Numerical analysis of the LP01 mode excitation in a dual-core directional coupler based on two different fibers inserted in a microstructured cane

We propose a new asymmetric directional coupler including two different fibers for LP01 mode excitation. Two methods are presented to selectively excite the LP01 mode in a few mode fiber (FMF) from a single mode fiber (SMF). The fibers are inserted, parallel to the propagation axis, on either side of the central hole in the microstructured cane before the assembly is tapered. We numerically study this coupler by calculating the effective indices of the propagated modes. By optimizing the index difference between the two fibers, the phase matching condition is satisfied and the power is totally coupled in the reduced zone. At the output of the structure, a broadband coupler with various power splitting ratios is achieved with excellent modal selectivity (>= 96%) with negligible excess and insertion losses (<= 0.33 dB). The principle of reciprocity is validated by exciting the LP01 mode in the SMF from the FMF with low modal conversion losses.