Example wavelength tunable lasers are described. One example wavelength tunable laser includes a reflective semiconductor optical amplifier, three couplers, and at least two microring resonators. The reflective semiconductor optical amplifier is connected to one port of the first coupler. Some of the at least two microring resonators are arranged between another port of the first coupler and one port of the second coupler, the others of the at least two microring resonators are arranged between a third port of the first coupler and a second port of the second coupler, and a third port and a fourth port of the second coupler are connected to two ports of the third coupler.