A multi-channel optical transmitter or transceiver includes an optical multiplexer with input and output ports on a single side. The optical multiplexer receives optical signals at different channel wavelengths on a plurality of mux input ports on one side and combines the optical signals into a multiplexed optical signal, which is output on an optical output port on the same side. The optical multiplexer may be located at a distal end of a transceiver or transmitter housing. In one embodiment, the optical multiplexer is a reversed planar lightwave circuit (PLC) splitter including splitter output ports that are used as the mux input ports and a splitter input port that is used as the mux output port. The mux input ports may be optically coupled to respective transmitter optical subassembly (TOSA) modules with optical fibers.