There is a gap in the multimode fiber fusion splice

Gaps after multimode fiber fusion splicing are typically caused by fiber misalignment, poor cleave quality, or differences in fiber geometry, which can lead to increased splice loss and reduced optical performance. Common Causes1. Fiber Misalignment: Even small transverse or longitudinal offsets between fiber cores can create gaps at the splice point.

Multimode fibers are particularly sensitive due to their larger core diameters and multiple propagation modes, which make precise alignment critical for low-loss splicing. 2. Poor Cleave Quality: The angle and smoothness of the fiber end faces directly affect the fusion process.

Rough or angled cleaves can prevent the fiber ends from fully contacting, leaving microscopic gaps that reduce light coupling efficiency. 3. Fiber Geometry Mismatch: Differences in core diameter, numerical aperture, or refractive index profiles between fibers can result in incomplete fusion or apparent gaps, even when the fibers are aligned.

This is common when splicing fibers from different manufacturers or types (e.g., 50/125 µm vs. 62. 5/125 µm multimode fibers).

4. Contamination: Dust, oil, or debris on the fiber ends or in the splicer V-grooves can prevent proper contact and fusion, creating gaps. 5.

Fusion Parameters: Incorrect arc power, duration, or environmental factors (temperature, humidity, altitude) can lead to under- or over-fusion, resulting in voids or bubbles at the splice point.

Prevention and Correction

Proper Cleaving: Use a precision fiber cleaver recommended by the splicer manufacturer to ensure perpendicular, smooth end faces. Thorough Cleaning: Clean fiber ends and splicer V-grooves with alcohol to remove dust and debris. Accurate Alignment: Use optical core alignment or LID core alignment systems to ensure precise core-to-core contact.

Adjust Fusion Settings: Calibrate the splicer for local conditions and fiber type to optimize arc parameters. Re-cleaving and Re-splicing: If gaps persist, re-cleave the fibers and perform a new splice, checking for bubbles or misalignment during the process.

Impact

Gaps at the splice increase insertion loss and may cause back reflections, reducing overall system performance. In multimode fibers, even small gaps can significantly affect mode coupling and signal quality. By carefully preparing fiber ends, maintaining clean equipment, and using precise alignment and fusion settings, gaps can be minimized, ensuring low-loss, reliable multimode fiber splices.