Improvement of the pump power coupling in double cladding photonic crystal fiber

An optical coupler constituted by a long-period grating (LPG) written into the single-mode core of a double- cladding photonic crystal fiber (DCPCF) is designed. The LPG allows an optimal power transfer from the inner cladding modes toward the fundamental mode guided in the core. The optical coupler feasibility is numerically demonstrated and its refinement is obtained via a large number of simulations. The calculations highlight that the 25% of the total input power is transferred from the inner cladding modes toward the fundamental mode guided into the core.