Pairs of distributed feedback (DFB) lasers are provided on a substrate. An arrayed waveguide grating (AWG) is also provided on the substrate having input waveguides, each of which being connected to a corresponding pair of DFB lasers. The wavelengths of optical signals supplied from each pair of DFB lasers may be spectrally spaced from one another by a free spectral range (FSR) of the AWG. By selecting either a first or second DFB laser in a pair and temperature tuning to adjust the wavelength, each pair of DFB lasers can supply optical signals at one of four wavelengths, pairs of which are spectrally spaced from one another by the FSR of the AWG. A widely tunable transmitter may thus be obtained.