So you cut a fiber too short. Or you may be adding a Lamplighter™ 2 and needing to extend the reach of some of the fibers you have already installed. All is not lost! You need to couple a new fiber with the old using a suitable connector.
Dwarvin recommends using Aluminum tubing of the appropriate diameter. E.g. when coupling 1.5mm fibers, use 3/32” aluminum tubing. The fibers can be secured further by wrapping tape around the connector. The length of the connector should be at least ~ 10X the diameter of the fiber. So for a 1.5mm connector, the length should be 15mm, or 1.5cm, or 0.6”. Will there be any loss” Yes, there will be a small loss, but only of the order of 5% which is unnoticeable to the eye.
The picture above shows an aluminum connector holding two fibers together.