Seven-core neodymium-doped phosphate all-solid photonic crystal fibers

We demonstrate a single-mode seven-core Nd-doped phosphate photonic crystal fiber with all-solid structure with an effective mode field diameter of 108 mu m. The multicore fiber is first theoretically investigated through the finite-difference time-domain method. Then the in-phase mode is selected experimentally by a far-field mode-filtering method. The obtained in-phase mode has 7 mrad mode field divergences, which approximately agrees with the predicted 5.6 mrad in seven-core fiber. Output power of 15.5 W was extracted from a 25 cm fiber with slope efficiency of 57%.