Development of 32-GBaud DP-QPSK free space optical transceiver using homodyne detection and advanced digital signal processing for future optical networks

Free space optical (FSO) communication provides the capacity to deliver high-speed digital data links into the far off and rural factions where topography, set-up cost or groundwork safety pose acute barriers to deployment. The challenges in any FSO system are the transmission impairments and space loss which deteriorate the link performance. This article deals with the design and analysis of a single channel Gray-coded dual polarization-quadrature phase shift keying (DP-QPSK) based FSO communication system with balanced homodyne detection (BHD) and digital signal processing (DSP). We have implemented a series of high-level digital impairment compensation algorithms strategically between the BHD and signal retrieval stages to mitigate the amplitude and phase noise, and compensate for free-space loss. The proposed system exhibits a 3 dB greater receiver sensitivity using optical homodyne detection compared to heterodyne detection. The system performance has been numerically evaluated with regard to bit error rate (BER $$\le 2\times {10}^{-3},$$ i.e. FEC limit), error vector magnitude (EVM), and constellation diagram based on OptiSystem V.16 photonic software. Furthermore, we investigate the joint BER and EVM performance of the proposed system under the influence of launched optical power, laser linewidth, and beam divergence. We obtain the transmission of 32 GBaud DP-QPSK data bearing optical signal up to a link distance of 2.65 km at 128-Gb/s data rate, and an optical signal-to-noise ratio penalty lower than 2.5 dB compared to the back-to-back case. The outcomes of this research demonstrate direct practical relevance and could therefore form the basis for the implementation of next-generation optical wireless networks.