Numerical analysis of eigenmodes and splice losses of thermally diffused expanded core fibers

Field distributions and far-field patterns (FFP's) of the eigenmodes of the rmally diffused expanded core (TEC) fibers are clarified by numerical analy sis. The spot size of the TEC fiber is estimated by using the FFP that can be measured more easily than the near-field pattern (NFP). Splice losses of two TEC fibers are analyzed numerically considering a single or composite effect of gap, offset, and tilt. The results are useful for estimating isol ations of fiber-integrated optical isolators and insertion losses of other fiber-integrated type optical devices. Splice losses considering multiple r eflection between two endfaces of the TEC fibers with gaps are also analyze d numerically. This is useful for the design of fiber-integrated tunable wa velength filters.