterized in that, The optical fiber preform defect detection device as described in any one of claims 1 to 4 includes the following steps: Starting from one end of the fiber preform to be tested, a first laser is emitted through the first laser emitting device and passes through the center of the fiber preform to be tested, and the first laser is received through the first laser receiving device. The first laser intensity received by the first laser receiving device at multiple radial angles through the center of the fiber preform under test is obtained. The ratio of the first laser intensity received by the first laser receiving device through the center of the fiber preform under test to the preset first laser intensity is used to determine whether the current angular position is the defect position of the fiber preform under test. The first laser intensity passing through the center of the fiber preform under test is obtained by the first laser receiving device at multiple axial positions. The ratio of the first laser intensity passing through the center of the fiber preform under test received by the first laser receiving device to the preset first laser intensity is used to determine whether the current axial position is the defect position of the fiber preform under test. After determining the axial position and angle of the defect in the fiber preform under test, a second laser is emitted through the second laser emitting device and receives the second laser passing through the fiber preform under test. The radial height is then determined to be the location of the defect in the fiber preform under test based on the ratio of the intensity of the second laser passing through the fiber preform received by the second laser receiving device to the preset intensity of the second laser.

6. The method for detecting defects in optical fiber preforms as described in claim 5, characterized in that, The first laser receiving device, which acquires radial measurements at multiple angles of the fiber preform under test, receives the first laser intensity passing through the center of the fiber preform. The determination of whether the current angular position is a defect location in the fiber preform under test based on the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform to a preset first laser intensity includes: Rotate the fiber preform under test circumferentially at a first preset angle; The intensity of the first laser passing through the center of the fiber preform is obtained by a first laser receiving device at multiple radial angles of the fiber preform under test. If the ratio of the intensity of the first laser passing through the center of the fiber preform under test received by the first laser receiving device to the preset first laser intensity does not meet the first threshold, then the current angle is the circumferential position of the defect in the fiber preform under test.

7. The method for detecting defects in optical fiber preforms as described in claim 5, characterized in that, The first laser receiving device, which acquires the first laser intensity passing through the center of the fiber preform under test at multiple axial positions, receives the first laser intensity. The determination of whether the current axial position is a defect location of the fiber preform under test based on the ratio of the first laser intensity received by the first laser receiving device passing through the center of the fiber preform under test to a preset first laser intensity includes: A laser emitting device and a first laser receiving device are moved simultaneously along the axial direction of the optical fiber preform to be tested at a first preset rate. The intensity of the first laser passing through the center of the fiber preform under test is obtained by the first laser receiving device at multiple axial positions of the fiber preform under test. If the ratio of the intensity of the first laser passing through the center of the optical fiber preform to be tested, received by the first laser receiving device, to the preset first laser intensity does not meet the second threshold, it indicates that the current axial position is the axial defect position of the optical fiber preform to be tested.

8. The method for detecting defects in optical fiber preforms as described in claim 5, characterized in that, After determining the axial position and angle of the defect in the fiber preform under test, a second laser is emitted through the second laser emitting device and receives the second laser passing through the fiber preform. The determination of whether the current radial height corresponds to the defect location in the fiber preform under test is based on the ratio of the intensity of the second laser received by the second laser receiving device to a preset second laser intensity includes: After determining the axial position and angle of the defect in the fiber preform to be tested, the second laser emitting device and the second laser receiving device are moved at a second preset rate in the radial direction of the fiber preform to be tested, starting from the center of the fiber preform to be tested. A second laser is emitted through the fiber preform under test by a second laser emitting device, and the intensity of the second laser transmitted through the fiber preform under test is obtained by a second laser receiving device. If the ratio of the intensity of the second laser received by the second laser receiving device passing through the fiber preform under test to the preset second laser intensity does not meet the third threshold, then the current radial height is the radial defect location of the fiber preform under test.

9. The method for detecting defects in optical fiber preforms as described in claim 8, characterized in that, The radial defect location of the optical fiber preform under test satisfies the following formula: ； Where h is the distance from the radial position of the defect in the fiber preform to be tested to the center of the circle; n1 is the refractive index of air; n2 is the refractive index of the cladding of the optical fiber preform under test; θ1 is the incident angle of the second laser; θ2 is the refraction angle of the second laser beam; R O The radius at the measurement section of the fiber preform to be tested; α is the horizontal tilt angle of the incident laser.

10. The method for detecting defects in optical fiber preforms as described in claim 5, characterized in that, The preset laser intensity is corrected according to the following formula: ； Among them, P O The preset laser intensity; P i To increase the intensity of the laser emitted by the laser emitting device; R is the reflection coefficient of the fiber preform-air interface under test, which is the ratio of the reflected light intensity to the incident light intensity. k is the fitting correction coefficient; ε is the random noise constant.

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