Reduction of coupling loss to photonic crystal fibers by controlled hole collapse: A numerical study

The mode profile evolution of small-core photonic crystal fibers (PCFs) during a gradual collapse of the cladding airholes is investigated. The mode overlap with standard step-index fibers having a small index contrast is calculated, and it is found that overlaps around 90% can be achieved in all cases studied, with the proper degree of hole collapse. Thus, hole collapse induced by, e.g. laser irradiation could prove an efficient and practical way of reducing splice losses when coupling small-core PCFs to other fiber types.