Fiber core diameter testing platform and method

Abstract

The invention relates to the technical field of optical fibers, and provides a fiber core diameter testing platform and method, and the platform comprises a light source, a to-be-tested optical fiber of a step structure, a light spot detector, and a high-folding coating passive optical fiber. The light outlet end of the high-refraction coating passive optical fiber is connected with the light inlet end of the optical fiber to be measured, the coating refractive index of the high-refraction coating passive optical fiber is higher than the cladding refractive index, and the fiber core refractive index is higher than the cladding refractive index; light generated by the light source enters from the light inlet end of the high-refractive-index coating passive optical fiber and is output from the light outlet end of the optical fiber to be detected; and the light spot detector is used for detecting the output light spot and determining the fiber core diameter or the step diameter of the optical fiber to be detected based on the light intensity distribution of the output light spot. According to the fiber core diameter testing platform and method provided by the invention, the light intensity of the fiber core and the light intensity of the step part are obviously compared, so that the boundary of the fiber core and the step can be identified, and the problem that the diameter of the fiber core cannot be tested by a traditional testing platform is solved.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber technology, and in particular to a fiber core diameter testing platform and method. Background Art

[0002] With the development of the optical fiber industry, there are more and more types of optical fibers, and the structure of optical fibers is no longer the traditional core plus cladding structure. Step-structured optical fibers introduce a circle of steps with a higher refractive index than the cladding around the core, which reduces the refractive index of the core relative to the steps, thereby reducing the numerical aperture of the core. Therefore, step-structured optical fibers can ensure good beam quality.

[0003] However, for optical fibers with a step structure, when a traditional test platform is used to test the core diameter, the problem of being unable to measure the core diameter will occur. Summary of the invention

[0004] The invention provides a fiber core diameter testing platform and method, which are used to solve the defect that the fiber core diameter cannot be measured in the prior art.

[0005] The present invention provides a fiber core diameter testing platform, comprising a light source, an optical fiber to be tested with a step structure, and a light spot detector, and the platform further comprises: A high-refractive-coated passive optical fiber, wherein the light-emitting end of the high-refractive-coated passive optical fiber is connected to the light-incoming end of the optical fiber to be tested, the coating refractive index of the high-refractive-coated passive optical fiber is higher than the cladding refractive index, and the core refractive index is higher than the cladding refractive index; The light generated by the light source enters from the light inlet end of the high-refractive-coated passive optical fiber and is output from the light outlet end of the optical fiber to be tested; The light spot detector is used to detect the output light spot and determine the core diameter or step diameter of the optical fiber to be tested based on the light intensity distribution of the output light spot.

[0006] According to the fiber core diameter test platform provided by the present invention, the difference between the core diameter of the high-refractive coating passive optical fiber and the core diameter of the optical fiber to be tested is within a first threshold range; or, The optical fiber to be tested has a multi-step structure, and the difference between the core diameter of the high-refractive-coated passive optical fiber and the step diameter of any step in the optical fiber to be tested is within the first threshold range.

[0007] According to the fiber core diameter testing platform provided by the present invention, the first threshold is ±2 microns.

[0008] According to the fiber core diameter testing platform provided by the present invention, the difference between the cladding diameters of the high-refractive coating passive optical fiber and the optical fiber to be tested is within the second threshold range; the difference between the core numerical apertures of the high-refractive coating passive optical fiber and the optical fiber to be tested is within the third threshold range.

[0009] According to the fiber core diameter testing platform provided by the present invention, the second threshold is ±5 microns, and the third threshold is ±0.01.

[0010] According to the fiber core diameter testing platform provided by the present invention, the light output end of the high-refractive-coated passive optical fiber is connected to the light input end of the optical fiber to be tested by fusion splicing.

[0011] According to the fiber core diameter testing platform provided by the present invention, the step refractive index of the optical fiber to be tested is lower than the core refractive index, and the step refractive index is higher than the cladding refractive index.

[0012] According to the fiber core diameter testing platform provided by the present invention, the light spot detector includes an image acquisition device and an image processing device, the image acquisition device is used to acquire a light spot image of the output light spot, and the image processing device is used to determine the light intensity distribution based on the light spot image, and determine the core diameter of the optical fiber to be tested based on the light intensity distribution.

[0013] The present invention also provides a method for testing the fiber core diameter, the method comprising: Building the fiber core diameter testing platform; Turn on the light source, so that light enters from the light input end of the high-refractive index coated passive optical fiber and is output from the light output end of the optical fiber to be tested; The output light spot is detected by using a light spot detector, and the core diameter or step diameter of the optical fiber to be tested is determined based on the light intensity distribution of the output light spot.

[0014] According to the fiber core diameter testing method provided by the present invention, if the difference between the core diameter of the high-refractive coating passive optical fiber and the core diameter of the optical fiber to be tested is within a first threshold range, the light spot detector determines the core diameter of the optical fiber to be tested based on the light intensity distribution of the output light spot; If the optical fiber to be tested has a multi-step structure, and the difference between the core diameter of the high-refractive-coated passive optical fiber and the step diameter of any step in the optical fiber to be tested is within the first threshold range, the light spot detector determines the step diameter of any step in the optical fiber to be tested based on the light intensity distribution of the output light spot.

[0015] The fiber core diameter testing platform and method provided by the present invention connect the light output end of the high-refractive-coated passive optical fiber with the light input end of the optical fiber to be tested. The light generated by the light source enters from the light input end of the high-refractive-coated passive optical fiber and is output from the light output end of the optical fiber to be tested, thereby ensuring that the light intensity of the fiber core and the step part has a very obvious contrast, so that the boundary between the fiber core and the step can be identified by the processing software.

[0016] The fiber core diameter test platform and method provided by the present invention solve the problem that the traditional test platform cannot test the core diameter of the step-structured refractive index distribution optical fiber. It can also be used to test the step diameters of each level of a multi-step structure, solving the problem that the traditional test platform cannot test the step diameters of each level of a multi-step structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is a schematic diagram of the optical fiber structure in the related technology.

[0019] Figure 2 It is a light path diagram of a test platform in related technology.

[0020] Figure 3 It is the light intensity distribution diagram obtained by traditional structure optical fiber in traditional test platform.

[0021] Figure 4 It is a light propagation route map of a stepped optical fiber in a traditional test platform.

[0022] Figure 5 It is the end face spot diagram of the optical fiber to be tested.

[0023] Figure 6 This is one of the schematic diagrams of the fiber core diameter testing platform provided by the present invention.

[0024] Figure 7 It is a schematic diagram of the refractive index distribution of the optical fiber to be tested and the high-refractive index coated passive optical fiber provided by the present invention.

[0025] Figure 8 It is a light propagation route map of the fiber core diameter testing platform provided by the present invention.

[0026] Fig. 9 It is a schematic diagram of the light spot obtained by the fiber core diameter testing platform provided by the present invention.

[0027] Fig.10 This is the second schematic diagram of the fiber core diameter testing platform provided by the present invention.

[0028] Fig.11 It is the traditional method to test the spot pattern.

[0029] Fig.12 This is the spot diagram obtained by the test platform provided by the present invention.

[0030] Fig.13 It is the refractive index distribution diagram of the optical fiber to be tested with a multi-step structure.

[0031] Fig.14 It is the refractive index distribution diagram of the optical fiber to be tested with a multi-step structure and the high-refractive index coated passive optical fiber. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In the description of the embodiments of the present invention, 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, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0034] Figure 1 It is a schematic diagram of the optical fiber structure in the related technology, such as Figure 1 As shown in the figure, the left side is the traditional structure fiber, and the right side is the step structure fiber. The reason for making the step structure is that this type of fiber needs to meet two requirements: one is that it needs a high ion doping concentration to ensure high absorption characteristics; the other is that it needs a lower core numerical aperture to ensure good beam quality.

[0035] The traditional structure of optical fiber cannot meet these two requirements at the same time, because although the high ion doping concentration ensures the high absorption characteristics of the optical fiber, the higher the ion doping concentration, the higher the refractive index of the core, which increases the numerical aperture of the core part, and the optical fiber cannot guarantee good beam quality. The step-structured optical fiber introduces a circle of steps with a higher refractive index than the cladding around the core, which reduces the refractive index of the core relative to the steps, thereby reducing the numerical aperture of the core. Therefore, the step-structured optical fiber can meet these two requirements at the same time.

[0036] However, the step structure will bring a problem, that is, the diameter of the core part cannot be tested. The reasons for this are as follows: Figure 2 This is the optical path diagram of the test platform in the related technology. The optical path of the traditional test platform is as follows Figure 2As shown in the figure, from left to right are the light source, the optical fiber to be tested, the spot detector and the processing software. During the test, light is passed through one end face of the optical fiber to be tested, and the coating of the optical fiber to be tested is removed and coated with high-refractive glue. The light-emitting end face is obtained from the other end of the optical fiber to be tested, and the end face light intensity distribution is obtained through the spot detector. The processing software determines the core and cladding boundaries based on the obvious light intensity difference boundaries detected by the spot detector, thereby calculating the core and cladding diameters.

[0037] For traditional structure optical fiber, traditional test platforms are applicable. For traditional structure optical fiber, since the core refractive index is higher than the cladding refractive index, the light transmitted from the end face into the core satisfies the total reflection principle and can be stably transmitted in the core with less light loss. However, since the cladding is coated with a layer of high refractive index glue with a higher refractive index than the cladding, the total reflection condition of the cladding light is destroyed, resulting in the inability to stably transmit in the cladding and the loss of most of the light when entering the coating. As a result, the light intensity of the core and cladding captured by the spot detector will have obvious differences in strength, and the spot end face diagram will be as follows: Figure 3 As shown, Figure 3 This is the light intensity distribution diagram of traditional structure optical fiber in traditional test platform. Image processing software can find the boundary between the core and cladding through the difference of light intensity. Then, through certain algorithms, the diameter of the core and cladding can be calculated.

[0038] However, for optical fibers with step structures, when using traditional test platforms to test the core diameter, the problem of being unable to measure the core diameter will occur. Figure 4 It is the light propagation route map of the step-structured optical fiber in the traditional test platform, such as Figure 4 As shown: 1. The light entering the core of the optical fiber to be tested from the end face can be transmitted stably with almost no light loss because the core refractive index is greater than the step refractive index, which satisfies the total reflection condition; 2. The light that enters the step of the optical fiber to be tested from the end face can be transmitted stably with almost no light loss because the refractive index of the step is greater than the refractive index of the cladding, which satisfies the total reflection condition; 3. The light entering the cladding from the end face has a high refractive index lower than that of the high refractive index because the cladding is coated with high refractive loss resin, which destroys the total reflection condition and cannot be transmitted stably, resulting in a large amount of light loss.

[0039] The light in the core and step parts can be transmitted stably, but the light in the cladding part cannot be transmitted stably. This results in no light intensity difference between the core and step parts, while the light intensity in the cladding part is weak. In this case, the end face of the optical fiber to be tested is Figure 5As shown in the figure, since there is almost no light intensity difference between the cladding and the step part, the processing software cannot find the boundary between the core and the step part, but can only find the boundary between the step and the cladding, so it can only calculate the diameter of the step and the cladding, but cannot calculate the diameter of the core part.

[0040] In view of the above problems, an embodiment of the present invention provides a fiber core diameter testing platform. Figure 6 FIG. 1 is one of the schematic diagrams of the fiber core diameter testing platform provided by the present invention, such as Figure 6 As shown, the platform includes a light source, a stepped optical fiber to be tested and a spot detector, and the platform also includes: A high-refractive-coated passive optical fiber, wherein the light-emitting end of the high-refractive-coated passive optical fiber is connected to the light-incoming end of the optical fiber to be tested, the coating refractive index of the high-refractive-coated passive optical fiber is higher than the cladding refractive index, and the core refractive index is higher than the cladding refractive index; The light generated by the light source enters from the light inlet end of the high-refractive-coated passive optical fiber and is output from the light outlet end of the optical fiber to be tested; The light spot detector is used to detect the output light spot and determine the core diameter or step diameter of the optical fiber to be tested based on the light intensity distribution of the output light spot.

[0041] Specifically, Figure 7 Schematic diagram of the refractive index distribution of the optical fiber to be tested and the high-refractive index coated passive optical fiber provided by the present invention, such as Figure 7 As shown, the upper part is a schematic diagram of the refractive index distribution of the optical fiber to be tested with a step structure, and the lower part is a schematic diagram of the refractive index distribution of the high-refractive-coated passive optical fiber. The step refractive index of the optical fiber to be tested is lower than the core refractive index, and the step refractive index is higher than the cladding refractive index. The high-refractive-coated passive optical fiber itself is a non-step structure, that is, it has only two layers of structure, the core and the cladding. The coating refractive index of the high-refractive-coated passive optical fiber is higher than the cladding refractive index, and the core refractive index is higher than the cladding refractive index. The optical fiber to be tested and the high-refractive-coated passive optical fiber can be connected by fusion or by coupling, and the embodiments of the present invention do not specifically limit this.

[0042] Figure 8 It is a light propagation route map of the fiber core diameter test platform provided by the present invention. Figure 8As shown, in this embodiment, part of the light emitted by the light source enters the cladding of the high-refractive index coated passive optical fiber, and part of the light enters the core of the high-refractive index coated passive optical fiber. The light entering the cladding cannot be stably transmitted because the refractive index of the cladding is lower than the refractive index of the coating and the cladding does not meet the total reflection condition. Most of it will be lost, and thus cannot enter the step of the optical fiber to be tested, resulting in weak light intensity on the step. The light entering the core of the step stripper meets the total reflection condition because the core refractive index is higher than the refractive index of the cladding. Therefore, the light transmitted by the core can be stably transmitted without being lost, thereby ensuring that the light intensity in the core of the optical fiber to be tested is strong, thereby ensuring that the light intensity of the core and the step part has a very obvious contrast, so that the boundary between the core and the step can be identified by the processing software. Fig. 9 It is a schematic diagram of the light spot obtained by the fiber core diameter testing platform provided by the present invention.

[0043] Preferably, the difference between the core diameter of the high-refractive-coated passive optical fiber and the core diameter of the optical fiber to be tested is within a first threshold range; or, The optical fiber to be tested has a multi-step structure, and the difference between the core diameter of the high-refractive-coated passive optical fiber and the step diameter of any step in the optical fiber to be tested is within a first threshold range.

[0044] Specifically, the fiber core diameter test platform provided by the embodiment of the present invention can not only test the core diameter of the optical fiber to be tested with a step structure, but can also be used to test the diameter of each step of a multi-step structure, thereby solving the problem that traditional test platforms cannot test the diameter of each step of a multi-step structure.

[0045] If the core diameter of the high-refractive-coated passive optical fiber is close to the core diameter of the optical fiber to be tested, that is, when the difference between the core diameter of the high-refractive-coated passive optical fiber and the core diameter of the optical fiber to be tested is within the first threshold range, the core diameter of the optical fiber to be tested can be tested by light intensity distribution.

[0046] If the core diameter of the high-refractive-coated passive optical fiber is close to the step diameter of any step in the optical fiber to be tested, that is, when the difference between the core diameter of the high-refractive-coated passive optical fiber and the step diameter of any step in the optical fiber to be tested is within the first threshold range, the step diameter of any step in the optical fiber to be tested can be tested by light intensity distribution.

[0047] That is, for an optical fiber with a multi-layer step structure, the test platform provided in the embodiment of the present invention can be used to measure the diameter of any step. It is only necessary to select a high-refractive-coated passive optical fiber with a core diameter close to the diameter of the step to measure the diameter of the step at that level.

[0048] Here, the first threshold value may be preset. Preferably, the first threshold value is ±2 micrometers.

[0049] In some embodiments, the difference between the cladding diameters of the high-refractive-coated passive fiber and the optical fiber to be tested is within a second threshold range; the difference between the core numerical apertures of the high-refractive-coated passive fiber and the optical fiber to be tested is within a third threshold range.

[0050] Specifically, when the cladding diameter and core numerical aperture of the high-refractive-coated passive optical fiber are relatively close to those of the optical fiber to be tested, it can further ensure that most of the light in the optical fiber to be tested is stably transmitted in the core of the optical fiber to be tested, and a very small part is transmitted in the steps and cladding. The light intensity in the core of the optical fiber to be tested is relatively strong, thereby ensuring that there is a clear contrast in the light intensity between the core and the step part, so that the boundary between the core and the step can be identified by the processing software.

[0051] Here, the second threshold value can be represented by the difference between the cladding diameters of the high-refractive coating passive optical fiber and the optical fiber to be tested, and the third threshold value can be represented by the ratio of the core numerical apertures of the high-refractive coating passive optical fiber and the optical fiber to be tested. The second threshold value and the third threshold value can be preset.

[0052] Preferably, the second threshold is ±5 microns and the third threshold is ±0.01.

[0053] Preferably, the light output end of the high-refractive-coated passive optical fiber is connected to the light input end of the optical fiber to be tested by fusion splicing, which is fast, convenient, and can save costs.

[0054] In some embodiments, the spot detector includes an image acquisition device and an image processing device, the image acquisition device is used to acquire a spot image of the output spot, and the image processing device is used to determine the light intensity distribution based on the spot image, and determine the core diameter of the optical fiber to be tested based on the light intensity distribution.

[0055] Based on any of the above embodiments, a method for testing a fiber core diameter is provided, including: S1, build a fiber core diameter test platform. Select a high-refractive-coated passive fiber that matches the fiber to be tested. The characteristics of the high-refractive-coated passive fiber are: first, the high-refractive-coated passive fiber is actually a high-refractive-coated passive fiber, that is, the fiber coating refractive index is higher than the cladding refractive index; second, the cladding light stripper itself is a non-step structure, that is, it has only two layers of structure, the core and the cladding, and the core numerical aperture (NA) is close to the NA of the step structure refractive index fiber core. The cladding diameter of the high-refractive-coated passive fiber is close to that of the fiber to be tested.

[0056] Take 0.5-1m high-fold passive optical fiber and fuse it with 0.2-0.5m long step optical fiber to be tested. The un-fused end of the high-fold passive optical fiber faces the light source and is fixed, and the un-fused end of the step optical fiber to be tested faces the camera and is fixed.

[0057] Fig.10This is the second schematic diagram of the fiber core diameter testing platform provided by the present invention. Fig.10 As shown, from left to right are the light source, high-refractive-coated passive optical fiber, the optical fiber to be tested, and the light spot detector (including camera and processing software).

[0058] S2, turn on the light source, so that light enters from the light input end of the high-refractive index coated passive optical fiber and is output from the light output end of the optical fiber to be tested.

[0059] The light source is an ordinary incandescent light source. The difference between the cladding diameter of the passive high-refractive coated optical fiber and the cladding diameter of the step optical fiber to be tested is ±5 microns, the NA difference is ±0.01, and the refractive index of the coating material is higher than the refractive index of the cladding to destroy the total reflection condition of the cladding.

[0060] S3, using a spot detector to detect the output spot, and determining the core diameter or step diameter of the optical fiber to be tested based on the light intensity distribution of the output spot. The camera is used to photograph the end face of the optical fiber to be tested, and the image processing software is used to calculate the core diameter or step diameter of the step optical fiber to be tested through the light intensity distribution of the end face of the optical fiber to be tested.

[0061] If the difference between the core diameter of the high-refractive-coated passive optical fiber and the core diameter of the optical fiber to be tested is within a first threshold range, the spot detector determines the core diameter of the optical fiber to be tested based on the light intensity distribution of the output light spot.

[0062] The present invention has practical application results. Different methods are used to test optical fibers with a core design diameter of 25 microns, a step design diameter of 42 microns, and a cladding design diameter of 300 microns. The test results are shown in Table 1.

[0063] Table 1

[0064] Fig.11 It is the traditional method to test the spot pattern. Fig.12 This is the spot diagram obtained by the test platform provided by the present invention. From the spot diagrams and test results of the two methods, it can be seen that when using the traditional test platform, the core diameter test value is 42.2, which is actually the diameter of the step, not the core diameter. When using the test platform of the present invention, the core diameter is 25.2, which is consistent with the core design value. This can also be seen from the spot diagram. When using the test platform of the present invention, the spot measured has a clear contrast in light intensity between the step part and the core part, and its diameter can be easily obtained.

[0065] In some embodiments, if the optical fiber to be tested has a multi-step structure, and the difference between the core diameter of the high-refractive-coated passive optical fiber and the step diameter of any step in the optical fiber to be tested is within a first threshold range, the spot detector determines the step diameter of any step in the optical fiber to be tested based on the light intensity distribution of the output light spot.

[0066] Fig.13 It is the refractive index distribution diagram of the optical fiber to be tested with a multi-step structure. For a multi-step optical fiber with a more complex core structure, if you want to test the core or a certain step of the optical fiber, you only need to select a high-refractive index passive optical fiber with a core diameter close to the diameter of the step to measure its accurate diameter. Fig.14 It is the refractive index distribution diagram of the optical fiber to be tested and the high-refractive-coating passive optical fiber with a multi-step structure. To test the diameter of step 1, the refractive index distribution of the selected high-refractive-coating passive optical fiber is as follows: Fig.14 As shown in the figure below.

[0067] By analogy, using the test platform of the present invention, if the step diameter needs to be tested, the corresponding high-refractive-coated passive optical fiber can be selected to measure it.

[0068] The test platform provided by the embodiment of the present invention solves the problem that the traditional test platform cannot test the core diameter of the step-structured refractive index distribution optical fiber. It can also be used to test the step diameters of each level of a multi-step structure, solving the problem that the traditional test platform cannot test the step diameters of each level of a multi-step structure.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber core diameter test platform, comprising a light source, a step-structured optical fiber to be tested, and a spot detector, characterized in that: The platform also includes: A high-refractive-coated passive optical fiber, wherein the light-emitting end of the high-refractive-coated passive optical fiber is connected to the light-incoming end of the optical fiber to be tested, the coating refractive index of the high-refractive-coated passive optical fiber is higher than the cladding refractive index, and the core refractive index is higher than the cladding refractive index; The light generated by the light source enters from the light inlet end of the high-refractive-coated passive optical fiber and is output from the light outlet end of the optical fiber to be tested; The light spot detector is used to detect the output light spot and determine the core diameter or step diameter of the optical fiber to be tested based on the light intensity distribution of the output light spot.

2. The fiber core diameter testing platform according to claim 1, characterized in that: The difference between the core diameter of the high-refractive-coated passive optical fiber and the core diameter of the optical fiber to be tested is within a first threshold range; or, The optical fiber to be tested has a multi-step structure, and the difference between the core diameter of the high-refractive-coated passive optical fiber and the step diameter of any step in the optical fiber to be tested is within the first threshold range.

3. The fiber core diameter testing platform according to claim 2, characterized in that: The first threshold is ±2 microns.

4. The fiber core diameter testing platform according to claim 1, characterized in that: The difference between the cladding diameters of the high-refractive coating passive optical fiber and the optical fiber to be tested is within a second threshold range; the difference between the core numerical apertures of the high-refractive coating passive optical fiber and the optical fiber to be tested is within a third threshold range.

5. The fiber core diameter testing platform according to claim 4, characterized in that: The second threshold is ±5 micrometers, and the third threshold is ±0.

01.

6. The fiber core diameter testing platform according to claim 1, characterized in that: The light output end of the high-refractive-coated passive optical fiber is connected to the light input end of the optical fiber to be tested by fusion splicing.

7. The fiber core diameter testing platform according to claim 1, characterized in that: The step refractive index of the optical fiber to be tested is lower than the core refractive index, and the step refractive index is higher than the cladding refractive index.

8. The fiber core diameter testing platform according to claim 1, characterized in that: The light spot detector includes an image acquisition device and an image processing device. The image acquisition device is used to acquire a light spot image of the output light spot. The image processing device is used to determine the light intensity distribution based on the light spot image and determine the core diameter of the optical fiber to be tested based on the light intensity distribution.

9. A method for testing a fiber core diameter, characterized in that: The method comprises: Construct a fiber core diameter testing platform as claimed in any one of claims 1 to 8; Turn on the light source, so that light enters from the light input end of the high-refractive index coated passive optical fiber and is output from the light output end of the optical fiber to be tested; The output light spot is detected by using a light spot detector, and the core diameter or step diameter of the optical fiber to be tested is determined based on the light intensity distribution of the output light spot.

10. The fiber core diameter testing method according to claim 9, characterized in that: If the difference between the core diameter of the high-refractive-coated passive optical fiber and the core diameter of the optical fiber to be tested is within a first threshold range, the light spot detector determines the core diameter of the optical fiber to be tested based on the light intensity distribution of the output light spot; If the optical fiber to be tested has a multi-step structure, and the difference between the core diameter of the high-refractive-coated passive optical fiber and the step diameter of any step in the optical fiber to be tested is within the first threshold range, the light spot detector determines the step diameter of any step in the optical fiber to be tested based on the light intensity distribution of the output light spot.

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