Bubble in multimode optical cable fusion splicer

A bubble in a multimode fiber fusion splice is a void caused by contamination or improper fusion, leading to high splice loss and requiring re-cleaning, re-cleaving, and re-splicing.

What Causes Bubbles

Bubbles appear as dark circular or oval voids in the splice region and indicate high splice loss. They are typically caused by: Contamination on fiber end-faces, such as skin oil, dust, or residual coating not fully stripped. Dirty cleaver blades, which can transfer debris to the fiber during cleaving.

Incorrect arc energy or fiber overlap, where too much heat or excessive fiber contact displaces molten glass outward. Multimode fibers are particularly sensitive because their larger core and graded-index profile make precise alignment more challenging, increasing the risk of bubbles if the fiber ends are not perfectly prepared.

How to Fix Bubbles

To correct a bubble in a multimode splice: Cut back the fiber past the affected area. Re-strip and re-clean the fiber using 99% isopropyl alcohol and lint-free wipes. Re-cleave the fiber with a precision cleaver to ensure a flat, perpendicular end-face.

Re-splice using the correct fusion program for the fiber type. Check cleaver and splicer cleanliness, including V-grooves and electrodes, to prevent recurring contamination. If the bubble persists, verify that the arc calibration matches environmental conditions and fiber specifications, as improper arc settings can exacerbate void formation.

Preventive Measures

Always handle fibers with gloves or tweezers to avoid skin oil contamination. Maintain clean cleaver blades and splicer V-grooves. Use the manufacturer-recommended fusion program for multimode fibers.

Perform regular arc calibration and inspect electrodes for wear. Conduct visual inspection of the splice after fusion to detect bubbles early. By following these steps, technicians can minimize the occurrence of bubbles, ensuring low-loss, high-strength multimode fiber splices suitable for reliable optical network performance.