Reduced Diameter Optical Fiber Dual-Layer Coating Design
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Solution Overview
Problem
Existing optical fibers with reduced diameters face increased micro bending losses and mechanical reliability issues due to excessive differences in primary and secondary coating moduli, leading to coating delamination and fiber attenuation, especially at low temperatures.
Innovation Solution
An optical fiber with a 125 μm outer diameter glass cladding and a dual-layer coating system, where the primary coating has a thickness between 10 and 18 μm and an in-situ tensile modulus of 0.10 to 0.18 MPa, and the secondary coating has a thickness ≤18 μm and an in-situ tensile modulus of 700 to 1200 MPa, satisfying a specific ratio equation to balance micro bending losses and mechanical reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the primary coating has high in-situ modulus to reduce micro bending loss, then micro bending loss decreases, but coating delamination occurs due to excessive difference in thermal expansion coefficients
Solution Approach 1:
The patent applies parameter changes by precisely controlling the in-situ modulus of the primary coating to fall within 0.05-0.20 MPa and the secondary coating within 600-1300 MPa. This parameter optimization resolves the contradiction by finding the optimal balance point where the primary coating is sufficiently compliant to match thermal expansion with the glass cladding, preventing delamination, while still providing adequate micro bending protection.
Solution Approach 2:
The patent uses composite materials by implementing a dual-layer coating system with distinctly different modulus characteristics. The primary coating uses soft polymer materials (acrylate, polyurethane, or silicone-based) with low modulus, while the secondary coating uses harder materials for mechanical protection. This composite structure allows each layer to perform its specific function without compromising the other.
2Volume of moving object
If the fiber diameter is reduced to increase cable density, then cable size decreases, but micro bending losses increase due to coating delamination
Solution Approach 1:
The patent applies parameter changes by optimizing the thickness ratio between primary and secondary coatings, with the primary coating thickness t1 satisfying 8 μm ≤ t1 ≤ 20 μm and the thickness ratio t1/t2 between 0.20 and 0.50. This parameter control ensures that the reduced 180 μm diameter fiber maintains adequate coating protection while achieving the desired size reduction for high-density cable applications.
3Strength
If the primary coating modulus is increased to improve mechanical reliability, then mechanical strength improves, but micro bending losses increase due to thermal expansion mismatch
Solution Approach 1:
The patent applies parameter changes by precisely controlling the in-situ modulus of the primary coating to fall within 0.05-0.20 MPa, which is sufficiently low to match the thermal expansion coefficient of the glass cladding. This parameter optimization ensures that the primary coating remains compliant under thermal stress, preventing delamination and maintaining mechanical reliability without inducing micro bending losses.
4Strength
If the secondary coating thickness is increased to improve mechanical protection, then mechanical reliability improves, but the fiber diameter increases beyond reduced size requirements
Solution Approach 1:
The patent applies parameter changes by optimizing the secondary coating thickness t2 to satisfy 16 μm ≤ t2 ≤ 22 μm and controlling the thickness ratio t1/t2 between 0.20 and 0.50. This parameter control allows the secondary coating to provide adequate mechanical protection and handling strength while keeping the overall fiber diameter within the reduced 180 μm specification, achieving both mechanical reliability and size reduction.
Data Source
AI summary
The invention relates to an optical fiber 1 comprising a core 2 and a cladding 3 surrounding the core 2 and having an outer diameter of 125 μm, the optical fiber 1 comprising a cured primary coating 4 directly surrounding the cladding 3 and a cured secondary coating 5 directly surrounding the cured primary coating 4, said cured primary coating 4 having a thickness t1 between 10 and 18 μm and an in-situ tensile modulus Emod1 between 0.10 and 0.18 MPa, said cured secondary coating 5 having a thickness t2 between 10 microns and 18 microns and an in-situ tensile modulus Emod2 between 700 and 1200 MPa, wherein said first and second thicknesses and said first and second in-situ tensile moduli satisfy the following equation:4%<(t1×t2×E mod1×E mod23)/(t1_norm×t2_norm×E mod1_norm×E mod2_norm3)<50%.