A transmitter comprising a plurality of modulator and multiplexer (Mod-MUX) units, each Mod-MUX unit operating at an optical wavelength different from the other Mod-MUX units. The transmitter can additional include in each Mod-MUX unit two optical taps and three photodetectors that are configured to allow the respective Mod-MUX unit to be tuned to achieve thermal stabilization and achieve effective modulation and WDM operation across a range of temperatures. The Mod-MUX transmitter avoids the use of a frequency comb. The Mod-MUX transmitter avoids cross-modulation between different modulators for different laser signals.