Thin-film (DE)MUX based on step-like spatial beam shifting

WDM systems create a strong need for compact wavelength multiplexing and demultiplexing devices that can be manufactured cost-effectively. We focus here on thin-film structures, as they are easy to fabricate with well-known technology. In contrast to typical dielectric interference filters though, we use group velocity effects to separate multiple beams of different wavelengths with a single multilayer structure. Fig. 1 shows a schematic of our device. Polychromatic light is incident under an angle onto a dielectric stack. The dielectric stack is designed such that beams of different wavelength are spatially shifted along the x-direction upon reflection. The spatial offset between different wavelengths is increased by performing multiple bounces through the structure. This device concept is by no means limited to three channels. Depending on the dispersion characteristics of the dielectric stack and the beam size more channels can be multiplexed or demultiplexed.