Abstract: In the manufacture and application of a PLC-ECL type wavelength tunable light source, provided is a wavelength tunable mechanism with improved performance and stability, a light source with improved packaging performance and mass productivity, and a light source applied to a WDM-PON with initialization and stabilization functions. The wavelength tunable light source having a PLC (planar lightwave circuit)-ECL (external cavity laser) structure includes a first housing in which a semiconductor optical gain medium is mounted, a second housing in which a PLC device is mounted, and a third housing in which an optical fiber is mounted. The first, second, and third housings make an optical axis alignment through an optical coupling lens and combined in a laser welding method.