Abstract: The invention relates to methods, devices, systems and uses of such systems for the generation and detection of electromagnetic fields carrying orbital angular momentum. An electromagnetic wave placed in a resonator having a closed-loop waveguide supporting a guided wave propagating at resonance with angular order, p, and with an angular grating patterned in the closed-loop waveguide, the angular grating having a integer number, q, of grating elements. The angular grating selectively couples the guided wave mode to a free space radiation mode having an OAM quantity, l, and out-of-plane wave vector component, krad,z, and wherein significant coupling to the grating occurs only when the following wave matching condition is satisfied: l=p?mq where: m is the diffraction order of the angular grating, m=1, 2, 3, . . . ,.

Abstract: The invention relates to methods, devices, systems and uses of such systems for the generation and detection of electromagnetic fields carrying orbital angular momentum. An electromagnetic wave placed in a resonator having a closed-loop waveguide supporting a guided wave propagating at resonance with angular order, p, and with an angular grating patterned in the closed-loop waveguide, the angular grating having a integer number, q, of grating elements. The angular grating selectively couples the guided wave mode to a free space radiation mode having an OAM quantity, l, and out-of-plane wave vector component, krad,z, and wherein significant coupling to the grating occurs only when the following wave matching condition is satisfied: l=p?mq where: m is the diffraction order of the angular grating, m=1, 2, 3, . . . ,.