Sample structure for testing curing degree of inner coating of optical fiber, sample preparation device and detection system

Abstract

The utility model belongs to the technical field of optical fiber detection, and particularly relates to a sample structure for testing the curing degree of an inner coating of an optical fiber, a sample preparation device and a detection system.The sample structure comprises a bonding layer and a plurality of to-be-tested optical fiber fragments which are laid and bonded to the bonding layer; the optical fiber segment to be detected is an optical fiber segment with a cutting plane obtained by cutting along the contact surface of the cladding and the inner coating of the optical fiber and parallel to the axial direction of the optical fiber, the optical fiber segment does not contain a glass part, the glass part comprises a fiber core and the cladding wrapping the fiber core, and the cutting plane is exposed out of the inner coating. The sample structure prepared in this way exposes a large-area internal coating, so that the acquisition of an infrared light signal of the internal coating is facilitated, and the accuracy of the curing degree test of the internal coating is ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical fiber detection, and more particularly, to a sample structure for testing the curing degree of an inner coating of an optical fiber, a sample preparation device, and a detection system. BACKGROUND

[0002] In the production process of quartz optical fibers, the optical fibers drawn from the drawing furnace have a small geometric diameter and are prone to breakage. The bare optical fibers are prone to oxidation after being exposed to air and to adsorbing dust and moisture in the environment, thereby affecting the performance (such as microbend loss) and mechanical strength of the optical fibers. Therefore, it is necessary to rapidly coat a coating material on the surface of the bare optical fibers to protect the optical fibers.

[0003] Ultraviolet curing coating has the advantages of fast curing speed, no large amount of solvent evaporation, and excellent coating film performance. Acrylate coating is widely used as ultraviolet curing coating in the industry to coat optical fibers. Generally, ultraviolet curing coating is composed of oligomers, photoinitiators, diluents, various additives, and the like. Under the irradiation of ultraviolet light, free radicals or cations are generated from the photoinitiators in the ultraviolet curing coating. The photoinitiators are sensitive to light and stable to heat. Then, the free radicals or cations initiate the polymerization and crosslinking reaction of the oligomers and active diluents, so that the ultraviolet curing coating coated on the surface of the optical fibers forms a network coating film with certain performance (pressure resistance, wear resistance, chemical resistance, etc.), i.e., the coating of the optical fibers.

[0004] For conventional optical fibers, the coating is usually coated twice: the inner layer is coated with a polymer coating having a larger refractive index than quartz glass and a lower elastic modulus (only a few megapascals), which is used to absorb excess light transmitted through the cladding and protect the surface of the optical fiber from damage, and plays a role in buffering external stress in use; the outer layer is harder, and a polymer coating with a higher elastic modulus (up to several hundred megapascals) is usually selected, which is beneficial to preventing wear and providing strength. In the actual production of optical fibers, it is necessary to ensure that the inner and outer ultraviolet curing coatings coated on the surface of the optical fibers have good curing effect, so as to ensure that the peeling force of the optical fiber coating and the adhesion between the coating and the cladding are within the appropriate index range, which puts forward a quantitative test requirement for the ultraviolet curing degree of the inner and outer coatings of the optical fibers, i.e., the curing degree of the optical fiber coating needs to be accurately tested.

[0005] The current methods for testing the curing degree of optical fiber ultraviolet coating mainly include: a. Fourier transform infrared spectroscopy (FTIR) is used for infrared spectrum analysis. The method measures the percentage of final reaction acrylate unsaturated groups by FTIR. According to the infrared spectrum of the coating obtained by FTIR, the peak area of the change peak and the reference peak of different coatings is calculated to obtain the curing degree of the optical fiber ultraviolet coating. b. Sogliat extraction method. The method uses Sogliat extraction method to determine the gel fraction to evaluate the curing degree of the ultraviolet coating. c. Anti-solvent wiping method. The method evaluates the curing degree of the ultraviolet coating by testing the anti-solvent wiping performance of the optical fiber ultraviolet coating. The method b is complex and time-consuming, and the method c has solvent volatilization in the operation process, and has high requirements for environmental ventilation and operation safety, so the method a is usually used for analyzing and testing the curing degree of the optical fiber because of its convenient operation and short time consumption.

[0006] There are several sample preparation methods for method a: tabletting method (suitable for samples that can be ground into powder), film coating method (suitable for samples that can be dissolved), solution method (suitable for samples that can be dissolved), thin film method (solution film forming, hot pressing film forming, ultra-thin sectioning) and total emission method (suitable for surface coating, thin film and other samples). Since the optical fiber is a long and thin linear object, and the coating diameter of the conventional optical fiber is usually only a few hundred microns (mostly 250 microns), the sampling method is very critical when the curing degree is tested by infrared spectrum analysis. For the outer coating of the optical fiber, no additional sample preparation is required. Only the surface of the outer coating of the optical fiber needs to be cleaned, and then a plurality of optical fibers are arranged side by side to cover the detection area of the FTIR, and the test can be started. The method is relatively mature.

[0007] However, for the inner coating, the existing technology lacks an effective method for testing the curing degree of the inner coating. It is difficult to obtain the complete and sufficient inner coating material from the optical fiber for testing the curing degree. In addition to the difficulty in sampling, the problem of low signal-to-noise ratio caused by the small amount of inner coating sample to be tested also needs to be effectively solved. For some application scenarios that require the stripping of the optical fiber coating, the stripping force of the optical fiber coating is a crucial parameter. The stripping force of the optical fiber coating needs to be within a suitable parameter range, so that the optical fiber coating will not abnormally fall off and delaminate, and at the same time, there will be no excessive coating residue when stripping, so as to ensure the smooth application process of the optical fiber rear end. The type of the inner coating of the optical fiber is confirmed, and the curing degree directly affects the adhesion between the inner coating and the glass cladding layer, and the adhesion further affects the value of the coating stripping force. Therefore, the curing degree of the inner coating of the optical fiber is an essential test parameter to ensure the normal application of the optical fiber rear end. Therefore, an effective method for testing the curing degree of the inner coating is urgently needed. Content of the utility model

[0008] In view of the defects of the prior art, the present application aims to provide a sample structure for testing curing degree of inner coating of optical fiber, a sample preparation device and a detection system, aiming to solve the technical problems of the prior art that sample preparation for testing curing degree of inner coating is difficult and effective testing means for curing degree of inner coating of optical fiber is lacking.

[0009] To achieve the above-mentioned purpose, in a first aspect, the present application provides a sample structure for testing curing degree of inner coating of optical fiber, the optical fiber comprising a cladding, an inner coating and an outer coating arranged in sequence outside a fiber core, the sample structure comprising an adhesive layer and a plurality of to-be-tested optical fiber segments arranged in parallel and adhered to the adhesive layer in sequence;

[0010] The to-be-tested optical fiber segment is an optical fiber segment with a cutting plane obtained by cutting along the contact surface of the cladding and the inner coating of the optical fiber and parallel to the axis of the optical fiber, the optical fiber segment not containing a glass part comprising a fiber core and a cladding covering the fiber core, and the cutting plane exposing the inner coating, the side of the cutting plane being away from the adhesive layer.

[0011] Preferably, the adhesive layer is a pressure-sensitive adhesive tape made of natural rubber pressure-sensitive adhesive.

[0012] Preferably, the thickness of the adhesive layer is less than 60 μm, and the width is greater than 2 mm.

[0013] In a second aspect, the present application provides a sample preparation device for preparing the sample structure, comprising a pressing unit, a cutting unit and a supporting unit, the cutting unit being used for cutting the optical fiber along the contact surface of the cladding and the inner coating of the optical fiber and parallel to the axis of the optical fiber to obtain the to-be-tested optical fiber segment; the pressing unit being an external power source for pressing and fixing the optical fiber during cutting; the supporting unit being used for supporting and fixing the optical fiber during cutting; the supporting unit and the pressing unit clamping the optical fiber during cutting.

[0014] Preferably, the supporting unit is a glass plate; and / or, the cutting unit is a cutting blade.

[0015] In a third aspect, the present application provides a detection system for testing curing degree of inner coating of optical fiber by using an infrared spectrometer, comprising an infrared light source, a sampling table and the sample structure arranged on the sampling table.

[0016] Preferably, the sampling table is a zinc selenide crystal ATR sampling table, a germanium crystal ATR sampling table or a diamond ATR sampling table.

[0017] Preferably, the sampling table has an inverted prism structure, the surface of the sampling table in contact with the sample structure during detection is the upper base of the sampling table, the upper base and the lower base of the sampling table are both rectangular, the area of the upper base is greater than that of the lower base, the prism structure comprises two sets of opposite sides, one set of opposite sides is rectangular with the same area, and the other set of opposite sides is isosceles trapezoid with the same area, and the top angle of the isosceles trapezoid is 45°.

[0018] Preferably, the cutting plane of the optical fiber to be tested in the sample structure is in contact with the upper base of the sampling table; and the total width of the optical fiber segment to be tested laid and bonded on the bonding layer in the sample structure in any direction is greater than or equal to the width of the upper base of the sampling table in the same direction.

[0019] Preferably, the sampling table is further coated with a reflective film below; the reflective film is an aluminum film with a thickness greater than 10 μm.

[0020] Overall, compared with the prior art, the above technical solutions conceived by the present application have the following beneficial effects:

[0021] (1) The present application provides a sample structure for testing the curing degree of the inner coating of an optical fiber, comprising a bonding layer and a plurality of optical fiber segments to be tested closely laid and bonded on the bonding layer; the optical fiber segment to be tested is a fiber segment with a cutting plane obtained by cutting along the contact surface of the cladding and the inner coating of the optical fiber and parallel to the axial direction of the optical fiber, the fiber segment does not contain a glass part, the glass part comprises a core and a cladding covering the core, and the cutting plane exposes the inner coating, the side where the cutting plane is located is away from the bonding layer, that is, the bonding layer is in direct contact with the outer coating of the laid and arranged optical fiber. The sample structure prepared in this way exposes a large area of the inner coating, facilitates the acquisition of the infrared light signal of the inner coating, and thus ensures the accuracy of the curing degree test of the inner coating.

[0022] (2) The present application adopts total reflection method to test the inner coating of optical fiber, and the total reflection method needs to use ATR (Attenuated Total Reflectance) sampling crystal. In the preferred embodiment of the present application, the structure of the ATR reflection crystal sampling table in the infrared detection system is redesigned, and the crystal sampling table with an inverted prism structure is adopted. The upper and lower bottom surfaces are rectangular, one group of side surfaces is rectangular with the same area size, and the other group of side surfaces is isosceles trapezoid with the same area size, and the top angle of the isosceles trapezoid is 45°. Unlike the single reflection of the traditional sampling table structure, the ATR reflection crystal adopted in the present application can realize multiple reflections, thereby enhancing the infrared reflection signal of the inner coating of the optical fiber. During detection, the incident direction and the exit direction of the light signal emitted by the infrared light source are perpendicular to the two side rectangular surfaces of the crystal sampling table, respectively, to realize the vertical incidence and vertical exit of the infrared light signal at the two side surfaces of the crystal, and to realize the reflection between the upper and lower bottom surfaces of the sampling table, thereby realizing the multiple reflections of the infrared light and ensuring that the infrared light signal will not cause excessive loss between the air and the crystal interface and thus cause energy loss.

[0023] (3) The sample structure and the detection system for testing the curing degree of the inner coating of the optical fiber provided in the present application have simple structure but high detection precision, and skillfully solve the difficulties such as sample preparation, large test fluctuation and improper background subtraction encountered in the prior art when testing the curing degree of the inner coating material of the optical fiber, and can accurately test the curing degree of the inner coating of the optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a sample structure schematic diagram for testing the curing degree of the inner coating of the optical fiber provided by the embodiment of the present application;

[0025] Figure 2 is a sample structure preparation cutting section view for testing the curing degree of the inner coating of the optical fiber provided by the embodiment of the present application;

[0026] Figure 3 is a sample structure preparation device schematic diagram for testing the curing degree of the inner coating of the optical fiber provided by the embodiment of the present application;

[0027] Figure 4 is a sampling table structure schematic diagram provided by the embodiment of the present application;

[0028] Figure 5 is a main view structure schematic diagram of a detection system for testing the curing degree of the inner coating of the optical fiber provided by the embodiment of the present application;

[0029] Figure 6 is a side view structure schematic diagram of a detection system for testing the curing degree of the inner coating of the optical fiber provided by the embodiment of the present application;

[0030] Figure 7is a schematic diagram of a sampling table corresponding to the infrared spectrum of the air environment collected in the embodiments of the present application;

[0031] Figure 8 is a schematic diagram of a detection system when collecting the infrared spectrum of the liquid coating of the same material as the inner coating in the embodiments of the present application;

[0032] Figure 9 is a schematic diagram of a sampling table corresponding to the infrared spectrum of the outer coating collected in the embodiments of the present application;

[0033] Figure 10 is a schematic diagram of a detection system when collecting the infrared spectrum of the adhesive layer in the embodiments of the present application.

[0034] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

[0035] 1-adhesive layer; 1-1-fiber segment to be measured; 2-cladding layer; 3-inner coating layer; 4-cutting plane; 5-outer coating layer; 6-supporting unit; 7-sampling table; 71-upper bottom surface; 72-lower bottom surface; 73-left side surface; 74-right side surface; 75-front side surface; 76-rear side surface; 8-reflective film; 9-liquid coating; 10-incoming light; 11-outgoing light; 12-optical fiber. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0037] Infrared spectrum analysis is an analysis technique for identifying the structure of a material by measuring the absorption of electromagnetic waves in the infrared region by the material. The curve recording the relationship between the absorbance or percentage transmittance of infrared light irradiated to the sample and its wave number or wavelength is the infrared spectrum, and the infrared spectrum described in the present application refers to the curve of the relationship between the absorbance of infrared light by the sample and its wave number. The infrared spectrum can be used to study the breaking and recombination of functional groups during the curing process, understand the mechanism of the curing reaction, and judge the degree of the curing reaction, so as to achieve the purpose of testing the curing degree of the optical fiber coating. The basis is the basic theory of light absorption: Lambert-Beer's law, that is, the absorbance of a certain component in a substance is proportional to the concentration of the component.

[0038] The coating layer of the optical fiber is an acrylate material. After the acrylate material is cured by ultraviolet light, the olefin structure is destroyed, and the main change in the molecular structure is that the carbon-carbon double bond (C=C) is opened and polymerized to form a carbon-carbon single bond. In the infrared spectrum, the infrared absorption peak corresponding to C=C changes to be flat or even disappears (at this time, the curing degree is 100%). The infrared absorption peak corresponding to C=C is called a change peak. The characteristic absorption peak of the olefin C=C double bond (wavenumber 1637 nearby) is usually selected. However, the structure of some groups is unchanged before and after the coating is cured, such as the carbon-oxygen double bond (C=O). The infrared absorption peak corresponding to C=O is called a reference peak, and is usually at a wavenumber of 1480 nearby. Therefore, by calculating the ratio of the peak areas of the change peak M' and the reference peak R' of the optical fiber coating, and the ratio of the peak areas of the change peak M and the reference peak R of the liquid coating before curing, the relative change between the two ratios can reflect the change in the concentration of C=C. By using the ratio of the change peak to the reference peak, the error caused by the thickness of the optical fiber coating and other external factors can be reduced.

[0039] According to the prior art, the specific calculation formula of the curing degree RAU is as follows:

[0040] (1)

[0041] wherein, is the ratio of the change peak and the reference peak of the coating (after curing); is the ratio of the change peak and the reference peak of the liquid coating (before curing).

[0042] In order to test the curing degree of the inner coating of the optical fiber, the present application has attempted to peel off the inner coating of the optical fiber in sections and lay the peeled inner coating flat on the detection area of the FTIR device for testing. However, because the cross-sectional area of the peeled inner coating of the optical fiber is much smaller than the surface area of the sampling table ATR crystal, when testing the curing degree of the inner coating, the amount of the material to be tested is small, the FTIR detection signal strength is weak, the test signal-to-noise ratio is low, the environmental interference is large, and finally the test fluctuation of the infrared spectrum of the inner coating is large, and the curing degree of the inner coating of the optical fiber cannot be accurately tested. Therefore, the present application provides a sample structure, a sample preparation device and a detection system for testing the curing degree of the inner coating of the optical fiber.

[0043] Specifically, the present application provides a sample structure for testing the curing degree of the inner coating of the optical fiber. The optical fiber includes a cladding, an inner coating and an outer coating arranged in sequence outside the fiber core. The sample structure provided by the present application is as follows: Figure 1As shown, the sample structure comprises an adhesive layer 1 and a plurality of to-be-tested fiber segments 1-1 laid flat on the adhesive layer 1, where "laid flat" means that a plurality of to-be-tested fiber segments are arranged in sequence in parallel, and any two adjacent to-be-tested fiber segments are in contact with each other; as shown in Figure 2 As shown, the to-be-tested fiber segment 1-1 is a fiber segment with a cutting plane 4 obtained by cutting along the contact surface of the cladding layer 2 and the inner coating layer 3 of the fiber and in parallel to the fiber axis, the fiber segment does not contain a glass part, the glass part includes a core and a cladding layer 2 covering the core, the cutting plane 4 exposes the inner coating layer 3, and the side where the cutting plane 4 is located is away from the adhesive layer 1, that is, the adhesive layer 1 is in direct contact with the outer coating layer 5 of the laid flat fiber.

[0044] The selection of the adhesive layer material of the present application preferably meets the following requirements: first, the adhesive layer needs to have an infrared spectrum different from that of the inner coating layer material of the to-be-tested fiber, so that the infrared signal of the adhesive layer does not interfere with the infrared spectrum result of the fiber inner coating layer itself during infrared testing. Specifically, at the change peak and the reference peak, the adhesive layer cannot have the same characteristics as the fiber coating (acrylic resin), that is, the infrared absorption peak of the fiber inner coating layer cannot be interfered by the infrared absorption peak of the adhesive layer. Second, the adhesive layer needs to have high cohesive strength and elasticity, so that the natural rubber adhesive layer can be adhered to the smooth surface of the fiber outer coating layer using a small pressure, and the adhesive layer can be removed without contaminating the adhered fiber coating surface. In addition, the adhesive force between the fiber outer coating layer and the adhesive layer needs to be less than the peeling force of the to-be-tested fiber itself, and is preferably controlled to be less than 0.5 N, so that the fiber coating can be effectively combined with the adhesive layer, but the fiber coating itself will not be peeled off during the process of adhering the fiber. A preferable adhesive layer material that meets the above conditions is a pressure-sensitive adhesive tape made of natural rubber pressure-sensitive adhesive, which is a complex mixture mainly composed of natural rubber elastomer, with tackifying resin, softening agent, antioxidant, pigment and filler, and crosslinking (vulcanization) agent and other additives.

[0045] In order to ensure appropriate optical signal intensity during testing and certain mechanical strength during sample preparation, the thickness of the adhesive layer is preferably less than 60 μm, and the width is greater than 2 mm. The adhesive layer with a thickness of 30-50 μm, a width of 4-6 mm, and a length of 80-120 mm is preferentially selected.

[0046] The present application also provides a sample preparation device for preparing the sample structure, as shown in Figure 3As shown, the sample structure comprises a pressing unit, a cutting unit and a supporting unit 6, the cutting unit is used to cut the optical fiber along the contact surface of the cladding and the inner coating of the optical fiber and parallel to the optical fiber axis to obtain the optical fiber segment to be tested; the pressing unit is an external power source used to press and fix the optical fiber when cutting the optical fiber; the supporting unit is used to support and fix the optical fiber when cutting the optical fiber; the supporting unit and the pressing unit clamp the optical fiber when cutting. The pressing unit and the cutting unit are not shown in the figure.

[0047] In some embodiments, the supporting unit 6 is a glass plate; and the cutting unit is a cutting blade. For example, in some embodiments, the optical fibers with clean surfaces are closely arranged on the adhesive surface of the adhesive layer, ensuring that there is no obvious gap between the optical fibers and the area of the optical fiber arrangement is sufficient to cover the surface of the sampling table; the adhesive layer with a row of optical fiber samples is inverted on a glass plate, a certain pressure is applied on the inverted glass plate by external force, and a cutting blade is used to tightly adhere to the glass cladding of the optical fiber, and the optical fiber is cut along the contact surface of the glass part of the optical fiber and the inner coating and parallel to the optical fiber axial surface to obtain a flat inner coating. At this time, the outer coating adjacent to the flat inner coating is bonded to the adhesive layer, as shown in Figure 3 .

[0048] The application also provides a detection system for testing the curing degree of the inner coating of the optical fiber by using an infrared spectrometer, which comprises a sampling table, the above-mentioned sample structure arranged on the sampling table 7 and an infrared light source.

[0049] In some embodiments, the sampling table is a zinc selenide crystal ATR sampling table, a germanium crystal ATR sampling table or a diamond ATR sampling table.

[0050] In combination with the characteristics of the difficulty in sampling the inner coating of the optical fiber, in order to enhance the infrared signal intensity of the inner coating, in a preferred embodiment of the application, the sampling table is specially designed as an inverted prism structure, as shown in Figure 4 The surface of the sampling table in contact with the sample structure is defined as the upper bottom surface 71 of the sampling table, the upper bottom surface 71 and the lower bottom surface 72 are both rectangular, and the area of the upper bottom surface 71 is greater than that of the lower bottom surface 72. The prism structure contains two groups of opposite sides, one group of opposite sides is a rectangle with the same area, for example, Figure 4 the left side 73 and the right side 74 in FIG. 8 are rectangles with the same area; the other group of opposite sides is an isosceles trapezoid with the same area, for example, Figure 4 the front side 75 and the rear side 76 in FIG. 8 are isosceles trapezoids with the same area, and the top angle β of the isosceles trapezoid is 45° (as shown in Figure 4 FIG. 8). The lower bottom surface 72, the left side 73 and the rear side 76 are not labeled in FIG. 8). The sampling table designed in this way can realize multiple reflections, enhance the infrared reflection signal of the inner coating and improve the testing accuracy.Figure 4 L represents the length of the upper bottom surface 71 of the sampling stage, W represents the width of the upper bottom surface 71 of the sampling stage, and H represents the height of the sampling stage 7.

[0051] Figure 5 and Figure 6 are respectively the front view and side view of the detection system in a preferred embodiment of the present application. As shown in Figure 5 and Figure 6 , the cut plane 4 of the sample structure of the optical fiber to be measured is in contact with the upper bottom surface 71 of the sampling stage 7; and the total width of the sample structure of the optical fiber segment to be measured, which is laid and bonded on the bonding layer 1 in any direction, is greater than or equal to the width of the upper bottom surface 71 of the sampling stage in the same direction, so that the sample to be measured covers the entire surface of the sampling stage during testing, ensuring that there is no excessive air gap on the sampling stage, and thus ensuring that the infrared spectrometer receives sufficient infrared signals of the inner coating. The incident light 10 of the infrared light source is incident vertically from the left side 73 during detection Figure 5 , the outgoing light 11 is emitted vertically from the right side 74, and the ATR crystal sampling stage of the inverted prism structure cooperates with the specific incident direction of the infrared light source, so that the incident direction and the outgoing direction of the light signal emitted by the infrared light source during testing are perpendicular to the left and right sides of the sampling stage, respectively, thereby realizing the vertical incidence and vertical emission of the infrared light signal at the two side interfaces of the crystal, and realizing multiple reflections on the upper bottom surface and the lower bottom surface of the crystal, so as to enhance the collected infrared signals of the inner coating as much as possible, and to ensure that the infrared light signal will not cause excessive loss between the air and the crystal interface, thereby causing energy loss.

[0052] In some embodiments, the sampling stage 7 adopts a germanium crystal ATR sampling stage, and a reflective film 8 is further coated below the sampling stage 7. The refractive index of the reflective film 8 is controlled to be between 1-2 @1000 The refractive index of the germanium crystal is 4.0±0.1 @1000 The reflective film 8 and the crystal sampling stage 7 form a total reflection condition, so that the infrared light signal can be constrained inside the crystal for propagation, avoiding the scattering of the light signal at the lower bottom surface of the crystal and thus avoiding excessive energy loss, realizing multiple total reflections, and finally enhancing the intensity of the infrared light signal carrying the absorbance information of the material to be measured emitted from the inside of the crystal.

[0053] In some embodiments, the reflective film 8 is an aluminum film, which can be an aluminum film made of The film thickness is greater than 10 μm to meet the condition of interference reinforcement. The film thickness needs to meet the condition of interference reinforcement, so as to realize the design of multiple reflections at the total reflection interface, and the change peak position of the infrared spectrum of the aluminum film will not coincide with the optical fiber coating material, avoiding the interference of the absorbance information of the reflective aluminum film on the optical fiber coating to be measured.

[0054] To test the curing degree of the inner coating of optical fibers, this application improves the sample preparation method and proposes a sample structure specifically for testing the curing degree of the inner coating to obtain sufficient and complete inner coating material; it also improves the FTIR hardware structure, especially the structure of the sampling stage, thereby improving the infrared detection signal in principle; and it further optimizes the data processing method to improve the signal-to-noise ratio and avoid interference caused by fluctuations in the test environment, so as to ensure the stability and accuracy of the test results.

[0055] In one embodiment, the curing degree of the inner coating of a 125 / 250 optical fiber (cladding diameter 125 μm / inner coating diameter 190 μm / outer coating diameter 250 μm) was tested using the detection system of this application. The specific steps are as follows:

[0056] Step 1: Installation Figure 4 The germanium crystal ATR sampling stage shown uses germanium as the ATR crystal material, and its measurable spectral range is 675-4000 nm. The penetration depth of the infrared light signal is 0.66 μm at 45° & 1000°. The germanium crystal has a hardness of 550 Knoops. The sampling stage is an inverted frustum structure with rectangular upper and lower bases, the upper base having a larger area than the lower base. The left and right sides are also rectangular, while the front and rear sides are isosceles trapezoids with a 45° apex angle. The crystal has a lateral length of 30mm, a longitudinal width of 2mm, and a vertical thickness of 2mm. From the front, the germanium crystal sampling stage has a 45° inverted isosceles trapezoidal cross-section. The incident and exit directions of the infrared light signal are perpendicular to the planes containing the left and right sides of the isosceles trapezoid, ensuring perpendicular incident and exit of the infrared light signal at the crystal's interfaces. This prevents excessive energy loss due to air-crystal interface loss. A reflective film is coated beneath the crystal. The aluminum film, made of a certain material, has a refractive index of 1.7 @1000. The refractive index of germanium crystal is 4.0@1000. The reflective film and the crystal form a total internal reflection condition, which confines the infrared light signal within the crystal for propagation, preventing excessive energy loss due to scattering at the lower interface of the crystal. This achieves multiple total internal reflections, ultimately enhancing the intensity of the infrared light signal carrying the absorbance information of the material under test emitted from the crystal. The reflective film has a thickness of 50 μm. This satisfies the condition for constructive interference, enabling the design of multiple reflections at the total internal reflection interface. Furthermore, the peak positions of the infrared spectrum of the aluminum film do not coincide with those of the fiber coating material, ensuring that the absorption information of the reflective aluminum film does not interfere with the fiber coating under test.

[0057] Step 2: Turn on the infrared spectrometer and the matching test software, wait for the device initialization to complete, confirm that the device is in normal operating condition, and confirm that the device drying indicator light is in the qualified state of blue; check the optical bench state, confirm the interferogram quality, the specific steps are: open the settings page, find the diagnostic and collimation function menu bar, and perform automatic collimation of the interferometer to obtain the maximum detection signal; the infrared light signal intensity enhanced by multiple total reflections formed by the germanium crystal is fed back through the real-time intensity data of the detector signal, and the absolute value of the center peak (maximum and minimum) intensity corresponding to the horizontal coordinate 2048 position of the optical bench is displayed as 2.5V, which meets the ATR test requirements;

[0058] Step 3: Click "Collect" in the main menu, select "Experiment Settings", set the spectral scan range to 4000~675 , the number of scans to 256, the resolution to 4, and the final format to absorbance;

[0059] Step 4: Use a dust-free paper dipped in anhydrous ethanol to wipe the surface of the germanium crystal clean, let it stand for half a minute, and then collect the infrared spectrum after the anhydrous ethanol is completely volatilized. Save it as infrared spectrum a. Infrared spectrum a represents the information of water and carbon dioxide in the air (hereinafter referred to as air environment) and the germanium crystal. At this time, the germanium crystal sampling table schematic diagram is shown in Figure 7 ;

[0060] Step 5-1: Use a disposable dropper to suck a small amount of liquid coating material that is the same as the inner coating material of the optical fiber to be tested, and drop it on the surface of the upper bottom of the germanium crystal. Visually confirm that the liquid coating completely covers the crystal (the liquid coating can overflow appropriately), and there are no visible bubbles in the liquid coating. Then collect the liquid coating infrared spectrum and save it as infrared spectrum b1. Infrared spectrum b1 represents the information of the air environment, the germanium crystal, and the liquid coating. At this time, the germanium crystal sampling table schematic diagram is shown in Figure 8 ;

[0061] Step 5-2: Use a dust-free paper dipped in anhydrous ethanol to wipe the surface of the germanium crystal sampling table clean, remove the liquid coating, and let it stand for half a minute until the anhydrous ethanol is completely volatilized. Get the initial germanium crystal. Arrange a plurality of optical fibers 12 in parallel on the corresponding surface of the upper bottom of the germanium crystal sampling table. Collect the infrared spectrum of the outer coating of the optical fiber and save it as infrared spectrum b2. Infrared spectrum b1 represents the information of the air environment, the germanium crystal, and the outer coating. At this time, the germanium crystal sampling table schematic diagram is shown in Figure 9 ;

[0062] Step 6: Remove the outer coating of the sampling stage surface, use a dust-free paper dipped in anhydrous ethanol to wipe the germanium crystal sampling stage surface, and let it stand for half a minute until the anhydrous ethanol completely evaporates. Take a piece of adhesive layer material, place it on the germanium crystal surface with the adhesive surface facing down, collect the infrared spectrum of the adhesive layer and save it as infrared spectrum c. Infrared spectrum c represents the information of the air environment, germanium crystal, and adhesive layer. At this time, the germanium crystal sampling stage schematic diagram is shown in Figure 10 ; The adhesive layer is a pressure-sensitive adhesive tape made of natural rubber pressure-sensitive adhesive, which has a completely different infrared spectrum from the inner coating material of the optical fiber to be tested, and will not interfere with the infrared spectrum results of the optical fiber inner coating itself. The adhesion between the germanium crystal and the adhesive layer is 0.4N, which allows the optical fiber coating to effectively combine with the adhesive layer, but does not cause the optical fiber coating itself to peel off during the process of adhering the optical fiber. The thickness of the adhesive layer is 40μm, the width is 5mm, and the length is 100mm;

[0063] Step 7: Remove the adhesive layer, use a dust-free paper dipped in anhydrous ethanol to wipe the germanium crystal surface, and let it stand for half a minute until the anhydrous ethanol completely evaporates.

[0064] Step 8: For optical fibers with a diameter of 250μm, take 15 pieces of optical fibers to be tested, the cumulative diameter is slightly larger than the longitudinal width of the germanium crystal, and the length of the optical fiber to be tested is slightly larger than the transverse length of the germanium crystal. Use dry dust-free paper to wipe off the dust, oil stains, sweat stains, etc. on the outer surface of the optical fiber. Use a dust-free paper dipped in anhydrous ethanol to wipe the optical fiber, remove the surface foreign matter, and let it stand for half a minute until the anhydrous ethanol completely evaporates. Arrange these optical fibers closely on the adhesive surface of the adhesive layer, ensure that there is no obvious gap between the optical fibers, and the area of the optical fiber arrangement is sufficient to cover the surface of the germanium crystal. Place the adhesive layer with a row of optical fiber samples upside down on a glass plate, apply a certain pressure on the glass plate with one hand, and use a knife blade to tightly adhere to the glass cladding of the optical fiber. Cut the optical fiber parallel to the contact surface between the glass part and the inner coating of the optical fiber along the optical fiber axis, and get a flat inner coating. At this time, the outer coating adjacent to the flat inner coating is bonded to the adhesive layer, as shown in Figure 3 ;

[0065] Step 9: The prepared sample is laid on the surface of the germanium crystal with the inner coating facing the germanium crystal. The optical fiber is placed along the long edge of the germanium crystal, and the length of the optical fiber should cover the length of the germanium crystal, and the width of the optical fiber should cover the width of the germanium crystal, so as to ensure that the sample covers the entire surface of the germanium crystal. The automatic pressure rod device above the existing technology is used to apply uniform pressure to the pressure plate and the inner coating of the sample, ensuring that the inner coating of the sample is in close contact with the zinc selenide surface without large gaps, no coating or glass debris. At this time, the structure from bottom to top is reflective film-germanium crystal-fiber inner coating & fiber outer coating-adhesive layer. The infrared spectrum is collected and saved as infrared spectrum d1. Infrared spectrum d1 represents the information of air environment, germanium crystal, fiber inner coating, fiber outer coating, and adhesive layer. The schematic diagram of the detection system at this time is shown in Figure 5 and Figure 6 ;

[0066] Step 10: Repeat steps 6-9 to retest the curing degree of the inner coating of the new optical fiber. The results are saved as infrared spectrum d2.

[0067] Step 11: Open the previous spectrum b using the "File" >> "Open" function of the main menu. Use the "Peak Area Integration" tool to record the corrected peak area of the characteristic peak (wavenumber 1637 nearby) and the reference peak (wavenumber 1480 nearby) of the liquid coating, respectively, and record them as M and R.

[0068] Step 12: Open the previous spectrum d using the "File" >> "Open" function of the main menu. In the background correction item of the spectrum setting, check infrared spectrum c and infrared spectrum b2 as the background deduction of the infrared spectrum of the fiber inner coating. Then, as above, use the "Peak Area Integration" tool to record the corrected peak area of the characteristic peak (wavenumber 1637 nearby) and the reference peak (wavenumber 1480 nearby) of the fiber inner coating, respectively, and record them as and ;

[0069] Step 13: Substitute the peak area values M, R, and into formula (1) to calculate the curing degree of the inner coating of the optical fiber. The specific data is as follows:

[0070]

[0071] It can be seen that the curing degree test results of the inner coating of the optical fiber are only 0.22% different in two tests, and the stability of the test results is obviously improved compared with the conventional method.

[0072] The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A sample structure for testing the degree of cure of an inner coating of an optical fiber, the optical fiber comprising, in order, a cladding, an inner coating, and an outer coating disposed peripherally of a core, characterized by, The sample structure comprises an adhesive layer and a plurality of to-be-tested fiber segments arranged in parallel on the adhesive layer; The to-be-tested fiber segment is a fiber segment with a cutting plane, which is obtained by cutting the fiber along the contact surface of the cladding and the inner coating of the fiber and parallel to the fiber axis, the fiber segment does not contain a glass part, the glass part comprises a core and a cladding covering the core, and the cutting plane exposes the inner coating, and the side where the cutting plane is located is away from the adhesive layer.

2. The sample structure of claim 1, wherein, The adhesive layer is a pressure-sensitive adhesive tape made of natural rubber pressure-sensitive adhesive.

3. The sample structure of claim 1, wherein, The thickness of the adhesive layer is less than 60 μm, and the width is greater than 2 mm.

4. A sample preparation device for preparing a sample structure as claimed in any one of claims 1 to 3, characterized in that The cutting unit is used to cut the fiber along the contact surface of the cladding and the inner coating of the fiber and parallel to the fiber axis to obtain the to-be-tested fiber segment; the pressing unit is an external power source, which is used to press and fix the fiber during cutting; the supporting unit is used to support and fix the fiber during cutting; the supporting unit and the pressing unit clamp the fiber during cutting.

5. The sample preparation device of claim 4, wherein, The supporting unit is a glass plate; and / or the cutting unit is a cutting blade.

6. A detection system for testing the degree of cure of an optical fiber coating using an infrared spectrometer, characterized in that, The sample structure comprises an adhesive layer and a plurality of to-be-tested fiber segments arranged in parallel on the adhesive layer; 7. The detection system of claim 6, wherein, The sampling table is a zinc selenide crystal ATR sampling table, a germanium crystal ATR sampling table or a diamond ATR sampling table.

8. The detection system of claim 7, wherein, The sampling table has an inverted prism structure, the surface of the sampling table in contact with the sample structure during detection is the upper base of the sampling table, the upper base and the lower base of the sampling table are both rectangular, and the area of the upper base is greater than that of the lower base, the prism structure comprises two groups of opposite sides, one group of opposite sides is a rectangle with the same area, and the other group of opposite sides is an isosceles trapezoid with the same area, and the top angle of the isosceles trapezoid is 45°.

9. The detection system of claim 8, wherein, The cutting plane of the to-be-tested fiber in the sample structure is in contact with the upper base of the sampling table; and the total width of the to-be-tested fiber segment laid and bonded on the adhesive layer in the sample structure in any direction is greater than or equal to the width of the upper base of the sampling table in the same direction.

10. The detection system of claim 7, wherein, The sampling table is further coated with a reflective film below; the reflective film is an aluminum film with a thickness greater than 10 μm.

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