The orbital angular momentum (OAM) of light is used for increasing the optical communication capacity in the mode division multiplexing (MDM) technique. A novel and simple structure of ring-core photonic crystal fiber (RC-PCF) is proposed in this paper. The ring core is doped by the Schott sulfur difluoride material and the cladding region is composed of fused silica with one layer of well-patterned air-holes. The guiding of Terahertz (THz) OAM beams with 58 OAM modes over 0.70 THz (0.20 THz–0.90 THz) frequency is supported by this proposed RC-PCF. The OAM modes are well-separated for their large refractive index difference above 10−4. The dispersion profile of each mode is varied in the range of 0.23–7.77 ps/THz/cm. The ultra-low confinement loss around 10−9 dB/cm and better mode purity up to 0.932 is achieved by this RC-PCF. For these good properties, the proposed fiber is a promising candidate to be applied in the THz OAM transmission systems with high feasibility and high capacity.
Arbitrary polarization and orbital angular momentum generation based on spontaneously broken degeneracy in helically twisted ring-core photonic crystal fibers
