Toward generation of mid-infrared orbital angular momentum beams by tailoring four-wave mixing in chalcogenide photonic crystal fiber

The nonlinear process of orbital angular momentum (OAM) beams in multimode fiber has attracted renewed interest due to its enhanced intermodal nonlinear interactions. Here, we designed and simulated a novel photonic crystal fiber (PCF) based on As2Se3 glass that supports stable OAM modes. By optimizing the structure parameters of the fiber, both the effective index separation and the phase-matching condition of OAM modes were satisfied in the fiber. Mid-infrared OAM light can be generated by intermodal four-wave mixing in the chalcogenide fiber. The idler conversion efficiency at the 5 mu m waveband and the signal optical gain spectrum near 1.9 mu m is calculated when the pump light is around 2.8 mu m. Furthermore, the crosstalk of the FWM process from the other vector modes vanished due to the lower overlap factor compared with the interacting OAM modes. Our work demonstrates that the vortex beam at 5 mu m could be generated, and its conversion efficiency can reach 21.96% with appropriate optimization. (C) 2021 Optical Society of America