Novel large-core-diameter double-core optical fiber and preparation method thereof, and micro stress monitoring system and method

Abstract

According to the novel large-core-diameter double-core optical fiber, the preparation method and the micro-stress monitoring system and method based on the double-core optical fiber, the novel double-core optical fiber has the advantages of being large in core diameter, extremely narrow in core spacing and low in numerical aperture, strong evanescent field coupling between double cores is achieved through the extremely narrow core spacing and consistent double-core parameters, and the micro-stress monitoring system and method based on the novel large-core-diameter double-core optical fiber are obtained. Balance can be destroyed when external micro stress is sensed, obvious change of the light intensity of the double cores is caused, and high-sensitivity monitoring of the external stress is achieved through the linear relation between the light intensity ratio of the double cores and the magnitude of the external stress; the MCVD process is matched with the stacking-pulling method to prepare the double-core optical fiber with the pole-core distance, the wall thickness limit of the traditional drilling technology is broken through, the edge distance between cores of the double-core optical fiber is smaller than 3 microns, and the prepared double-core optical fiber has extremely high optical coupling sensitivity; the micro-stress monitoring system and method based on the double-core optical fiber, the low-coherence light source and the CCD detector have the advantages of being simple in structure, low in cost, rapid in response and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of special optical fiber manufacturing and optical fiber sensing technology, and particularly relates to a novel large-core double-core optical fiber and a preparation method, and a micro stress monitoring system and method based on the double-core optical fiber. BACKGROUND

[0002] Optical fiber sensing has a very broad application in civil air defense engineering, infrastructure, civil structure and the like, and as a new type of photonic device, the optical fiber stress sensor not only has the advantages of small size, light weight, high precision and corrosion resistance, but also has realized commercialization beyond the laboratory. For optical fiber stress sensing, improving the detection sensitivity has been one of the core goals pursued by the industry, especially in the field of micro stress and micro vibration sensing and monitoring, and high detection sensitivity is particularly important.

[0003] At present, multi-core optical fiber stress sensing mainly uses 19-core, 7-core and 5-core multi-core optical fibers. Such optical fibers have a large number of cores, and in the preparation process, they face problems such as complicated process, high cost, long cycle and low fault tolerance. On the premise of ensuring the sensing and monitoring performance, reducing the number of cores as much as possible can improve the product yield, shorten the production cycle and reduce the production cost.

[0004] Meanwhile, in the field of optical fiber stress sensing, optical fiber gratings, long period gratings and optical fiber interference are mainly used for sensing, and the main core principles include Bragg wavelength shift, cladding mode coupling loss change and optical path difference phase change. The above-mentioned testing methods face problems such as complex testing system, high cost and complex analysis and calculation method in the actual sensing and monitoring process. SUMMARY

[0005] Based on the above, the present application provides a novel double-core special optical fiber with a large core diameter, an extremely narrow core spacing and a low numerical aperture, which has a very high monitoring sensitivity and can be used to detect subtle stress and subtle vibration changes in the external environment. A corresponding micro stress monitoring system and method are also provided. In addition, a preparation method of the novel special optical fiber is provided, which realizes a double-core optical fiber with a core spacing less than 3 microns. The prepared double-core optical fiber has a very high optical coupling sensitivity.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a novel large-core double-core optical fiber, which comprises a core and a cladding. The cladding covers the core. The core is divided into a main core and a side core. The parameters of the main core and the side core are completely consistent. The main core is located at the geometric center of the cladding, and the side core is located beside the main core. The edge spacing of the main core and the side core is less than or equal to one tenth of the diameter of the core.

[0008] In an alternative way, the material of the cladding is pure quartz glass, the material of the core is doped quartz glass, and the core is a doped core.

[0009] In an alternative way, the numerical aperture of the core is 0.035-0.055.

[0010] In an alternative way, the diameter of the cladding is 390-410 μm, the diameter of the core is 20-35 μm, and the edge-to-edge distance between the main core and the side core is 1-3 μm.

[0011] In a second aspect, the embodiments of the present application provide a preparation method of the novel large-core dual-core optical fiber, which is applied to any of the novel large-core dual-core optical fibers and comprises the following steps.

[0012] Preparation of an optical fiber preform, which comprises a doped region on the inside and a pure quartz wall on the outside;

[0013] Polishing of the optical fiber preform, wherein most of the pure quartz wall on the outside of the optical fiber preform is polished away, and a pure quartz thin wall with a desired thickness is reserved;

[0014] Cutting of the optical fiber preform, wherein the polished optical fiber preform is cut at the midpoint of its length into two optical fiber preform sub-rods which are identical;

[0015] Casing of the optical fiber preform sub-rods, wherein the two optical fiber preform sub-rods are placed side by side in a pure quartz casing tube, the inner diameter of the pure quartz casing tube is equal to twice the outer diameter of the optical fiber preform sub-rods, and the length of the pure quartz casing tube is equal to that of the optical fiber preform sub-rods;

[0016] Filling of the pores of the pure quartz casing tube, wherein a plurality of pure quartz thin rods are inserted between the pores of the pure quartz casing tube and the two optical fiber preform sub-rods, and the pores are filled as much as possible, and the length of the pure quartz thin rods is equal to that of the optical fiber preform sub-rods;

[0017] High-temperature drawing of the optical fiber, wherein the pure quartz casing tube and the optical fiber preform sub-rods and the pure quartz thin rods in the tube are placed on a high-temperature drawing tower for high-temperature drawing, and a vacuumizing process is simultaneously performed to close the pores in the pure quartz casing tube, thereby forming the novel large-core dual-core optical fiber.

[0018] In an alternative way, the preparation of the optical fiber preform is performed by using the MCVD process.

[0019] In an alternative way, the doped region of the optical fiber preform comprises quartz, fluorine, germanium or aluminum, the numerical aperture of the novel large-core dual-core optical fiber is controlled by a deep fluorine doping process, the diameter of the doped region is 2-2.2 mm, and the thickness of the pure quartz thin wall is 50-170 μm.

[0020] In a third aspect, the embodiments of the present application provide a micro stress monitoring system based on any of the novel large-core dual-core optical fibers, comprising the novel large-core dual-core optical fiber, a light source, a detection unit and a signal processing unit, the light source serving as an input end, the detection unit at an output end through the novel large-core dual-core optical fiber, and the signal processing unit receiving and processing the dual-core optical signal received by the detection unit.

[0021] In an optional manner, the light source is an ASE light source, the detection unit is a CCD detector, and the signal processing unit is an upper computer.

[0022] In a fourth aspect, the embodiments of the present application provide a micro stress monitoring method applied to the micro stress monitoring system, comprising the following steps:

[0023] The light source is injected into the main core of the novel large-core dual-core optical fiber;

[0024] The detection unit is used to collect a dual-core optical signal image at the output end, and the dual-core optical intensities received by the signal processing unit are approximately equal when there is no external stress;

[0025] When the novel large-core dual-core optical fiber is subjected to external stress, the dual-core optical intensities decrease simultaneously, the optical intensity of the main core gradually decreases and the optical intensity of the side core gradually increases with the increase of the external stress, the signal processing unit processes the image, extracts the optical intensities of the main core and the side core, and calculates a dual-core optical intensity ratio;

[0026] The dual-core optical intensity ratio is proportional to the size of the external stress, and the signal processing unit calculates and outputs the value of the external stress according to a preset linear relationship and the value of the dual-core optical intensity ratio.

[0027] The present application has the following advantages:

[0028] (1) A novel large-core, extremely narrow core spacing and low numerical aperture dual-core optical fiber is proposed, strong evanescent field coupling between the dual cores is achieved through extremely narrow core spacing and consistent dual-core parameters, external micro stress can break the balance and cause significant changes in the dual-core optical intensity, and high sensitivity monitoring of external stress is achieved through the linear relationship between the dual-core optical intensity ratio and the size of the external stress;

[0029] (2) The MCVD process is used in combination with the stack-drawing method to prepare a dual-core optical fiber with extremely narrow core spacing, the thickness limit of the traditional drilling technology is broken, the core spacing of the dual-core optical fiber is less than 3 μm, and the prepared dual-core optical fiber has extremely high optical coupling sensitivity;

[0030] (3) A new micro stress sensing system and monitoring method based on double-core optical fiber, low-coherence light source and CCD detector are proposed, which has the advantages of simple monitoring system structure, low cost, rapid response, etc., further improving the monitoring sensitivity of micro stress and micro vibration. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments of the present application will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the contents of the embodiments of the present application and these drawings.

[0032] Figure 1 is a schematic diagram of a double-core optical fiber structure provided by the embodiments of the present application;

[0033] Figure 2 is a schematic diagram of the change of light intensity of the double-core optical fiber under the action of micro stress and micro vibration provided by the embodiments of the present application;

[0034] Figure 3 is a flow chart of the preparation method of the new large-core double-core optical fiber provided by the embodiments of the present application;

[0035] Figure 4 is a schematic diagram of the structure of the sleeved optical fiber preform sub-rod and the filled pure quartz sleeve hole provided by the embodiments of the present application;

[0036] Figure 5 is a schematic diagram of the micro stress monitoring system structure based on the double-core optical fiber provided by the embodiments of the present application;

[0037] Figure 6 is a double-core physical cross-sectional view provided by the embodiments of the present application;

[0038] Figure 7 is a double-core optical fiber sensing test output light spot diagram provided by the embodiments of the present application;

[0039] Figure 8 is a stress test double-core optical fiber light intensity distribution change diagram provided by the embodiments of the present application.

[0040] Reference signs:

[0041] 1 - fiber core; 2 - cladding; 3 - main core; 4 - side core; 5 - doped region; 6 - pure quartz thin wall; 7 - optical fiber preform sub-rod; 8 - pure quartz sleeve; 9 - pure quartz thin rod. DETAILED DESCRIPTION

[0042] The application will be described in further detail below with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the application. In addition, it should be noted that, for the purpose of description, only the parts related to the application are shown in the drawings rather than all the structures.

[0043] In the description of the application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0044] In the present application, unless otherwise explicitly specified and limited, the "upper" or "lower" of the first feature to the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the "upper", "upper" and "upper" of the first feature to the second feature include that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The "below", "below" and "below" of the first feature to the second feature include that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0045] In the description of the present embodiment, the terms "upper", "lower", "left", "right" and other orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the application. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more. In addition, the terms "first", "second" are only used to distinguish in the description and have no special meaning.

[0046] The present application provides a new large core diameter double core optical fiber, as shown in Figure 1 The present application provides a new large core diameter double core optical fiber, as shown in

[0047] Preferably, the material of the cladding 2 is pure quartz glass, the material of the core 1 is germanium-doped or aluminum-doped quartz glass, and the numerical aperture of the new large-core dual-core optical fiber is controlled in an extremely low numerical range through a deep fluorine-doping process.

[0048] Specifically, the numerical aperture of the core 1 is 0.035-0.055, the diameter of the cladding 2 is 390-410 μm, the diameter of the core 1 is 20-35 μm, and the edge-to-edge distance of the main core 3 and the side core 4 is 1-3 μm. In actual application, the light source is injected from the main core 3. Due to the extremely narrow core spacing, the low numerical aperture, and the complete consistency of the dual-core parameters, the light signal will be strongly evanescent field coupled, and after a certain distance of transmission, the light signal will be uniformly dispersed into the main core 3 and the side core 4. At this time, as shown in Figure 2 When the optical fiber is subjected to micro-stress or micro-vibration, the peak intensity ratio of the light spots in the dual core will change significantly. The change of the light spot intensity in the dual core is detected in real time by the detection unit, so that the external micro-stress can be sensed and monitored. The peak intensity ratio of the light spots in the dual core serves as a basis for judging the size of the micro-stress.

[0049] More specifically, the smaller the edge-to-edge distance of the dual core, the more the evanescent field overlaps, the stronger the coupling effect, and the faster the energy exchange. Controlling the edge-to-edge distance of the main core 3 and the side core 4 to be an extremely narrow core spacing of 1-3 μm is to realize strong coupling of the light signal.

[0050] Meanwhile, the lower the numerical aperture, the smaller the difference between the refractive index of the core 1 and the cladding 2, and the weaker the ability of the light signal to be constrained in the core 1. The evanescent field can penetrate into the cladding to a greater extent, thereby producing a stronger coupling effect. The low numerical aperture also makes the optical fiber more sensitive to bending and deformation, thereby improving the monitoring sensitivity to micro-stress and micro-vibration.

[0051] In addition, the refractive index and diameter of the main core 3 and the side core 4 must be highly consistent. If the parameters are mismatched, their propagation constants will not be equal, and the coupling efficiency will be greatly reduced or even unable to effectively couple.

[0052] The embodiment of the present application provides a preparation method of a new large-core dual-core optical fiber, which is applied to the new large-core dual-core optical fiber as shown in Figure 3 The preparation method comprises the following steps:

[0053] S101, preparing an optical fiber preform by using an MCVD process. The optical fiber preform comprises an inner doped region 5 and an outer pure quartz wall.

[0054] S102, polishing the optical fiber preform. Most of the outer pure quartz wall of the optical fiber preform is polished away, and a pure quartz thin wall 6 with a required thickness is reserved.

[0055] S103, cutting the optical fiber preform rod, cutting the polished optical fiber preform rod at its length midpoint into two identical optical fiber preform sub-rods 7;

[0056] S104, packaging the optical fiber preform sub-rods 7, as shown in the figure, placing the two optical fiber preform sub-rods 7 side by side into a pure quartz sleeve 8, the inner diameter of the pure quartz sleeve 8 is equal to twice the outer diameter of the optical fiber preform sub-rod 7, and the length of the pure quartz sleeve 8 and the optical fiber preform sub-rod 7 is equal; Figure 4

[0057] S105, filling the pores of the pure quartz sleeve 8, referring again to Figure 4 , inserting a plurality of pure quartz rods 9 between the pores of the pure quartz sleeve 8 and the two optical fiber preform sub-rods 7, filling the pores as much as possible, and the length of the pure quartz rod 9 and the optical fiber preform sub-rod 7 is equal;

[0058] S106, high-temperature drawing of optical fiber, placing the pure quartz sleeve 8 and the optical fiber preform sub-rods 7 and pure quartz rods 9 inside the tube into a high-temperature drawing tower for high-temperature drawing, and simultaneously performing vacuum pumping treatment to close the air holes in the pure quartz sleeve 8, thereby forming a dense large core diameter, extremely narrow core spacing, new type of double core optical fiber, the doping area 5 is drawn into the core 1, and the pure quartz thin wall 6, the pure quartz sleeve 8 and the pure quartz rod 9 are collectively drawn into the cladding 2.

[0059] The above-mentioned MCVD process is used in combination with the stack-and-pull method to prepare a double-core optical fiber with extremely narrow core spacing, breaking through the thickness limit of traditional drilling technology, realizing a double-core optical fiber with a core spacing of less than 3 μm, and the prepared double-core optical fiber has extremely high optical coupling sensitivity, and the obtained optical fiber needs to have good consistency, the difference between the two core diameters is ≤1 μm, the difference between the core numerical apertures is ≤0.0005, and the core spacing is ≤3 μm.

[0060] Specifically, the doping area 5 of the optical fiber preform rod contains quartz, fluorine and germanium, and the numerical aperture of the new type of large core diameter double core optical fiber is controlled to be 0.035-0.055 through a deep fluorine doping process, the diameter of the doping area 5 is 2-2.2 mm, and the thickness of the pure quartz thin wall is 50-170 μm.

[0061] More specifically, according to the diameter of the core 1 of 20-35 μm, the diameter of the doping area 5 of 2-2.2 mm, the doping area 5 is reduced to about one percent of the original size after high-temperature drawing to become the core 1; and the pure quartz thin wall 6 with a thickness of 50-170 μm is reserved, and after the two optical fiber preform sub-rods 7 are closely attached, the thickness of the two layers of pure quartz thin walls 6 is 100-340 μm, which is reduced to about 1-3 μm after being reduced to one percent of the original size, achieving the design goal of a double-core optical fiber with a core spacing of less than 3 μm.

[0062] ​The embodiment of the application provides a micro stress monitoring system based on the new large-core double-core optical fiber, which comprises the new large-core double-core optical fiber, a light source, a detection unit and a signal processing unit, the light source is used as an input end, the detection unit is used for receiving a double-core optical signal from the new large-core double-core optical fiber, and the signal processing unit is used for receiving and processing the double-core optical signal.

[0063] Preferably, as shown in the figure, the light source is an ASE light source, the detection unit is a CCD detector, and the signal processing unit is an upper computer. Figure 5 The ASE light source is a kind of low-coherence self-luminous light source, and the low-coherence caused by self-luminous can sufficiently suppress noise: in addition to the main interference signal between the two cores 1 in the optical fiber, the optical signal can also generate parasitic interference at the optical fiber end face, the connection point and the like, and the optical path difference of the parasitic interference is much larger than the coherence length of the low-coherence light, so that a stable interference signal cannot be formed, and thus is effectively suppressed, thereby greatly improving the signal-to-noise ratio and stability of the monitoring system. The CCD is a surface array detector, can simultaneously and in parallel acquire the complete two-dimensional intensity distribution of the light spots output by the two cores 1, and can intuitively and stably acquire the spatial information of the light intensity.

[0064] Specifically, the power parameter of the ASE light source is 1-10 mW, and the wavelength is 1 mu m or 1.5 mu m. The power range of 1-10 mW can provide good signal strength, ensure that the CCD detector can detect clear light spots, and has sufficient signal-to-noise ratio, and will not cause nonlinear effects or damage the optical fiber and other optical elements due to excessive power. The wavelength is selected according to the compatibility, cost and availability of the monitoring system.

[0065] The embodiment of the application provides a micro stress monitoring method applied to the micro stress monitoring system, and the method comprises the following steps.

[0066] S201, injecting the light source into the main core 3 of the new large-core double-core optical fiber through spatial coupling or fusion coupling;

[0067] S202, using the detection unit to collect a double-core optical signal image at the output end, and the double-core light intensity received by the signal processing unit is approximately equal when there is no external stress;

[0068] S203, when the new large-core double-core optical fiber is subjected to external stress, the double-core light intensity decreases simultaneously, with the increase of the external stress, the light intensity of the main core 3 gradually decreases, the light intensity of the side core 4 gradually increases, the signal processing unit processes the image, extracts the light intensity of the main core 3 and the side core 4, and calculates the double-core light intensity ratio;

[0069] S204, the double-core light intensity ratio is proportional to the size of the external stress, the signal processing unit calculates and outputs the value of the external stress according to the preset linear relationship and the value of the double-core light intensity ratio.

[0070] In a specific embodiment, a GeO2, F co-doped optical fiber preform is prepared by using MCVD process, a deep fluorine doping process is adopted, the refractive index of the doping region 5 is about 1.45785, the refractive index of pure quartz is about 1.4573, and the numerical aperture is calculated by the following formula:

[0071]

[0072] Wherein, NA is the numerical aperture, n1 is the refractive index of the doping region 5 and the core 1, and n2 is the refractive index of pure quartz. According to the above formula, the numerical aperture is about 0.04, which meets the interval of 0.035-0.055.

[0073] The pure quartz wall outside the optical fiber preform is ground as much as possible, only a 83 μm thick pure quartz thin wall is reserved, the diameter of the GeO2, F doping region 5 is about 2.17 mm, the optical fiber preform is cut into two equal optical fiber preform sub-rods 7 from the middle point, and the double core consistency of the optical fiber is ensured.

[0074] The two optical fiber preform sub-rods 7 are placed side by side in the pure quartz sleeve 8, a plurality of pure quartz rods 9 with different diameters are inserted into the pores to fill all the areas inside the pure quartz sleeve 8 as much as possible, and the optical fiber is drawn on the high-temperature drawing tower, the drawing temperature is 2000 ℃, the whole drawing process is treated in a vacuum tube, and a dense solid double-core optical fiber is formed. The actual cross section of the optical fiber is shown in Figure 6 The diameter of the main core 3 and the side core 4 is about 30 μm, the core numerical aperture is about 0.04, the edge-to-edge distance of the main core 3 and the side core 4 is about 2.3 μm, the diameter difference between the main core 3 and the side core 4 is about 0.8 μm, the numerical aperture difference is about 0.0004, and the double-core parameters have high consistency. According to the diameter of the doping region 5 of 2.17 mm and the diameter of the core 1 of 30 μm, the diameter of the doping region 5 before high-temperature drawing is 72.3 times the diameter of the core 1 after high-temperature drawing, and the thickness of the pure quartz thin wall is 83 μm. The double-core edge-to-edge distance after high-temperature drawing is 83×2÷72.3≈2.3 μm, which is consistent with the actual result.

[0075] A 10 mW, 1 μm ASE light source is injected into the main core 3 by spatial coupling, a stress applying device is placed on the optical fiber to apply variable stress to the optical fiber for sensing test, a CCD detector is used to receive the output optical signal as shown in Figure 7 , and real-time processing is performed.

[0076] It can be observed that the light intensity of the main core 3 and the side core 4 decreases simultaneously after the stress is applied, the light intensity in the main core 3 gradually decreases and the light intensity in the side core 4 gradually increases as the applied stress gradually increases, and the light intensity ratio of the main core 3 to the side core 4 shows a linear relationship with the size of the applied stress, as shown in Figure 8 . Figure 8The horizontal axis is the cladding radius (m) and the vertical axis is the time-averaged power flow, z-component (W / m 2 ), Figure 8 The left side of the diagram in the middle is the linear relationship between the ratio of the main core light intensity and the side core light intensity and the applied stress, and the right side of the diagram is a local enlarged schematic diagram at the wave peak. The monitoring system based on the novel optical fiber can achieve a minimum monitoring accuracy of 5 mN, which is significantly improved compared with the minimum detectable stress of 9.2 mN of the existing three-dimensional FBG sensor.

[0077] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the disclosure being indicated by the following claims.

[0078] It should be understood that the present disclosure is not limited to the precise structures as herein described and illustrated in the drawings, and that various modifications and changes can be made without departing from its scope. The scope of the present disclosure is limited only by the claims that follow.

Claims

1. A novel large core dual core optical fiber characterized by, The fiber core and the cladding, the cladding covers the fiber core, the fiber core is divided into a main core and a side core, the parameters of the main core and the side core are completely consistent, the main core is located at the geometric center of the cladding, the side core is located beside the main core, and the edge distance of the main core and the side core is less than or equal to one tenth of the diameter of the fiber core.

2. The novel large core dual core optical fiber according to claim 1, characterized by, The material of the cladding is pure quartz glass, and the material of the fiber core is germanium-doped or aluminum-doped quartz glass.

3. The novel large core dual core optical fiber according to claim 2, characterized by, The numerical aperture of the fiber core is 0.035-0.

055.

4. The novel large core dual core optical fiber according to claim 1, characterized by, The diameter of the cladding is 390-410 μm, the diameter of the fiber core is 20-35 μm, and the edge distance of the main core and the side core is 1-3 μm.

5. A method for manufacturing a novel large core dual core optical fiber, applied to the novel large core dual core optical fiber according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: Preparation of a fiber preform rod, the fiber preform rod comprises a doped region on the inside and a pure quartz wall on the outside; Polishing the fiber preform rod, grinding off most of the pure quartz wall on the outside of the fiber preform rod, and retaining a required thickness of the pure quartz thin wall; Cutting the fiber preform rod, cutting the polished fiber preform rod at the midpoint of its length into two fiber preform sub-rods that are exactly the same; Sleeving the fiber preform sub-rods, placing the two fiber preform sub-rods side by side in a pure quartz sleeve, the inner diameter of the pure quartz sleeve being equal to twice the outer diameter of the fiber preform sub-rods, and the lengths of the pure quartz sleeve and the fiber preform sub-rods being equal; Filling the pores of the pure quartz sleeve, inserting a plurality of pure quartz thin rods between the pores of the pure quartz sleeve and the two fiber preform rods, and filling the pores as much as possible, the lengths of the pure quartz thin rods and the fiber preform sub-rods being equal; High-temperature fiber drawing, placing the pure quartz sleeve and the fiber preform sub-rods and the pure quartz thin rods in the pure quartz sleeve in a high-temperature fiber drawing tower for high-temperature fiber drawing, and simultaneously performing vacuumizing treatment to close the pores in the pure quartz sleeve, thereby forming the new large-core double-core fiber.

6. The method of claim 5, wherein the new large core dual core optical fiber is prepared by the steps of: The preparation of the fiber preform rod adopts the MCVD process.

7. The method of claim 5, wherein the new large core dual core optical fiber is prepared by the steps of: The doped region of the fiber preform rod comprises quartz, fluorine, germanium or aluminum, the numerical aperture of the new large-core double-core fiber is controlled through a deep fluorine doping process, the diameter of the doped region is 2-2.2 mm, and the thickness of the pure quartz thin wall is 50-170 μm.

8. A microstress monitoring system based on the novel large- core dual- core optical fiber according to any one of claims 1 to 4, characterized in that, The new large-core double-core fiber, a light source, a detection unit and a signal processing unit are provided, the light source serves as an input end, the new large-core double-core fiber is used to transmit light to the detection unit at an output end, and the signal processing unit receives and processes the double-core optical signal received by the detection unit.

9. The microstress monitoring system of claim 8, wherein, The light source is an ASE light source, the detection unit is a CCD detector, and the signal processing unit is an upper computer.

10. A microstress monitoring method applied to the microstress monitoring system of claim 8 or 9, characterized in that, The method comprises the following steps: Injecting the light source into the main core of the new large-core double-core fiber; Using the detection unit at the output end to collect a double-core optical signal image, and when there is no external stress, the double-core light intensity received by the signal processing unit is approximately equal. The new large-core double-core optical fiber is subjected to external stress, the light intensity of the double-core optical fiber decreases simultaneously, with the increase of the external stress, the light intensity of the main core gradually decreases, the light intensity of the side core gradually increases, the signal processing unit processes the image, extracts the light intensity of the main core and the side core, and calculates the double-core light intensity ratio; The double-core light intensity ratio is proportional to the size of the external stress, and the signal processing unit calculates and outputs the value of the external stress according to the preset linear relationship and the value of the double-core light intensity ratio.

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