The extinction ratio (ER) for the downstream and upstream transmission signals needs to be compromised for the WDM-PON systems with directly modulated lasers at the center office and reflective semiconductor optical amplifiers at the user ends. We propose to enhance the performance by adding a FP etalon before the receiver of each optical network unit (ONU). The etalon performs spectral reshaping and then waveform reshaping to the downstream signals. This allows the use of low- ER downstream signals that reduce the intensity fluctuation of RSOA-remodulated upstream signals. This approach can also extend the transmission distance by reducing the transient chirp. Colorless operation can still be obtained since the same etalon can be used to enhance multiple wavelength channels. Experimental results verify considerable performance improvement on WDM-PONs with 10-Gbps and 1.25-Gbps data rates for the downstream and upstream transmission, respectively.