There are some marks on the fusion spliced ​​optical cable

Connection marks on a fusion-spliced optical cable are typically normal and indicate the location of the splice, but their appearance should be inspected to ensure splice quality.

Understanding Fusion Splice Marks

Fusion splicing permanently joins two optical fibers using an electric arc, creating a continuous path for light with minimal reflection and attenuation . The "marks" you see are usually the result of the fusion process itself, where the fiber ends are melted and fused together. These marks are often visible through the protective splice sleeve or on the fiber under magnification.

When Marks Are Normal

• Visual indication of the splice: The mark shows where the fibers were joined and is expected in all fusion splices .
• Protected by a heat-shrink sleeve: After splicing, a heat-shrink sleeve is applied to protect the joint from moisture and mechanical stress, which may make the mark more noticeable .
• No impact on signal: If the splice was performed correctly, the mark does not affect optical transmission, and insertion loss is typically below 0.1 dB .

When to Be Concerned

• Irregularities or bubbles: Visible bubbles, uneven fusion, or fiber offset may indicate a defective splice .
• High splice loss: If the mark corresponds with signal loss or attenuation higher than expected, the splice may need rework .
• Mechanical damage: Marks accompanied by cracks or microfractures in the fiber coating could compromise long-term reliability .

Best Practices

• Inspect the splice under a microscope to ensure a flat, mirror-like surface and proper core alignment .
• Ensure the protective sleeve is properly heat-shrunk to prevent environmental damage .
• Avoid excessive tension or bending near the splice, as this can create microbends or stress points . In summary, connection marks on a fusion splice are normal, but careful inspection is essential to confirm that the splice is high quality and will maintain reliable optical performance.