Design and Fabrication of Low Loss Hole-Assisted Few-Mode Fibers With Consideration of Surface Imperfection of Air Holes

We designed and fabricated a low loss hole-assisted few-mode fiber (HA-FMF) taking the surface imperfections of air holes into consideration. We employed a simulation model with a “defective layer” to estimate the modal loss dependence on the surface imperfections of air holes. We confirmed that the experimental result agrees well with the theoretical calculation. The theoretical studies suggest that the radius of an inscribed circle linking the air holes C has the greatest influence on the additional loss due to the surface imperfections of the air holes in the HA-FMF. We designed and fabricated the hole-assisted two-mode fibers (HA-TMF) according to our theoretical study. We obtained an HA-TMF with losses of 0.20 dB/km in the LP01mode and 0.26 dB/km in the LP11mode in the 1550 nm band. The additional loss induced by surface imperfections can be reduced by controlling the parameter C and this improves the bending properties of the LP11mode even without employing a polishing process for the air holes. Our results show the great potential of the HA-FMF for space-division multiplexing applications.