Optical multiplexers and demultiplexers are provided. In one implementation an apparatus is provided. The apparatus includes a first laser diode pair, a second laser diode pair, a polarization rotator coupled between the first and the second laser diode pairs, and an output port. The first and second laser diode pairs include a first laser diode, a polarization beam splitter, a first quarter waveplate, a filter; a second quarter waveplate, and a second laser diode. The first and second laser diode pairs are coupled to the polarization rotator at the polarization beam splitter of each laser diode pair. In one implementation the apparatus is operable to multiplex distinct light signals emitted from the first and second laser diodes. In another implementation, an apparatus is provided that is operable to demultiplex an input light beam having a plurality of distinct channels.