The wavelength tunable laser includes a thermo-electric cooler (TEC), a distributed feedback portion, and a semiconductor optical amplifier (SOA). The distributed feedback portion is disposed on the thermo-electric cooler and has a plurality of distributed feedback (DFB) lasers connected in series. Each DFB laser is configured to output an optical signal within a different temperature dependent tunable range of wavelengths. Therefore, the distributed feedback portion outputs an optical signal from one of the DFB lasers. The SOA is optically connected to the distributed feedback portion. The SOA amplifies and modulates the optical signal outputted from the distributed feedback portion.