Annular chalcogenide photonic crystal fiber for broadband mid-IR optical vortex modes supercontinuum generation

We propose a ring shaped sulfide based-chalcogenide photonic crystal fiber (PCF) that supports mono-radial pure vector modes (m=1). It consists of an As2S3 ring PCF composed from an annular core within a central air-hole and a ring of six missing air-holes. The proposed design is found to enforce wavelength independent “doughnut-shaped” mono-annular guided modes. This property is prominent since it opens the possibility to achieve the broadest and purest fiber SC vortex light supported by fiber eigenmodes of the fundamental radial order. By pumping the designed structure at 2.5 μm with 50 fs-5 nJ pulses, the generation of broadband coherent optical vortex supercontinuum in the mid-IR region extending from 1120 to 3650 nm at -20 dB level is obtained. This structure with such mid-IR transmission window provides large nonlinearities and shows to be very promising for SC generation and mode division multiplexing applications by means of OAM modes.