Twisted moiré photonic crystal enabled optical vortex generation through bound states in the continuum

The twisted stacking of two layered crystals has led to the emerging moire physics as well as intriguing chiral phenomena such as chiral phonon and photon generation. In this work, we identified and theoretically formulated a non-trivial twist-enabled coupling mechanism in twisted bilayer photonic crystal (TBPC), which connects the bound state in the continuum (BIC) mode to the free space through the twist-enabled channel. Moreover, the radiation from TBPC hosts an optical vortex in the far field with both odd and even topological orders. We quantitatively analyzed the twist-enabled coupling between the BIC mode and other non-local modes in the photonic crystals, giving rise to radiation carrying orbital angular momentum. The optical vortex generation is robust against geometric disturbance, making TBPC a promising platform for well-defined vortex generation. As a result, TBPCs not only provide a new approach to manipulating the angular momentum of photons, but may also enable novel applications in integrated optical information processing and optical tweezers. Our work broadens the field of moire photonics and paves the way toward the novel application of moire physics. The Authors in this work predict the radiation of twisted bilayer photonic crystals to host an optical vortex in the far field, which is enabled by connecting BIC modes in photonic crystals with the free space through a 'moire channel'.

Automated summary

In this work, a non-trivial twist-enabled coupling mechanism was identified and formulated in twisted bilayer photonic crystals, resulting in the generation of optical vortices. This study expands the field of moire photonics and opens up new possibilities for its applications.