Expanding Bandwidth through Coupled Silicon and Hyperbolic Waveguides in the Near- and Mid-Infrared

Silicon photonics has enabled large-scale manipulation and processing of optical signals on chip-based architectures. Yet, there is significant desire to expand the operational bandwidth of such integrated systems. While one solution is to spatially multiplex channels operating at the same frequency, an alternative is to expand existing architectures by integrating waveguides that operate at different frequencies within the same form factor. To realize this, the modal wavelength in each waveguide should be closely matched for effective confinement. Here, we integrate hyperbolic phonon polariton (HPhP) waveguides within a slab of hexagonal boron nitride (hBN) onto a silicon photonics platform, enabling dual-band operation at both telecom (1.55 µm) and mid-infrared (6.1-7.4 µm) frequencies simultaneously. Dual band operation is demonstrated as the deeply sub-diffractional, volume-confined nature of HPhPs allows the polariton wavelength to be designed to directly match that of the silicon waveguide, yet operate at drastically different operational frequencies. This eliminates potential challenges from modal cross-talk, with the index contrast between the silicon waveguide and surrounding air sufficient to induce waveguiding of the HPhPs in the hBN without patterning.