If the tube expands quickly and the fiber expands slowly, will the fiber break at high temperatures?
In short, yes. Under specific encapsulation structures, if the thermal expansion coefficient of the protection tube is much larger than that of the optical fiber, the violent expansion of the tube can completely pull the fiber apart when the temperature rises.
To understand the physical mechanism behind this, we need to analyze it from three dimensions: thermal expansion coefficient, encapsulation coupling method, and the ultimate tensile strength of the optical fiber.
1. Physical Differences in Thermal Expansion Coefficients
- Quartz Fiber:** Its main component is silicon dioxide ( \text{SiO}_2 ), which has an extremely low thermal expansion coefficient, typically around \alpha_{\text{fiber}} \approx 0.5 \times 10^{-6}\ /\text{K} (or 0.5\ \mu\varepsilon/^{\circ}\text{C} ).
- Protection Tube (e.g., Stainless Steel Tube): Metallic materials generally have large thermal expansion coefficients. For example, a commonly used 316L stainless steel seamless tube has a thermal expansion coefficient of approximately \alpha_{\text{tube}} \approx 16 \times 10^{-6}\ /\text{K} (or 16\ \mu\varepsilon/^{\circ}\text{C} ).
- Expansion Difference: The difference in thermal expansion coefficients between the two is \Delta\alpha \approx 15.5 \times 10^{-6}\ /\text{K} . This means that when the temperature rises, the free expansion tendency of the steel tube is more than 30