An orbital angular momentum assisted extended reach CPDM-Ro-FSO system under diverse weather instabilities

Abstract

An orbital angular momentum (OAM)-assisted 640 Gbps circular polarization division multiplexing (CPDM) based extended reach radio over free space optical (Ro-FSO) system is presented in this research paper. For the data modulation, a highly spectrum efficient 256-quadrature amplitude modulation (256-QAM) is employed and proposed system is investigated in the presence of diverse weather instabilities such as clear weather, haze, and rain. CPDM is a highly advanced method that dominates linear PDM (LPDM) since it does not need polarization axis alignment and scattering light is distributed uniformly. For the implementation of OAM, the same wavelength channel has been assigned Laguerre-Gaussian (LG) modes such as LG0,0 and LG13,0, respectively. The detailed performance comparisons of OAM beams and right/left circular polarization states (R/L CPS) are conducted at varied Ro-FSO link lengths using digital signal processing (DSP)-enabled receivers in terms of quality factor (Q-factor) and bit error rate (BER). The proposed system is competent to cover a 45 km distance under clear weather carrying an 80 GHz RF signal, 10 km under haze, and 4 km under the rain with the highest Q factor for all weathers at LG0,0 right circular polarization state (RCPS). Further, a mathematical modelling of the proposed system is presented, and pointing errors are investigated in Optisystem version 20. Results revealed that higher symbol error rates (SERs) can be discernible at higher misalignments between the FSO transmitter and receiver. After doing the comprehensive literature survey, it is observed that the presented system has covered the maximum distance at 640 Gbps capacity using OAM and CPDM.