Embodiments of the present invention are directed to multiplexer/demultiplexer systems. In one aspect, a multiplexer/demultiplexer system includes an input/output waveguide, two or more output/input waveguides, and a planar, non-periodic, sub-wavelength grating. The grating is configured so that when the system is operated as a multiplexer, each wavelength of light output from one of the two or more output/input waveguides is reflected by the grating toward the input/output waveguide. When the system is operated as a demultiplexer, each wavelength of light output from the input/output waveguide is reflected toward one of the two or more output/input waveguides.