Spatial mode converter of higher order modes by coupling between two different fibers inserted in a microstructured cane

Abstract

We propose a novel mode selective directional coupler based on microstructured cane for higher order modes excitation. The coupler is composed by a single mode fiber (SMF) and a few mode fiber (FMF) inserted in a periodic air-silica microstructured cane (ASMC) on either side of the central hole. The internal geometry of the cane is adjusted to satisfy the phase matching condition between the selected modes of the ASMC and thus to allow the modal conversion between them. The intermodal coupling is minimized by optimizing the structure to improve the beam quality at the output of the component. The proposed technique is linked to mode division multiplexing (MDM) to increase the capacity of the optical communication systems. At the output of the directional coupler SMF-FMF, the LP02 and LP11 are properly excited by satisfying the MDM systems requirements in terms of fiber isolation (≥15 dB), modal crosstalk (≥17 dB) and total losses (≤0.8 dB).