Bending-resistant optical fiber preform and preparation method thereof

Abstract

The invention relates to the technical field of optical fiber preforms, in particular to a bending-resistant optical fiber preform and a preparation method thereof, a core layer, an inner cladding, a low-folding layer and an outer cladding are sequentially prepared, the ratio of the thickness of the inner cladding to the diameter of the core layer is 0.8-1.2, and the ratio of the thickness of the low-folding layer to the thickness of the inner cladding is 1: 1.5-1: 3. According to the bending-resistant optical fiber prepared by the preparation method, under the condition that the bending-resistant optical fiber is wound for 25 circles and an optical fiber ring with the diameter of 10mm is bent ultimately, the bending additional loss at 1550nm is less than or equal to 0.02 dB, and the bending-resistant optical fiber shows excellent bending resistance.

Description

Technical Field

[0001] This invention relates to the field of optical fiber preform technology, and specifically to a bend-resistant optical fiber preform and its preparation method. Background Technology

[0002] Bending-resistant optical fiber, through precise control of the refractive index gradient and geometric parameters of the core and cladding, can significantly suppress optical signal leakage loss under bending conditions, playing a crucial role in scenarios such as fiber-to-the-home, high-density interconnection of data centers, industrial sensing, and portable optical devices. Its core requirement is to ensure optical signal transmission performance while possessing excellent bending resistance to adapt to frequent bending and folding scenarios in complex cabling environments.

[0003] Current methods for preparing bend-resistant optical fiber preforms largely rely on traditional techniques: Plasma-chemical vapor deposition (PCVD) is used to prepare a high-refractive-index core layer, ensuring strong optical signal confinement by precisely controlling the concentration distribution of dopants (e.g., introducing elements like germanium to increase refractive index); low-refractive-index cladding (including inner cladding, outer cladding, and special functional layers such as low-fold layers) is prepared using vapor phase axial deposition (VAD), utilizing the refractive index difference between the core and cladding (the core layer is typically 0.3%-0.5% higher) to construct the bend-resistant structure; finally, mechanical polishing is used to adjust the cladding dimensions, ensuring that parameters such as inner cladding thickness and outer cladding diameter match the designed bend resistance parameters (e.g., cladding thickness).

[0004] However, traditional processes have significant limitations: during VAD coating, the axial distribution of coating thickness is uneven due to the influence of air source and temperature; mechanical polishing exacerbates dimensional deviations due to abrasive wear or feed fluctuations, resulting in poor consistency of bending loss and excessive loss in some areas, failing to meet the requirements of high-density wiring; mechanical polishing requires high precision and is prone to scrapping preforms due to over-polishing or deviation, and the utilization rate of VAD deposition materials is low, resulting in serious waste, with the master rod qualification rate generally below 60%, significantly increasing costs; traditional VADs have difficulty accurately controlling the change in cladding refractive index and geometry, causing the actual bending resistance to deviate from the design (such as insufficient cladding depression leading to poor leakage light absorption and increased loss).

[0005] Patent CN118270974A discloses a method for preparing a square power transmission optical fiber preform and the preform itself. The method involves grinding a high-purity quartz rod to prepare the preform, which is then drawn into a square power transmission optical fiber. However, this method requires high precision in grinding the quartz rod; uneven grinding can affect the shape consistency of the square quartz core rod, and the process is quite cumbersome. These problems result in poor stability and high cost of existing bend-resistant optical fibers, limiting their large-scale application in high-density, miniaturized optical communication scenarios. Summary of the Invention

[0006] The purpose of this invention is to provide a bend-resistant optical fiber preform and its preparation method, thereby solving the technical problems of poor performance stability and high cost of bend-resistant optical fibers in the prior art, which limit their large-scale application in high-density, miniaturized optical communication scenarios.

[0007] This invention discloses a method for preparing a bend-resistant optical fiber preform, wherein a core layer, an inner cladding layer, a low-fold layer, and an outer cladding layer are prepared sequentially, wherein the ratio of the inner cladding layer thickness to the core layer diameter is 0.8-1.2, and the ratio of the inner cladding layer thickness to the low-fold layer thickness is 1:1-2:1.

[0008] Furthermore, the core layer is fabricated using a PCVD (plasma chemical vapor deposition) process.

[0009] Furthermore, in the cutoff wavelength band of ≤1550nm and the mode field diameter of 6.2-7.0μm, the bending-induced additional loss at 1550nm is ≤0.02dB when a fiber loop with 25 turns and a diameter of 10mm is wound.

[0010] Furthermore, the inner cladding layer, the low-fold layer, and the outer cladding layer are all prepared using a VAD spraying process.

[0011] Furthermore, the inner cladding is deposited using a hydrogen-oxygen flame hydrolysis reaction.

[0012] Furthermore, the inner cladding layer is polished after preparation to control the thickness error of the inner cladding layer to ≤ ±0.1 mm and the longitudinal dimension uniformity deviation to ≤ 0.3%, thus providing a flat substrate for the low-fold layer.

[0013] Furthermore, the refractive index of the low-refractive layer is 0.3%-0.4% lower than that of the core layer, which enhances the light field confinement.

[0014] Furthermore, the low-refractive layer is polished after preparation to ensure that the thickness deviation of the low-refractive layer is ≤ ±0.1 mm and the radial uniformity is ≤ 0.2%, and to suppress bending light leakage through the refractive index gradient.

[0015] Furthermore, the outer cladding layer is made of high-purity quartz.

[0016] Furthermore, the thickness of the outer cladding layer is 1.5-2 times the thickness of the folded layer.

[0017] Furthermore, the thickness of the outer coating is controlled by the spraying rate and the flame temperature, wherein the spraying rate is 3L / min and the spraying flame temperature range is 1100℃-1300℃.

[0018] Furthermore, the refractive index distribution of the optical fiber preform satisfies the condition of core layer > inner cladding layer > low-fold layer > outer cladding layer, which meets the condition of total internal reflection.

[0019] Furthermore, the longitudinal uniformity of each layer of mechanical polishing has a total dimensional fluctuation of ≤±0.1mm, and the interlayer interface roughness is ≤0.02mm, reducing scattering loss.

[0020] A bend-resistant optical fiber preform is prepared using the method described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are: The optical fiber fabricated using the process of this invention ensures a cladding non-circularity of ≤0.7% and a core / cladding concentricity deviation of ≤0.6μm; in terms of mechanical properties, the screening tension is 200Kpsi. This process improves structural control precision by more than 20%, increasing the master rod qualification rate from 70%-80% to over 90%, thereby reducing production costs. The bend-resistant optical fiber fabricated using this invention exhibits excellent bend resistance performance with a bending-added loss of ≤0.02dB at 1550nm under extreme bending conditions of a 10mm diameter fiber ring wound with 25 turns. This invention precisely controls the geometric dimensions such as the inner cladding thickness, low-refractive-index layer thickness, and outer cladding thickness based on the fiber core diameter; and achieves precise control of the fiber cutoff wavelength range (λc=2πaNA / 2.405) based on the fiber core diameter and numerical aperture (NA0.18±0.005). The one-step forming process improves the consistency and production efficiency of the preform structure, reduces the performance fluctuation risk caused by multi-process manufacturing, and provides technical support for the large-scale production of bend-resistant optical fibers. Attached Figure Description To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the optical fiber preform structure of the present invention.

[0023] Figure 2 This is a schematic diagram of light propagating in this bend-resistant optical fiber. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Example 1 This embodiment discloses a bend-resistant optical fiber preform and its preparation method, such as... Figure 1-Figure 2 As shown, it includes the following steps: Step S1: The core layer is prepared using PCVD technology. The flow rate of the reactive gas and the deposition temperature are controlled to make the mode field diameter of the core layer in the 1550nm band 6.5μm, forming a uniform high refractive index distribution, which meets the requirement of numerical aperture of 0.18±0.005. At the same time, the core layer diameter is measured.

[0026] Step S2: Prepare the inner cladding layer by spraying VAD onto the outside of the core layer, deposit silane raw material by hydrogen-oxygen flame hydrolysis reaction, and polish it with a high-precision grinding machine after preparation to control the thickness of the inner cladding layer. The inner cladding layer thickness / core layer diameter = 1, the error is ±0.1mm, and the longitudinal dimension uniformity deviation is 0.25%.

[0027] Step S3: A low-refractive-index layer is sprayed onto the inner cladding surface using VAD, introducing fluorine to lower the refractive index by 0.35% compared to the core layer. The ratio of cladding thickness to low-refractive-index layer thickness is 2. After preparation, the surface is polished to ensure a low-refractive-index layer thickness deviation of ±0.2 μm and a radial uniformity of 0.15%.

[0028] Step S4: Use VAD spraying to form an outer cladding layer on the outside of the low-fold layer, mainly using high-purity silicon tetrachloride, and adjust the parameters so that the outer cladding layer diameter / core layer diameter is ≥14.55.

[0029] Step S5: Obtain the refractive index distribution map of the preform using a preform tester. Calculate the actual outer diameter of the preform based on the core-cladding size of the target fiber 5.5 / 80. Then, grind the preform to the required outer diameter using a high-precision grinder.

[0030] Step S6: Use a wire drawing tower to draw the preform into wires.

[0031] Step S7: Test the drawn optical fiber.

[0032] This bend-resistant optical fiber has a bending diameter of 10mm, a loop diameter of 25 turns, a bending-induced loss of 0.017dB at 1550nm, and a screening tension ≥200Kpsi. It exhibits excellent bending and tensile strength.

[0033] Example 2 Based on Example 1, the only changes are that when the inner cladding thickness / core diameter = 1:0.8, the inner cladding thickness / low-fold layer thickness = 1:1. This yields a cutoff wavelength ≤1550nm, a mode field diameter in the range of 6.5±0.5μm, and an optical fiber loop with a diameter of 10mm wound 25 times. The additional bending loss at 1550nm is 0.017dB, while also exhibiting excellent tensile strength.

[0034] Example 3 The only change based on Example 1 is that when the inner cladding thickness / core diameter = 1:0.8, the inner cladding thickness / low-fold layer thickness = 2:1. This results in a cutoff wavelength ≤1550nm, a mode field diameter in the range of 6.5±0.5μm, and an additional bending loss of 0.018dB at 1550nm when the fiber is wound with 25 turns of 10mm diameter, while also exhibiting excellent tensile strength.

[0035] Example 4 Based on Example 1, the only changes are that when the inner cladding thickness / core diameter = 1:1.2, the inner cladding thickness / low-fold layer thickness = 1:1. This yields a cutoff wavelength ≤1550nm, a mode field diameter within the range of 6.5±0.5μm, and an additional bending loss of 0.016dB at 1550nm when the fiber is wound with 25 turns of 10mm diameter, while also exhibiting excellent tensile strength.

[0036] Example 5 Based on Example 1, the only changes are that when the inner cladding thickness / core diameter = 1:1.2, the inner cladding thickness / low-fold layer thickness = 2:1. This yields a cutoff wavelength ≤1550nm, a mode field diameter within the range of 6.5±0.5μm, and an optical fiber loop with a diameter of 10mm wound 25 times. The additional bending loss at 1550nm is 0.018dB, while also exhibiting excellent tensile strength.

[0037] Comparative Example 1 The only change from Example 1 is that the inner cladding thickness / core diameter = 1.5.

[0038] The bending-resistant fiber preform has a screening tension ≥200Kpsi, but its bending resistance is poor, with bending-related losses reaching 0.05dB.

[0039] Comparative Example 2 The only change from Example 1 is that the inner cladding thickness / core diameter = 0.6.

[0040] The bending-resistant fiber preform has a screening tension ≥200Kpsi, but its bending resistance is poor, with bending-induced additional loss exceeding 0.08dB. Furthermore, light leakage is significant after bending.

[0041] Comparative Example 3 The only change from Example 1 is that when the inner cladding thickness / low-fold layer thickness is 0.75, the bending resistance is obvious and the bending additional loss is 0.019dB, but the core layer loss increases and the screening tension decreases slightly.

[0042] Comparative Example 4 The only change from Example 1 is that when the inner cladding thickness / low-fold layer thickness is 2.5, the bending resistance is no different from that of ordinary single-mode fiber, and it does not exhibit excellent bending resistance. However, the screening tension can still be maintained at ≥200Kpsi.

[0043] As can be seen from the above embodiments and comparative examples, neither too large nor too small an inner cladding thickness / core diameter can achieve good bending resistance, resulting in significant light leakage; both too large and too small an inner cladding thickness / low-fold layer ratio will increase core layer loss and reduce screening tension.

[0044] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments based on the inspiration of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A method for preparing a bend-resistant optical fiber preform, characterized in that: The core layer, inner cladding layer, low-fold layer, and outer cladding layer are prepared sequentially, wherein the ratio of the inner cladding layer thickness to the core layer diameter is 0.8-1.2, and the ratio of the inner cladding layer thickness to the low-fold layer thickness is 1:1-2:

1.

2. The method for preparing a bend-resistant optical fiber preform according to claim 1, characterized in that: When the cutoff wavelength is ≤1550nm and the mode field diameter is 6.2-7.0μm, the bending-induced additional loss at 1550nm is ≤0.02dB for a 10mm diameter fiber loop wound with 25 turns.

3. The method for preparing a bend-resistant optical fiber preform according to claim 1, characterized in that: The core layer is fabricated using the PCVD process.

4. The method for preparing a bend-resistant optical fiber preform according to claim 1, characterized in that: The inner cladding, low-fold layer, and outer cladding are all prepared using a VAD spraying process.

5. The method for preparing a bend-resistant optical fiber preform according to claim 1, characterized in that: After the inner cladding is prepared, it is polished to control the thickness error of the inner cladding to ≤ ±0.1 mm and the longitudinal dimension uniformity deviation to ≤ 0.3%, so as to provide a flat base for the low-fold layer.

6. The method for preparing a bend-resistant optical fiber preform according to claim 1, characterized in that: The refractive index of the low-refractive layer is 0.3%-0.4% lower than that of the core layer.

7. The method for preparing a bend-resistant optical fiber preform according to claim 1, characterized in that: The low-fold layer is polished after preparation to ensure that the thickness deviation of the low-fold layer is ≤ ±0.1 mm and the radial uniformity is ≤ 0.2%.

8. The method for preparing a bend-resistant optical fiber preform according to claim 1, characterized in that: The thickness of the outer cladding layer is 1.5-2 times the thickness of the folded layer.

9. The method for preparing a bend-resistant optical fiber preform according to claim 1, characterized in that: The refractive index distribution of the optical fiber preform satisfies the following order: core layer > inner cladding layer > low-fold layer > outer cladding layer.

10. A bend-resistant optical fiber preform, characterized in that, The fiber optic preform is prepared by the method described in any one of claims 1-9.

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