Cracks in fiber optic multimode fusion splice

Cracks in multimode fiber fusion splices are typically caused by improper fiber preparation, excessive mechanical stress, or incorrect splicing parameters, and they can significantly increase splice loss or cause complete signal failure.

Causes of Cracks

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 propagate during fusion, leading to cracks in the splice region . A poor cleave angle or a worn cleaver blade can also produce uneven end-faces that stress the fiber during the arc .
2. Excessive Arc Energy or Misalignment: Using the wrong fusion program for multimode fibers or applying too much arc energy can overheat the fiber, causing the glass to expand unevenly and crack . Misalignment of the fiber cores during splicing can also introduce stress points that result in fractures .
3. Contamination: Dust, skin oil, or residual coating on the fiber end-face can create localized weak points. During fusion, these contaminants vaporize and may form bubbles or cracks in the glass .
4. Mechanical Stress Post-Splice: Bending, pulling, or improper handling of the fiber after splicing can propagate existing microfractures into visible cracks, especially in multimode fibers with larger cores .

Detection

• Visual Inspection: Modern fusion splicers provide a magnified image of the splice region. Cracks may appear as irregular lines or dark streaks within the splice area .
• Optical Loss Testing: Elevated splice loss or inconsistent backscatter readings can indicate cracks or microfractures affecting light transmission .
• Microscopy: For critical applications, inspecting the splice under a high-power microscope can reveal microcracks not visible on the splicer screen .

Solutions and Prevention

1. Proper Fiber Preparation: Use calibrated strippers and cleavers, apply uniform pressure, and avoid twisting the fiber. Ensure the cleaver blade is sharp and properly maintained .
2. Correct Splice Settings: Select the appropriate fusion program for the multimode fiber type (e.g., OM3/OM4) and verify arc energy settings to prevent overheating .
3. Cleanliness: Thoroughly clean fibers with 99% isopropyl alcohol and lint-free wipes before splicing. Keep the splicer and electrodes free of dust and residue .
4. Electrode Maintenance: Replace or clean electrodes regularly to maintain a stable arc and prevent uneven heating that can cause cracks .
5. Careful Handling: Avoid bending or stressing the fiber immediately after splicing. Use protective sleeves and proper routing to minimize mechanical stress . By following these practices, technicians can minimize the risk of cracks in multimode fusion splices, ensuring low-loss, reliable connections.