  Point-to-multi-point (PtMP) optical networks become the main solutions for
network-edge applications such as passive optical networks and radio access
networks. Entropy-loading digital subcarrier multiplexing (DSCM) is the core
technology to achieve low latency and approach high capacity for flexible PtMP
optical networks. However, the high peak-to-average power ratio of the
entropy-loading DSCM signal limits the power budget and restricts the capacity,
which can be reduced effectively by clipping operation. In this paper, we
derive the theoretical capacity limitation of the flexible PtMP optical
networks based on the entropy-loading DSCM signal. Meanwhile, an optimal
clipping ratio for the clipping operation is acquired to approach the highest
capacity limitation. Based on an accurate clipping-noise model under the
optimal clipping ratio, we establish a three-dimensional look-up table for
bit-error ratio, spectral efficiency, and link loss. Based on the
three-dimensional look-up table, an optimization strategy is proposed to
acquire optimal spectral efficiencies for achieving a higher capacity of the
flexible PtMP optical networks.
