The cost and backward compatibility are the key factors for next passive optical network(PON) evolution after commercial 10G PON readiness. To leverage the investment from operator for current optical distribution network(ODN) deployment and support co-existed PON system, this article focuses on the technical solution at physical layer for 25G PON with relevant cost control based on time division multiplexing(TDM) mode related with single wavelength. To support 50G PON evolution, it briefly introduces the characteristics of modulation scheme and the newly introduced digital signal processing (DSP) technology. Finally, it summarizes the latest industrial situation and gives the forecast evolution of 25G and 50G PON.