This paper describes the design of a burst-mode ultra-long haul PON trunk fiber protector based on SOA. It's
transparent to protocols and thus compatible with various PON systems. With this technology, the robustness
and transmission distance of PON network can be greatly improved and extended. The fiber protector supports
a maximum transmission distance of 50km and a 1:128 branching ratio. It supports automatic protection
switching of trunk fiber whose longest protection switching time is less than 20ms. In addition, in the design of
the ultra-long haul PON system, by EPON as an example, the ranging of EPON system, RTT compensation
and other parameters also need to be amended. As a result, this article also makes research and description
on synchronization, ranging, time delay compensation, and other key parameters of the EPON system.