Wavelength tunable laser

A wavelength tunable laser comprising:

• a thermo-electric cooler;
• a distributed feedback portion disposed on the thermo-electric cooler and having a plurality of distributed feedback lasers connected in series, each distributed feedback laser configured to output an optical signal within a different temperature dependent tunable range of wavelengths, the distributed feedback portion outputting an optical signal from one of the distributed feedback lasers;
• and
• a semiconductor optical amplifier optically connected to one end of the distributed feedback portion, the semiconductor optical amplifier amplifying and modulating the optical signal outputted from the distributed feedback portion;
• wherein the semiconductor optical amplifier amplifies and modulates the optical signal based on a location of which a distributed feedback laser within the series of distributed feedback lasers outputs the optical signal, the semiconductor optical amplifier amplifying the optical signal of a first distributed feedback laser greater than a second distributed feedback laser, wherein the first distributed feedback laser is positioned in the series of distributed feedback lasers further away from the semiconductor optical amplifier than the second distributed feedback laser.