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Orbital angular momentum (OAM), inherent to light beams characterized by helical phase fronts, represents an alternative spatial degree of freedom for photons. In recent years, OAM-based communication has gained significant attention as a potential solution to increase the capacity and spectral efficiency of optical fiber communication systems. In optical fibers, OAM modes can be generated and manipulated by utilizing specialized optical components and techniques. One approach involves using specially designed optical fibers, such as ring–core fibers, which have the capability to support multiple OAM modes. In the manufacturing process, the ring fiber is hardly made perfectly, especially the doped-cores. The introduced defect breaks the symmetry of the ring–core, which has a serious impact on OAM mode transmission. Using a material with a slightly higher refractive index than the cladding to wrap the ring–core is effective in reducing impairment of defects. After numerical simulation, the proposed method improves the walk-off length by a factor of 2–40. [ABSTRACT FROM AUTHOR]

A prototype of a high temperature superconducting (HTS) transceiver sub-system for applications in a TD-SCDMA, one of the third generation (3G) communication standards, base station has been developed. Both the HTS sub-system and the conventional counterpart have been implemented into a TD-SCDMA commercial communication network and comparison test studies were carried out. The measured results showed that the HTS sub-system could remarkably improve the RF performance of both transmitting and receiving chains. [ABSTRACT FROM AUTHOR]

In order to improve the performance of a communication system, a novel concept of low-crosstalk demodulating vortex beams by a combination of partial-receiving apertures (PRAs) is proposed. The corresponding theory analysis and simulations are performed for certifying the valid of the proposed concept in theory. A proof-of-concept experiment is also proposed and established to verity the feasibility of the proposed concept in practice. Based on the captured intensity-array profiles in experiments, the total crosstalk, which is induced by partial receiving apertures, can be evenly distributed among the parasitic orbital angular momentum (OAM) modes, then the maximum ratio of intensity between the induced parasitic OAM modes and the propagated OAM modes can be notably decreased when two unsymmetrical PRAs are utilized. The measured bit error rate curves (with respect to the differently-placed PRAs) also show that the performance of system can be improved in sequence when three ways of one PRA, two symmetric PRAs and two asymmetric PRAs are orderly utilized for demodulating OAM beams, respectively. Besides, the measured results also demonstrate that the proposed system performances are declined with the increases of data rates or propagation distances. Consequently, our proposed concept in this paper is valid and reliable in both theory and practice, and then can be used to demodulate the vortex beams with low crosstalk for free-space optical communication in future. [ABSTRACT FROM AUTHOR]