Transient propagation mode of fiber fuse leaving no voids.

Fiber fuse ignition and self-termination through a single-mode silica glass fiber pumped by 1480 nm light were observed in situ. The formation of void-free segments is discussed on the basis of examinations of corresponding damage sites and in comparison with known periodic void formation. As an optical discharge pumped at near the propagation threshold power loses its energy, it frequently emits a light pulse instead of forming periodic voids. A similar mode was found just before a stable optical discharge appeared during fiber fuse ignition. This transient mode conversion is the origin of the previously reported irregular void patterns.