Numerical evaluation of bidirectional high-speed data transmission over turbulence tolerable FSO link employing WDM-OAM multiplexing and DP-QPSK modulation techniques

Abstract

Orbital angular momentum (OAM) mode multiplexing is achieving utmost interest for the enhancement of transmission capacity and spectral efficiency. We have reported a (2 × 8 × 112 Gbps) 1792 Gbps bi-directional FSO link based on WDM-OAM multiplexing and dual-polarization quadrature phase-shift keying (DP-QPSK) modulation technique. An optical frequency comb lines (OFCL) generator, capable to generate 44 comb lines with flatness∼0 dB is employed as a broadband laser source. The efficiency of the system is not only checked for clear weather but also for different turbulence situations (weak, moderate, and strong atmospheric turbulence). According to the best of our knowledge, this is the first one where the effect of atmospheric turbulence on DP-QPSK data carrying OAM modes has been checked for a bidirectional link. The combination of coherent detection with digital signal processing is utilized for compensating wave-form distortion and noise cancellation due to atmospheric turbulence. A very low power penalty of 1.65 dB in clear weather and 4.91 dB in strong atmospheric turbulence at a BER∼10 −9 with open eye and clear constellation diagrams depicts the feasibility of the proposed system.