Integrated subwavelength bimodal interferometer using a multilayer hyperbolic metamaterial

Bimodal interferometry can be implemented in a photonic integrated waveguide by inserting structures supporting-at least-two modes to connect an input and an output single-mode waveguide. The length of the bimodal section is inversely proportional to the index difference between the involved modes, which can be quite small in multimode dielectric waveguides. We propose and numerically demonstrate an ultrashort bimodal interferometer by embedding a multilayer hyperbolic metamaterial in a subwavelength gap separating two dielectric waveguides. We use the large index difference (>1.5) between the bulk and the plasmonic-guided modes of the metamaterial to reduce the total length of the interferometer to less than 1 µm. Our system, which is potentially fabricable with standard nanofabrication tools, could be used to build ultra-compact integrated bimodal interferometers for signal processing and biosensing.