Optical fiber with scattering enhancement characteristic and low loss characteristic and preparation method

Abstract

The invention discloses an optical fiber with scattering enhancement characteristic and low loss characteristic and a preparation method, the optical fiber comprises a fiber core, a cladding and a low-loss ultraviolet curing coating which are sequentially arranged from inside to outside, nano points are distributed in the fiber core, and at least one metal is doped in the nano points. The technical bottleneck that low loss and strong scattering cannot coexist is broken through innovatively through collaborative design of a fiber core and a cladding material (a fluoride and silicon oxide composite fiber core and a cladding of silicon fluoride glass), precise regulation and control of nanodots (the size is 20-50 nm and erbium and germanium are doped) and refractive index distribution optimization, the loss is reduced to the theoretical limit 0.14 dB / km in the 1550 nm waveband, and the loss is reduced to the theoretical limit 0.14 dB / km in the 1550 nm waveband. And the rayleigh scattering intensity is improved by about 30%, the compatibility of scattering enhancement and low loss is realized for the first time, the problem that a single optical fiber cannot meet the requirements of long-distance communication and high-sensitivity sensing at the same time is solved, and the requirements of the fields of optical fiber sensing and long-distance optical communication are met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fibers, and particularly relates to an optical fiber with scattering enhancement characteristics and low-loss characteristics and a preparation method. BACKGROUND

[0002] In the actual application of optical fiber technology, there is a significant conflict between the core requirements of optical fiber performance in the fields of optical communication and optical fiber sensing: In the field of optical communication, especially in the 1550nm band, the optical fiber needs to achieve a theoretical loss limit of 0.14dB / km to ensure long-distance signal transmission, which requires the optical fiber material to be pure and the structure to be uniform, and the signal attenuation caused by scattering to be reduced as much as possible. In the field of optical fiber sensing, strong scattering characteristics (such as Rayleigh scattering) are relied on to improve sensitivity, and existing technologies often enhance scattering by introducing doping or structural defects, which inevitably leads to a significant increase in transmission loss.

[0003] This technical bottleneck that "low loss and strong scattering cannot coexist" makes existing solutions need to deploy independent optical fibers for communication and sensing, which not only increases system complexity and cost, but also makes it difficult to achieve efficient integration of sensing and communication data.

[0004] Based on this, the application discloses an optical fiber with scattering enhancement characteristics and low-loss characteristics and a preparation method. SUMMARY

[0005] To solve the problems in the prior art, the purpose of the application is to provide an optical fiber with scattering enhancement characteristics and low-loss characteristics and a preparation method.

[0006] To achieve the above-mentioned purposes and achieve the above-mentioned technical effects, the technical solution adopted by the application is: An optical fiber with scattering enhancement characteristics and low-loss characteristics, comprising a core, a cladding and a low-loss ultraviolet curing coating arranged in order from inside to outside, wherein the core is distributed with nanodots, and at least one metal is doped in the nanodots.

[0007] Further, the core comprises a central region and an outer edge region arranged in order from inside to outside, and the refractive index of the outer edge region is 0.1%-0.2% lower than that of the central region.

[0008] Further, the diameter of the core is 8.2μm, the radius of the central region is 0-2μm, and the radius of the outer edge region is 2-4.1μm.

[0009] Further, the core is uniformly distributed with nanodots with a size of 20-50nm.

[0010] Further, the nanodots are doped with erbium and germanium, the doping concentration of erbium is 50-80 ppm, and the doping concentration of germanium is 20000-30000 ppm.

[0011] Further, the core is made of a composite material doped with fluoride and silicon oxide, and the molar ratio of fluoride to silicon oxide is 0.8%-1.5%.

[0012] Further, the cladding is made of low-refractive-index fluorinated silicon glass, and the doping concentration of fluorine in the cladding is 3%-5%.

[0013] Further, the refractive index of the cladding is 0.3%-0.5% lower than that of the core.

[0014] Further, the thickness of the low-loss ultraviolet curing coating is 25-30 microns.

[0015] The application also discloses a preparation method of the optical fiber with the scattering enhancement characteristic and the low-loss characteristic. 1) Preform manufacturing: First, a chemical vapor deposition method is used to form a composite material substrate doped with fluoride and silicon oxide in the core area by precisely controlling the deposition temperature and gas flow, and erbium and germanium doping is introduced to uniformly distribute nanodots with a size of 20-50 nm in the core. Then, low-refractive-index fluorinated silicon glass material is deposited outside the core to form a cladding; 2) Drawing: The preform obtained in step 1) is drawn into an optical fiber, and the size precision of the core and the cladding is strictly controlled; 3) Coating and packaging: A low-loss ultraviolet curing coating with a thickness of 25-30 microns is coated outside the optical fiber obtained in step 2), and the optical fiber is packaged after ultraviolet curing to form the required optical fiber with the scattering enhancement characteristic and the low-loss characteristic.

[0016] Compared with the prior art, the application has the following advantages: The application discloses an optical fiber with scattering enhancement characteristic and low-loss characteristic and a preparation method, innovatively breaks the technical bottleneck that low loss and strong scattering cannot coexist through the collaborative design of core and cladding materials (fluoride and silicon oxide composite core, fluorinated silicon glass cladding), precise regulation of nanodots (size of 20-50 nm and doped with erbium and germanium), and optimization of refractive index distribution, reduces the loss to the theoretical limit of 0.14 dB / km at the 1550 nm waveband, and increases the Rayleigh scattering intensity by about 30%, which is the first time to realize the compatibility of scattering enhancement and low loss, solves the problem that a single optical fiber cannot simultaneously meet the needs of long-distance communication and high-sensitivity sensing, and meets the needs of the optical fiber sensing and long-distance optical communication fields. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic diagram of the three-dimensional structure of the present application; Figure 2 is a cross-sectional view of the present application; Figure 3 is a flow chart of the present application; Figure 4 is a schematic diagram of the working principle of scattering and low loss in the present application; Figure 5 is a diagram of the relationship between the nanodot size and the performance of the optical fiber of the present application; Figure 6 is a diagram of the relationship between the fluorine doping concentration and the performance of the cladding of the present application. DETAILED DESCRIPTION

[0018] The present application will be described in detail below so that the advantages and features of the present application can be more easily understood by those skilled in the art, and the scope of protection of the present application can be more clearly defined.

[0019] The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0020] As shown in Figures 1-6 , the present application discloses an optical fiber with scattering enhancement and low loss characteristics, comprising a core 1, a cladding 2 and a low-loss ultraviolet curing coating 3 arranged in order from inside to outside, the core 1 is uniformly distributed with nanodots with a size of 20-50 nm with high scattering enhancement inside, and at least one metal is doped in the nanodots.

[0021] In some embodiments, the core 1 is made of a composite material doped with fluoride and silicon oxide, specifically a glassy composite material formed by fluoride and silicon oxide, wherein fluoride is selected from MgF2 or CaF2, and mixed with SiO2 at a molar ratio of 0.8%-1.5% to form a stable network structure, and the composite material has high light transmittance (1550 nm waveband transmittance ≥ 99.9%) and mechanical stability (Young's modulus ≥ 70 GPa).

[0022] In some embodiments, the nanodots are doped with erbium and germanium, the doping concentration of erbium (Er) is 50-80 ppm, and the doping concentration of germanium (Ge) is 20,000-30,000 ppm, to enhance the Rayleigh scattering signal at 1550 nm wavelength.

[0023] Erbium doped at 1550nm waveband has strong absorption-radiation characteristics, which can enhance the Rayleigh scattering cross section, and germanium doped can further strengthen the scattering effect by adjusting the refractive index gradient.

[0024] In some embodiments, the fiber core 1 includes a central region 1-1 and an outer edge region 1-2 arranged in order from inside to outside, the diameter of the fiber core 1 is 8.2μm, the radius of the central region 1-1 is 0-2μm, and the radius of the outer edge region 1-2 is 2-4.1μm. The fiber core 1 adopts a step refractive index design, the central region retains high scattering characteristics, the nanodot density is high (10 15 / cm 3 ), the refractive index is 1.468, which serves as the main scattering center, and the refractive index of the outer edge region 1-2 is 0.1%-0.2% lower than that of the central region 1-1, the nanodot density is reduced by 30%, and the scattering loss of the optical signal at the edge is reduced.

[0025] In some embodiments, the cladding 2 is made of low-refractive-index fluorinated silicon glass, the doping concentration of fluorine in the cladding is 3%-5%, the infrared absorption is reduced (absorption loss at 1550nm waveband ≤0.02dB / km) by fluorine doping, and the chemical stability is improved (salt spray corrosion resistance level ≥1000h), the refractive index of the cladding 2 is 0.3%-0.5% lower than that of the fiber core 1, and the optical signal is effectively constrained in the fiber core 1 for transmission.

[0026] In some embodiments, the thickness of the low-loss ultraviolet curing coating 3 is 25-30μm, the low-loss ultraviolet curing acrylate coating is used, and after being cured by 365nm ultraviolet light with a power of 500-600mW / cm 2 , a uniform and dense protective layer is formed.

[0027] The refractive index of the low-loss ultraviolet curing coating 3 is 1.52, which is matched with the cladding 2 to reduce interface reflection, the Young's modulus is ≥1.2GPa, and the tensile strength is ≥80MPa, which can withstand ±0.5% strain without breaking.

[0028] The optical fiber disclosed in the present application has scattering enhancement characteristics and low loss characteristics, and the optical loss at 1550nm waveband is less than or equal to 0.14dB / km.

[0029] As shown in Figure 3 , the present application also discloses a preparation method of an optical fiber with scattering enhancement characteristics and low loss characteristics, comprising the following steps: 1) Preform manufacturing: First, using chemical vapor deposition method, by precisely controlling the deposition temperature and gas flow, the deposition temperature is controlled at 1300-1400℃, the core area is formed by fluorinated compound material matrix doped with silicon oxide, and erbium and germanium are introduced to make the nanodots with a size of 20-50nm uniformly distributed in the core, which lays the foundation for the subsequent scattering enhancement characteristics; Preparation of the central region 1-1: Reaction chamber preparation: The high-purity quartz glass tube is fixed in the reaction chamber with precise temperature control and rotation function to ensure stable and uniform reaction environment; Gas flow control: SiCl4 (flow rate set to 20-30sccm), CF4 (flow rate 0.5-1sccm) are introduced as basic raw materials, and ErCl3 (flow rate 0.01-0.05sccm), GeCl4 (flow rate 0.5-1.5sccm) are introduced for doping. These gases are fully mixed in the reaction chamber to provide the basis for subsequent reactions; Deposition temperature regulation: The temperature of the reaction chamber is raised to 1300-1400℃, and in this high-temperature environment, SiCl4, CF4 and other raw materials react to form a fluorinated compound material matrix doped with erbium (Er) and germanium (Ge) elements from ErCl3 and GeCl4, which promotes the formation of nanodots with a size of 20-50nm and a density of 10 15 / cm 3 .

[0030] Central region 1-1 formation: As the reaction continues, the nanodots are stably distributed in the matrix to form the central region 1-1. The refractive index of this region is accurately controlled at 1.468, which serves as the main scattering center and lays the foundation for the scattering enhancement characteristics of the optical fiber; Preparation of the outer edge region 1-2: Gas flow adjustment: Keep the flow rate of SiCl4 and CF4 unchanged, and slightly adjust the flow rate of ErCl3 (flow rate reduced to 0.007-0.035sccm) and GeCl4 (flow rate reduced to 0.35-1.05sccm) to reduce the amount of erbium and germanium elements entering the reaction chamber; Deposition process: In the same high-temperature environment as the central region, due to the reduction of doping elements, the density of nanodots generated is reduced by about 30% compared to the central region. The composite material matrix formed at this time constitutes the outer edge region 1-2; Refractive index control: By adjusting the proportion of doping elements and reaction conditions, the refractive index of the outer edge region 1-2 is 0.1%-0.2% lower than that of the central region 1-1. This refractive index difference design effectively reduces the scattering loss of optical signals at the edge of the core, while ensuring the effective confinement and transmission of optical signals in the core; Then a low refractive index fluorinated silica glass material is deposited outside the core to form the cladding 2, preparing for low loss characteristics; 2) Drawing: The preform obtained in step 1) is drawn into an optical fiber using a high-precision drawing machine, the drawing temperature is 2100-2200°C, the drawing speed is 800-1000 m / min, and finally an optical fiber structure with an outer diameter of 125 μm and a core diameter of 8.2 μm is formed; during the drawing process, the size precision of the core and the cladding is strictly controlled, the step refractive index distribution of the core 1 is retained, the high scattering enhanced nanodot structure of the central region 1-1 and the low loss optimized refractive index distribution of the outer edge region 1-2 remain stable, and the structure basis of scattering enhancement and low loss characteristics is ensured; 3) Coating and packaging: A low-loss ultraviolet curing coating 3 with a thickness of 25-30 μm is coated on the outside of the optical fiber obtained in step 2), and after ultraviolet curing, it is packaged, the ultraviolet light wavelength is 365 nm, and the power is 500-600 mW / cm 2 , forming the required optical fiber with scattering enhancement characteristics and low loss characteristics, the low-loss ultraviolet curing coating 3 reduces the influence of the external environment (such as mechanical friction, humidity, etc.) on the performance of the optical fiber, and further ensures the stability of the optical fiber in complex environments.

[0031] When the optical signal of the 1550 nm band is transmitted in the optical fiber, the nanodots doped with erbium and germanium in the core 1 enhance the intensity of Rayleigh scattering (about 30% increase), meeting the demand of optical fiber sensing for scattering signals; at the same time, the fluorinated silica glass material of the cladding 2 reduces the infrared absorption band due to the doping of fluorine elements, combined with the use of ultra-pure gas and high-precision process (the surface defect density of the optical fiber is ≤10 15 mm 2 ) during preparation, the transmission loss of the 1550 nm band is reduced to the theoretical limit of 0.14 dB / km, meeting the low loss requirement of long distance optical communication, so as to realize the synergistic work of scattering enhancement and low loss characteristics.

[0032] In the present application, the nanodots act as scattering centers, providing sufficient signals for sensing by enhancing Rayleigh scattering; the low nanodot density design of the outer edge region of the core combined with the synergistic effect of the fluorine doping of the cladding to reduce infrared absorption, realizes low loss transmission of optical signals, the transmission loss is ≤0.14 dB / km, realizes the core advantages of meeting the requirements of scattering enhancement (sensing requirement) and low loss transmission (communication requirement) at the same time, and can be used for one fiber and two purposes, as shown in Figure 4 .

[0033] Figure 5 The figure shows the relationship between the nanodot size and the performance of the optical fiber, using a double vertical axis design, the horizontal axis is the nanodot size (nm), the left vertical axis represents the Rayleigh scattering intensity (relative value), and the right vertical axis represents the 1550 nm transmission loss (dB / km).Figure 5 Two key curves are clearly shown in the figure: The scattering intensity curve gradually increases from 1.30 to 1.50 as the nanodot size increases from 20 nm to 50 nm, which is marked as "30%-50% enhancement", directly reflecting the promotion effect of size increase on the scattering signal; The transmission loss curve slowly increases from 0.14 dB / km to 0.16 dB / km as the nanodot size increases, which is marked as "always ≤0.16 dB / km", indicating that the loss change is within a controllable range; The nanodot size in the range of 20-50 nm can simultaneously meet the dual requirements of scattering enhancement and low loss, which is the optimal size range for balancing the sensitivity of optical fiber sensing and the transmission performance of communication, and provides a key basis for process control of nanodot size.

[0034] Figure 6 The figure shows the relationship between the fluorine doping concentration and the cladding performance of the present application, the horizontal axis represents the fluorine doping concentration (%), the left vertical axis is the cladding refractive index, and the right vertical axis is the infrared absorption loss (dB / km). Figure 6 Two curves are included in the figure: the blue curve represents the cladding refractive index, and the red curve represents the infrared absorption loss. The blue curve shows a trend that as the fluorine doping concentration gradually increases from 1% to 7%, the cladding refractive index gradually decreases from about 1.468 to about 1.458, and in Figure 6 The figure is marked as "refractive index decreases with increasing F concentration", which clearly shows that the fluorine doping concentration is negatively correlated with the cladding refractive index; the red curve shows that the infrared absorption loss decreases as the fluorine doping concentration increases, and especially after the fluorine doping concentration reaches 3%, the decreasing trend gradually slows down, Figure 6 The figure is marked as "3%-5% interval tends to be stable", indicating that within this concentration range, the infrared absorption loss changes little and tends to be stable. At the same time, Figure 6 The green rectangular area in the figure is "preferred concentration 3%-5%", which is based on the comprehensive consideration of the change trend of the two curves. Within this concentration range, the cladding refractive index is at a relatively reasonable level, and the infrared absorption loss can also be kept at a low and stable state, which can better meet the requirements of optical fiber cladding performance, so it is determined as the preferred concentration interval of fluorine doping.

[0035] The parts or structures not specifically described in the present application can use existing technology or existing products, which are not described here.

[0036] The above description is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation based on the content of the present application specification, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. An optical fiber having both scattering enhancement characteristics and low loss characteristics, characterized in that: The fiber core comprises a fiber core, a cladding and a low-loss ultraviolet curing coating which are sequentially arranged from the inside to the outside. Nano dots are distributed inside the fiber core and are doped with at least one metal.

2. The optical fiber having both scattering enhancement and low loss characteristics according to claim 1, characterized in that: The fiber core includes a central region and an outer edge region sequentially arranged from the inside to the outside, and the refractive index of the outer edge region is 0.1%-0.2% lower than the refractive index of the central region.

3. The optical fiber having both scattering enhancement and low loss characteristics according to claim 2, characterized in that: The diameter of the fiber core is 8.2 μm, the radius of the central region is 0-2 μm, and the radius of the outer edge region is 2-4.1 μm.

4. The optical fiber having both scattering enhancement and low loss characteristics according to claim 1 or 2, characterized in that: Nanodots with a size of 20-50 nm are evenly distributed inside the fiber core.

5. The optical fiber having both scattering enhancement and low loss characteristics according to claim 4, characterized in that: The nanodots are doped with erbium and germanium, with the erbium doping concentration being 50-80 ppm and the germanium doping concentration being 20,000-30,000 ppm.

6. The optical fiber having both scattering enhancement and low loss characteristics according to claim 1 or 2, characterized in that: The fiber core is made of a composite material doped with fluoride and silicon oxide, and the molar ratio of fluoride to silicon oxide is 0.8%-1.5%.

7. The optical fiber having both scattering enhancement and low loss characteristics according to claim 1, wherein: The cladding is made of low-refractive-index silicon fluoride glass, and the fluorine doping concentration in the cladding is 3%-5%.

8. The optical fiber having both scattering enhancement and low loss characteristics according to claim 1, characterized in that: The refractive index of the cladding is 0.3%-0.5% lower than the refractive index of the core.

9. The optical fiber having both scattering enhancement and low loss characteristics according to claim 1, characterized in that: The thickness of the low-loss UV-cured coating is 25-30 μm.

10. The method for preparing an optical fiber having both scattering enhancement and low loss characteristics according to any one of claims 1 to 9, characterized in that: The following steps are involved: 1) Preform manufacturing: First, chemical vapor deposition (CVD) is used to form a composite matrix of fluoride and silicon oxide in the fiber core region by precisely controlling the deposition temperature and gas flow rate. Erbium and germanium doping are also introduced to uniformly distribute nanodots with a size of 20-50 nm inside the fiber core. Then, a low-refractive-index fluorinated silica glass material is deposited outside the fiber core to form a cladding; 2) Brushed: Drawing the preform obtained in step 1) into an optical fiber, strictly controlling the dimensional accuracy of the core and cladding; 3) Coating and packaging: The optical fiber obtained in step 2) is coated with a low-loss UV-curable coating with a thickness of 25-30 μm, and then encapsulated after UV curing to form the desired optical fiber with both scattering enhancement and low-loss characteristics.

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