SSB Single Carrier and Multicarrier in C-Band FSO Transmission With KK Receiver

Abstract

With the increasing demand of bandwidth, a higher capacity communication system is required for optical short link and access network. Intensity modulation/direct detection (IM-DD) is considered as a reasonable method in access network, due to its low cost and power consumption. However, it reduces the spectral efficiency compared with IQ modulation. In addition, single-sideband (SSB) signal occupies less bandwidth than double-sideband signal (DSB). However, SSB systems suffer from signal-signal beat interference (SSBI) from photodiodes (PDs). Recently, Kramers–Kronig (KK) receiver is proposed to mitigate SSBI. Meanwhile, single-sideband (SSB) signal is the prerequisite for KK scheme, and this kind of signal is also tolerant to fiber chromatic dispersion and multipath-fading. On the other hand, free-space optical (FSO) communication is becoming a promising candidate for next generation optical access network. Thus we experimentally demonstrate the KK scheme in 20 km SSMF and 20 m FSO links with both single carrier signal and multicarrier signal. We compare the performance between them with and without pre-equalization (pre-EQ). With the help of probabilistically shaped (PS) mapping to gives an increase in the sensitivity over an additive white Gaussian noise (AWGN). We reach a 117bit/s transmission with a spectral efficiency of 5.85 bit/s/Hz of 20 Ghz bandwidth with single modulator and single photodiode (PD) in fiber-FSO system.