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Evaluation of a high-speed hybrid OAM-OFDM-MDM multiplexed coherent FSO system under desert conditions

Sinha Shivaji, Kumar Chakresh

Optica Applicata

2023

Vol. 53, nr 3

431--445

To meet the needs of future wireless optical networks, this paper introduces a high-speed, hybrid multiplexed, coherent free-space optical (FSO) communication system that integrates an orbital angular momentum (OAM) multiplexed signal with an orthogonal frequency division multiplexing (OFDM) technique. Two independent QAM polarized beams, each carrying in-phase and quadrature (I/Q) phase 16-QAM-OFDM modulated data, are combined using mode division multiplexing (MDM) to increase the capacity of the proposed system. The reason of choosing OFDM is its capability to support higher data rate, and mitigating intersymbol interference (ISI). The signal is detected using a coherent detection-based digital signal processing (DSP) algorithm at the receiver end. The proposed hybrid FSO system is evaluated in low and heavy dust environments using bit error rate (BER), link distance, optical signal-to-noise ratio (OSNR), and received optical power performance matrices. The simulation results demonstrate the successful transmission of a 120 Gb/s single carrier over the longest link ranges of 1.5 and 0.40 km, respectively, under low and heavy dust weather environments below the signal degradation threshold value (forward error correction (FEC) limit) of BER 2.2 × 10–3 in strong turbulent conditions.

Signal-to-noise analysis in a counter-pumped fiber Raman amplifier

Felinskyi G, Dyriv M

Optica Applicata

2014

Vol. 44, nr 4

493--501

The light gain efficiency due to Raman scattering in a distributed fiber Raman amplifier is a subject of our investigation. The detailed analysis of noise properties at one-wave optical signal amplification in a single-mode fiber in the scheme of counter-pumped fiber Raman amplifier is realized in the paper. Experimental results of the amplified spontaneous emission with backward pumping as a base of optical noise evaluation are presented. Raman gain spectrum for a coherent Stokes low-powered signal is calculated and it is compared with the observed spectrum of non-coherent amplified spontaneous emission noise. It is shown that an output optical signal has higher gain than the amplified spontaneous emission and it results in the appreciable growth in the output optical signal-to-noise ratio.