Systems and apparatus for data communications comprising a plurality of wavelength tunable submodules in an array is provided. Each submodule has a wavelength tunable laser, and each submodule comprises, as an individual unit, a self-contained wavelength locker having optical and/or optoelectronic functions. The system may be a transponder array comprising a plurality of WDM or DWDM modules. In some embodiments, the individual submodules may comprise photonic integrated wavelength tunable lasers with other optical, electrical and optoelectronic components. Each wavelength tunable submodule incorporated into the module or array can have the same or different optical wavelength and other parameters including but not limited to modulation format. By utilizing the wavelength tunable laser submodules to build a module or array, the need for individual modules dedicated to wavelength sub-bands in the array is eliminated. The same tunable module can be used to fill all the wavelengths on a transmission fiber.