Cracks or microfractures after multimode fiber fusion splicing are usually caused by improper fiber preparation, excessive mechanical stress, or suboptimal splicing parameters, and they can compromise splice quality and signal transmission.

Causes of Cracks in Multimode Fiber Splices

1. Improper Fiber Stripping and Cleaving Applying too much force or twisting the fiber during stripping can create microfractures that are invisible to the naked eye but manifest as cracks after fusion splicing. Using the correct stripper for the fiber coating (typically 250µm for bare fibers and 900µm for coated fibers) and maintaining uniform pressure is essential to prevent damage .
2. Poor Cleave Quality Uneven or angled cleaves increase the likelihood of cracks forming at the splice point. A precision cleaver with a sharp blade ensures smooth, perpendicular end faces, reducing stress concentrations during the fusion process .
3. Contamination and Gas Trapping Dust, dirt, or residual coating material on the fiber ends can trap gas during the fusion arc, forming bubbles or cracks in the molten glass . Cleaning fibers with lint-free wipes and 99% isopropyl alcohol before splicing is critical.
4. Incorrect Splicing Parameters Arc power, duration, and alignment settings must match the fiber type. Multimode fibers are more tolerant than single-mode, but excessive arc energy or misalignment can induce stress fractures . Performing arc calibration for the current environmental conditions helps prevent over- or under-fusing.
5. Environmental and Mechanical Stress Temperature fluctuations, humidity, or handling stress after splicing can exacerbate microfractures. Fibers should be handled gently and protected from bending or vibration immediately after splicing .

Implications

Cracks in multimode fiber splices can lead to:

• Increased splice loss and signal attenuation
• Reduced mechanical strength of the fiber
• Potential long-term reliability issues in optical networks

Prevention and Mitigation

• Use proper stripping and cleaving techniques to avoid microfractures.
• Ensure clean fiber ends and a dust-free splicing environment.
• Perform arc calibration and adjust splicing parameters for multimode fibers.
• Inspect splices using the fusion splicer's camera system to detect bubbles or cracks before deployment.
• Handle spliced fibers carefully and avoid bending or twisting near the splice point. By following these best practices, technicians can minimize the risk of cracks and achieve low-loss, high-strength multimode fiber splices .