MoOCl2 as a Natural Hyperbolic Platform for Integrated Nanophotonics at Telecommunication Bands

Abstract

On-chip optoelectronics underpins modern telecommunications, yet its integration density is fundamentally bottlenecked by the diffraction limit of light. Hyperbolic polaritons─hybrid light-matter excitations in materials with opposite-signed dielectric permittivity tensor components─emerge as a powerful solution, offering deep subwavelength confinement and unique phenomena such as large momentum, canalization, and negative refraction. Nevertheless, the most widely studied hyperbolic van der Waals crystals, such as hexagonal boron nitride and α-MoO3, operate predominantly in the mid-infrared frequency range, leaving a critical gap in the telecommunication bands (1260–1675 nm). Molybdenum oxychloride (MoOCl2) has recently been identified as a natural van der Waals crystal with pronounced hyperbolicity spanning the telecommunication range. Here, we analyze the key properties of MoOCl2 plasmon polaritons regarding their applicability for integrated optical telecommunication devices and propose a set of prospective device-level implementations, including diffraction-free waveguides based on polariton canalization, polaritonic crystals, and high-efficiency spontaneous-emission-enhancement platforms. These architectures encompass the essential functions of on-chip information processing: emission, propagation, and modulation, highlighting MoOCl2 as a promising material for exploring hyperbolic plasmon polaritons at telecommunication bands, with potential relevance for compact photonic components.