An apparatus comprising a polarization beam splitter optically coupled to a first light path and a second light path and configured to receive a CW light having a plurality of wavelengths, forward a first light beam of the CW light along the first light path, and forward a second light beam of the CW light along the second light path. A first multiplexer coupled to the first light path and configured to de-multiplex the first light beam into a first plurality of channels each corresponding to one of the plurality of wavelengths. A second multiplexer coupled to the second light path and configured to de-multiplex the second light beam into a second plurality of channels each corresponding to one of the plurality of wavelengths. A modulator coupled to the first multiplexer and the second multiplexer and configured to modulate the first plurality of channels and the second plurality of channels.