Cladding-Free Hyperbolic Waveguide Arrays

Traditional waveguide arrays necessitate cladding layers, thereby impeding the pursuit of high-density integration. This study presents cladding-free waveguide arrays comprising alternating dielectric and hyperbolic waveguides with zero spacing between them. By deliberately mismatching the spatial dispersions of dielectrics and hyperbolic metamaterials along the waveguiding direction, each waveguide acts as a transmission channel and an effective cladding for its neighboring counterparts. The hyperbolic nature of the system facilitates a plethora of subwavelength-scale waveguide modes. Moreover, the appearance of surface plasmons at the interfaces introduces an alternative transmission channel. Verification of transmission through these three channels in cladding-free waveguide systems has been achieved through microwave experiments and numerical simulations. Our work paves the way for cladding-free photonic integrated circuits exploiting bulk and surface waves.