An on-line measuring device and method for carbon coating fiber carbon film thickness

Abstract

The application discloses an online measurement device and method for carbon film thickness of carbon-coated optical fiber. The online measurement device comprises a linearly polarized light detection unit, which comprises a first light source, a first light barrier, a first polarizer, a first focusing lens, a first quarter-wave plate, a first light splitting module, a first polarimeter, a first PD, a second polarimeter and a second PD. A voltage signal related to the carbon film thickness is obtained through the linearly polarized light detection unit, and is calibrated with the actual thickness of the optical fiber. The current carbon film thickness of the carbon-coated optical fiber to be measured is determined according to the real-time voltage difference of the carbon-coated optical fiber to be measured and a carbon film thickness-voltage difference mapping table. The application can eliminate the influence of the position of the optical fiber on the carbon film thickness measurement, improve the accuracy of the carbon film thickness measurement result and improve the uniformity of the carbon film preparation of the carbon-coated optical fiber.

Description

Technical Field

[0001] The present application belongs to the field of special optical fiber manufacturing and testing, and more specifically, relates to an online measurement device and method for the thickness of a carbon film on a carbon-coated optical fiber. Background Art

[0002] Traditional fused silica optical fibers are prepared by preforms using methods such as outside vapor deposition (OVD) and axial vapor deposition (VAD). The preforms are then drawn to produce bare fibers, which are then coated with at least one layer of polymer coating to create the finished fiber. Polymer coatings can effectively improve the mechanical and optical properties of optical fibers. However, polymer coatings are generally unable to block the entry of certain molecules, such as water and hydrogen, especially under high-temperature and high-pressure environments. Water molecules react with silica bonds on the fiber surface, accelerating the growth of microcracks on the fiber surface and reducing the fiber's fatigue resistance. Furthermore, the diffusion of hydrogen molecules within the fiber causes attenuation of the absorption peak of the hydrogen molecules themselves and the absorption peak of the Si-OH molecules resulting from their reaction with Si-O, adversely affecting the fiber's performance. To prevent damage to the fiber from foreign molecules in harsh environments, a dense graphite-like amorphous carbon coating is applied between the fiber and the polymer coating to prevent foreign molecules from penetrating. This dense graphite-like amorphous carbon provides an excellent barrier to both hydrogen and water molecules.

[0003] The carbon coating can be formed by chemical vapor deposition (CVD) by inducing polymerization and pyrolysis of raw gas (such as acetylene, benzene, etc.) after the optical fiber is drawn from the drawing furnace, and finally forming a graphite-like amorphous carbon coating on the surface of the optical fiber. Usually, a heating furnace, a carbon dioxide laser, and other methods are used to provide a heat source for thermal CVD. In order to obtain a carbon-coated optical fiber with better performance, it is necessary to monitor and control the thickness of the carbon film so that it is within the most preferred parameter range; if the carbon coating is too thin to form an effective sealing layer, for example, the coating thickness is less than 20nm, then the hydrogen and water resistance is weak; if the carbon coating is too thick, for example, the thickness is greater than 200nm, then the carbon coating may produce microcracks under the action of external stress, affecting the mechanical properties of the optical fiber. Therefore, it is necessary to monitor and control the thickness of the carbon coating during the preparation process of the optical fiber carbon coating, so as to obtain a carbon-coated optical fiber with excellent performance.

[0004] Existing online carbon coating testing equipment for carbon-coated optical fibers utilizes the conductive properties of the carbon coating and its absorption of electromagnetic waves in microwave or radio frequency fields to indirectly monitor the thickness of the optical fiber carbon coating. Since the microwave method usually uses a resonant cavity or waveguide for confinement, the power distribution of microwaves in space will directly affect the test results of the optical fiber film thickness. Therefore, in actual use, the position offset and jitter of the optical fiber will affect the carbon film thickness test results. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide an online measurement device and method for the carbon film thickness of carbon-coated optical fibers, aiming to solve the problem of inaccurate carbon film thickness measurement caused by the position offset or jitter of the optical fiber in the prior art.

[0006] The present application provides an online measurement device for the carbon film thickness of carbon-coated optical fibers, comprising a linearly polarized light detection unit, which comprises a first light source, a first diaphragm, a first polarizer, a first focusing lens, a first quarter-wave plate, a first light splitting module, a first polarimeter, a first PD, a second polarimeter and a second PD; the first diaphragm is arranged between the first light source and the optical fiber, for adjusting the spot diameter incident on the optical fiber so that the spot diameter is slightly larger than the diameter of the optical fiber; the first polarizer is arranged between the first light source and the optical fiber, for generating linearly polarized light at an angle of 45 degrees to the drawing direction of the optical fiber; the first quarter-wave plate is used to convert parallel elliptical polarized light into linearly polarized light; the first light splitting module is arranged between the first quarter-wave plate and the first polarimeter, for splitting the linearly polarized light from the first quarter-wave plate into two paths of linearly polarized light with equal power; the first polarimeter and the first PD are arranged in sequence on the first exit light path of the first light splitting module, the first polarimeter is used to decompose the linearly polarized light component in a specific direction from one of the linearly polarized light paths split by the first light splitting module, the specific direction being at an angle of +45 degrees to the direction of the polarized light generated by the first polarizer; the first PD is used to detect the size of the polarized light component decomposed by the first polarimeter and obtain a first voltage signal; the second polarimeter and the second PD are arranged in sequence on the second exit light path of the first light splitting module, the second polarimeter is used to decompose the linearly polarized light component in a specific direction from the other linearly polarized light path split by the first light splitting module, and the second PD is used to detect the size of the polarized light component decomposed by the second polarimeter and obtain a second voltage signal, the specific direction being at an angle of 45 degrees to the first polarizer.

[0007] Wherein the principal axis of the first quarter-wave plate is parallel to the principal axis of the first polarizer, both being at an angle of 45 degrees to the drawing direction of the optical fiber. The first polarimeter is at an angle of +45 degrees to the direction of the polarized light generated by the first polarizer, and the second polarimeter is at an angle of -45 degrees to the direction of the polarized light generated by the first polarizer. The first exit light path of the first light splitting module is perpendicular to the second exit light path of the first light splitting module.

[0008] In an embodiment of the present application, the online measurement device also includes another route polarization light detection unit, and the other route polarization light detection unit includes: a second light source, a second aperture, a second polarizer, a second focusing lens, a second quarter wave plate, a second spectroscopic module, a third analyzer, a third PD, a fourth analyzer and a fourth PD; the second aperture is arranged between the second light source and the optical fiber, and is used to adjust the diameter of the light spot incident on the optical fiber so that the diameter of the light spot is slightly larger than the diameter of the optical fiber; the second polarizer is arranged between the second light source and the optical fiber, and the second polarizer is used to generate linearly polarized light at 45 degrees to the drawing direction of the optical fiber; the second quarter wave plate is used to convert parallel elliptically polarized light into linearly polarized light; the second spectroscopic module is arranged between the second quarter wave plate and the third analyzer, and is used to convert the first The linearly polarized light of the second quarter-wave plate is divided into two paths of linearly polarized light with equal power; the third polarizer and the third PD are sequentially arranged on the first outgoing light path of the second optical splitter module, and the third polarizer is used to decompose the polarized light component of the linear polarized light separated by the second optical splitter module in a specific direction, and the specific direction is +45 degrees to the direction of the polarized light generated by the second polarizer; the third PD is used to detect the size of the polarized light component decomposed by the third polarizer and obtain a third voltage signal; the fourth polarizer and the fourth PD are sequentially arranged on the second outgoing light path of the second optical splitter module; the fourth PD is used to detect the size of the polarized light component decomposed by the fourth polarizer and obtain a fourth voltage signal; the first outgoing light path of the second optical splitter module and the second outgoing light path of the second optical splitter module are perpendicular to each other.

[0009] The principal axis of the second polarizer is at a 45-degree angle to the fiber drawing direction; the principal axis of the second quarter-wave plate is parallel to the principal axis of the second polarizer, and both the principal axis of the second quarter-wave plate and the principal axis of the second polarizer are at a 45-degree angle to the fiber drawing direction. The third analyzer is at a +45-degree angle to the polarized light generated by the second polarizer, and the fourth analyzer is at a -45-degree angle to the polarized light generated by the second polarizer.

[0010] In the embodiment of the present application, the first light source and the second light source have different transmittances to the optical fiber carbon film.

[0011] Furthermore, the difference between the transmittance of the first light source to the carbon film of the optical fiber and the transmittance of the second light source to the carbon film of the optical fiber is greater than 10%.The difference between the transmittance of the uncoated optical fiber to the first light source and the transmittance to the second light source is not greater than 10%.

[0012] The present application also provides a method for online measurement of the thickness of a carbon film on a carbon-coated optical fiber based on the above-mentioned online measurement device, comprising the following steps:

[0013] Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light; the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer;

[0014] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0015] Converting parallel elliptically polarized light into parallel second linearly polarized light;

[0016] Splitting the second linearly polarized light into two paths of third linearly polarized light, wherein the power of each third linearly polarized light is equal;

[0017] Decomposing a first light component of a third linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees;

[0018] detecting the magnitude of the first light component and converting the first component into a first voltage signal;

[0019] Decomposing another third linearly polarized light to obtain a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees;

[0020] detecting the magnitude of the second light component and converting the second light component into a second voltage signal;

[0021] Obtaining a real-time first voltage difference value of the carbon-coated optical fiber to be tested according to the difference between the first voltage signal and the second voltage signal;

[0022] The current carbon film thickness of the carbon coated optical fiber to be tested is determined according to the real-time first voltage difference of the carbon coated optical fiber to be tested and the first carbon film thickness-voltage difference mapping table.

[0023] The first carbon film thickness-voltage difference mapping table is formed by mapping the actual carbon film thickness of existing carbon-coated optical fibers prepared by adjusting the carbon coating process under the same optical fiber type and the same drawing tension conditions to the actual first voltage difference.

[0024] The present application also provides an online measurement method for the thickness of a carbon film on a carbon-coated optical fiber, characterized in that it comprises the following steps:

[0025] Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light; the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through the first polarizer;

[0026] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0027] Converting the parallel elliptically polarized light into a parallel second linearly polarized light; the second linearly polarized light overlaps the center position of the first linearly polarized light and has a different polarization direction;

[0028] Splitting the second linearly polarized light into two third linearly polarized lights; wherein the power of each third linearly polarized light is equal;

[0029] Decomposing a first light component of a third linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees;

[0030] detecting the magnitude of the first light component and converting the first component into a first voltage signal;

[0031] Decomposing another third linearly polarized light to obtain a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees;

[0032] detecting the magnitude of the second light component and converting the second light component into a second voltage signal;

[0033] Obtaining a real-time first voltage difference value of the carbon-coated optical fiber to be tested according to the difference between the first voltage signal and the second voltage signal;

[0034] Irradiating the carbon-coated optical fiber to be tested with fourth linearly polarized light along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light; the first direction is 45 degrees to the drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the fourth linearly polarized light is polarized by the second light source through the second polarizer;

[0035] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0036] Convert parallel elliptically polarized light into parallel fifth linearly polarized light;

[0037] Splitting the fifth linearly polarized light into two sixth linearly polarized lights, wherein the power of each sixth linearly polarized light is equal;

[0038] Decomposing a first light component of a sixth linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees;

[0039] detecting the magnitude of the first light component and converting the first component into a third voltage signal;

[0040] Decomposing another path of the sixth linearly polarized light to obtain a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees;

[0041] detecting the magnitude of the second light component and converting the second light component into a fourth voltage signal;

[0042] Obtaining a real-time second voltage difference value of the carbon-coated optical fiber to be tested according to the difference between the third voltage signal and the fourth voltage signal;

[0043] The real-time third voltage difference of the carbon-coated optical fiber to be tested is obtained according to the difference between the real-time second voltage difference of the carbon-coated optical fiber to be tested and the real-time first voltage difference.

[0044] The current carbon film thickness of the carbon coated optical fiber to be predicted is determined according to the real-time third voltage difference of the carbon coated optical fiber to be tested and the second carbon film thickness-voltage difference mapping table.

[0045] The second carbon film thickness-voltage difference mapping table is formed by mapping components according to the actual carbon film thickness of the existing carbon-coated optical fiber, the first voltage difference, the second voltage difference and the third voltage difference.

[0046] The present application also provides a method for online measurement of the thickness of a carbon film on a carbon-coated optical fiber based on the above-mentioned online measurement device, comprising the following steps:

[0047] Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light; the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer;

[0048] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0049] Converting parallel elliptically polarized light into parallel second linearly polarized light;

[0050] Splitting the second linearly polarized light into two third linearly polarized lights; wherein the power of each third linearly polarized light is equal;

[0051] Decomposing a first light component of a third linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees;

[0052] detecting a magnitude of a first light component and converting the first component into a first voltage signal;

[0053] Decomposing another third linearly polarized light to obtain a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees;

[0054] detecting the magnitude of the second light component and converting the second light component into a second voltage signal;

[0055] Obtaining a real-time first voltage difference value of the carbon-coated optical fiber to be tested according to the difference between the first voltage signal and the second voltage signal;

[0056] Irradiating an uncoated carbon optical fiber with a first linearly polarized light along a first direction, causing the uncoated carbon optical fiber to scatter and thereby generate diffused elliptically polarized light; the first direction is at a 45-degree angle to a drawing direction of the uncoated carbon optical fiber, the uncoated carbon optical fiber is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer;

[0057] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0058] Converting parallel elliptically polarized light into parallel second linearly polarized light;

[0059] Splitting the second linearly polarized light into two third linearly polarized lights; wherein the power of each third linearly polarized light is equal;

[0060] Decomposing a first light component of a third linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees;

[0061] detecting the magnitude of the first light component and converting the first component into a fifth voltage signal;

[0062] Decomposing another third linearly polarized light into a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees;

[0063] detecting the magnitude of the second light component and converting the second light component into a sixth voltage signal;

[0064] Obtaining a real-time fourth voltage difference of the carbon-coated optical fiber to be tested according to a difference between the fifth voltage signal and the sixth voltage signal;

[0065] The fifth real-time voltage difference of the carbon-coated optical fiber to be tested is obtained according to the difference between the fourth real-time voltage difference of the carbon-coated optical fiber to be tested and the first real-time voltage difference.

[0066] The current carbon film thickness of the carbon coated optical fiber to be predicted is determined according to the real-time fifth voltage difference of the carbon coated optical fiber to be tested and the third carbon film thickness-voltage difference mapping table.

[0067] The third carbon film thickness-voltage difference mapping table is formed by mapping components according to the actual carbon film thickness of the existing carbon-coated optical fiber and the actual fifth voltage difference.

[0068] The present application can eliminate the influence of the optical fiber position on the carbon film thickness measurement and control the carbon film thickness according to the measurement results; since the wavelength of the first light source in the present application is different from the wavelength of the second light source; different wavelengths and polarization light intensities can be combined to eliminate the influence of geometric position, optical fiber size and type on light intensity, and finally obtain a light signal related only to the carbon film; the influence of the optical fiber position change on the carbon film thickness measurement value can be eliminated and the position of the reaction cavity can be controlled by feedback so that the carbon coating of the optical fiber is within the optimal thickness range.

[0069] In general, the above technical solutions conceived by this application have the following technical advantages compared with the existing technology:

[0070] (1) This application adopts the method of polarized light detection to eliminate the influence of optical fiber jitter on carbon film thickness testing, and uses two light sources for differential measurement to ensure the accuracy of carbon film thickness monitoring and eliminate the influence of optical fiber parameters on carbon coating measurement.

[0071] (2) The present application realizes associating the test result with the position of the reaction chamber by feeding back the deviation between the test result and the set value to the stepper motor, monitoring in real time and controlling through PID feedback, thereby realizing real-time dynamic control of the position of the reaction chamber, and ultimately achieving improved uniformity of carbon film preparation of carbon-coated optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 This is a horizontal schematic diagram of the principle structure of the online measurement device for the carbon film thickness of a carbon-coated optical fiber provided in the first embodiment of the present application;

[0073] Figure 2 This is a horizontal schematic diagram of the principle structure of an online measurement device for the carbon film thickness of a carbon-coated optical fiber provided in a second embodiment of the present application;

[0074] Figure 3 This is a horizontal schematic diagram of the principle structure of an online measurement device for the carbon film thickness of a carbon-coated optical fiber provided in a third embodiment of the present application;

[0075] Figure 4 This is a schematic diagram of the principle structure of the online measurement device for the thickness of the carbon film on a carbon-coated optical fiber provided by the present application, viewed from above;

[0076] Figure 5 is a diagram of the interaction between the probe light and the optical fiber to be tested provided by this application;

[0077] Figure 6 This is a schematic diagram of the detection light trace under different optical fiber position conditions provided by this application.

[0078] In all the drawings, the same reference numerals are used to represent the same elements or structures, wherein: 101 is a first light source, 102 is a first aperture, 103 is a first polarizer, 104 is a first focusing lens, 105 is a first quarter-wave plate, 106 is a first polarization-insensitive beam splitter, 107 is a first analyzer, 108 is a first PD, 109 is a second analyzer, 110 is a second PD, 111 is a second light source, 112 is a second aperture, 113 is a second polarizer, 114 is a second focusing lens, 115 is a second quarter-wave plate, 116 is a second polarization-insensitive beam splitter, 117 is a third analyzer, 118 is a third PD, 119 is a fourth analyzer, 120 is a fourth PD, and 200 is an optical fiber to be tested. DETAILED DESCRIPTION

[0079] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0080] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0081] Additionally, references throughout this specification to "one embodiment," "one embodiment," "an example," or similar language indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. Thus, appearances of the phrase "in one embodiment," "in one embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0082] In addition, the described features, structures or features of the present application can be combined in one or more embodiments in any suitable manner. In the following description, a lot of specific details are provided, such as programming examples, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding. Embodiments of the present application. However, those skilled in the relevant art will recognize that the present application can be implemented without one or more specific details, or using other methods, components, materials, etc. In other cases, well-known structures, materials or operations are not shown or described in detail to avoid confusing aspects of the present application.

[0083] The present application proposes an online measurement device and method for the thickness of the carbon film of a carbon-coated optical fiber. The device uses an optical path to test the thickness of the carbon film, combines light of different wavelengths and polarization intensities, and uses polarization light differential measurement to eliminate the influence of the optical fiber geometry on the light intensity. This is achieved by detecting polarized light in two directions using two PDs. The optical path can eliminate power fluctuations caused by optical fiber position jitter. When two light sources are used to detect the optical fiber before and after carbon coating, the first path can confirm the type of optical fiber itself and the drawing stress information, and the second path can confirm the detection voltage containing the carbon film signal. The difference between the two is finally used to obtain an optical signal related only to the carbon film. The influence of the optical fiber type and the change of the optical fiber position on the carbon film thickness measurement value can be eliminated, and the position of the reaction cavity can be controlled by feedback so that the carbon coating of the optical fiber is within the optimal thickness range.

[0084] In this application, the preparation of carbon-coated optical fibers is usually carried out on the basis of a traditional drawing tower. The traditional drawing tower includes, from top to bottom, a preform rod clamping device, an induction furnace, a wire diameter tester, a tensiometer, a coating system, a coating curing system, a coating diameter tester, and a take-up device. The carbon-coated optical fiber preparation device is to add a heating furnace and a reaction chamber and corresponding gas supply equipment to the traditional drawing tower, wherein the heating furnace can be an induction furnace or a carbon dioxide laser heating furnace, which is used to heat the optical fiber and provide a reaction heat source. In some special cases, the heat of the drawing furnace can be used as a reaction heat source to simplify the carbon coating reaction device, wherein the carbon coating monitoring device is located below the carbon coating chamber to monitor the thickness of the carbon film after the optical fiber is carbon-coated.

[0085] This application is an online measurement device for the carbon film thickness of a carbon-coated optical fiber, which can eliminate the influence of the optical fiber position on the carbon film thickness measurement and control the carbon film thickness based on the measurement results. The specific technical solution is as follows:

[0086] The preform is heated in an induction furnace (1800°C to 1900°C) and drawn into a bare optical fiber. The fiber then enters the carbon-coated fiber cavity. Depending on the distance between the cavity and the lower opening of the drawing furnace, the temperature of the fiber entering the cavity ranges from several hundred to 1500°C. At this point, feed gas, such as acetylene, entering the cavity through a gas line is evenly distributed around the fiber and diffuses from top to bottom as the vacuum pump operates and the fiber moves. When the feed gas comes into contact with the hot fiber, polymerization and pyrolysis reactions occur, ultimately forming a graphite-like amorphous carbon coating on the fiber surface. The carbon-coated fiber cavity is sealed with nitrogen and argon gas at the top and bottom to isolate it from air. After the fiber is pulled out of the cavity's lower opening, it passes through an online carbon film thickness measurement device, which provides a reference thickness value and feeds it back to the film thickness control equipment to ensure it reaches the optimal range, consistent with conventional optical fiber production processes.

[0087] Specifically, the structure of the online measuring device for the carbon film thickness of the carbon-coated optical fiber in the first embodiment of the present application is as follows: Figure 1As shown, the linearly polarized light detection unit includes a first light source 101, a first light diaphragm 102, a first polarizer 103, a first focusing lens 104, a first quarter-wave plate 105, a first light splitting module 106, a first polarimeter 107, a first PD 108, a second polarimeter 109, and a second PD 110.

[0088] The first light source 101, the first light diaphragm 102, and the first polarizer 103 are arranged on one side of the optical fiber 200, and the first light diaphragm 102 is arranged between the first light source 101 and the optical fiber 200 to adjust the spot diameter of the light incident on the optical fiber, and the spot diameter is slightly larger than the diameter of the optical fiber; the first polarizer 103 is arranged between the first light source 101 and the optical fiber 200 to generate linearly polarized light at an angle of 45 degrees to the fiber drawing direction; the principal axis of the first polarizer 103 is at an angle of 45 degrees to the fiber drawing direction.

[0089] The first light diaphragm 102 can be arranged in front of or behind the first polarizer 103.

[0090] The direction of the linearly polarized light generated by the first polarizer 103 is consistent with the direction of the principal axis of the first polarizer 103.

[0091] The first focusing lens 104, the first quarter-wave plate 105, and the first light splitting module 106 are sequentially arranged on the other side of the optical fiber 200 along the optical axis, the principal axis of the first quarter-wave plate 105 is parallel to the principal axis of the first polarizer 103, and both are at an angle of 45 degrees to the fiber drawing direction; the first quarter-wave plate 105 is used to convert parallel elliptically polarized light into linearly polarized light.

[0092] The first light splitting module 106 is arranged between the first quarter-wave plate 105 and the first polarimeter 107, and is used to split the linearly polarized light from the first quarter-wave plate 105 into two linearly polarized lights with equal power; wherein the first light splitting module 106 can use a polarization-insensitive light splitter.

[0093] The first polarimeter 107 and the first PD 108 are sequentially arranged on the first exit light path of the first light splitting module 106, wherein the first polarimeter 107 is at an angle of +45 degrees to the direction of the polarized light generated by the first polarizer 103, and the first polarimeter 107 is used to decompose the polarized light component in a specific direction from one of the linearly polarized lights split by the first light splitting module 106, and the specific direction is at an angle of +45 degrees to the direction of the polarized light generated by the first polarizer 103. The first PD 108 is used to detect the size of the polarized light component decomposed by the first polarimeter 107 to obtain a first voltage signal.

[0094] The second polarizer 109 and the second PD 110 are sequentially arranged on the second outgoing light path of the first spectrometer module 106; the second polarizer 109 is -45 degrees to the direction of the polarized light generated by the first polarizer 103, and the second PD 110 is used to detect the polarized light component decomposed by the second polarizer 109 to obtain a second voltage signal.

[0095] The first outgoing light path and the second outgoing light path of the first light splitting module 106 are perpendicular to each other.

[0096] The first embodiment of the present application utilizes a line polarization light detection unit to achieve the technical effect of eliminating the optical power changes caused by tiny jitters of the optical fiber. It mainly utilizes the convergence effect of the lens to limit the angle of light scattered through the optical fiber; at the same time, the method of polarization light differentiation is used to eliminate the influence of optical fiber geometry on the signal, and finally realizes a voltage signal containing carbon film information.

[0097] Based on the above-mentioned online measurement device, the embodiment of the present application further provides an online measurement method for the thickness of a carbon film on a carbon-coated optical fiber, comprising the steps of:

[0098] Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light, wherein the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer;

[0099] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0100] Converting the parallel elliptically polarized light into a parallel second linearly polarized light; the second linearly polarized light overlaps the center position of the first linearly polarized light and has a different polarization direction;

[0101] Splitting the second linearly polarized light into two paths of third linearly polarized light, wherein the power of each third linearly polarized light is equal;

[0102] Decomposing a first light component of a third linearly polarized light in a second direction, wherein the angle between the second direction and the first direction is +45 degrees;

[0103] detecting the magnitude of a first light component and converting the first component into a first voltage signal;

[0104] Decomposing another third linearly polarized light to obtain a second light component in a third direction, wherein the angle between the third direction and the first direction is -45 degrees;

[0105] detecting the magnitude of the second light component and converting the second light component into a second voltage signal;

[0106] According to the difference between the first voltage signal and the second voltage signal, a first voltage difference value of the carbon-coated optical fiber to be measured in real time is obtained;

[0107] According to the first voltage difference value of the carbon-coated optical fiber to be measured in real time and the first carbon film thickness-voltage difference mapping table, the current carbon film thickness of the carbon-coated optical fiber to be measured is determined,

[0108] The first carbon film thickness-voltage difference mapping table is mapped according to the actual carbon film thickness and the actual first voltage difference of the existing carbon-coated optical fiber prepared under the condition of the same fiber type (refractive index profile / doping element) and the same drawing process (drawing tension) and by adjusting the carbon coating process (raw material gas flow, reaction temperature, etc.).

[0109] In the embodiment of the present application, the construction of the first carbon film thickness-voltage difference mapping table is mainly through the preparation of a standard sample carbon-coated optical fiber under the condition of the same bare fiber type and drawing tension and by using different carbon coating process conditions (such as raw material flow, reaction temperature, etc.), the first voltage difference value corresponding to the carbon film of different thickness of the standard sample carbon-coated optical fiber is obtained by testing the standard sample carbon-coated optical fiber using the detection light path in the first embodiment, and the SEM (scanning electron microscope) thickness standard sample of the standard sample carbon-coated optical fiber is obtained, thereby obtaining the first carbon film thickness-voltage difference mapping table corresponding to the first voltage difference signal and the thickness one-to-one.

[0110] Figure 2 A principle structure horizontal direction schematic diagram of the online measurement device for the carbon film thickness of the carbon-coated optical fiber provided by the second embodiment of the present application is shown; only the part related to the second embodiment of the present application is shown for the convenience of description, and the principle structure horizontal direction schematic diagram of the online measurement device for the carbon film thickness of the carbon-coated optical fiber provided by the second embodiment of the present application is shown in FIG. 2. Figure 2 The details are as follows:

[0111] The online measurement device for the carbon film thickness of the carbon-coated optical fiber provided by the second embodiment of the present application comprises two linearly polarized light detection units, the first one confirms the fiber type and the drawing stress information of the optical fiber itself, and the second one confirms the detection voltage containing the carbon film signal, and the signal of the carbon film thickness can be obtained by the difference between the two. The linearly polarized light detection unit is the same as that in the first embodiment, and will not be described here. The other linearly polarized light detection unit comprises a second light source 111, a second diaphragm 112, a second polarizer 113, a second focusing lens 114, a second quarter-wave plate 115, a second light splitting module 116, a third polarizer 117, a third PD 118, a fourth polarizer 119, and a fourth PD 120.

[0112] Among them, the second light source 111, the second aperture 112 and the second polarizer 113 are arranged on one side of the optical fiber 200, and the second aperture 112 is arranged between the second light source 111 and the optical fiber 200, and is used to adjust the diameter of the light spot incident on the optical fiber, and the light spot diameter is slightly larger than the diameter of the optical fiber; the second polarizer 113 is arranged between the second light source 111 and the optical fiber 200, and is used to generate linearly polarized light at 45 degrees to the direction of optical fiber drawing; the main axis of the second polarizer 113 is 45 degrees to the direction of optical fiber drawing.

[0113] The second aperture 112 may be arranged before or after the second polarizer 113 .

[0114] The second focusing lens 114, the second quarter-wave plate 115 and the second splitting module 116 are arranged in sequence along the optical axis on the other side of the optical fiber 200. The main axis of the second quarter-wave plate 115 is parallel to the main axis of the second polarizer 113, and both are at 45 degrees to the direction of optical fiber drawing; the second quarter-wave plate 115 is used to convert parallel elliptically polarized light into linearly polarized light.

[0115] The second splitting module 116 is disposed between the second quarter-wave plate 115 and the third analyzer 117 and is used to split the linearly polarized light of the second quarter-wave plate 115 into two linearly polarized lights of equal power. The second splitting module 116 may be a polarization-insensitive splitter.

[0116] A third polarizer 117 and a third PD 118 are sequentially disposed on the first outgoing optical path of the second optical splitter module 116. The third polarizer 117 is oriented at a +45-degree angle to the polarized light generated by the second polarizer 113. The third polarizer 117 is configured to decompose a polarized light component of a line of polarized light separated by the second optical splitter module 116 in a specific direction, which is oriented at a +45-degree angle to the polarized light generated by the second polarizer 113. The third PD 118 is configured to detect the magnitude of the polarized light component decomposed by the third polarizer 117 to generate a third voltage signal.

[0117] The fourth polarizer 119 and the fourth PD 120 are sequentially arranged on the second outgoing light path of the second splitter module 116; the fourth polarizer 119 is -45 degrees to the direction of the polarized light generated by the second polarizer 113, and the fourth PD 120 is used to detect the polarized light component decomposed by the fourth polarizer 119 to obtain a fourth voltage signal.

[0118] The first outgoing light path and the second outgoing light path of the second light splitting module 116 are perpendicular to each other.

[0119] The second embodiment of the present application adopts a two-way polarized light detection unit, and utilizes the different sensitivities of the two light sources to the carbon film to obtain two numerical values ​​of one voltage signal and two differential voltage signals. The optical fiber type and drawing tension information can be eliminated, and finally a voltage signal combination including the carbon film thickness is obtained.

[0120] In the second embodiment of the present application, two different wavelengths of probe light are emitted from an LED and converted into linearly polarized light by polarizers of corresponding wavelength bands. The polarizer's principal axis is at a 45° angle to the optical fiber, and the light component perpendicular to the optical fiber and parallel to the optical fiber are equal in magnitude. After polarization, the light is irradiated onto the side of the optical fiber. After passing through the optical fiber, a portion of the light generated by optical fiber scattering passes through a quarter-wave plate, a polarization-independent beam splitter, and an analyzer, where it is collected by two photodetectors. The two analyzers are respectively at an angle of 45° and -45° to the principal axis of the quarter-wave plate (specifically, the first analyzer 107 is at a 45° angle to the principal axis of the first quarter-wave plate 105, and the second analyzer 109 is at a -45° angle to the principal axis of the first quarter-wave plate 105; the third analyzer 117 is at a 45° angle to the principal axis of the second quarter-wave plate 115, and the fourth analyzer 119 is at a -45° angle to the principal axis of the second quarter-wave plate 115). The first light source can be an LED light source with a wavelength of 1550nm, and a polarized light detection unit is used as a reference benchmark. Since the graphite-like amorphous carbon coating has a high transmittance of 1550nm, the absorption of the detection light by the carbon coating is not considered; the second light source can be an LED light source with a wavelength of 650nm, and 650nm has a higher absorption rate at the absorption peak of graphite-like amorphous carbon. It is used as a monitoring device for the carbon coating. The voltage signals obtained by the two PDs in the one polarized light detection unit are used to make a difference to obtain the reference detection voltage of the optical fiber, and the detection voltage of the optical fiber containing the carbon film is obtained by making a difference between the two PD signals in the other polarized light detection unit; the voltages obtained by monitoring the two light sources are then differentiated to finally obtain a voltage signal related to the thickness of the carbon film, and calibrated with the actual thickness of the optical fiber to monitor the thickness of the optical fiber carbon coating.

[0121] By continuously adjusting the temperature and distance, the final detection voltage related to the carbon film thickness is made to correspond to the detection voltage in the mapping table. Specifically, the PID feedback circuit can be used to control the one-dimensional translation stage of the carbon coating reaction chamber holding device. By controlling the step of the translation stage to adjust the distance between the carbon coating reaction chamber and the drawing furnace, the reaction temperature can be finely adjusted to ultimately achieve the purpose of controlling the carbon film thickness.

[0122] As an embodiment of the present application, the LED light source can be realized by using a laser + a beam expander; the lens can use various focusing lenses or lens groups.

[0123] Based on the above-mentioned online measurement device, the embodiment of the present application further provides an online measurement method for the thickness of a carbon film on a carbon-coated optical fiber, comprising the steps of:

[0124] Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light, wherein the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer;

[0125] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0126] Converting the parallel elliptically polarized light into a parallel second linearly polarized light; the second linearly polarized light overlaps the center position of the first linearly polarized light and has a different polarization direction;

[0127] Splitting the second linearly polarized light into two paths of third linearly polarized light, wherein the power of each third linearly polarized light is equal;

[0128] Decomposing a first light component of a third linearly polarized light in a second direction, wherein the angle between the second direction and the first direction is +45 degrees;

[0129] detecting the magnitude of a first light component and converting the first component into a first voltage signal;

[0130] Decomposing another third linearly polarized light to obtain a second light component in a third direction, wherein the angle between the third direction and the first direction is -45 degrees;

[0131] detecting the magnitude of the second light component and converting the second light component into a second voltage signal;

[0132] Obtaining a real-time first voltage difference value of the carbon-coated optical fiber to be tested according to a difference between the first voltage signal and the second voltage signal;

[0133] The first linearly polarized light of the polarizer 113 is polarized by the second light source through the polarizer, wherein the second light source has a wavelength different from that of the first light source;

[0134] The photodetector 118 obtains a third voltage signal; the photodetector 120 obtains a fourth voltage signal;

[0135] Obtaining a real-time second voltage difference value of the carbon-coated optical fiber to be tested according to a difference between the third voltage signal and the fourth voltage signal;

[0136] Obtaining a real-time third voltage difference value of the carbon-coated optical fiber to be tested according to a difference between the real-time second voltage difference value of the carbon-coated optical fiber to be tested and the real-time first voltage difference value;

[0137] determining a current carbon film thickness of the carbon coated optical fiber to be predicted according to the real-time third voltage difference of the carbon coated optical fiber to be tested and the second carbon film thickness-voltage difference mapping table;

[0138] The second carbon film thickness-voltage difference mapping table is formed by mapping components according to the actual carbon film thickness of the existing carbon-coated optical fiber, the first voltage difference, the second voltage difference and the third voltage difference.

[0139] In an embodiment of the present application, the second carbon film thickness-voltage difference mapping table can be constructed specifically in the following manner: without limiting the type of bare fiber and the drawing process parameters, the bare fiber is subjected to standard sample preparation under different carbon coating process conditions, the standard carbon-coated optical fiber is tested through the detection optical path of this embodiment to obtain the first voltage difference, the second voltage difference and the third voltage difference of the standard carbon-coated optical fiber with different carbon film thicknesses prepared under different carbon coating process conditions, the standard carbon-coated optical fiber is subjected to SEM thickness calibration, and a second carbon film thickness-voltage difference mapping table with two voltage difference combinations corresponding to the thickness is obtained. The combination of voltage differences can eliminate the single voltage difference change caused by the type of optical fiber to be tested and the drawing conditions.

[0140] This application adopts the method of polarized light detection to eliminate the influence of optical fiber jitter on carbon film thickness test, and uses two light sources for differential measurement to ensure the accuracy of carbon film thickness monitoring and eliminate the influence of optical fiber parameters on carbon coating measurement.

[0141] Figure 3 The schematic diagram of the horizontal direction of the principle structure of the online measurement device for the carbon film thickness of the carbon-coated optical fiber provided by the third embodiment of the present application is shown; for the convenience of explanation, only the relevant parts of the third embodiment of the present application are shown. Figure 3 Details are as follows:

[0142] The online measurement device for the carbon film thickness of a carbon-coated optical fiber provided in the third embodiment of the present application includes a linear polarized light detection unit. The structure of the linear polarized light detection unit is the same as that of the linear polarized light detection unit in the first embodiment. The difference is that in the third embodiment of the present application, a linear polarized light detection unit is used to perform two detections in a time-sharing manner. One detection is for the optical fiber before carbon coating, and the other detection is for the optical fiber after carbon coating. The reason for using two detections is to differentially eliminate the signal brought by the parameters of the optical fiber itself and only retain the carbon film.

[0143] The third embodiment of the present application can completely eliminate the voltage signal brought by the optical fiber itself, and the voltage difference finally obtained by differential only contains the signal of the carbon film, thereby improving the measurement accuracy.

[0144] Based on the above-mentioned online measurement device, the embodiment of the present application further provides an online measurement method for the thickness of a carbon film on a carbon-coated optical fiber, comprising the steps of:

[0145] Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light, wherein the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer;

[0146] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0147] Converting the parallel elliptically polarized light into a parallel second linearly polarized light; the second linearly polarized light overlaps the center position of the first linearly polarized light and has a different polarization direction;

[0148] Splitting the second linearly polarized light into two paths of third linearly polarized light, wherein the power of each third linearly polarized light is equal;

[0149] Decomposing a first light component of a third linearly polarized light in a second direction, wherein the angle between the second direction and the first direction is +45 degrees;

[0150] detecting the magnitude of a first light component and converting the first component into a first voltage signal;

[0151] Decomposing another third linearly polarized light to obtain a second light component in a third direction, wherein the angle between the third direction and the first direction is -45 degrees;

[0152] detecting the magnitude of the second light component and converting the second light component into a second voltage signal;

[0153] Obtaining a real-time first voltage difference value of the carbon-coated optical fiber to be tested according to a difference between the first voltage signal and the second voltage signal;

[0154] Irradiating an uncoated carbon optical fiber with a first linearly polarized light along a first direction, causing the uncoated carbon optical fiber to scatter and thereby generate diffused elliptically polarized light, wherein the first direction is at a 45-degree angle to a drawing direction of the uncoated carbon optical fiber, the uncoated carbon optical fiber is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer;

[0155] The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens;

[0156] Converting parallel elliptically polarized light into parallel second linearly polarized light;

[0157] Splitting the second linearly polarized light into two paths of third linearly polarized light, wherein the power of each third linearly polarized light is equal;

[0158] Decomposing a first light component of a third linearly polarized light in a second direction, wherein the angle between the second direction and the first direction is +45 degrees;

[0159] detecting the magnitude of the first light component and converting the first component into a fifth voltage signal;

[0160] Decomposing another third linearly polarized light into a second light component in a third direction, wherein the angle between the third direction and the first direction is -45 degrees;

[0161] detecting the magnitude of the second light component and converting the second light component into a sixth voltage signal;

[0162] Obtaining a real-time fourth voltage difference of the carbon-coated optical fiber to be tested according to a difference between the fifth voltage signal and the sixth voltage signal;

[0163] According to the difference between the fourth real-time voltage difference of the carbon-coated optical fiber to be tested and the first real-time voltage difference, a fifth real-time voltage difference of the carbon-coated optical fiber to be tested is obtained.

[0164] determining a current carbon film thickness of the carbon coated optical fiber to be predicted according to the real-time fifth voltage difference of the carbon coated optical fiber to be tested and the third carbon film thickness-voltage difference mapping table;

[0165] Among them, the third carbon film thickness-voltage difference mapping table is mapped based on the actual carbon film thickness of the existing carbon-coated optical fiber and the actual fifth voltage difference. The method for obtaining the actual fifth voltage difference of the existing carbon-coated optical fiber is the same as the method for obtaining the real-time fifth voltage difference of the carbon-coated optical fiber to be tested, and will not be repeated here.

[0166] Figure 4 The schematic diagram of the principle structure of the online measurement device for the thickness of the carbon film of a carbon-coated optical fiber provided by the present application is shown from a top view. For ease of explanation, only the parts related to the present application are shown. The following is a detailed description in conjunction with the accompanying drawings:

[0167] like Figure 4 As shown, the light emitted by the LED passes through the aperture and is irradiated onto the polarizer. The linearly polarized light passing through the polarizer passes through the optical fiber to be tested. The linearly polarized light beam generated by the polarizer has two components with equal power and orthogonal directions, which are parallel and perpendicular to the drawing direction of the optical fiber. During the optical fiber drawing process, the tensile stress applied to the optical fiber and the thermal stress generated by the optical fiber itself convert the optical fiber from an isotropic structure to an anisotropic structure. After the linearly polarized light from the polarizer is emitted to the carbon-coated optical fiber, the carbon-coated optical fiber causes a phase delay between the two orthogonal components of the linearly polarized light, thereby forming elliptically polarized light. The phase delay R(y) is given by the following formula:

[0168]

[0169] Where C is the stress optical coefficient, y is the distance between the linear polarized light of the polarizer and the center of the optical fiber, r is the distance between the center line of the optical fiber along the incident direction in the optical fiber cross section, y is the distance between the linear polarized light of the polarizer and the symmetry axis of the optical fiber cross section along the incident direction, b is the radius of the optical fiber, σ z (r) is the distribution of the axial (z-direction) component of stress on the fiber cross section.

[0170] like Figure 5 As shown, the polarized light incident on the optical fiber is considered to be a uniform plane wave with a power density of I. If the PD only receives the output angle The range of light, then the position range of the input light is y1 <y<y2。然后,这些光线通过光轴与起偏器主轴方向相同的四分之一波片并将光纤相延产生的椭圆偏振光重新变为线偏振光,但线偏振角度发生变化,最终该线偏振光通过与起偏器偏振方向呈±45°的检偏器最终由光电管接收。则探测器上的功率为P: in, is the maximum angle between the scattered light and the incident light of the polarizer, is the minimum angle between the scattered light and the incident light of the polarizer, R(y) is the phase delay, and Φ is the phase change value introduced by the analyzer.

[0171] Then the detection powers P1 and P2 of the detectors whose main optical axes of the two analyzers and polarizers are ±45° are:

[0172] Then the power measured by two detectors with different polarizations can be subtracted to obtain:

[0173]

[0174] The light diameter and stress photoelastic effect in this application determine that the phase difference must be small. For small phase changes, sin(R(y))≈R(y).

[0175] For the phase delay R(y), its values ​​y1 / b and y2 / b are related to the tensile stress and the stress photoelastic coefficient. For the optical path provided in this application, its values ​​y1 / b and y2 / b are constant for a type of optical fiber because the light Therefore, y1 / b and y2 / b are determined, and the influence of the optical fiber position on the monitoring optical power within a certain range can be ignored (see optical path), so the measured power difference is less affected by the fluctuation of the optical fiber position, such as Figure 6 shown.

[0176] The voltage signal measured by the linear polarization light detection unit with a wavelength of 1550nm is used as the reference value. The linear polarization light detection unit with a wavelength of 650nm has a high absorption rate relative to the carbon coating, so the optical power P1 of the first PD 108 and the optical power P2 of the second PD 110 monitored by it are respectively:

[0177]

[0178] The final monitoring voltage also needs to be calculated based on the transmittance T and the optical power is converted into the output voltage V 1550nm With V 650nm The carbon film information can be obtained by taking the difference between the two monitoring voltages. The specific carbon film information needs to be calibrated according to the SEM test to determine the absolute value information of the carbon coating. 1550nm -V 650nm By adjusting the change of the reaction chamber temperature, the slide position of the reaction chamber is controlled through PID feedback, and the reaction temperature is controlled to achieve uniform and ideal carbon coating preparation.

[0179] The online measurement device and method provided by this application have the following technical advantages:

[0180] (1) Can eliminate the influence of optical fiber jitter and improve measurement accuracy:

[0181] Because the optical fiber is located near the focal point of one side of the lens, and the detection surface of the detector is located on the focal plane of the other side of the lens, assuming that the parallel light received by the detector passes through the lens, the maximum angle between the corresponding scattered light and the incident light of the polarizer is The minimum angle is defined as Then, through the arrangement of optical fiber and detector relative to the lens, and The angle between them is only affected by the carbon film thickness, fiber material, fiber geometry, and fiber drawing tension. and The angle between them will not be affected by the fiber jitter position (refer to Figure 4 Therefore, the influence of optical fiber jitter can be eliminated and the measurement accuracy can be improved.

[0182] (2) It can reduce the influence of fiber geometry and thus improve measurement accuracy:

[0183] Specifically, the influence of the fiber geometry is eliminated by differentiating the first voltage signal and the second voltage signal.

[0184] (3) It can reduce the influence of optical fiber material and optical fiber drawing tension, thereby improving measurement accuracy: Specifically, the optical path of two light sources can be used to eliminate the influence of optical fiber material and optical fiber drawing tension, thereby reducing the influence of optical fiber material and optical fiber drawing tension and improving measurement accuracy.

[0185] In order to further illustrate the online measurement method and device for the thickness of the carbon film of a carbon-coated optical fiber provided by the present application, the following is described in detail with reference to specific embodiments:

[0186] Example 1:

[0187] The samples prepared by different carbon coating processes were mapped between voltage difference and thickness using SEM and the monitoring system of this embodiment to establish a first carbon film thickness-voltage difference mapping table;

[0188] A standard single-mode optical fiber is drawn in a drawing furnace to a 125µm bare fiber and fed into the reaction chamber at a speed of 250m / s. The upper end of the reaction chamber is approximately 15cm from the initial position of the optical fiber preform. The drawing tension is 60g. Infrared temperature measurement indicates that the fiber temperature before entering the chamber is approximately 1280°C. The reaction chamber seal gas is pure nitrogen, with an upper seal flow rate of 2L / min and a lower seal flow rate of 2L / min. The reaction feed gas is argon-diluted acetylene at a concentration of 30% vol, with a flow rate of 2L / min. The exhaust gas treatment device has a flow rate of 3L / min.

[0189] After passing through the reaction cavity, the single-mode optical fiber containing the carbon coating passes through the carbon coating monitoring device, where the differential voltage value of the detector of the 1550nm light source monitoring unit is 0.52V. According to the mapping table established for this type of optical fiber and 60g drawing tension conditions, the carbon film thickness should be 58nm. The optical fiber sample was then taken for SEM testing, and the actual average thickness was about 56.8nm, which is consistent with the mapping relationship table, and the thickness monitoring of the optical fiber carbon film can be realized.

[0190] When the fiber diameter was changed to 130µm, the drawing speed to 250m / s, and the drawing tension to 60g, while the carbon coating experimental conditions remained unchanged, the differential voltage of the monitoring unit under the 1550nm light source was 0.42V. This voltage change was due to the increase in fiber diameter, which led to an increase in fiber temperature. The measured temperature before the fiber entered the cavity was approximately 1350°C. PID feedback control restored the differential voltage of the monitoring unit to 0.52V. Fiber samples were then taken for SEM testing, and the average thickness was approximately 57.2nm, demonstrating that the monitoring unit can differentiate the fiber's geometric information to monitor the actual thickness of the carbon coating.

[0191] Without changing the fiber drawing process parameters, the monitoring device was offset by 1 mm in one direction. The PD differential voltage of the two polarized light detection paths did not change, proving that if the fiber jitters during the production process, its effect on the carbon film thickness measurement can be ignored.

[0192] Example 2:

[0193] The online measuring device for the carbon film thickness of carbon-coated optical fiber is the same as the conventional carbon coating reaction chamber, which is fixedly connected to the one-dimensional electric slide and performs PID control through the voltage signal output by the carbon coating detection device.

[0194] The optical fiber is drawn from a drawing furnace to a 125µm bare fiber and enters the reaction chamber at a speed of 200m / s. The upper end of the reaction chamber is approximately 20cm from the initial position of the optical fiber preform. According to infrared temperature measurement, the temperature of the optical fiber before entering the chamber is approximately 1200°C. The reaction chamber seal gas is pure nitrogen, with an upper seal flow rate of 2L / min and a lower seal flow rate of 2L / min. The reaction feed gas is argon-diluted acetylene with a concentration of 30% vol and a flow rate of 2L / min. The exhaust gas treatment device has a flow rate of 3L / min.

[0195] After passing through the reaction chamber, the optical fiber containing the carbon coating passes through the carbon coating monitoring device, where the differential voltage value of the linear polarized light detection unit detector at a wavelength of 1550nm is 0.58V, and the differential voltage value of the linear polarized light detection unit at a wavelength of 650nm is 0.35V. At this time, the differential value of the differential voltage of the two light sources is (0.58-0.35)V, which is the final differential voltage. After calibration with an electron microscope, the thickness of the carbon film prepared under the experimental conditions is approximately 33±1nm, and the corresponding differential voltage is 0.23V, which serves as a mapping relationship between thickness and voltage.

[0196] Then, in actual production, the difference between the voltage detected by the linear polarization light detection unit at a wavelength of 1550nm of the carbon-coated optical fiber and the voltage detected by the linear polarization light detection unit at a wavelength of 650nm was set at 0.23V, and the differential voltage detected at 1550nm was set to 0.58V. The raw gas flow rate was 1.5L / min, then the voltage difference was 0.15V, and the differential voltage at 1550nm was 0.42V. The reaction device of the carbon-coated cavity was connected to the PID control system, and the one-dimensional translation stage raised the reaction cavity to 18cm away from the cone of the preform rod. The voltage difference was restored to 0.23V, and the differential voltage at 1550nm was 0.58V. After electron microscopy testing, the thickness of the carbon film was about 32±1nm, proving that the mapping relationship and the test system have good consistency and feasibility.

[0197] Example 3:

[0198] The online measurement device for the carbon film thickness of carbon-coated optical fiber is the same as that of a conventional carbon-coated reaction chamber. The optical fiber is heated by an infrared heating device before entering the reaction chamber. The driving power of the infrared heating device is PID-controlled by the voltage signal output by the carbon coating detection device.

[0199] The optical fiber is drawn from a drawing furnace to a bare fiber of 125 um and passes through a first monitoring unit at a speed of 200 m / s, the differential voltage measured by the 1550 nm wavelength monitoring unit is 0.78 V, the drawing tension is 55 g, which is the reference voltage of the optical fiber, mainly including the tension information and the type information of the optical fiber; then heated to about 1400 DEG C by an infrared heating device and enters the reaction cavity.

[0200] The reaction cavity gas sealing gas is pure nitrogen, the upper gas sealing flow is 2 L / min, the lower gas sealing is 2 L / min, the reaction raw material gas is argon diluted acetylene, the concentration is 30%vol, the flow is 2 L / min, and the tail gas treatment device flow is 3 L / min.

[0201] After passing through the reaction cavity, the optical fiber containing the carbon coating passes through a carbon coating monitoring device, wherein the differential voltage value of the 1550 nm wavelength linearly polarized light detection unit probe is 0.6 V, and the carbon film thickness prepared under the experimental conditions is about 45±2 nm, and the differential voltage before and after coating carbon is 0.18 V, which is the third thickness and voltage mapping relationship.

[0202] Then in actual production, the voltage difference between the voltage detected by the 1550 nm wavelength linearly polarized light detection unit of the uncoated carbon optical fiber and the voltage detected by the 1550 nm wavelength linearly polarized light detection unit after coating carbon is set to 0.18 V. Change the optical fiber drawing tension to 80 g, the raw gas flow to 2 L / min, and the initial driving power of the infrared heating device to make the heating temperature about 1300 DEG C. At this time, the differential voltage of the 1550 nm monitoring unit before coating carbon is 0.98 V, the differential voltage of the 1550 nm after coating carbon is 0.84 V, and the difference is 0.14 V. The power supply driving of the infrared heating device is connected to the PID control system, and the driving voltage is feedback controlled according to the differential voltage difference before and after coating carbon. After a certain period of time, the differential voltage difference before and after coating carbon returns to 0.18 V; the carbon film thickness is about 46±2 nm by electron microscope test, which proves that the mapping relationship and the test system have good consistency and realizability and completely eliminate the optical fiber type and the drawing parameters.

[0203] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An online measuring device for carbon film thickness of carbon-coated optical fiber, characterized in that: The invention comprises a linear polarized light detection unit, wherein the linear polarized light detection unit comprises: a first light source (101), a first aperture (102), a first polarizer (103), a first focusing lens (104), a first quarter-wave plate (105), a first light splitting module (106), a first polarizer (107), a first PD (108), a second polarizer (109) and a second PD (110); The first light source (101), the first aperture (102), and the first polarizer (103) are arranged on one side of the optical fiber (200); The first aperture (102) is arranged between the first light source (101) and the optical fiber (200), and is used to adjust the diameter of the light spot incident on the optical fiber so that the light spot diameter is slightly larger than the diameter of the optical fiber; The first polarizer (103) is arranged between the first light source (101) and the optical fiber (200), and is used to generate linearly polarized light at a 45-degree angle to the optical fiber drawing direction; The first focusing lens (104), the first quarter-wave plate (105), and the first light splitting module (106) are sequentially arranged along the optical axis on the other side of the optical fiber (200); The first quarter-wave plate (105) is used to convert parallel elliptically polarized light into linearly polarized light; The first light splitting module (106) is arranged between the first quarter-wave plate (105) and the first polarizer (107), and is used to split the linearly polarized light of the first quarter-wave plate (105) into two paths of linearly polarized light with equal power; The first polarizer (107) and the first PD (108) are sequentially arranged on the first outgoing light path of the first optical splitter module (106); the first polarizer (107) is used to decompose a polarized light component in a specific direction of a line of polarized light separated by the first optical splitter module (106); the specific direction is +45 degrees to the direction of the polarized light generated by the first polarizer (103); the first PD (108) is used to detect the size of the polarized light component decomposed by the first polarizer (107) and obtain a first voltage signal; The second polarizer (109) and the second PD (110) are sequentially arranged on the second outgoing light path of the first light splitting module (106); the second polarizer (109) is used to decompose the polarized light component of the other polarized light separated by the first light splitting module (106) in a specific direction; the second PD (110) is used to detect the size of the polarized light component decomposed by the second polarizer (109) and obtain a second voltage signal; the specific direction is 45 degrees to the polarization direction of the linear polarized light generated by the first polarizer after the propagation direction is changed by the light splitting module; The first focusing lens (104) is used to focus the light to limit the angle of light scattered by the optical fiber, thereby achieving the technical effect of eliminating the optical power variation caused by the slight jitter of the optical fiber; By utilizing the PD difference of the two detection polarized lights, the influence of the optical fiber geometry on the signal is eliminated, and finally a voltage signal containing carbon film information is realized.

2. The online measuring device according to claim 1, characterized in that The main axis of the first quarter-wave plate (105) is parallel to the main axis of the first polarizer (103), and both are at 45 degrees to the optical fiber drawing direction; The first analyzer (107) and the direction of the polarized light generated by the first polarizer (103) are at +45 degrees, and the second analyzer (109) and the direction of the polarized light generated by the first polarizer (103) are at -45 degrees; The first outgoing light path of the first light splitting module (106) and the second outgoing light path of the first light splitting module (106) are perpendicular to each other.

3. The online measuring device according to claim 1, wherein The online measurement device further comprises another route polarized light detection unit, which comprises: a second light source (111), a second aperture (112), a second polarizer (113), a second focusing lens (114), a second quarter-wave plate (115), a second light splitting module (116), a third analyzer (117), a third PD (118), a fourth analyzer (119) and a fourth PD (120); The second light source (111), the second aperture (112), and the second polarizer (113) are arranged on one side of the optical fiber (200); The second diaphragm (112) is arranged between the second light source (111) and the optical fiber (200), and is used to adjust the diameter of the light spot incident on the optical fiber so that the light spot diameter is slightly larger than the diameter of the optical fiber; The second polarizer (113) is arranged between the second light source (111) and the optical fiber (200), and the second polarizer (113) is used to generate linearly polarized light at a 45-degree angle to the optical fiber drawing direction; The second focusing lens (114), the second quarter-wave plate (115), and the second light splitting module (116) are sequentially arranged along the optical axis on the other side of the optical fiber (200); The second quarter-wave plate (115) is used to convert parallel elliptically polarized light into linearly polarized light; The second light splitting module (116) is arranged between the second quarter-wave plate (115) and the third polarizer (117), and is used to split the linearly polarized light of the second quarter-wave plate (115) into two paths of linearly polarized light with equal power; The third polarizer (117) and the third PD (118) are sequentially arranged on the first outgoing light path of the second light splitting module (116); the third polarizer (117) is used to decompose a polarized light component in a specific direction of a line of polarized light separated by the second light splitting module (116); the specific direction is +45 degrees to the direction of the polarized light generated by the second polarizer (113); the third PD (118) is used to detect the size of the polarized light component decomposed by the third polarizer (117) and obtain a third voltage signal; The fourth polarizer (119) and the fourth PD (120) are sequentially arranged on the second outgoing light path of the second light splitting module (116); the fourth polarizer (119) is used to decompose the polarized light component of the other path polarized light separated by the second light splitting module (116) in a specific direction, and the specific direction is +45 degrees to the direction of the polarized light generated by the second polarizer (113); the fourth PD (120) is used to detect the size of the polarized light component decomposed by the fourth polarizer (119) and obtain a fourth voltage signal; The first outgoing light path of the second light splitting module (116) and the second outgoing light path of the second light splitting module (116) are perpendicular to each other; A two-way polarized light detection unit is used, and the different sensitivities of the two light sources to the carbon film are utilized to obtain two values: one voltage signal and two differential voltage signals. The optical fiber type and drawing tension information are eliminated, and finally a voltage signal combination including the carbon film thickness is obtained.

4. The online measuring device according to claim 3, characterized in that The main axis of the second polarizer (113) is at 45 degrees to the optical fiber drawing direction; The main axis of the second quarter wave plate (115) is parallel to the main axis of the second polarizer (113), and the main axis of the second quarter wave plate (115) is at 45 degrees to the optical fiber drawing direction; The third analyzer (117) is at a +45 degree angle to the direction of the polarized light generated by the second polarizer (113), and the fourth analyzer (119) is at a -45 degree angle to the direction of the polarized light generated by the second polarizer (113).

5. The online measuring device according to claim 3, characterized in that: The first light source and the second light source have different transmittances to the optical fiber carbon film.

6. The online measuring device according to claim 3, characterized in that: A difference between a transmittance of the first light source to the carbon film on the optical fiber and a transmittance of the second light source to the carbon film on the optical fiber is greater than 10%.

7. The online measuring device according to claim 3, characterized in that: The difference between the transmittance of the uncoated optical fiber to the first light source and the transmittance to the second light source is no more than 10%.

8. A method for online measurement of the thickness of a carbon film on a carbon-coated optical fiber based on the online measurement device according to claim 1, characterized in that: The steps include: Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light; the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens; Converting the parallel elliptically polarized light into a parallel second linearly polarized light; the second linearly polarized light overlaps the center position of the first linearly polarized light and has a different polarization direction; Splitting the second linearly polarized light into two paths of third linearly polarized light, wherein the power of each third linearly polarized light is equal; Decomposing a first light component of a third linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees; detecting the magnitude of the first light component and converting the first light component into a first voltage signal; Decomposing another third linearly polarized light to obtain a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees; detecting the magnitude of the second light component and converting the second light component into a second voltage signal; Obtaining a real-time first voltage difference value of the carbon-coated optical fiber to be tested according to the difference between the first voltage signal and the second voltage signal; determining a current carbon film thickness of the carbon-coated optical fiber to be tested according to the real-time first voltage difference of the carbon-coated optical fiber to be tested and a first carbon film thickness-voltage difference mapping table; The first carbon film thickness-voltage difference mapping table is formed by mapping the actual carbon film thickness of existing carbon-coated optical fibers prepared by adjusting the carbon coating process and the actual first voltage difference under the same optical fiber type and the same drawing tension conditions.

9. A method for online measurement of the thickness of a carbon film on a carbon-coated optical fiber based on the online measurement device according to claim 3, characterized in that: The steps include: Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light; the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through the first polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens; Converting the parallel elliptically polarized light into a parallel second linearly polarized light; the second linearly polarized light overlaps the center position of the first linearly polarized light and has a different polarization direction; Splitting the second linearly polarized light into two third linearly polarized lights; wherein the power of each third linearly polarized light is equal; Decomposing a first light component of a third linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees; detecting the magnitude of the first light component and converting the first light component into a first voltage signal; Decomposing another third linearly polarized light to obtain a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees; detecting the magnitude of the second light component and converting the second light component into a second voltage signal; Obtaining a real-time first voltage difference value of the carbon-coated optical fiber to be tested according to the difference between the first voltage signal and the second voltage signal; irradiating the carbon-coated optical fiber to be tested with a fourth linearly polarized light along the first direction, so that the carbon-coated optical fiber to be tested is scattered to generate diffused elliptically polarized light; The first direction is 45 degrees to the drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near the focus of one side of the lens, and the fourth linearly polarized light is obtained by polarizing the second light source through the second polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens; Convert parallel elliptically polarized light into parallel fifth linearly polarized light; Splitting the fifth linearly polarized light into two sixth linearly polarized lights; The powers of the sixth linear polarized lights are equal; Decomposing a first light component of a sixth linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees; detecting the magnitude of the first light component and converting the first light component into a third voltage signal; Decomposing another path of the sixth linearly polarized light to obtain a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees; detecting the magnitude of the second light component and converting the second light component into a fourth voltage signal; Obtaining a real-time second voltage difference value of the carbon-coated optical fiber to be tested according to the difference between the third voltage signal and the fourth voltage signal; The real-time third voltage difference of the carbon-coated optical fiber to be tested is obtained according to the difference between the real-time second voltage difference of the carbon-coated optical fiber to be tested and the real-time first voltage difference. determining a current carbon film thickness of the carbon coated optical fiber to be predicted according to the real-time third voltage difference of the carbon coated optical fiber to be tested and the second carbon film thickness-voltage difference mapping table; The second carbon film thickness-voltage difference mapping table is formed by mapping components according to the actual carbon film thickness of the existing carbon-coated optical fiber, the first voltage difference, the second voltage difference, and the third voltage difference.

10. The online measurement method according to claim 9, wherein: The wavelength of the first light source is different from the wavelength of the second light source.

11. A method for online measurement of carbon film thickness of carbon-coated optical fiber based on the online measurement device according to claim 1, characterized in that: The steps include: Irradiating a first linearly polarized light toward the carbon-coated optical fiber to be tested along a first direction, causing the carbon-coated optical fiber to be tested to scatter and thereby generate diffused elliptically polarized light; the first direction is 45 degrees to a drawing direction of the carbon-coated optical fiber to be tested, the carbon-coated optical fiber to be tested is located near a focal point on one side of the lens, and the first linearly polarized light is polarized by the first light source through a polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens; Converting the parallel elliptically polarized light into a parallel second linearly polarized light; the second linearly polarized light overlaps the center position of the first linearly polarized light and has a different polarization direction; Splitting the second linearly polarized light into two third linearly polarized lights; wherein the power of each third linearly polarized light is equal; Decomposing a first light component of a third linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees; detecting a magnitude of a first light component and converting the first light component into a first voltage signal; Decomposing another third linearly polarized light to obtain a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees; detecting the magnitude of the second light component and converting the second light component into a second voltage signal; Obtaining a real-time first voltage difference value of the carbon-coated optical fiber to be tested according to the difference between the first voltage signal and the second voltage signal; irradiating the uncoated carbon optical fiber with a first linearly polarized light along a first direction, so that the uncoated carbon optical fiber is scattered to generate diffused elliptically polarized light; The first direction is 45 degrees to the drawing direction of the uncoated carbon fiber, the uncoated carbon fiber is located near the focus of one side of the lens, and the first linearly polarized light is obtained by polarizing the first light source through the polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light using a lens; Converting parallel elliptically polarized light into parallel second linearly polarized light; Splitting the second linearly polarized light into two third linearly polarized lights; wherein the power of each third linearly polarized light is equal; Decomposing a first light component of a third linearly polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees; detecting the magnitude of the first light component and converting the first light component into a fifth voltage signal; Decomposing another third linearly polarized light into a second light component in a third direction; wherein the angle between the third direction and the first direction is -45 degrees; detecting the magnitude of the second light component and converting the second light component into a sixth voltage signal; Obtaining a real-time fourth voltage difference of the carbon-coated optical fiber to be tested according to a difference between the fifth voltage signal and the sixth voltage signal; The fifth real-time voltage difference of the carbon-coated optical fiber to be tested is obtained according to the difference between the fourth real-time voltage difference of the carbon-coated optical fiber to be tested and the first real-time voltage difference. determining a current carbon film thickness of the carbon coated optical fiber to be predicted according to the real-time fifth voltage difference of the carbon coated optical fiber to be tested and the third carbon film thickness-voltage difference mapping table; The third carbon film thickness-voltage difference mapping table is formed by mapping components according to the actual carbon film thickness of the existing carbon-coated optical fiber and the actual fifth voltage difference; A polarized light detection unit is used to perform two tests in a time-sharing manner. One test is for the optical fiber before carbon coating, and the other test is for the optical fiber after carbon coating. By using two tests, the signal brought by the parameters of the optical fiber itself is differentially eliminated, and only the carbon film is retained.

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