A multi-channel optical transmitter or transceiver uses a reversed planar lightwave circuit (PLC) splitter as an optical multiplexer to combine optical signals at different channel wavelengths into a multiplexed optical signal. The reversed PLC splitter includes 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 or without optical fibers. The PLC splitter includes wavelength independent branched waveguides that combine the optical signals received on the mux input ports into the multiplexed optical signal on the mux output port.