Tunable Parity-Time Symmetry Vortex Laser from Phase Change Material Based Microcavity

Abstract

Abstract Traditional light sources cannot emit the electromagnetic (EM) field with orbital angular momentum (OAM), limiting their applications in modern optics. The recent development of the OAM laser, mainly based on micro- and nanostructures, can satisfy the increasing requirements for on-chip photonics and information capacities. Nevertheless, the static nature of constitutive parameters of photonics structure inherently forbids the attainment of a dynamically tunable OAM laser. Here, we propose a tunable vortex lasing from a micro-ring cavity integrated by a phase change material, Ge2Sb2Te5 (GST225). By modulating the complex refractive index to create an exceptional point (EP) to break the degeneracy of oppositely oriented whispering gallery modes, the micro-laser working at EP can impart an artificial angular momentum, thus emitting vortex beams with well-defined OAM. The grating scatter on the edge of the micro-ring can offer efficient vertical radiation. We find that the vortex laser wavelength from the GST225/InGaAsP dual-layered micro-ring cavity can be dynamically tuned by switching the state of GST225 between amorphous and crystalline while fixing the micro-ring geometry. An electric-thermal model is built to show a tuning range of operating wavelength (EP) from 1544.5 to 1565.9 nm in ~ 25 ns. Our exploration of high-speed tunable PT-symmetry vortex laser opens the door to the next generation of integrated optoelectronic devices for optical computing and communications in both classical and quantum regions.