Image of a bubble at the fusion splice between two ordinary multimode fiber optics. This bubble causes extreme fiber optics splicing high loss as shown visually via Visual Fault Locator (VFL) on the right hand side image.
This bubble resulted from dirt on the fiber end surface. Proper care should be taken care of during cleaning process of fiber optics by using appropriate cleaning device such as isoprophyl alcohol.
It is better to redo the splicing immediately so as to obtain minimum splicing loss possible.
I have been in the field of fiber optics since early 1990s. I gained fiber optics skills and knowledge via my working experience as end-user, main contractor and sub-contractor and finally as an optical fiber enterpreneur.