Temperature-sensing multimode optical fiber

Abstract

The utility model relates to a temperature-sensing multimode optical fiber. The temperature-sensing multimode optical fiber comprises a core layer, a flat inner cladding layer, a first transition cladding layer, a flat sunken cladding layer, a second transition cladding layer and an outer cladding layer which are sequentially arranged from inside to outside in the radial direction, the core layer and the flat inner cladding layer are both made of fluorine-germanium co-doped silicon dioxide, and the flat sunken cladding layer is made of fluorine-doped silicon dioxide; the relative refractive index difference of the core layer relative to the pure silicon dioxide is delta 1, the relative refractive index difference of the flat inner cladding layer relative to the pure silicon dioxide is delta 2, the relative refractive index difference of the flat sunken cladding layer relative to the pure silicon dioxide is delta 4, and delta 1 > delta 2 > delta 4; the relative refractive index difference delta 3 of the first transition cladding relative to the pure silicon dioxide is linearly reduced from inside to outside along the radial direction; and the relative refractive index difference delta 5 of the second transition cladding relative to the pure silicon dioxide is linearly increased from inside to outside along the radial direction. According to the invention, the problem that the stress between optical fiber interfaces is increased due to the fact that the numerical aperture is increased by highly doping germanium in order to enhance the spontaneous Raman scattering light signal detection capability of the optical fiber in the prior art can be solved.

Description

Technical Field

[0001] This application relates to the field of optical fiber technology, and in particular to a temperature-sensing multimode optical fiber. Background Technology

[0002] Distributed fiber optic sensing technology, using light waves as the carrier, optical fibers as the medium, and scattering as the mechanism, leverages the characteristics of light scattering or nonlinear effects in optical fibers that change with the external environment. It treats the measured quantity as a function of the fiber's length and position, fully utilizing the advantages of integrated fiber optic sensing and measurement. This provides a technical means to simultaneously acquire the spatial distribution and time-varying state of the measured physical quantity, enabling the acquisition and sensing of environmental parameters along the fiber optic line. Fiber optic sensing technology possesses extremely high sensitivity and accuracy, excellent resistance to electromagnetic interference, high insulation strength, and advantages such as high temperature resistance, corrosion resistance, small size, lightweight, and flexibility. In recent years, with the development of fiber optic sensor technology and the improvement of manufacturing processes, the application of fiber optic sensors has been widely promoted. Fiber optic sensors have broad applications in automatic control, online detection, and fault diagnosis in the fields of machinery, electronic instrumentation, aerospace, and oil well exploration.

[0003] Anti-Stokes scattering is the most important component of Raman scattering. It occurs when a photon from incident radiation and a thermally excited phonon simultaneously annihilate, producing a new photon with higher energy. It is highly sensitive to changes in ambient temperature. To enhance spontaneous Raman scattering signals, much research has been conducted on DTS systems to improve fiber optic transmission performance.

[0004] The sensing element in a DTS system is optical fiber, which can both transmit signals and sense changes in ambient temperature. Commonly used sensing fibers in DTS systems are single-mode and multimode fibers. Single-mode fibers have a smaller effective cross-sectional area and higher optical power density, making them prone to stimulated Raman scattering (SRS), but they only transmit one mode of light. Multimode fibers can transmit multiple modes of light and have greater transmission capacity, but their anti-Stokes signals are very weak, significantly increasing the difficulty of signal extraction and processing. Therefore, a structure needs to be designed to enhance the spontaneous Raman scattering signal of the fiber to improve detection capabilities.

[0005] A higher germanium doping level in the fiber core is beneficial for increasing the numerical aperture, thereby enhancing the ability to collect backscattered light signals. However, simply increasing the numerical aperture can easily lead to increased stress at the fiber interface. Summary of the Invention

[0006] This application provides a temperature-sensitive multimode optical fiber to solve the problem in related technologies where increasing the numerical aperture by high germanium doping leads to increased stress at the fiber interface in order to enhance the detection capability of spontaneous Raman scattering light signals in optical fibers.

[0007] In one aspect, a temperature-sensing multimode optical fiber is provided, comprising a core layer, a flat inner cladding, a first transition cladding, a flat sunken cladding, a second transition cladding, and an outer cladding arranged radially from the inside to the outside.

[0008] The core layer and the flat inner cladding are both made of fluorine-germanium co-doped silicon dioxide, and the flat sunken cladding is made of fluorine-doped silicon dioxide.

[0009] The relative refractive index difference between the core layer and pure silicon dioxide is Δ1, the relative refractive index difference between the flat inner cladding layer and pure silicon dioxide is Δ2, and the relative refractive index difference between the flat sunken cladding layer and pure silicon dioxide is Δ4, where Δ1 > Δ2 > Δ4.

[0010] The relative refractive index difference Δ3 between the first transition cladding layer and pure silicon dioxide decreases linearly from the inside to the outside along the radial direction;

[0011] The relative refractive index difference Δ5 between the second transition cladding and pure silicon dioxide increases linearly from the inside to the outside along the radial direction.

[0012] In some embodiments, the rate of change of the relative refractive index difference Δ3 of the first transition cladding layer relative to pure silicon dioxide is k1, and -0.08% / μm≤k1≤-0.02% / μm;

[0013] And / or, the rate of change of the relative refractive index difference Δ5 of the second transition cladding relative to pure silicon dioxide is k2, and 0.02% / μm≤k2≤0.08% / μm.

[0014] In some embodiments, the maximum value of the refractive index n3 of the first transition cladding is equal to the refractive index n2 of the flat inner cladding, and the minimum value is equal to the refractive index n4 of the flat depressed cladding.

[0015] And / or, the minimum refractive index n5 of the second transition cladding is equal to the refractive index n4 of the flat-depressed cladding, and the maximum refractive index n6 of the outer cladding 6 is equal to that of the outer cladding 6.

[0016] In some embodiments, the refractive index n1 of the core layer is distributed radially from the inside to the outside in an α-power function, where α is the refractive index profile distribution parameter of the core layer, and the refractive index is largest at the center of the core layer;

[0017] The relative refractive index difference between the center of the core layer and pure silicon dioxide is Δ. 中心 And 2% ≤ Δ 中心 ≤3.5%.

[0018] In some embodiments, 1.84 ≤ α ≤ 1.96.

[0019] In some embodiments, 0.65% ≤ Δ2 ≤ 0.75%;

[0020] And / or, -0.195% ≤ Δ4 ≤ -0.185%.

[0021] In some embodiments, the radius R1 of the core layer is ≤31.5 μm;

[0022] And / or, the outer diameter R2 of the flat inner cladding is ≤32μm;

[0023] And / or, the outer diameter R4 of the flat, sunken cladding is ≤34 μm.

[0024] And / or, the outer diameter of the outer cladding layer is R6, which is 62-63 μm.

[0025] In some embodiments, the first transition cladding is made of fluorine-germanium co-doped silicon dioxide;

[0026] And / or, the second transition cladding is made of fluorine-doped silicon dioxide or fluorine-germanium co-doped silicon dioxide.

[0027] In some embodiments, the outer cladding layer includes a first outer cladding layer and a second outer cladding layer arranged radially from the inside to the outside. The first outer cladding layer is made of fluorine-germanium co-doped silicon dioxide, and the second outer cladding layer is made of pure silicon dioxide. The refractive indices of the first outer cladding layer and the second outer cladding layer are equal.

[0028] In some embodiments, the outer cladding layer is provided with an acrylic resin coating, a graphene coating, and a metal coating in a radial pattern from the inside to the outside.

[0029] The beneficial effects of the technical solution provided in this application include:

[0030] This application designs a flat inner cladding between the core layer and the recessed cladding, with the relative refractive index difference of the flat inner cladding falling between that of the core layer and the recessed cladding. Firstly, this reduces the viscosity difference between the core layer and the recessed cladding, decreasing the interfacial stress between them after the numerical aperture of the core layer is increased through high germanium doping. This reduces attenuation during Anti-Stokes signal transmission, enhances the spontaneous Raman scattering signal of the optical fiber, thereby improving detection capability and increasing fiber sensing resolution and detection distance. Secondly, it effectively prevents higher-order modes from entering the recessed cladding, thus increasing the full injection bandwidth of the optical fiber, reducing latency, and improving the detection sensitivity to Anti-Stokes signals, thereby improving the spatial resolution of the optical fiber.

[0031] This application designs a first transition cladding and a second transition cladding between the flat inner cladding and the flat depressed cladding, and between the flat depressed cladding and the outer cladding, respectively. By designing the transition cladding, firstly, the problem of abnormal fluctuations in the refractive index profile caused by flowmeter counter-current can be eliminated. Secondly, it can reduce interfacial stress, reduce attenuation, improve the transmission performance of the optical fiber, and enhance its spatial resolution. Thirdly, it improves the optical fiber's ability to withstand repeated bending while avoiding the introduction of interfacial stress. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of a temperature-sensing multimode optical fiber provided in an embodiment of this application;

[0034] Figure 2 This is a diagram of a temperature-sensing multimode fiber waveguide structure provided in an embodiment of this application.

[0035] In the figure: 1. Core layer; 2. Flat inner cladding; 3. First transition cladding; 4. Flat sunken cladding; 5. Second transition cladding; 6. Outer cladding. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] To make the statement clearer and avoid any ambiguity, the refractive index is explained as follows:

[0038] In this application, the relative refractive index difference of a certain layer relative to pure silicon dioxide (or pure quartz glass) is mentioned, and the relative refractive index difference Δ is calculated using the following formula. i :

[0039]

[0040] In this application, the refractive index of the core layer 1 is defined as n1, and the relative refractive index difference of the core layer 1 relative to pure silicon dioxide is Δ1; the refractive index of the planar inner cladding layer 2 is n2, and the relative refractive index difference of the planar inner cladding layer 2 relative to pure silicon dioxide is Δ2; the refractive index of the first transition cladding layer 3 is n3, and the relative refractive index difference of the first transition cladding layer 3 relative to pure silicon dioxide is Δ3; the refractive index of the planar recessed cladding layer 4 is n4, and the relative refractive index difference of the planar recessed cladding layer 4 relative to pure silicon dioxide is Δ4; the refractive index of the second transition cladding layer 5 is n5, and the relative refractive index difference of the second transition cladding layer 5 relative to pure silicon dioxide is Δ5; the refractive index of the outer cladding layer 6 is n6, and when the outer cladding layer 6 is made of pure silicon dioxide, n6 = n 纯二氧化硅 .

[0041] For the purposes of this application, when calculating the relative refractive index difference Δ4 between the flat, depressed cladding 4 and pure silicon dioxide, n in the formula... i The refractive index n4 is the same for the flat, depressed cladding 4, and so on for the other layers.

[0042] See Figure 1 As shown, this application embodiment provides a temperature-sensing multimode optical fiber, which includes a core layer 1, a flat inner cladding 2, a first transition cladding 3, a flat sunken cladding 4, a second transition cladding 5, and an outer cladding 6 arranged sequentially from the inside to the outside along the radial direction of the optical fiber. The core layer 1 and the flat inner cladding 2 are both made of fluorine-germanium co-doped silicon dioxide, and the flat sunken cladding 4 is made of fluorine-doped silicon dioxide.

[0043] This application optimizes the waveguide structure of multimode fiber, specifically as follows: Figure 2 As shown, the relative refractive index difference Δ1 of the core layer 1, the relative refractive index difference Δ2 of the flat inner cladding layer 2, and the relative refractive index difference Δ4 of the flat sunken cladding layer 4 satisfy Δ1>Δ2>Δ4; the relative refractive index difference Δ3 of the first transition cladding layer 3 relative to pure silicon dioxide decreases linearly from the inside to the outside in the radial direction; the relative refractive index difference Δ5 of the second transition cladding layer 5 relative to pure silicon dioxide increases linearly from the inside to the outside in the radial direction.

[0044] This application designs a flat inner cladding between the core layer and the recessed cladding, with the relative refractive index difference of the flat inner cladding falling between that of the core layer and the recessed cladding. Firstly, this reduces the viscosity difference between the core layer and the recessed cladding, decreasing the interfacial stress between them after the numerical aperture of the core layer is increased through high germanium doping. This reduces attenuation during Ant i-Stokes signal transmission, enhances the spontaneous Raman scattering signal of the optical fiber, thereby improving detection capability and increasing fiber sensing resolution and detection distance. Secondly, it effectively prevents higher-order modes from entering the recessed cladding, thus increasing the full injection bandwidth of the optical fiber, reducing latency, and improving the detection sensitivity to Ant i-Stokes signals, thereby improving the spatial resolution of the optical fiber.

[0045] This application designs a first transition cladding 3 and a second transition cladding 5 between the flat inner cladding 2 and the flat recessed cladding 4, and between the flat recessed cladding 4 and the outer cladding 6, respectively. By designing these transition claddings, firstly, the problem of abnormal fluctuations in the refractive index profile caused by flowmeter counter-current can be eliminated. Secondly, it can reduce interfacial stress, lower attenuation values, improve the transmission performance of the optical fiber, and enhance its spatial resolution. Thirdly, it improves the optical fiber's ability to withstand repeated bending while avoiding the introduction of interfacial stress.

[0046] Understandably, in this application, the core layer 1 uses fluorine-germanium co-doped silicon dioxide. The introduction of germanium can increase the refractive index of the optical fiber, increase the numerical aperture of the optical fiber, increase the Ant i-Stokes signal, and improve the acquisition capability of spontaneous Raman backscattered light signals, thereby improving the spatial resolution of the optical fiber. The introduction of fluorine can compensate for the defects in the silicon dioxide crystal structure caused by the introduction of germanium in the optical fiber, thus reducing the appearance of impurity absorption peaks, thereby reducing Rayleigh scattering caused by defects in the optical fiber and improving the attenuation performance of the optical fiber. At the same time, the refractive index profile of the core layer adopts a graded structure, which can also reduce the dispersion between different modes and improve the spatial resolution of the optical fiber.

[0047] See Figure 2 As shown, the refractive index of the flat inner cladding 2 is greater than that of pure silicon dioxide.

[0048] Preferably, the rate of change of the relative refractive index difference Δ3 between the first transition cladding 3 and pure silicon dioxide is k1, and -0.08% / μm ≤ k1 ≤ -0.02% / μm. When the rate of change of the relative refractive index difference Δ3 between the first transition cladding 3 and pure silicon dioxide is within this range, fiber mode dispersion can be further reduced, thereby improving the spatial resolution of the fiber. Values ​​of k1 include, but are not limited to, -0.02% / μm, -0.04% / μm, -0.06% / μm, or -0.08% / μm.

[0049] Preferably, the rate of change of the relative refractive index difference Δ5 between the second transition cladding 5 and pure silicon dioxide is k2, and 0.02% / μm ≤ k2 ≤ 0.08% / μm. When the rate of change of the relative refractive index difference Δ5 between the second transition cladding 5 and pure silicon dioxide is within this range, fiber mode dispersion can be further reduced, thereby improving the spatial resolution of the fiber. Values ​​of K2 include, but are not limited to, 0.02% / μm, 0.04% / μm, 0.06% / μm, or 0.08% / μm.

[0050] Preferably, the maximum value of the refractive index n3 of the first transition cladding 3 is equal to the refractive index n2 of the flat inner cladding 2, and the minimum value is equal to the refractive index n4 of the flat depressed cladding 4. The minimum value of the refractive index n5 of the second transition cladding 5 is equal to the refractive index n4 of the flat depressed cladding 4, and the maximum value is equal to the refractive index n6 of the outer cladding 6.

[0051] It is understood that, since this application provides a multimode optical fiber, the refractive index n1 of its core layer 1 is distributed in a power-law function from the inside to the outside along the radial direction, where α is the refractive index profile distribution parameter of the core layer 1, and the refractive index at the center of the core layer 1 is the largest.

[0052] The refractive index n1 of core layer 1 is calculated using the following formula:

[0053]

[0054] n 中心 Let r be the refractive index at the center of core layer 1, where r = 0 and n = 0. 中心 =(1+Δ 中心 )n 纯二氧化硅 ;

[0055] Δ 中心 The relative refractive index difference between the center of core layer 1 and pure silicon dioxide;

[0056] R1 represents the relative refractive index difference of a point within core layer 1 at a distance R1 from the center of core layer 1 relative to pure silicon dioxide.

[0057] R1 is the radius of core layer 1;

[0058] r is the distance from any point within core layer 1 to the center of core layer 1.

[0059] The relative refractive index difference between the center of the core layer 1 and pure silicon dioxide is Δ. 中心 And 2% ≤ Δ 中心 ≤3.5%, the relative refractive index difference at the center of the core layer 1 is within this range, which allows the refractive index of the core layer 1 to be greater than that of silicon dioxide, thereby improving the Anti-Stokes signal of the multimode fiber; Δ 中心 The possible values ​​are, but are not limited to, 2%, 2.5%, 3%, and 3.5%.

[0060] 1.84≤α≤1.96. When α is within this range, the refractive index of the core layer 1 can be distributed in a gradually changing manner, thereby reducing intermodal dispersion and improving the spatial resolution of the fiber. Values ​​of α include, but are not limited to, 1.84, 1.86, 1.88, 1.90, 1.92, 1.94, or 1.96.

[0061] 0.65% ≤ Δ2 ≤ 0.75%; Δ2 within this range for the flat inner cladding 2 can prevent higher-order modes from entering the core layer, thereby reducing intermodal dispersion and improving the spatial resolution of the fiber. Values ​​of Δ2 include, but are not limited to, 0.65%, 0.68%, 0.71%, 0.73%, and 0.75%.

[0062] -0.195% ≤ Δ4 ≤ -0.185%. The Δ4 value of the flat, recessed cladding 4 falls within this range, ensuring that light does not leak even when bent, thereby reducing fiber optic attenuation and improving the accuracy of fiber optic signal transmission. Values ​​of Δ4 include, but are not limited to, -0.185%, -0.188%, -0.190%, -0.192%, and -0.194%.

[0063] The radius R1 of the core layer 1 is ≤ 31.5 μm. Within this radius range, the dispersion of the optical fiber can be reduced, improving the accuracy of optical fiber signal transmission. The values ​​of R1 include, but are not limited to, 31.0 μm, 31.1 μm, 31.2 μm, 31.3 μm, 31.4 μm, and 31.5 μm.

[0064] The outer diameter R2 of the flat inner cladding 2 is ≤32μm. Within this range, higher-order modes are prevented from entering the core layer, thereby reducing intermodal dispersion and improving the spatial resolution of the fiber. Values ​​of R2 include, but are not limited to, 31.5μm, 31.6μm, 31.7μm, 31.8μm, 31.9μm, and 32μm.

[0065] The outer diameter R4 of the flat, recessed cladding 4 is ≤34μm. Within this range, the outer diameter of the flat, recessed cladding 4 prevents light leakage even when bent, thereby reducing fiber attenuation and improving the accuracy of fiber signal transmission. Values ​​of R4 include, but are not limited to, 33μm, 33.2μm, 33.4μm, 33.6μm, 33.8μm, and 34μm.

[0066] The outer diameter of the outer cladding layer 6 is R6, which is 62-63 μm.

[0067] It should be particularly noted that in some embodiments provided in this application, when 2% ≤ Δ 中心 When the spatial resolution and temperature resolution are ≤3.5%, 0.65%≤Δ2≤0.75%, -0.195%≤Δ4≤-0.185%, -0.08% / μm≤k1≤-0.02% / μm, and 0.02% / μm≤k2≤0.08% / μm, the temperature-sensing multimode fiber can simultaneously meet the requirements of optimal spatial resolution and temperature resolution.

[0068] In some embodiments provided in this application, the temperature-sensing multimode fiber has an attenuation of ≤3.0dB / km at a wavelength of 850nm, ≤1.0dB / km at a wavelength of 1300nm, ≤0.5dB / km at a wavelength of 1550nm, and ≤0.6dB / km at a wavelength of 1650nm.

[0069] In some embodiments provided in this application, the temperature-sensing multimode optical fiber has a bandwidth of ≥200MHz·km at a wavelength of 850nm, ≥1000MHz·km at a wavelength of 1300nm, ≥1000MHz·km at a wavelength of 1550nm, and ≥1000MHz·km at a wavelength of 1650nm.

[0070] In some embodiments provided in this application, the temperature-sensing multimode optical fiber has a temperature resolution of ≤1.7℃ and a spatial resolution of ≤1.7m over a distance of 50km.

[0071] In this application, the first transition cladding 3 is made of fluorine-germanium co-doped silicon dioxide. By adjusting the doping amounts of fluorine and germanium, the relative refractive index difference is linearly reduced. The germanium doping amount is highest at the position where the first transition cladding 3 contacts the flat inner cladding 2, while the germanium doping amount is 0 at the position where it contacts the flat sunken cladding 4.

[0072] The second transition cladding 5 is made of fluorine-doped silicon dioxide or fluorine-germanium co-doped silicon dioxide. When fluorine-germanium co-doped silicon dioxide is used, the germanium doping level is highest at the contact point between the second transition cladding 5 and the outer cladding 6, while the germanium doping level is 0 at the contact point with the flat, sunken cladding 4.

[0073] In this application, the outer cladding layer 6 includes a first outer cladding layer and a second outer cladding layer arranged radially from the inside to the outside. The first outer cladding layer is made of fluorine-germanium co-doped silicon dioxide, which can reduce the viscosity difference between the sunken cladding layer and pure silicon dioxide, and reduce the stress at the interface. The second outer cladding layer is made of pure silicon dioxide, and the refractive indices of the first and second outer cladding layers are equal.

[0074] In this application, the outer cladding layer 6 is provided with an acrylic resin coating, a graphene coating and a metal coating in sequence from the inside to the outside along its outer radial edge.

[0075] Acrylic resin coating can protect bare optical fibers, improve their resistance to external forces, and enable them to work stably during their expected service life.

[0076] The graphene coating is relatively dense, which not only resists the entry of hydrogen to a certain extent, but also enhances its resistance to hydrogen damage.

[0077] The metal coating further improves the high-temperature resistance of optical fibers and enhances their resistance to external impacts.

[0078] The technical solutions provided in this application will be described in detail below with reference to the embodiments.

[0079] Example 1

[0080] A temperature-sensing multimode optical fiber is provided, wherein:

[0081] Core layer: Utilizing fluorine-germanium co-doped silicon dioxide, the relative refractive index difference Δ at the center of the core layer... 中心 The refractive index is 3.0%, the refractive index profile distribution parameter α of the core layer is 1.92, and the radius R1 is 31.5 μm.

[0082] Flat inner cladding: fluorine-germanium co-doped silicon dioxide with a relative refractive index difference Δ2 of 0.7% compared to pure silicon dioxide and an outer diameter R2 of 32 μm.

[0083] k1 takes a value of -0.05% / μm, and k2 takes a value of 0.05% / μm.

[0084] Flat, sunken cladding: Fluorine-doped silicon dioxide is used, with a relative refractive index difference Δ4 of -0.19% compared to pure silicon dioxide, and an outer diameter R4 of 34 μm.

[0085] Outer cladding: Made of pure silicon dioxide material, with an outer diameter R6 of 62.5 μm.

[0086] Example 2

[0087] A temperature-sensing multimode optical fiber is provided, wherein:

[0088] Core layer: Utilizing fluorine-germanium co-doped silicon dioxide, the relative refractive index difference Δ at the center of the core layer... 中心 The refractive index is 3.2%, the refractive index profile distribution parameter α of the core layer is 1.95, and the radius R1 is 31.5 μm.

[0089] Flat inner cladding: fluorine-germanium co-doped silicon dioxide with a relative refractive index difference Δ2 of 0.73% compared to pure silicon dioxide and an outer diameter R2 of 31.5 μm.

[0090] k1 takes a value of -0.04% / μm, and k2 takes a value of 0.04% / μm.

[0091] Flat, sunken cladding: Fluorine-doped silicon dioxide is used, with a relative refractive index difference Δ4 of -0.188% compared to pure silicon dioxide, and an outer diameter R4 of 34 μm.

[0092] Outer cladding: Made of pure silicon dioxide material, with an outer diameter R6 of 62.5 μm.

[0093] Example 3

[0094] A temperature-sensing multimode optical fiber is provided, wherein:

[0095] Core layer: Utilizing fluorine-germanium co-doped silicon dioxide, the relative refractive index difference Δ at the center of the core layer... 中心 The refractive index is 2.5%, the refractive index profile distribution parameter α of the core layer is 1.89, and the radius R1 is 31.5 μm.

[0096] Flat inner cladding: fluorine-germanium co-doped silicon dioxide with a relative refractive index difference Δ2 of 0.67% compared to pure silicon dioxide and an outer diameter R2 of 31.8 μm.

[0097] k1 takes a value of -0.05% / μm, and k2 takes a value of 0.05% / μm.

[0098] Flat, sunken cladding: Fluorine-doped silicon dioxide is used, with a relative refractive index difference Δ4 of -0.192% compared to pure silicon dioxide, and an outer diameter R4 of 33.6 μm.

[0099] Outer cladding: Made of pure silicon dioxide material, with an outer diameter R6 of 62.5 μm.

[0100] Comparative Example 1:

[0101] Compared to Example 1, the relative refractive index difference Δ at the center of the core layer 中心 The content is 1.5%, with no flat inner cladding, no first transition cladding, no second transition cladding, and no flat sunken cladding. Other processes and parameters are completely consistent.

[0102] Comparative Example 2:

[0103] Compared to Example 2, the relative refractive index difference Δ at the center of the core layer 中心 The content is 1.2%, with no flat inner cladding, no first transition cladding, and no second transition cladding. Other processes and parameters are completely consistent.

[0104] Comparative Example 3:

[0105] Compared to Example 3, the relative refractive index difference Δ at the center of the core layer 中心 The percentage is 1.4%, and the other processes and parameters are completely consistent.

[0106] The test was conducted according to the general specification standard for fiber optic sensors, IEC 61757:2018. Temperature resolution over a 30km range was achieved using a high-power fiber laser as the light source. The optical signal output from the filter was injected into the fiber under test via wavelength division multiplexing (WDM). The WDM module filtered out the Raman scattered light returned at each moment, separating the Stokes and Ant i-Stokes beams, and sent them to the corresponding photodetectors. The photodetectors converted their respective input optical signals into electrical signals, which were then amplified and acquired by a data acquisition card. Subsequent averaging processing was performed to obtain high signal-to-noise ratio Stokes and Ant i-Stokes waveform curves. The ratio of the two waveforms was calculated, and the corresponding temperature value at each point was obtained using the appropriate formula, thus completing a measurement of the temperature distribution of the fiber under test. The spatial resolution of the system refers to the shortest distance between two points where an external temperature change can be measured. Temperature resolution is defined as the magnitude of the temperature difference when the signal amplitude and noise amplitude are equal.

[0107] The test results are shown in Table 1 below:

[0108] Table 1

[0109] Spatial resolution (m) Temperature resolution (°C) Temperature measurement length (km) Example 1 1.5 1.0 62 Example 2 1.3 0.8 59 Example 3 1.5 0.6 64 Comparative Example 1 3.0 5.5 25 Comparative Example 2 3.2 4.5 20 Comparative Example 3 2.5 5 24

[0110] Analysis of the data in the table shows that the waveguide structure design of temperature-sensing multimode fiber has significant advantages over that of ordinary multimode fiber, and can greatly improve spatial resolution, temperature measurement distance and temperature resolution.

[0111] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0112] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0113] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A temperature-sensing multimode optical fiber, characterized in that, It includes a core layer (1), a flat inner cladding layer (2), a first transition cladding layer (3), a flat sunken cladding layer (4), a second transition cladding layer (5), and an outer cladding layer (6) arranged radially from the inside to the outside. The core layer (1) and the flat inner cladding layer (2) are both made of fluorine-germanium co-doped silicon dioxide, and the flat sunken cladding layer (4) is made of fluorine-doped silicon dioxide. The relative refractive index difference between the core layer (1) and pure silicon dioxide is Δ1, the relative refractive index difference between the flat inner cladding layer (2) and pure silicon dioxide is Δ2, and the relative refractive index difference between the flat sunken cladding layer (4) and pure silicon dioxide is Δ4, where Δ1 > Δ2 > Δ4. The relative refractive index difference Δ3 between the first transition cladding (3) and pure silicon dioxide decreases linearly from the inside to the outside along the radial direction; The relative refractive index difference Δ5 between the second transition cladding (5) and pure silicon dioxide increases linearly from the inside to the outside in the radial direction.

2. The temperature-sensing multimode optical fiber as described in claim 1, characterized in that: The rate of change of the relative refractive index difference Δ3 between the first transition cladding layer (3) and pure silicon dioxide is k1, and -0.08% / μm≤k1≤-0.02% / μm; And / or, the rate of change of the relative refractive index difference Δ5 of the second transition cladding (5) relative to pure silicon dioxide is k2, and 0.02% / μm≤k2≤0.08% / μm.

3. The temperature-sensing multimode optical fiber as described in claim 1, characterized in that: The maximum value of the refractive index n3 of the first transition cladding (3) is equal to the refractive index n2 of the flat inner cladding (2), and the minimum value is equal to the refractive index n4 of the flat depressed cladding (4). And / or, the minimum value of the refractive index n5 of the second transition cladding (5) is equal to the refractive index n4 of the flat-depressed cladding (4), and the maximum value is equal to the refractive index n6 of the outer cladding (6).

4. The temperature-sensing multimode optical fiber as described in claim 1, characterized in that: The refractive index n1 of the core layer (1) is distributed in a power-law function from the inside to the outside along the radial direction, where α is the refractive index profile distribution parameter of the core layer (1), and the refractive index of the center of the core layer (1) is the largest. The relative refractive index difference between the center of the core layer (1) and pure silicon dioxide is Δ 中心 And 2% ≤ Δ 中心 ≤3.5%.

5. The temperature-sensing multimode optical fiber as described in claim 4, characterized in that: 1.84≤α≤1.96。 6. The temperature-sensing multimode optical fiber as described in claim 1, characterized in that: 0.65% ≤ Δ2 ≤ 0.75%; And / or, -0.195% ≤ Δ4 ≤ -0.185%.

7. The temperature-sensing multimode optical fiber as described in claim 1, characterized in that: The radius R1 of the core layer (1) is ≤31.5μm; And / or, the outer diameter R2 of the flat inner cladding (2) is ≤32μm; And / or, the outer diameter R4 of the flat, sunken cladding (4) is ≤34 μm And / or, the outer diameter of the outer cladding layer (6) is R6, which is 62-63 μm.

8. The temperature-sensing multimode optical fiber as described in claim 1, characterized in that: The first transition cladding (3) is made of fluorine-germanium co-doped silicon dioxide; And / or, the second transition cladding (5) is made of fluorine-doped silicon dioxide or fluorine-germanium co-doped silicon dioxide.

9. The temperature-sensing multimode optical fiber as described in claim 1, characterized in that: The outer cladding layer (6) includes a first outer cladding layer and a second outer cladding layer arranged radially from the inside to the outside. The first outer cladding layer is made of fluorine-germanium co-doped silicon dioxide, and the second outer cladding layer is made of pure silicon dioxide. The refractive indices of the first outer cladding layer and the second outer cladding layer are equal.

10. The temperature-sensing multimode optical fiber as described in claim 1, characterized in that: The outer cladding layer (6) is provided with an acrylic resin coating, a graphene coating and a metal coating in sequence from the inside to the outside along its radial direction.

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