It is your lucky day! I have been working on an example dealing with this and based on:
 N. Cvijetic, M. Cvijetic, M.-F. Huang, E. Ip, Y.-K. Huang, and T. Wang, “Terabit Optical Access Networks Based on WDM-OFDMA-PON,” J. Light. Technol., vol. 30, no. 4, pp. 493–503, 2012.
It is pretty advanced stuff, but there are 4 3 GHz subbands.