Embodiments of a periodically filtered broadband light source are described. The periodically filtered broadband light source includes a periodic spectral filter coupled to an optical gain element to generate a light and to filter the light into a plurality of individual spectral slices. The broadband light source includes an isolator coupled to the optical gain element. The periodic filter can be a reflective filter. The periodic filter can adjust an optical power in each of the spectral slices. The periodic filter can include one or more control elements to control an optical power in each of the spectral slices. Further, a wavelength division multiplexing passive optical network system is described that includes the periodic broadband light source to send individual spectral slices to wavelength lock one or more transceivers. The individual spectral slices sent by the periodic broadband light source match wavelength channels of a wavelength division multiplexer/de-multiplexer.