Two-phased capacity upgrade method for NG-PON2 with hierarchical star 8-QAM and square 16-QAM

We propose a two-phased upgrade method of capacity per wavelength in NG-PON2. Coexistence with conventional NG-PON2 ONUs and a higher capacity are realized using star 8-QAM and square 16-QAM in phases 1 and 2, respectively.