Air bubbles at the multimode fiber fusion splice

Air bubbles in a multimode fiber fusion splice are voids caused by contamination or improper fusion, leading to high splice loss and reduced optical performance.Causes of Air BubblesAir bubbles appear as dark circular or oval voids within the splice region and are typically caused by contamination on the fiber end-faces. Common sources include:Skin oils from handling the fibersDust or debris from the work environmentResidue from fiber coatings not fully stripped During fusion, these contaminants can vaporize and become trapped in the molten glass, forming bubbles as the splice solidifies .Effects on Multimode Fiber PerformanceBubbles in the splice region can significantly increase insertion loss and reduce return loss. In multimode fibers, even small voids can disrupt the mode coupling, causing uneven light propagation and potential signal degradation . Typical fusion splice losses for multimode fibers are below 0.1 dB, but visible bubbles indicate that the splice will likely exceed acceptable loss thresholds .Prevention and FixesTo prevent or correct air bubbles:Clean the fiber end-faces thoroughly using 99% isopropyl alcohol and lint-free wipes before cleaving .Re-strip and re-cleave the fiber if contamination persists. Ensure the cleaver blade is clean, as a dirty blade can transfer debris to the fiber end .Check fusion parameters: Excessive or insufficient arc energy can worsen splice quality. Run an arc calibration to match the fiber type and environmental conditions .Inspect visually using the fusion splicer's microscope or a handheld scope to detect bubbles before finalizing the splice .Use proper handling techniques: Avoid touching the fiber ends and maintain a clean workspace to minimize contamination .Post-Splice VerificationAfter splicing, perform:Optical loss testing with an OTDR or power meter to ensure insertion loss is within acceptable limits (typically 0.02–0.05 dB for multimode fusion splices), .Mechanical pull tests to confirm splice strength and durability. By following these steps, technicians can minimize the occurrence of air bubbles and maintain high-quality multimode fiber splices.