Online measuring device and method for thickness of carbon film of carbon-coated optical fiber

Abstract

The invention discloses an online measurement device and method for the thickness of a carbon film of a carbon-coated optical fiber, and the device comprises 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 analyzer, and a first PD. A second analyzer and a second PD; and obtaining a voltage signal related to the thickness of the carbon film through the linearly polarized light detection unit, calibrating the voltage signal with the actual thickness of the optical fiber, and determining the current thickness of the carbon film of the to-be-detected carbon-coated optical fiber according to the real-time voltage difference value of the to-be-detected carbon-coated optical fiber and the carbon film thickness-voltage difference value mapping table. The method can eliminate the influence of the position of the optical fiber on the thickness measurement of the carbon film, improves the accuracy of the thickness measurement result of the carbon film, and improves the preparation uniformity of the carbon film of the carbon-coated optical fiber.

Description

Technical Field

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

[0002] Traditional fused silica optical fiber is prepared by outside vapor deposition (OVD), axial vapor deposition (VAD) and other methods to prepare a preform rod, and then the bare optical fiber is obtained by drawing, and then coated with at least one layer of polymer coating to obtain a finished optical fiber. The polymer coating can effectively improve the mechanical and optical properties of the optical fiber. However, the polymer coating usually cannot prevent some molecules from entering, especially under high temperature and high pressure environments, such as water molecules and hydrogen molecules. Water molecules react with the broken bonds of silica on the surface of the optical fiber, which accelerates the growth of microcracks on the surface of the optical fiber and reduces the fatigue resistance of the optical fiber. In addition, the diffusion of hydrogen molecules in the optical fiber will cause the absorption peak attenuation of the hydrogen molecules themselves and the absorption peak attenuation of Si-OH obtained by the reaction with Si-O, which has an adverse effect on the use of the optical fiber. In order to prevent damage to the optical fiber by foreign molecules in harsh environments, a dense graphite-like amorphous carbon coating is applied between the optical fiber and the polymer coating to prevent foreign molecules from penetrating. This type of graphite-like amorphous carbon is dense and has a good barrier effect on both hydrogen molecules and water molecules.

[0003] The carbon coating can be formed by inducing polymerization and pyrolysis of raw gas (such as acetylene, benzene, etc.) after the optical fiber is drawn from the drawing furnace by chemical vapor deposition, and finally generating 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 chemical vapor deposition. 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 resistance and water blocking ability are 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 of the optical fiber carbon coating, so as to obtain a carbon-coated optical fiber with excellent performance.

[0004] The existing online carbon coating test 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 test results of the carbon film thickness. Summary of the invention

[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 a carbon-coated optical fiber, aiming to solve the problem in the prior art of inaccurate carbon film thickness measurement results caused by position offset or jitter of the optical fiber.

[0006] The present application provides an online measurement device for the thickness of a carbon film of a carbon-coated optical fiber, comprising a linear polarization light detection unit, wherein the linear polarization light detection unit comprises: a first light source, a first aperture, a first polarizer, a first focusing lens, a first quarter-wave plate, a first spectroscopic module, a first analyzer, a first PD, a second analyzer, and a second PD; the first aperture is arranged between the first light source and the optical fiber, and is used to adjust the diameter of a 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 first polarizer is arranged between the first light source and the optical fiber, and is used to generate linear polarization light at 45 degrees to the drawing direction of the optical fiber; the first quarter-wave plate is used to convert parallel elliptically polarized light into linear polarization light; the first spectroscopic module is arranged between the first quarter-wave plate and the first analyzer, and is used to convert the linear polarization light of the first quarter-wave plate into linear polarization light; The first polarizer is used to decompose the polarized light component of one line of polarized light separated by the first beam splitter module in a specific direction, and the specific direction is +45 degrees with 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 polarizer and obtain a first voltage signal; the second polarizer and the second PD are sequentially arranged on the second output light path of the first beam splitter module, the second polarizer is used to decompose the polarized light component of another line of polarized light separated by the first beam splitter module in a specific direction, the second PD is used to detect the size of the polarized light component decomposed by the second polarizer and obtain a second voltage signal, and the specific direction is 45° with the first polarizer.

[0007] The main axis of the first quarter wave plate is parallel to the main axis of the first polarizer, and both are 45 degrees to the fiber drawing direction. The first analyzer is +45 degrees to the direction of polarized light generated by the first polarizer, and the second analyzer is -45 degrees to the direction of polarized light generated by the first polarizer. The first outgoing light path of the first splitter module is perpendicular to the second outgoing light path of the first splitter module.

[0008] In the 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 linear 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 linear 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 beam splitter module, and the third polarizer is used to decompose the polarized light component of a line of polarized light separated by the second beam splitter module in a specific direction, and the specific direction is +45 degrees with 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 beam 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 beam splitter module and the second outgoing light path of the second beam splitter module are perpendicular to each other.

[0009] The main axis of the second polarizer is 45 degrees to the fiber drawing direction; the main axis of the second quarter wave plate is parallel to the main axis of the second polarizer, and the main axis of the second quarter wave plate and the main axis of the second polarizer are both 45 degrees to the fiber drawing direction. The third analyzer is +45 degrees to the direction of the polarized light generated by the second polarizer, and the fourth analyzer is -45 degrees to the direction of 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 optical fiber carbon film and the transmittance of the second light source to the optical fiber carbon film 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 an online measurement method for the carbon film thickness of a carbon-coated optical fiber based on the above-mentioned online measurement device, comprising the following steps:

[0013] The first linear polarized light is irradiated toward the carbon-coated optical fiber to be tested along a 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 first linear polarized light is obtained by polarizing the first light source through a polarizer;

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

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

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

[0017] Decomposing a first light component of a third linear 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 linear polarized light to obtain a second light component in a third direction; 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 the existing carbon-coated optical fiber prepared by adjusting the carbon coating process under the same optical fiber type and the same drawing tension conditions with 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] The first linear polarized light is irradiated toward the carbon-coated optical fiber to be tested along a 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 first linear polarized light is obtained by polarizing the first light source through the first polarizer;

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

[0027] Converting parallel elliptically polarized light into 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 linear polarized light into two third linear polarized lights, wherein the power of each third linear polarized light is equal;

[0029] Decomposing a first light component of a third linear 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 linear polarized light to obtain a second light component in a third direction; 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] The fourth linear polarized light is irradiated toward the carbon-coated optical fiber to be tested 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 linear polarized light is obtained by polarizing the second light source through the second polarizer;

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

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

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

[0038] Decomposing a first light component of a sixth linear 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 into a second light component in a third direction; 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 an online measurement method for the carbon film thickness of a carbon-coated optical fiber based on the above-mentioned online measurement device, comprising the following steps:

[0047] The first linear polarized light is irradiated toward the carbon-coated optical fiber to be tested along a 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 first linear polarized light is obtained by polarizing the first light source through a polarizer;

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

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

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

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

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

[0053] Decomposing another third linear polarized light to obtain a second light component in a third direction; 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] The first linear polarized light is irradiated toward the uncoated carbon optical fiber 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 optical fiber, the uncoated carbon optical fiber is located near the focal point on one side of the lens, and the first linear polarized light is obtained by polarizing the first light source through a polarizer;

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

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

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

[0060] Decomposing a first light component of a third linear 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 linear 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;

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

[0064] Obtaining a fourth voltage difference value of the carbon-coated optical fiber to be tested in real time according to the 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 fifth real-time 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 result; 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 polarized 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 only related 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 prior art:

[0070] (1) The present application adopts the method of polarized light detection to eliminate the influence of optical fiber jitter on the 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 the optical fiber's own parameters on the 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, real-time monitoring and PID feedback control, thereby realizing real-time dynamic control of the position of the reaction chamber, and ultimately improving the uniformity of the carbon film preparation of the carbon-coated optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 It 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 It 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 the second embodiment of the present application;

[0074] Figure 3 It 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 the 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 carbon film thickness of 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 the present application;

[0077] Figure 6 This is a schematic diagram of the trace of the detection light 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 solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present 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 as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, 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 clearly and specifically defined.

[0081] In addition, references throughout this specification to "one embodiment"; "one embodiment", "an example" or similar language indicate that a particular feature, structure, or characteristic described in conjunction 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 features, structures or features of the described 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 application. However, those skilled in the relevant art can recognize that the 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 application.

[0083] The present application proposes an online measurement device and method for the thickness of a carbon film of a carbon-coated optical fiber. The thickness of the carbon film is tested by an optical path, and different wavelengths and polarized light intensities are combined. The influence of the optical fiber geometry on the light intensity can be eliminated by polarized light differential measurement. This is achieved by detecting polarized light in two directions with two PDs. The optical path can eliminate the power fluctuation caused by the jitter of the optical fiber position. When two light sources are used to detect the optical fiber before and after carbon coating, the first path can confirm the type of the 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 obtained 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 measured value of the carbon film thickness 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 fiber is usually carried out on the basis of a traditional drawing tower. The traditional drawing tower includes a preform rod clamping device, an induction furnace, a wire diameter tester, a tension meter, a coating system, a coating curing system, a coating diameter tester and a take-up device from top to bottom. 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 below the carbon coating cavity to monitor the thickness of the carbon film after the optical fiber is carbon-coated.

[0085] The present 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 according to the measurement results. The specific technical solution is as follows:

[0086] The preform rod is heated in an induction furnace (1800℃~1900℃) and then drawn into a bare optical fiber, which then enters the carbon-coated optical fiber cavity. According to the distance between the cavity and the lower furnace mouth of the drawing furnace, it can be determined that the temperature of the optical fiber entering the reaction chamber is between several hundred degrees Celsius and 1500 degrees Celsius. At this time, the raw gas such as acetylene entering the cavity from the gas pipeline will be evenly distributed around the optical fiber and diffuse from top to bottom with the operation of the vacuum pump and the movement of the optical fiber. When the raw gas contacts the high-temperature optical fiber, polymerization and pyrolysis reactions will occur, and finally a graphite-like amorphous carbon coating will be formed on the surface of the optical fiber. The carbon-coated reaction cavity is gas-sealed with nitrogen / argon gas at the top and bottom to isolate the influence of air. After the optical fiber is pulled out from the lower mouth of the reaction chamber, it passes through the online measurement device of the carbon film thickness of the carbon-coated optical fiber, and a reference value of the film thickness is given and fed back to the film thickness control device to make it reach the optimal range, which is consistent with the conventional optical fiber production process.

[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, a linear polarized light detection unit is included, and the linear polarized light detection unit includes: 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 analyzer 107, a first PD 108, a second analyzer 109 and a second PD 110;

[0088] The first light source 101, the first aperture 102 and the first polarizer 103 are arranged on one side of the optical fiber 200, and 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, and 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 linear polarized light at 45 degrees to the optical fiber drawing direction; the main axis of the first polarizer 103 is 45 degrees to the optical fiber drawing direction.

[0089] The first aperture 102 may be arranged before or after the first polarizer 103 .

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

[0091] The first focusing lens 104, the first quarter wave plate 105 and the first splitter module 106 are sequentially arranged along the optical axis on the other side of the optical fiber 200. The main axis of the first quarter wave plate 105 is parallel to the main axis of the first polarizer 103, and both are 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 disposed between the first quarter wave plate 105 and the first analyzer 107, and is used to split the linearly polarized light of the first quarter wave plate 105 into two linearly polarized lights of equal power; wherein the first light splitting module 106 may be a polarization insensitive light splitter.

[0093] The first polarizer 107 and the first PD 108 are sequentially arranged on the first outgoing light path of the first light splitting module 106, wherein the first polarizer 107 is +45 degrees to the direction of the polarized light generated by the first polarizer 103, and the first polarizer 107 is used to decompose the polarized light component of a line of polarized light separated by the first light splitting module 106 in a specific direction, and 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 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 splitter 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 also provides an online measurement method for the thickness of a carbon film of a carbon-coated optical fiber, comprising the steps of:

[0098] Irradiating the carbon-coated optical fiber to be tested with a first linear polarized light along a first direction, so that the carbon-coated optical fiber to be tested is scattered to generate diffused elliptically polarized light, wherein 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 first linear polarized light is obtained by polarizing the first light source through a polarizer;

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

[0100] Converting parallel elliptically polarized light into 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 linear polarized light into two third linear polarized lights, wherein the power of each third linear polarized light is equal;

[0102] Decomposing a first light component of a third linear 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 linear 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] 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;

[0107] Determine the 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 the first carbon film thickness-voltage difference mapping table,

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

[0109] In the embodiment of the present application, the construction of the first carbon film thickness-voltage difference mapping table is mainly through preparing a standard carbon-coated optical fiber under the same bare fiber type and drawing tension conditions, adopting different carbon coating process conditions (such as raw material flow rate, reaction temperature, etc.), testing the standard carbon-coated optical fiber using the detection optical path in Example 1 to obtain the first voltage difference corresponding to the carbon film of different thicknesses of the standard carbon-coated optical fiber, and performing SEM (scanning electron microscope) thickness calibration on the standard carbon-coated optical fiber to obtain the first carbon film thickness-voltage difference mapping table in which the first voltage difference signal corresponds to the thickness one by one.

[0110] Figure 2 FIG. 1 is a schematic diagram of the principle structure of an online measurement device for the carbon film thickness of a carbon-coated optical fiber provided in the second embodiment of the present application; for ease of explanation, only the relevant parts of the second embodiment of the present application are shown. Figure 2 Details are as follows:

[0111] The online measurement device for the carbon film thickness of a carbon-coated optical fiber provided in the second embodiment of the present application includes: two lines of polarized light detection units, the first line confirms the type of the optical fiber itself and the drawing stress information, and the second line confirms the detection voltage containing the carbon film signal, and the difference between the two can obtain the signal of the carbon film thickness. Among them, one line of polarized light detection unit has the same structure as the linear polarized light detection unit in the first embodiment, which will not be repeated here. The other line of polarized light detection unit includes: 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 splitter module 116, a third analyzer 117, a third PD118, a fourth analyzer 119 and a fourth PD120;

[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 linear polarized light at 45 degrees to the optical fiber drawing direction; the main axis of the second polarizer 113 is 45 degrees to the optical fiber drawing direction.

[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 splitter module 116 are sequentially arranged 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 45 degrees to the optical fiber drawing direction. The second quarter wave plate 115 is used to convert parallel elliptically polarized light into linearly polarized light.

[0115] The second light 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; wherein the second light splitting module 116 may be a polarization insensitive light splitter.

[0116] 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, wherein the third polarizer 117 is +45 degrees to the direction of the polarized light generated by the second polarizer 113, and the third polarizer 117 is used to decompose the polarized light component of a line of 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 third PD 118 is used to detect the size of the polarized light component decomposed by the third polarizer 117 to obtain a third voltage signal.

[0117] The fourth analyzer 119 and the fourth PD 120 are sequentially arranged on the second outgoing light path of the second splitter module 116; the fourth analyzer 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 analyzer 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 two-way polarized light detection units, and uses the different sensitivities of two light sources to the carbon film to obtain two 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, after two different wavelengths of detection light are emitted from the LED, they are converted into linear polarized light through the polarizer of the corresponding wavelength band. The main axis angle of the polarizer is 45° with the optical fiber, and the light component perpendicular to the optical fiber direction is equal to the light component parallel to the optical fiber direction. After polarization, it is irradiated on the side of the optical fiber. After passing through the optical fiber, a part of the light generated by optical fiber scattering passes through the quarter wave plate, polarization-independent beam splitter, and analyzer and is collected by two photodetectors. The two analyzers are respectively at an angle of 45° and -45° with the main axis direction of the 1 / 4 wave plate (specifically, the first analyzer 107 is at a 45° angle with the main axis direction of the first quarter wave plate 105, and the second analyzer 109 is at a -45° angle with the main axis direction of the first quarter wave plate 105; and the third analyzer 117 is at a 45° angle with the main axis direction of the second quarter wave plate 115, and the fourth analyzer 119 is at a -45° angle with the main axis direction 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 standard. 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. As a monitoring device for the carbon coating, the voltage signals obtained by the two PDs in one polarized light detection unit are used to differenciate the reference detection voltage of the optical fiber, and the detection voltage of the optical fiber containing the carbon film is obtained by differencing 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 corresponds 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 stepping 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 also provides an online measurement method for the thickness of a carbon film of a carbon-coated optical fiber, comprising the steps of:

[0124] Irradiating the carbon-coated optical fiber to be tested with a first linear polarized light along a first direction, so that the carbon-coated optical fiber to be tested is scattered to generate diffused elliptically polarized light, wherein 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 first linear polarized light is obtained by polarizing the first light source through a polarizer;

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

[0126] Converting parallel elliptically polarized light into 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 linear polarized light into two third linear polarized lights, wherein the power of each third linear polarized light is equal;

[0128] Decomposing a first light component of a third linear 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 linear 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 the difference between the first voltage signal and the second voltage signal;

[0133] The first linear polarized light of the polarizer 113 is obtained by polarizing the second light source through the polarizer, wherein the wavelength of the second light source is 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] According to the difference between the third voltage signal and the fourth voltage signal, a real-time second voltage difference value of the carbon-coated optical fiber to be tested is obtained;

[0136] Obtaining a real-time third voltage difference value of the carbon-coated optical fiber to be tested according to the 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] Determine the 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 the 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 optical 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, and the single voltage difference change caused by the type of optical fiber to be tested and the drawing conditions can be eliminated through the combination of voltage differences.

[0140] The present application adopts the method of polarized light detection to eliminate the influence of optical fiber jitter on the 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 the optical fiber's own parameters on the carbon coating measurement.

[0141] Figure 3 FIG. 1 is a schematic diagram of the principle structure of an online measurement device for the carbon film thickness of a carbon-coated optical fiber provided in the third embodiment of the present application in a horizontal direction; for ease 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 time division, 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 also provides an online measurement method for the thickness of a carbon film of a carbon-coated optical fiber, comprising the steps of:

[0145] Irradiating the carbon-coated optical fiber to be tested with a first linear polarized light along a first direction, so that the carbon-coated optical fiber to be tested is scattered to generate diffused elliptically polarized light, wherein 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 first linear polarized light is obtained by polarizing the first light source through a polarizer;

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

[0147] Converting parallel elliptically polarized light into 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 linear polarized light into two third linear polarized lights, wherein the power of each third linear polarized light is equal;

[0149] Decomposing a first light component of a third linear 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 linear 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 the difference between the first voltage signal and the second voltage signal;

[0154] Irradiating the uncoated carbon optical fiber with a first linear polarized light along a first direction, so that the uncoated carbon optical fiber is scattered to generate diffused elliptically polarized light, wherein the first direction is 45 degrees to the drawing direction of the uncoated carbon optical fiber, the uncoated carbon optical fiber is located near the focal point on one side of the lens, and the first linear polarized light is obtained by polarizing the first light source through a polarizer;

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

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

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

[0158] Decomposing a first light component of a third linear 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 linear 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;

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

[0162] According to the difference between the fifth voltage signal and the sixth voltage signal, a fourth voltage difference value of the carbon-coated optical fiber to be tested is obtained in real time;

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

[0164] Determine the current carbon film thickness of the carbon coated optical fiber to be predicted according to the fifth real-time 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 according to 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, which will not be repeated here.

[0166] Figure 4 The schematic diagram of the principle structure of the online measurement device for the carbon film thickness of the carbon-coated optical fiber provided by the present application is shown in a top view. For the convenience of explanation, only the part related to the present application is shown, which is now described in detail in conjunction with the accompanying drawings as follows:

[0167] like Figure 4 As shown, the light emitted by the LED is irradiated onto the polarizer through the aperture. 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 a co-directional structure to an anisotropic structure. After the linearly polarized light of 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 linear 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 linearly polarized light of the polarizer and the center of the optical fiber, r is the distance of the center line of the optical fiber along the incident direction within the cross-section of the optical fiber, y is the distance between the linearly 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, and σ z (r) is the distribution of the axial (z-direction) component of the stress on the optical fiber cross-section.

[0170] As Figure 5 shown, consider the polarized light incident on the optical fiber as a uniform plane wave with a power density of I. If the PD only receives the light rays with an exit angle within the range, then the position range of the input light rays is y1 < y < y2. Then, these light rays pass through a quarter-wave plate with the optical axis in the same direction as the main axis direction of the polarizer and convert the elliptically polarized light generated by the optical fiber phase delay back into linearly polarized light, but the linearly polarized angle changes. Finally, this linearly polarized light passes through an analyzer with a polarization direction of ±45° with respect to the polarizer and is finally received by a phototube. Then the power on the detector is P: Where, 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 two detectors with the analyzer at ±45° with respect to the main optical axis of the polarizer are respectively:

[0172] Then, subtracting the measured powers of the two detectors with different polarizations can obtain:

[0173]

[0174] The light ray diameter and stress-optic effect in this application determine that it must be a small phase difference. 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-optic coefficient. For the optical path provided in this application, the values y1 / b and y2 / b are constant for a certain optical fiber because the light rays are determined, so y1 / b and y2 / b are determined, and the influence on the monitored optical power within a certain range of the optical fiber position can be ignored (see the optical path). Therefore, the measured power difference is less affected by the fluctuation of the optical fiber position, as Figure 6 shown.

[0176] The voltage signal measured by the linear polarized light detection unit with a wavelength of 1550nm is used as the reference value, and the linear polarized 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 PD108 and the optical power P2 of the second PD110 monitored by it are respectively:

[0177]

[0178] The final monitoring voltage also needs to be calculated based on the transmittance T and convert the optical power into the output voltage V 1550nm With V 650nm The value of V can be used to obtain the carbon film information by subtracting 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 The slide position of the reaction chamber is controlled by PID feedback to control the reaction temperature, ultimately achieving 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 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 before passing 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 As shown in the figure), the influence of 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 materials and optical fiber drawing tension, thereby improving measurement accuracy: Specifically, the optical path of the two light sources can be used to eliminate the influence of optical fiber materials and optical fiber drawing tension, thereby reducing the influence of optical fiber materials and optical fiber drawing tension and improving measurement accuracy.

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

[0186] Embodiment 1:

[0187] The samples prepared by different carbon coating processes are 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] The standard single-mode optical fiber is drawn from the drawing furnace to a bare fiber of 125um and enters the reaction cavity at a speed of 250m / s. The upper end of the reaction cavity is about 15cm away from the initial position of the optical fiber preform rod, and the drawing tension is 60g; according to the infrared temperature measuring device, the temperature of the optical fiber before entering the cavity is about 1280℃. The reaction cavity gas seal gas is pure nitrogen, the upper gas seal flow rate is 2L / min, the lower gas seal is 2L / min, the reaction raw material gas is argon diluted acetylene, the concentration is 30%vol, the flow rate is 2L / min, and the tail gas treatment device flow rate is 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 samples are then taken for SEM testing, and the actual average thickness is about 56.8nm, which is in good agreement with the mapping relationship table, so the thickness monitoring of the optical fiber carbon film can be realized.

[0190] The fiber diameter was changed to 130um, the drawing speed was 250m / s, and the drawing tension was 60g; without changing the experimental conditions of carbon coating, the differential voltage value of the 1550nm light source monitoring unit was 0.42V. The voltage change was due to the increase in fiber diameter, which led to the increase in fiber temperature. The actual temperature of the fiber before entering the cavity was about 1350℃. Through PID feedback control, the differential voltage of the monitoring unit was restored to 0.52V, and then the fiber sample was sent to SEM for testing. The average thickness was about 57.2nm, which proved that the monitoring unit can differentiate the geometric information of the fiber and monitor the actual thickness of the carbon film.

[0191] Without changing the fiber drawing process parameters, the monitoring device was offset by 1 mm in one direction, and 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] Embodiment 2:

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

[0194] The optical fiber is drawn from the drawing furnace to a bare fiber of 125um and enters the reaction chamber at a speed of 200m / s. The upper end of the reaction chamber is about 20cm away from the initial position of the optical fiber preform. According to the infrared temperature measuring device, the temperature of the optical fiber before entering the cavity is about 1200℃. The reaction chamber gas seal gas is pure nitrogen, the upper gas seal flow rate is 2L / min, the lower gas seal is 2L / min, the reaction raw material gas is argon diluted acetylene, the concentration is 30%vol, the flow rate is 2L / min, and the tail gas treatment device flow rate is 3L / min.

[0195] After passing through the reaction chamber, the optical fiber containing the carbon coating passes through the carbon coating monitoring device, wherein 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 detector at a wavelength of 650nm is 0.35V. At this time, the differential value of the differential voltage of the two light sources (0.58-0.35)V 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 polarized light detection unit of the carbon-coated optical fiber at a wavelength of 1550nm and the voltage detected by the linear polarized 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 is 1.5L / min, then the voltage difference is 0.15V, and the differential voltage at 1550nm is 0.42V. The reaction device of the carbon-coated cavity is connected to the PID control system, and the one-dimensional translation stage raises the reaction cavity to 18cm away from the cone of the preform rod. The voltage difference is restored to 0.23V, and the differential voltage at 1550nm is 0.58V; after electron microscope testing, the thickness of the carbon film is about 32±1nm, which proves that the mapping relationship has good consistency and feasibility with the test system.

[0197] Embodiment 3:

[0198] The online measuring device for the carbon film thickness of the carbon-coated optical fiber is the same as the 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 into a 125um bare fiber in the drawing furnace and passes through the first monitoring unit at a speed of 200m / s. The differential voltage measured by the 1550nm wavelength monitoring unit is 0.78V, and the drawing tension is 55g, which serves as the reference voltage of the optical fiber and mainly includes the tension information and type information of the optical fiber. It is then heated to about 1400℃ by an infrared heating device and enters the reaction chamber.

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

[0201] After passing through the reaction chamber, the optical fiber containing the carbon coating passed through the carbon coating monitoring device, wherein the differential voltage value of the linear polarized light detection unit detector at a wavelength of 1550nm was 0.6V. After calibration with an electron microscope, the thickness of the carbon film prepared under the experimental conditions was approximately 45±2nm, and the corresponding differential voltage before and after carbon coating was 0.18V, which served as the mapping relationship between the third thickness and voltage.

[0202] Then, in actual production, the difference between the voltage detected by the linear polarized light detection unit at a wavelength of 1550nm of the uncoated carbon fiber and the voltage detected by the linear polarized light detection unit at a wavelength of 1550nm after carbon coating is set at 0.18V. The fiber drawing tension is changed to 80g, the raw gas flow rate is 2L / min, and the initial driving power of the infrared heating device is changed so that the heating temperature is about 1300℃. At this time, the differential voltage of the 1550nm monitoring unit before carbon coating is 0.98V, and the differential voltage of the 1550nm after carbon coating is 0.84V, with a difference of 0.14V. The power drive 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 carbon coating. After a certain period of time, the differential voltage difference before and after carbon coating is restored to 0.18V; after electron microscope testing, the carbon film thickness is about 46±2nm, which proves that the mapping relationship has good consistency and feasibility with the test system and completely eliminates the fiber type and drawing parameters.

[0203] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection 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 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 linear polarized light at an angle of 45 degrees to the optical fiber drawing direction; 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 a first outgoing light path of the first light splitting 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 light splitting module (106), and 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 output light path of the first splitter module (106); the second polarizer (109) is used to decompose the polarized light component in a specific direction of another linear polarized light separated by the first splitter module (106); 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 splitter module.

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 first polarizer (103) generate polarized light at a direction of +45 degrees, and the second analyzer (109) and the first polarizer (103) generate polarized light at a direction of -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, characterized in that: 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 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 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 linear polarized light at an angle of 45 degrees to the optical fiber drawing direction; 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 for splitting 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 another path of 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.

4. The online measuring device according to claim 3, characterized in that: The main axis of the second polarizer (113) is 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) and the second polarizer (113) generate polarized light with a direction of +45 degrees, and the fourth analyzer (119) and the second polarizer (113) generate polarized light with a direction of -45 degrees.

5. The online measuring device according to claim 3, characterized in that: The transmittance of the first light source to the optical fiber carbon film is different from that of the second light source; or the difference between the transmittance of the first light source to the optical fiber carbon film and the transmittance of the second light source to the optical fiber carbon film is greater than 10%; Or 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%.

6. A method for online measurement of carbon film thickness of carbon-coated optical fiber based on the online measurement device of claim 1, characterized in that: The steps include: The first linear polarized light is irradiated toward the carbon-coated optical fiber to be tested along a 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 first linear polarized light is obtained by polarizing the first light source through a polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light by using a lens; Converting parallel elliptically polarized light into 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 linear polarized light into two third linear polarized lights, wherein the power of each third linear polarized light is equal; Decomposing a first light component of a third linear 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 component into a first voltage signal; Decomposing another third linear polarized light to obtain a second light component in a third direction; 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; 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. The first carbon film thickness-voltage difference mapping table is formed by mapping the actual carbon film thickness of the existing carbon-coated optical fiber 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.

7. An online measurement method for the thickness of a carbon film on a carbon-coated optical fiber, characterized in that: The steps include: The first linear polarized light is irradiated toward the carbon-coated optical fiber to be tested along a 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 first linear polarized light is obtained by polarizing the first light source through the first polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light by using a lens; Converting parallel elliptically polarized light into 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 linear polarized light into two third linear polarized lights, wherein the power of each third linear polarized light is equal; Decomposing a first light component of a third linear 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 component into a first voltage signal; Decomposing another third linear polarized light to obtain a second light component in a third direction; 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 by using a lens; Convert parallel elliptically polarized light into parallel fifth linearly polarized light; Splitting the fifth linear polarized light into two sixth linear polarized lights; The powers of the sixth linear polarized lights are equal; Decomposing a first light component of a sixth linear 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 component into a third voltage signal; Decomposing another path of the sixth linearly polarized light into a second light component in a third direction; 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. Determine the 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.

8. The online measurement method according to claim 7, characterized in that: The wavelength of the first light source is different from the wavelength of the second light source.

9. An online measurement method for the thickness of a carbon film on a carbon-coated optical fiber based on the online measurement device of claim 1, characterized in that: The steps include: The first linear polarized light is irradiated toward the carbon-coated optical fiber to be tested along a 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 first linear polarized light is obtained by polarizing the first light source through a polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light by using a lens; Converting parallel elliptically polarized light into 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 linear polarized light into two third linear polarized lights, wherein the power of each third linear polarized light is equal; Decomposing a first light component of a third linear polarized light in a second direction; the angle between the second direction and the first direction is +45 degrees; Detecting the magnitude of a first light component and converting the first component into a first voltage signal; Decomposing another third linear polarized light to obtain a second light component in a third direction; 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 optical fiber, the uncoated carbon optical 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 a polarizer; The diffused elliptically polarized light is focused into parallel elliptically polarized light by using a lens; Converting parallel elliptically polarized light into parallel second linearly polarized light; Splitting the second linear polarized light into two third linear polarized lights, wherein the power of each third linear polarized light is equal; Decomposing a first light component of a third linear 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 component into a fifth voltage signal; Decomposing another third linear 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 sixth voltage signal; Obtaining a fourth voltage difference value of the carbon-coated optical fiber to be tested in real time according to the 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. Determine the current carbon film thickness of the carbon coated optical fiber to be predicted according to the fifth real-time 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.

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