Bending-resistant multi-core indoor optical cable and preparation method thereof

Abstract

The invention relates to the technical field of optical elements, and discloses a bending-resistant multi-core indoor optical cable and a preparation method thereof. The optical cable comprises an optical fiber unit, a water blocking layer, an inner sheath, an energy dissipation layer, a hydrogen blocking layer, an outer sheath and a gradually-changed braid layer which are sequentially arranged from inside to outside. The energy dissipation layer is formed by spirally twisting a plurality of superelastic nickel-titanium alloy wires and high-strength fibers at a specific pitch, wherein the surfaces of the superelastic nickel-titanium alloy wires are coated with ceramic coatings; and the gradually-changed braid layer is a high-strength fiber braid layer of which the braid density is continuously and gradually changed along the axial direction of the optical cable in a segmented manner. According to the invention, bending mechanical energy is actively dissipated through the spirally twisted superelastic alloy wires, intelligent constraint matched with stress distribution is provided in combination with the external segmented gradient braid layer, and hydrogen embrittlement is inhibited by using a double-layer protection mechanism; the problems that an existing optical cable is prone to fracture and loss is increased sharply due to energy accumulation and stress concentration under repeated bending are systematically solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical elements, in particular to a bend-resistant multi-core indoor optical cable and a preparation method thereof. BACKGROUND

[0002] With the rapid development of 5G communication, data center construction and other fields, the application scenarios of indoor optical cables are increasingly complex, and higher requirements are put forward for the bend resistance, transmission stability and installation convenience of optical cables. Multi-core indoor optical cables have become one of the mainstream choices for indoor communication wiring because they can realize multi-channel signal transmission and effectively save laying space. However, in actual application process, indoor optical cables often need to be laid in narrow spaces for multiple times of bending. After repeated bending, the traditional multi-core indoor optical cable is prone to problems such as increased optical fiber loss, jacket cracking and structure delamination, which seriously affects the communication quality and service life.

[0003] Therefore, in view of the problems of insufficient bend resistance, uneven stress distribution and poor transmission stability after repeated bending of the existing multi-core indoor optical cable, it is urgent to design a bend-resistant multi-core indoor optical cable which can reasonably disperse bending stress, improve bend resistance life and has a stable structure, and a corresponding preparation method. SUMMARY

[0004] The purpose of the present application is to provide a bend-resistant multi-core indoor optical cable and a preparation method thereof to solve the problems raised in the background.

[0005] In order to achieve the above-mentioned purpose, on the one hand, the present application provides a bend-resistant multi-core indoor optical cable, which comprises, from inside to outside, a fiber unit, a water-blocking layer, an inner jacket, an energy dissipation layer, a hydrogen barrier layer, an outer jacket and a gradient braid layer.

[0006] The energy dissipation layer is composed of a plurality of super-elastic nickel-titanium alloy wires and high-strength fibers (such as PET yarn) which are spirally twisted together. The braid density of the gradient braid layer decreases stepwise from both ends to the middle along the axial direction of the optical cable through at least three sections with different braid densities.

[0007] The energy dissipation layer adopts super-elastic nickel-titanium alloy wires with ceramic coating and spiral structure. The spiral structure ensures that the alloy wires mainly bear tension during bending, maximizes the super-elastic effect and actively dissipates the mechanical energy into phase change internal energy, rather than transferring it to the optical fiber. The outermost gradient braid layer adopts a segmented and continuously decreasing density design, which provides high-strength constraint at the cable end where the stress is concentrated, maintains good flexibility at the cable body which needs to be frequently bent, and avoids stress mutation through a sufficient length of transition zone. The hydrogen barrier layer serves as a system-level barrier and, together with the cable core water-blocking layer, forms a double protection against hydrogen environment erosion of the alloy wires.

[0008] Preferably, the braid density Dmax The ratio of the weaving density D of the middle part to the weaving density D of the end part is (2.0-3.5):1, which balances the strength of the two ends and the bending flexibility of the middle part, effectively improving the bending life and transmission stability of the optical cable. min The ratio of the weaving density D of the middle part to the weaving density D of the end part is (2.0-3.5):1, which balances the strength of the two ends and the bending flexibility of the middle part, effectively improving the bending life and transmission stability of the optical cable.

[0009] Preferably, the surface of the super-elastic nickel-titanium alloy wire is coated with an alumina or silicon nitride ceramic coating. The ceramic coating acts as a dense physical barrier to prevent the diffusion of hydrogen atoms in the environment into the interior of the nickel-titanium alloy wire, effectively inhibiting the hydrogen embrittlement phenomenon of the alloy wire and ensuring the stability of its super-elastic function in long-term use; at the same time, the coating can enhance the interfacial adhesion between the alloy wire and the surrounding polymer sheath material, improve stress transfer, and provide basic wear resistance protection during manufacturing and use.

[0010] Preferably, the phase transition end temperature Af of the super-elastic nickel-titanium alloy wire is less than 20℃, ensuring that the nickel-titanium alloy wire can stably remain in a super-elastic state in a normal temperature use environment, guaranteeing the reversible deformation and energy dissipation capacity during bending. The single wire diameter is 0.10mm-0.13mm, and the number is 6-10, which can ensure energy dissipation while avoiding the increase in cable diameter and the decrease in flexibility due to excessive alloy wire thickness or quantity.

[0011] Preferably, the gradient weaving layer is woven from polyethylene terephthalate or ultra-high molecular weight polyethylene fibers, and the thickness of the gradient weaving layer is 0.18mm-0.25mm. Such fibers have high strength, high wear resistance, and good flexibility, which can ensure the structural strength and bending adaptability of the gradient weaving layer. The total gradient length L of the gradient weaving layer from the highest density area at the end to the lowest density area in the middle g The ratio of the total length L of the gradient weaving layer to the total length L of the optical cable is 20%-35%, which can ensure a smooth transition of stress from both ends to the middle, avoid stress mutation due to a too short gradient area, or a decrease in flexibility of the optical cable due to a too long gradient area, further optimize the stress dispersion effect, and improve the bending resistance.

[0012] Preferably, the materials of the inner sheath and the outer sheath are both thermoplastic polyurethane; the thickness of the inner sheath is 0.15mm-0.22mm, and the thickness of the outer sheath is 0.20mm-0.30mm. Such materials have good elasticity, wear resistance, and flame retardance, which can meet the safety requirements for indoor use.

[0013] Preferably, the hydrogen barrier layer is made of a metalized polyester film or a co-extruded ethylene-vinyl alcohol copolymer layer, and the thickness is 0.03mm-0.08mm. These materials have extremely low hydrogen permeability and can encapsulate hydrogen sources from the outside, forming a systematic protection network from the inside to the outside in combination with the water barrier layer.

[0014] Preferably, the water-blocking layer is water-blocking powder or water-blocking yarn filled in the gap between the optical fiber units or wrapped around the optical fiber units, which can improve the water-blocking performance of the optical cable, prevent water from entering the optical fiber units to cause the increase of optical fiber loss or damage, and ensure the stable use of the optical cable in a humid indoor environment.

[0015] In another aspect, the application also discloses a preparation method of the above-mentioned bend-resistant multi-core indoor optical cable, which comprises the following steps: S1: twisting a plurality of colored optical fibers to form an optical fiber unit, wrapping aramid fibers around the outer periphery of the optical fiber unit, and applying a water-blocking material to form a water-blocking layer; S2: extruding an inner sheath covering the water-blocking layer; S3: spirally twisting a plurality of super-elastic nickel-titanium alloy wires and high-strength fibers outside the inner sheath to form an energy dissipation layer; S4: forming a hydrogen barrier layer outside the energy dissipation layer; S5: extruding an outer sheath outside the hydrogen barrier layer; S6: using a numerical control braiding machine to braid a gradient braid layer outside the outer sheath: through a preset program, the numerical control braiding machine is controlled to adopt different braiding pitches in different sections in the axial direction of the optical cable to form the gradient braid layer.

[0016] In step S3, during the twisting process, the single-wire tension is controlled to be 2.0 N±0.5 N, so as to ensure the uniformity of the energy dissipation layer, avoid fiber or alloy wire damage caused by excessive tension, or loose structure caused by insufficient tension; in step S6, the program control of the numerical control braiding machine can accurately realize the linear gradient of the density of the gradient braid layer, and ensure the stress dispersion effect.

[0017] Preferably, the braiding pitch is 1.5 mm-2.0 mm in the high-density area at both ends of the optical cable and 3.2 mm-4.5 mm in the low-density area in the middle part.

[0018] Mechanism of action: When an external bending force acts on the optical cable, the segmented gradient braid layer at the outermost layer first provides a gradient constraint matched with the axial stress distribution (high at both ends and low in the middle), strengthens the high stress area, and avoids local stress peaks through gentle transition. The energy dissipation layer composed of spirally twisted super-elastic nickel-titanium alloy wires becomes the main force-bearing and energy-dissipating unit. The alloy wires undergo stress-induced martensitic phase transition under tensile stress, convert a large amount of mechanical energy into reversible phase change energy in the material, and dissipate, thereby greatly attenuating the net stress transmitted to the optical fiber. The inner aramid fiber and the twisted optical fiber structure serve as the last buffer. Throughout the process, the protection system composed of the ceramic coating on the super-elastic nickel-titanium alloy wires and the external hydrogen barrier layer and the internal water-blocking layer ensures the stable performance of the energy dissipation element in long-term use. The functional layers are connected through the matched materials (such as the unified TPU sheath) to realize effective stress transmission and interface bonding.

[0019] The beneficial effects of the present application are: 1. Breakthrough improvement in repeated bending resistance: Through the active energy dissipation mechanism, the way of dealing with bending of the optical cable is fundamentally changed, so that the additional loss is stable ≤0.08dB after 1000 times of 180° folding test, and there is no broken fiber, solving the core pain points of traditional optical cable in such tests, such as large loss and easy broken fiber.

[0020] 2. Excellent ability to resist extreme mechanical stress: The gradient constraint structure combined with the high-strength braided layer makes the optical cable perform excellently in extreme bending (KINK) and compression test, with extremely low additional loss (≤0.03dB) and strong robustness.

[0021] 3. Long dynamic fatigue life: The super-elastic phase transition is reversible and fatigue-resistant, so that the performance attenuation of the optical cable is extremely small after thousands of bending cycles, suitable for scenarios that require frequent plugging or dynamic wiring.

[0022] 4. Systematic guarantee of long-term reliability: The innovative double-layer hydrogen protection design (ceramic coating + hydrogen barrier layer) effectively inhibits the hydrogen embrittlement risk of nickel-titanium alloy, and the key performance retention rate is more than 95% after high temperature and high humidity accelerated aging, and the life expectancy is greatly extended.

[0023] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the present application, and constitute a part of the specification, and together with the following specific embodiments, serve to explain the present application, but do not constitute a limitation on the present application. In the drawings: Figure 1 The structure diagram of the bending-resistant multi-core indoor optical cable of an embodiment of the present application is shown; Explanation of reference signs: 1, optical fiber unit; 2, water barrier layer; 3, inner sheath; 4, energy dissipation layer; 5, hydrogen barrier layer; 6, outer sheath; 7, gradient braided layer. DETAILED DESCRIPTION

[0025] The specific embodiments of the present application will be described in detail below in conjunction with the drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0026] It should be noted that all reagents and raw materials in the present application are obtained from the market, and the purity of the reagents is analytical pure.

[0027] The superelastic nickel-titanium alloy wire was purchased from Shanghai Shengtong Metal Technology Co., Ltd., model number St2082401; the thermoplastic polyurethane (TPU) was purchased from Wanhua Chemical Group Co., Ltd., model number Wanthane® WHT-1185N; the ethylene-vinyl alcohol copolymer (EVOH) was purchased from Kuraray International Trading (Shanghai) Co., Ltd., model number E105B; and the aluminum-plastic composite tape was purchased from Suzhou Jinxing Telecommunication Materials Co., Ltd.

[0028] Example 1: 12-core indoor optical cable, refer to Figure 1 1. Cable core preparation: After coloring 12 G.657.A2 optical fibers, they are stranded at a pitch of 90mm to obtain optical fiber unit 1. Then, a layer of aramid yarn (30g / m) is wrapped around the optical fiber unit 1 and water-blocking powder is sprinkled on it at the same time to form water-blocking layer 2. 2. Inner sheath 3: A layer of TPU (Shore hardness 82A) is extruded on the outside of the water-blocking layer 2 at an extrusion temperature of 190℃ and a thickness of 0.18mm; 3. Energy dissipation layer 4: Eight ultra-elastic nickel-titanium alloy wires coated with an alumina coating (approximately 2 μm thick) 0.12mm, Af=15℃) and 4 PET yarns (breaking strength about 30 cN / dtex) are twisted together by a auger to the outside of the inner sheath 3 to obtain the energy dissipation layer 4. The twisting pitch is 70mm, the pay-off tension is controlled at 2.0N, and all guide wheels have a diameter ≥6mm (to meet the requirement of 50 times the wire diameter). 4. Hydrogen barrier layer 5: A 12μm thick aluminum-plastic composite strip (aluminum layer facing inward) is wrapped around the energy dissipation layer 4 with an overlap rate of 25% to obtain the hydrogen barrier layer 5. 5. Outer sheath 6: A layer of TPU (Shore hardness 82A) is extruded on the outside of the hydrogen barrier layer 5 at an extrusion temperature of 190℃ and a thickness of 0.25mm; 6. Gradient Braided Layer 7: Utilizes a 24-spindle braiding machine and PET yarn. The braiding program is set as follows: 150mm at each end (approximately 15% of a 2-meter optical cable), pitch 1.8mm (high-density zone); a 100mm inward transition zone, pitch increasing to 2.5mm (medium-density zone); and approximately 1300mm in the middle, pitch 3.6mm (low-density zone). max :D min =2.0:1, weaving tension 10N±1.5N.

[0029] Example 2: 24-core indoor optical cable The main difference from Example 1 is: Step 1: The optical fiber has 24 cores and a stranding pitch of 75mm; Step 3: Energy Dissipation Layer 4: Use 10 [units / layers] 0.11 mm alloy wire (Af = 10 °C), PET yarn (breaking strength of about 25 cN / dtex), twisting pitch 60 mm; Step 4: Hydrogen barrier layer 5: 0.05 mm thick EVOH layer formed by co-extrusion; Step 6: Graduated braid layer 7: 200 mm at each end (26.7% of 1.5 meter long cable), pitch 1.6 mm; transition zone 100 mm, pitch 2.2 mm; middle section pitch 4.0 mm, D max :D min = 2.5:1.

[0030] Example 3

[0031] The main difference from Example 1 is that: Step 1: Optical fiber unit 1 is 8-core 200 pm outer-coated optical fiber; Step 3: Energy dissipation layer 4: 6 0.11 mm alloy wire (Af = 18 °C), PET yarn (breaking strength of about 35 cN / dtex), twisting pitch 85 mm; Step 5: Outer jacket 6 thickness is 0.20 mm; Step 6: Graduated braid layer 7: 100 mm at each end (20% of 1 meter long cable), pitch 2.0 mm; transition zone 80 mm, pitch 2.8 mm; middle section pitch 3.2 mm, D max :D min = 2.2:1.

[0032] Example 4 The main difference from Example 1 is that: Step 3: Energy dissipation layer 4 uses a silicon nitride coating; Step 4: Hydrogen barrier layer 5: first wrap aluminum plastic composite tape, then co-extrude EVOH layer (0.03 mm) to achieve double-layer isolation; Step 6: Graduated braid layer 7: uses ultra-high molecular weight polyethylene fiber (Dyneema ® SK75), pitch 1.5 mm at both ends; transition zone pitch 2.8 mm; middle section pitch 4.5 mm, D max :D min = 3.5:1.

[0033] Comparative Example 1 The difference from Example 1 is that when preparing the energy dissipation layer 4, the super-elastic nickel-titanium alloy wire is laid parallel (non-spiral) outside the inner jacket 3 by a guide roller, and then wrapped and fixed with a layer of glass fiber yarn with uniform braid density.

[0034] Comparative Example 2 The difference compared with Example 1 is that the gradient braid layer 7 is replaced by a simple two-section: 150mm pitch 1.8mm at both ends, and the middle part is directly switched to pitch 3.6mm without transition zone.

[0035] Comparative Example 3 The difference compared with Example 1 is that the energy dissipation layer 4 in Example 1 is cancelled, i.e. the hydrogen barrier layer 5 is directly applied around the inner sheath 3.

[0036] Comparative Example 4 The difference compared with Example 1 is that the super-elastic nickel-titanium alloy wire in the energy dissipation layer 4 is not coated with ceramic.

[0037] Comparative Example 5 The difference compared with Example 1 is that the hydrogen barrier layer 5 is cancelled.

[0038] Comparative Example 6 The difference compared with Example 1 is that the gradient braid layer 7 is modified to a uniform density reinforcing layer (pitch 2.5mm) without gradient.

[0039] The optical cables prepared in Examples 1-4 and Comparative Examples 1-6 are subjected to performance tests, and the test methods and standards are as follows: 1. Repeated bending performance: Referring to IEC 60794-1-21:2015 Optical Fibres, Cables and Accessories-Part 1-21: General Specification-Measurement Methods and Test Procedures- Mechanical Test Methods, a certain length of optical cable sample is taken, and the middle part of the optical cable is bent 180° around a cylinder with a specified diameter (such as a radius of 20mm) on a special device, and is repeatedly bent at a specified rate for 1000 times. After testing, it is checked whether the optical fiber is broken, and the additional loss (Δa) is tested.

[0040] 2. Limit bending performance: Referring to IEC 60794-1-21:2015 Optical Fibres, Cables and Accessories-Part 1-21: General Specification-Measurement Methods and Test Procedures- Mechanical Test Methods, the optical cable sample is bent at least one turn around a mandrel with a diameter of 10mm, and after being taken off, it is visually inspected whether the optical cable sheath appears permanent kink or obvious crease.

[0041] 3. Dynamic bending fatigue: Referring to IEC 60794-1-21:2015 Optical Fibres, Cables and Accessories-Part 1-21: General Specification-Measurement Methods and Test Procedures- Mechanical Test Methods, the optical cable sample is fixed on a clamp, and is cyclically bent within ±90° at a certain frequency (such as 1Hz), and the additional loss is recorded in real time or periodically until a predetermined number of cycles (such as 5000 times) is reached.

[0042] 4. Crush resistance: According to GB / T 7424.21-2021 "Optical fiber cables - Part 21: Mechanical test methods - Mechanical performance test methods", the optical cable sample is placed flat, and pressure is applied to the optical cable at a specified rate through two parallel flat plates until its outer diameter is compressed by 50%, and maintained for a certain period of time. During the entire process or after unloading, the additional loss of the optical fiber is immediately measured.

[0043] 5. Long-term reliability: Take the optical cable sample, first test the initial performance (such as repeated bending loss), place the sample in a constant temperature and humidity chamber, and continuously place it under severe conditions (such as 85°C, 85% RH) for 1000h, take it out after recovery in standard environment, test the same performance again, and calculate the performance retention rate.

[0044] The test results are shown in Table 1.

[0045] Table 1 Performance test results

[0046] Result analysis: Comparative Example 1: The parallel laying of the super-elastic nickel-titanium alloy wire leads to its inability to be fully stretched to trigger the super-elastic phase change when bending, and the energy dissipation efficiency is greatly reduced, so the repeated bending and dynamic fatigue performance is significantly worse than Example 1, proving that the spiral twisting structure is crucial to the function of the alloy wire.

[0047] Comparative Example 2: The gradient braided layer 7 has a density that jumps between high and low, forming a clear mechanical performance interface, which becomes a stress concentration point, so bending failure occurs in the extreme bending test, proving that the design without a transition zone is a structural weak point.

[0048] Comparative Example 3: After removing the energy dissipation layer 4, the optical cable loses the core mechanism of actively dissipating mechanical energy, and the bending stress is completely passively borne by the optical fiber, resulting in fiber breakage after repeated bending, and all mechanical properties are the worst, proving the fundamental necessity of the layer design.

[0049] Comparative Example 4: The super-elastic nickel-titanium alloy wire has no ceramic coating, losing the first barrier to hydrogen atoms. In the accelerated aging environment, hydrogen atoms invade the alloy wire lattice, causing hydrogen embrittlement, which severely degrades its super-elastic function, so the long-term reliability (performance retention rate 65%) decreases sharply, while the initial performance is less affected.

[0050] Comparative Example 5: After removing the system-level hydrogen barrier layer 5 (aluminum plastic composite tape / EVOH), only relying on the protection of the super-elastic nickel-titanium alloy wire itself. In severe aging conditions, insufficient protection increases the risk of hydrogen embrittlement, and the long-term reliability (retention rate 70%) also decreases significantly, but in combination with Comparative Example 4, it proves the effectiveness of the "ceramic coating + hydrogen barrier layer 5" double protection.

[0051] Comparative Example 6: The uniformly woven layer failed to provide targeted reinforcement at the high-stress ends and also failed to optimize the flexibility in the middle, resulting in an unreasonable stress distribution. Therefore, its repeated bending, extreme bending, and anti-flattening performance were all inferior to Example 1 with a gradient design, demonstrating the value of gradient optimization.

[0052] Based on all the comparative data, it is clear that the absence or improper design of any part of the triple collaborative design in the embodiments of the present invention will lead to significant shortcomings in the performance of the optical cable in specific aspects: The structure and integrity of the energy dissipation layer 4 directly determine the core performance of repeated bending resistance and fatigue resistance. The transition design of the gradient braided layer 7 determines the optical cable's ability to resist extreme bending and optimize stress distribution. The integrity of the hydrogen barrier layer 3 and the ceramic coating is the key to ensuring that the above-mentioned high performance does not degrade and maintains reliability during long-term use.

[0053] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0054] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A bend-resistant multi-core indoor optical cable, characterized in that, It includes, from the inside out, an optical fiber unit, a water-blocking layer, an inner sheath, an energy dissipation layer, a hydrogen barrier layer, an outer sheath, and a gradient braided layer; The energy dissipation layer is made of multiple super-elastic nickel-titanium alloy wires and high-strength fibers spirally twisted together. The braiding density of the gradient braided layer decreases in a stepwise manner from both ends to the middle along the optical cable axis through at least three sections with different braiding densities.

2. The bend-resistant multi-core indoor optical cable according to claim 1, characterized in that, The braiding density D at both ends of the optical cable max With the weave density D in the middle min The ratio is (2.0-3.5):

1.

3. The bend-resistant multi-core indoor optical cable according to claim 1, characterized in that, The surface of the superelastic nickel-titanium alloy wire is coated with an alumina or silicon nitride ceramic coating.

4. The bend-resistant multi-core indoor optical cable according to claim 3, characterized in that, The phase transformation end temperature Af of the superelastic nickel-titanium alloy wire is below 20℃, the diameter of a single wire is 0.10mm-0.13mm, and the number is 6-10.

5. The bend-resistant multi-core indoor optical cable according to claim 1, characterized in that, The gradient woven layer is made of polyethylene terephthalate or ultra-high molecular weight polyethylene fiber.

6. The bend-resistant multi-core indoor optical cable according to claim 1, characterized in that, Both the inner and outer sheaths are made of thermoplastic polyurethane.

7. The bend-resistant multi-core indoor optical cable according to claim 1, characterized in that, The hydrogen barrier layer is made of metallized polyester film or co-extruded ethylene-vinyl alcohol copolymer layer.

8. The bend-resistant multi-core indoor optical cable according to claim 1, characterized in that, The water-blocking layer is water-blocking powder filling the gaps between optical fiber units or water-blocking yarn wrapped around them.

9. A method for preparing a bend-resistant multi-core indoor optical cable according to any one of claims 1-8, characterized in that, Includes the following steps: S1: After coloring multiple optical fibers, they are twisted together to form an optical fiber unit. Aramid fibers are wrapped around the outer periphery of the optical fiber unit and a water-blocking material is applied to form a water-blocking layer. S2: Extrusion forming an inner sheath covering the water-blocking layer; S3: Multiple ultra-elastic nickel-titanium alloy wires and high-strength fibers are spirally twisted together on the outside of the inner sheath to form an energy dissipation layer; S4: A hydrogen barrier layer is formed outside the energy dissipation layer; S5: An outer sheath is formed by extrusion outside the hydrogen barrier layer; S6: Use a CNC braiding machine to braid a gradient braided layer on the outer sheath: Through a preset program, control the braiding machine to use different braiding pitches in different sections of the optical cable axis to form a gradient braided layer.

10. The method for preparing the bend-resistant multi-core indoor optical cable according to claim 9, characterized in that, The braiding pitch is 1.5mm-2.0mm in the high-density areas at both ends of the optical cable and 3.2mm-4.5mm in the low-density area in the middle.

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