We demonstrate a bidirectional 12-channel wavelength-division-multiplexing passive optical network (WDM-PON) with 50-GHz channel spacing based on wavelength-locked Fabry-Perot laser diodes. The maximum transmission length is 30 km including 20 km of feeder fiber and 10 km of distribution fiber. The proposed WDM-PON system can accommodate 80 channels with erbium-doped fiber amplifier-based broad-band light sources. We also propose a few methods for the wavelength-independent operation of an optical network termination.