“…The concept of using four-dimensional (4D) formats in a rate flexible transceiver 3 and a multi-rate IM-DD transceiver using 4D formats 4 have been proposed. Recently, 8D modulation format has been reported for coherent detection 5,6 and IM-DD systems 7 . In this paper, we propose, design and experimentally investigate a flexible IM-DD transceiver with software-controlled bit rate, using a newly designed 8D format family, which has a spectrum efficiency granularity of 0.125 bit/sym.…”