Optical Fiber Compressive Strained Layer Bending Strength
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Solution Overview
Problem
Existing optical fibers face challenges in maintaining strength when bent at small radii, leading to reduced long-term reliability and increased manufacturing costs due to methods like carbon coating and altering glass viscosity, which also complicate handling and identification.
Innovation Solution
A silica-based optical fiber with a compressive strained layer at the outermost circumferential portion, formed through controlled heating and stress imparting during manufacturing, achieving a compressive stress of 10 MPa or more and a static fatigue coefficient of 20 or more, without altering the glass composition or adding costly layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the rigidity of the cable is strengthened to prevent optical fibers from bending at a small radius of curvature, then the long-term reliability is improved, but the ease of handling optical fibers deteriorates
Solution Approach 1:
The patent applies local quality by creating a compressive strained layer only at the outermost circumferential portion of the optical fiber, rather than making the entire fiber rigid. This localized compression (10 MPa or more) provides bending resistance where needed while keeping the rest of the fiber flexible and easy to handle during installation.
2Reliability
If the elongation percentage of an optical fiber during screening is made larger to enhance long-term reliability, then the strength is improved, but the strength of glass constituting the optical fiber deteriorates due to increased tensile stress
Solution Approach 1:
The patent applies preliminary anti-action by pre-imparting compressive stress to the optical fiber during manufacturing before the fiber is put into service. This compressive strain (10 MPa or more) counteracts future tensile stresses that would occur during screening and bending, preventing crack propagation and maintaining glass strength throughout the fiber's lifecycle.
3Strength
If the outer surface of the optical fiber is coated with carbon to enhance strength, then the breaking strength is improved, but the manufacturing cost increases and identification function deteriorates
Solution Approach 1:
The patent applies the taking out principle by removing the carbon coating step from the manufacturing process entirely. Instead of adding a carbon layer (which would increase cost and obscure identification markings), the invention achieves strength enhancement through the compressive strained layer formed by controlled heating and stress imparting during the existing manufacturing process.
Solution Approach 2:
The patent uses a temporary compressive strain state created during manufacturing that becomes a permanent beneficial stress distribution. This approach avoids the need for expensive carbon coating materials while achieving comparable or superior strength effects through a simpler, lower-cost thermal and mechanical process.
4Strength
If a glass layer with lower viscosity than SiO2 is provided to transform the glass surface into a compressive stress layer, then the strength is improved, but the manufacturing cost increases due to additional process and the optical properties deteriorate
Solution Approach 1:
The patent applies parameter changes by modifying the stress state and temperature parameters during the existing glass drawing process, rather than changing the glass composition. By controlling heating temperature and applying mechanical stress during manufacturing, the invention creates a compressive strained layer using the same SiO2 glass material, avoiding the need for expensive TiO2-doped or F-doped glass layers and their associated manufacturing complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The optical fiber exhibits excellent strength and reliability while maintaining low manufacturing costs, with improved resistance to bending and reduced risk of stress-related degradation, suitable for FTTH installations and submarine applications.
Implementation Method 1
a compressive strained layer in which a compressive stress remains is formed at the outermost circumferential portion of the jacketing region
Implementation Method 2
the glass filament is heated to a temperature higher than the glass transition point, and then cooled, thereby a compressive strained layer is formed
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
An optical fiber having excellent strength that can be manufactured at low cost, as well as a method for making such optical fiber, is provided. An optical fiber 1 is a silica-based optical fiber comprising a core 11, an optical cladding 12 surrounding the core 11, and a jacketing region 13 surrounding the optical cladding 12 and having a uniform composition throughout from the internal circumference to the outer circumference. A compressive strained layer having a residual compressive stress is provided at the outermost circumference of the jacketing region 13.