Two-dimensional (2D) van der Waals layered materials are gaining prominence in hybrid photonics. These materials are often integrated with photonic structures, such as cavities, to enhance light-matter coupling and provide additional control and functionality. The standard approach to fabricating hybrid devices involves transferring mono- and few-layer 2D material flakes onto prefabricated nanocavities. While ultrathin, the presence of a 2D material flake can still alter cavity dielectric environment. Interestingly, this effect is typically overlooked or treated as a minor perturbation that can be mitigated by slight adjustments to the nanophotonic cavity design. The potential of 2D materials for deliberate dielectric environment engineering in hybrid nanophotonic devices remains largely untapped. Rather than being a limitation, the dielectric changes introduced by 2D materials can enable new approaches for enhancing cavity light-matter coupling.

In this work, we demonstrate a versatile method for forming self-aligned nanocavities by integrating two-dimensional (2D) material flakes onto photonic crystal (PhC) waveguides post-fabrication. When a 2D material flake partially overlays a PhC waveguide, the resulting perturbation to the guided mode enables localized optical confinement and cavity formation—without requiring any physical modification to the underlying PhC lattice. Building on our earlier work with hybrid cavities formed with a single 2D flake, we now show that these cavities remain robust even after the sequential transfer of multiple flakes, consistently maintaining high optical quality with quality factors (Q) on the order of 10⁴. By coupling optically active hBN/MoTe₂ heterostructures to these cavities, we observe enhanced photoluminescence (PL) and reduced emitter lifetimes, indicative of cavity-induced Purcell enhancement. Notably, we also report a significant increase in the cavity Q factor following hBN encapsulation, underscoring the importance of dielectric engineering in further improving optical performance. These results highlight the potential of 2D material integration for flexible, post-fabrication tuning of nanophotonic devices, and pave the way toward scalable hybrid photonic systems with tailored light–matter interactions.

To learn more about this work, please refer to
Chee Fai Fong, Daiki Yamashita, Nan Fang, Shun Fujii, Yih-Ren Chang, Takashi Taniguchi, Kenji Watanabe, and Yuichiro K. Kato Dielectric environment engineering via 2D material heterostructure formation on a hybrid photonic crystal nanocavity Opt. Mater. Express 16, 2159 (2025).