On-chip radially and azimuthally polarized vortex beam generation utilizing shallow-etched gratings

Cylindrical vector vortex (CVV) beams, complex light fields that exhibit a vector nature and carry quantized orbital angular momentum states, have been widely investigated due to their rich applications. Current technologies to generate CVV beams using individual polarization and spatial phase manipulations suffer from bulky size and low configurability. In this work, we propose and experimentally demonstrate an approach to generate CVV beams with an integrated device based on silicon nitride microring resonator and embedded top-gratings. The device is capable of generating broad-band radially and azimuthally polarized vortex beams by simply switching the polarization and wavelength of the excited whispering-gallery-modes. In addition, we develop a method to fabricate the devices of shallow-etched top-gratings with only one-step etching. This novel method provides new capabilities to develop on-chip integrated devices with great ease and flexibility.