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

Abstract

The application relates to the technical field of optical elements, and discloses a bending-resistant multi-core indoor optical cable and a preparation method. The optical cable comprises, from inside to outside, 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 formed by spirally twisting a plurality of super-elastic nickel-titanium alloy wires coated with a ceramic coating and high-strength fibers at a specific pitch; and the gradient braided layer is a high-strength fiber braided layer with a continuously and gradually changed braiding density along the axial direction of the optical cable. The super-elastic alloy wires spirally twisted in the application actively dissipate bending mechanical energy, the segmented and gradually changed outer braided layer provides intelligent constraints matched with stress distribution, and the double-layer protection mechanism is used to inhibit hydrogen embrittlement, so that the problems of easy breaking and rapid increase of loss of the existing optical cable caused by energy accumulation and stress concentration under repeated bending are systematically solved.

Description

Technical Field

[0001] This invention relates to the field of optical element technology, specifically to a bend-resistant multi-core indoor optical cable and its preparation method. Background Technology

[0002] With the rapid development of 5G communication, data center construction, and other fields, the application scenarios of indoor optical cables are becoming increasingly complex, placing higher demands on the bending resistance, transmission stability, and ease of installation of optical cables. Multi-core indoor optical cables, due to their ability to achieve multi-channel signal transmission and effectively save laying space, have become one of the mainstream choices for indoor communication cabling. However, in practical applications, indoor optical cables often need to be laid with multiple bends in narrow spaces. After repeated bending, traditional multi-core indoor optical cables are prone to problems such as increased fiber loss, sheath cracking, and structural delamination, which seriously affect communication quality and service life.

[0003] Therefore, in order to address the problems of insufficient bending resistance, uneven stress distribution, and poor transmission stability after repeated bending of existing multi-core indoor optical cables, there is an urgent need to design a bending-resistant multi-core indoor optical cable and a corresponding manufacturing method that can reasonably disperse bending stress, improve bending life, and have a stable structure. Summary of the Invention

[0004] The purpose of this invention is to provide a bend-resistant multi-core indoor optical cable and its manufacturing method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, on the one hand, the present invention provides a bend-resistant multi-core indoor optical cable, comprising, 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.

[0006] The energy dissipation layer is made of multiple super-elastic nickel-titanium alloy wires and high-strength fibers (such as PET yarn) 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.

[0007] The energy dissipation layer uses helically stranded, ceramic-coated, superelastic nickel-titanium alloy wires. The helical structure ensures that the alloy wires primarily bear tension during bending, maximizing their superelastic effect and converting mechanical energy into phase-change internal energy for active dissipation, rather than transferring it to the optical fiber. The outermost gradient braided layer employs a segmented, continuously decreasing density design, providing high-strength constraints at the cable ends where insertion and extraction stresses are concentrated, while maintaining good flexibility in the cable body where frequent bending is required, and avoiding abrupt stress changes through a sufficiently long transition zone. The hydrogen barrier layer acts as a system-level barrier, forming a dual protection against hydrogen corrosion of the alloy wires together with the core water-blocking layer.

[0008] Preferably, the braiding density D at both ends of the optical cablemax With the weave density D in the middle min The ratio is (2.0-3.5):1. This density ratio can balance the strength at both ends of the optical cable and the bending flexibility in the middle, effectively improving the bending life and transmission stability of the optical cable.

[0009] Preferably, the surface of the superelastic nickel-titanium alloy wire is coated with an alumina or silicon nitride ceramic coating. The ceramic coating acts as a dense physical barrier, preventing hydrogen atoms from diffusing into the nickel-titanium alloy wire, thereby effectively suppressing hydrogen embrittlement and ensuring the stability of its superelasticity during long-term use. Simultaneously, the coating enhances the interfacial adhesion between the alloy wire and the surrounding polymer sheath material, improves stress transmission, and provides basic wear-resistant protection during manufacturing and use.

[0010] Preferably, the phase transition end temperature Af of the superelastic nickel-titanium alloy wire is below 20°C, ensuring that the nickel-titanium alloy wire can remain stably in a superelastic state under normal operating conditions, guaranteeing reversible deformation and energy dissipation capability during bending. The diameter of a single wire is 0.10mm-0.13mm, and the number is 6-10, which can ensure the energy dissipation effect while avoiding the increase in optical cable diameter and decrease in flexibility due to excessively thick or numerous alloy wires.

[0011] Preferably, the gradient braided layer is woven from polyethylene terephthalate or ultra-high molecular weight polyethylene fibers, and the thickness of the gradient braided layer is 0.18mm-0.25mm. These fibers possess high strength, high abrasion resistance, and good flexibility, ensuring the structural strength and bending adaptability of the gradient braided layer. The total gradient length L in the gradient braided layer, from the highest density area at the end to the lowest density area in the middle, is... g The proportion of the fiber optic cable length L is 20%-35%, which can ensure a smooth transition of stress from both ends to the middle, avoid stress abrupt changes due to an excessively short transition zone, or a decrease in fiber optic cable flexibility due to an excessively long transition zone, further optimize the stress dispersion effect and improve the bending resistance.

[0012] Preferably, both the inner and outer sheaths are made of 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. This type of material has good elasticity, wear resistance, and flame retardant properties, and can meet the safety requirements for indoor use.

[0013] Preferably, the hydrogen barrier layer is made of metallized polyester film or co-extruded ethylene-vinyl alcohol copolymer layer with a thickness of 0.03mm-0.08mm. These materials have extremely low hydrogen permeability and can isolate the hydrogen source from the external encapsulation. Together with the water barrier layer, they form a systematic protection network from the inside out.

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

[0015] On the other hand, the present invention also discloses a method for preparing the above-mentioned bend-resistant multi-core indoor optical cable, comprising 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.

[0016] In step S3, during the twisting process, controlling the tension of the monofilament at 2.0N±0.5N can ensure the uniformity of the twisting of the energy dissipation layer and avoid damage to the fiber or alloy wire due to excessive tension, or loose structure due to insufficient tension. In step S6, the program control of the CNC braiding machine can accurately realize the linear gradient of the density of the gradient braided layer, ensuring the stress dispersion effect.

[0017] Preferably, 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.

[0018] Mechanism of action: When bending forces are applied to the optical cable, the outermost segmented gradient braided layer first provides a gradient constraint that matches the axial stress distribution (high at both ends, low in the middle), strengthening the high-stress area while avoiding local stress peaks through a smooth transition. As the external force is transmitted inward, the energy dissipation layer, composed of helically stranded superelastic nickel-titanium alloy wires, becomes the main load-bearing and energy-dissipating unit. Under tensile stress, the alloy wires undergo stress-induced martensitic phase transformation, converting a large amount of mechanical energy into reversible phase transformation energy within the material and dissipating it, thus significantly attenuating the net stress transmitted to the optical fiber. The inner aramid fiber and stranded optical fiber structure act as a final buffer. Throughout the entire process, a protective system consisting of a ceramic coating on the superelastic nickel-titanium alloy wires, an external hydrogen barrier layer, and an internal water-blocking layer ensures the stable performance of the energy dissipation components during long-term use. Each functional layer achieves effective stress transfer and interface bonding through matched materials (such as a uniform TPU sheath).

[0019] The beneficial effects of this invention are as follows: 1. Breakthrough improvement in repeated bending resistance: Through an active energy dissipation mechanism, the way optical cables cope with bending has been fundamentally changed. After 1000 tests with 180° folds, the additional loss of the product is stable at ≤0.08dB, and there is no fiber breakage. This solves the core pain points of traditional optical cables, such as high loss and easy fiber breakage in this type of test.

[0020] 2. Excellent resistance to extreme mechanical stress: The combination of gradient constraint structure and high-strength braided layer enables the optical cable to perform well in extreme bending (KINK) and anti-flattening tests, with extremely low additional loss (≤0.03dB) and strong robustness.

[0021] 3. Long dynamic fatigue life: The hyperelastic phase transition is reversible and fatigue resistant, which makes the performance of the optical cable very low after thousands of bending cycles, making it suitable for scenarios that require frequent plugging and unplugging or dynamic wiring.

[0022] 4. Long-term reliability is systematically guaranteed: The innovative double-layer hydrogen protection design (ceramic coating + hydrogen barrier layer) effectively suppresses the risk of hydrogen embrittlement of nickel-titanium alloys. After accelerated aging under high temperature and high humidity, the key performance retention rate exceeds 95%, and the expected lifespan is significantly extended.

[0023] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 A schematic diagram of the structure of a bend-resistant multi-core indoor optical cable according to an embodiment of the present invention is shown; Explanation of reference numerals in the attached figures: 1. Fiber optic unit; 2. Water-blocking layer; 3. Inner sheath; 4. Energy dissipation layer; 5. Hydrogen barrier layer; 6. Outer sheath; 7. Gradient braided layer. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] It should be noted that all reagents and raw materials used in this invention are commercially available, and the reagents are of analytical grade.

[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] 0.11mm alloy wire (Af=10℃), PET yarn (breaking strength approximately 25 cN / dtex), stranding pitch 60mm; Step 4: Hydrogen barrier layer 5: A 0.05 mm thick EVOH layer is formed by co-extrusion; Step 6: Gradient braided layer 7: 200mm at both ends (accounting for 26.7% of the 1.5-meter optical cable), pitch 1.6mm; transition zone 100mm, pitch 2.2mm; middle pitch 4.0mm, D max :D min =2.5:1.

[0030] Example 3

[0031] The main difference from Example 1 is: Step 1: Fiber unit 1 is an 8-core 200μm outer-coated fiber; Step 3: Energy Dissipation Layer 4: Use 6 roots 0.11mm alloy wire (Af=18℃), PET yarn (breaking strength approximately 35cN / dtex), stranding pitch 85mm; Step 5: The outer sheath 6 has a thickness of 0.20mm; Step 6: Gradient braided layer 7: 100mm at both ends (20% of a 1-meter optical cable), pitch 2.0mm; transition zone 80mm, pitch 2.8mm; middle pitch 3.2mm, D max :D min =2.2:1.

[0032] Example 4 The main difference from Example 1 is: Step 3: The energy dissipation layer 4 is coated with silicon nitride; Step 4: Hydrogen barrier layer 5: First wrap the aluminum-plastic composite tape, then co-extrude the EVOH layer (0.03mm) to achieve double-layer isolation; Step 6: Gradient braided layer 7: Using ultra-high molecular weight polyethylene fiber (Dyneema) ® SK75), pitch at both ends 1.5mm; pitch in the transition zone 2.8mm; pitch in the middle 4.5mm, D max :D min =3.5:1.

[0033] Comparative Example 1 Compared with Example 1, the difference is that when the energy dissipation layer 4 is prepared, the superelastic nickel-titanium alloy wire is laid parallel (non-spiral) on the outside of the inner sheath 3 through the guide wheel, and then fixed by a layer of glass fiber yarn with uniform weaving density.

[0034] Comparative Example 2 Compared with Example 1, the difference is that the gradient braided layer 7 is changed to a simple two-section design: each end has a 150mm pitch of 1.8mm, and the middle section directly switches to a pitch of 3.6mm, without a transition zone.

[0035] Comparative Example 3 Compared with Example 1, the difference is that the energy dissipation layer 4 in Example 1 is omitted, that is, the hydrogen barrier layer 5 is directly wrapped outside the inner sheath 3.

[0036] Comparative Example 4 The difference compared to Example 1 is that the superelastic nickel-titanium alloy wire in the energy dissipation layer 4 has no ceramic coating.

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

[0038] Comparative Example 6 Compared with Example 1, the difference is that the gradient braided 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 were subjected to performance tests. The test methods and standards are as follows: 1. Repeated bending performance: Refer to IEC 60794-1-21:2015 "Optical cable - Part 1-21: General specification - Basic optical cable test procedures - Mechanical test methods", take a certain length of optical cable sample, and bend the middle of the optical cable around a cylinder of specified diameter (e.g., radius 20mm) by 180° on a special equipment, and repeat the bending 1000 times at a specified rate. After the test, check whether the optical fiber is broken and test the additional loss (Δα).

[0040] 2. Extreme bending performance: Refer to IEC 60794-1-21:2015 "Optical cable - Part 1-21: General specification - Basic optical cable test procedures - Mechanical test methods", bend the optical cable sample around a 10mm diameter core at least once, and then visually inspect the optical cable sheath for permanent bending (Kink) or obvious creases.

[0041] 3. Dynamic bending fatigue: Refer to IEC 60794-1-21:2015 "Optical cable - Part 1-21: General specification - Basic optical cable test procedures - Mechanical test methods", fix the optical cable sample in the fixture and cyclically bend it at a certain frequency (e.g., 1Hz) within a range of ±90°. Record the additional loss in real time or periodically until the predetermined number of cycles (e.g., 5000 times) is reached.

[0042] 4. Compression resistance: Refer to GB / T 7424.21-2021 "General Specification for Optical Cables Part 21: Basic Test Methods for Mechanical Properties of Optical Cables", place the optical cable sample flat, pass it through two parallel plates, and apply pressure to the optical cable at a specified rate until its outer diameter is compressed by 50%, and maintain it for a certain period of time. During the entire process or immediately after unloading, measure the additional loss of the optical fiber.

[0043] 5. Long-term reliability: Take an optical cable sample, test the initial performance (such as repeated bending loss), place the sample in a constant temperature and humidity chamber, and place it under harsh conditions (such as 85℃, 85% RH) for 1000 hours. After taking it out, restore it under standard conditions, 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] Results analysis: Comparative Example 1: The parallel laying of the superelastic nickel-titanium alloy wires prevents them from being fully stretched to induce the superelastic phase transition when bent, resulting in a significant reduction in energy dissipation efficiency. Therefore, the repeated bending and dynamic fatigue performance is significantly worse than that of Example 1, proving that the helical stranding structure is crucial for the alloy wire to perform its function.

[0047] Comparative Example 2: The density of the gradient braided layer 7 changes abruptly between high and low, forming a clear mechanical property interface and becoming a stress concentration point. Therefore, it fails in bending during the ultimate bending test, proving that the design without a transition zone is a weak point in the structure.

[0048] Comparative Example 3: After removing the energy dissipation layer 4, the optical cable lost its core mechanism of actively dissipating mechanical energy. The bending stress was entirely passively borne by the optical fiber, resulting in fiber breakage after repeated bending. All mechanical properties were the worst, proving the fundamental necessity of this layer design.

[0049] Comparative Example 4: The superelastic nickel-titanium alloy wire lacks a ceramic coating, thus losing its first barrier against hydrogen atoms. In an accelerated aging environment, hydrogen atoms invade the alloy wire lattice, causing hydrogen embrittlement and severely degrading its superelasticity. As a result, its long-term reliability (performance retention rate of 65%) drops 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), protection relied solely on the coating of the superelastic nickel-titanium alloy wire. Under harsh aging conditions, insufficient protection led to an increased risk of hydrogen embrittlement, and long-term reliability (70% retention rate) also decreased significantly. However, when combined with Comparative Example 4, it demonstrated the effectiveness of the dual protection of "ceramic coating + hydrogen barrier layer 5".

[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 superelastic nickel-titanium alloy wires spirally twisted with high-strength fibers. The phase transformation end temperature Af of the superelastic nickel-titanium alloy wires is lower than 20°C. The surface of the superelastic nickel-titanium alloy wires is covered with an alumina or silicon nitride ceramic coating. The hydrogen barrier layer is made of metallized polyester film or co-extruded ethylene-vinyl alcohol copolymer layer; 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 diameter of a single superelastic nickel-titanium alloy wire is 0.10mm-0.13mm, and the number of superelastic nickel-titanium alloy wires is 6-10.

4. 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.

5. 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.

6. 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.

7. A method for preparing a bend-resistant multi-core indoor optical cable according to any one of claims 1-6, 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.

8. The method for preparing the bend-resistant multi-core indoor optical cable according to claim 7, 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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