Using a colorless weak-resonant-cavity (WRC) FPLD injected by a centralized light source, we have experimentally demonstrated a superior performance of 20-Gbps uplink transmission in a WDM-PON. Even though the typical modulation bandwidth of a WRC-FPLD is only ∼1.25 GHz, using spectrally-efficient 32-QAM OFDM or SC-FDE modulation, 20-Gbps uplink signals can achieve the FEC limit after 25-km dispersion-uncompensated single-mode fiber transmission. Because of the advantage of lower PAPR, the SC-FDE signals outperform the OFDM signals with the fixed 32-QAM format in the proposed system; moreover, SC-FDE scheme can be another promising candidate for uplinks in WDMPONs, for its simplification to ONUs. The signal at the mode of 1560.7 nm shows similar quality with the signal at the modes of 1545.3 nm and 1574.7 nm, the WRC-FPLD, accordingly, has wide injection wavelength range from at least 1545.3 nm to 1574.7 nm. With the mode spacing of 0.55 nm, consequently, we have demonstrated the applicability of the colorless WRC-FPLD on supporting up to 36 channels in the WDM-PON.