Steering Directional Light Emission and Mode Chirality through Postshaping of Cavity Geometry

Dielectric optical microcavities have been explored as an excellent platform to manipulate the light flow and investigate non-Hermitian physics in open optical systems. For whispering gallery mode optical microcavities, modifying the rotational symmetry is highly desirable for intriguing phenomena such as degenerated chiral modes and directional light emission. However, for the state-of-the-art approaches, namely deforming the cavity geometry by precision lithography or introducing local scatterers near the cavity boundary via micromanipulation, there is a lack of flexibility in fine-adjusting of chiral symmetry and far-field emission direction. Here, precise engineering of cavity boundary using electron-beam-induced deposition is reported based on rolled-up nanomembrane-enabled spiral-shaped microcavities. The deformation of outer boundary results in delicate tailoring of asymmetric backscattering between the outer and inner rolling edges, and hence deterministically strong mode chirality. Besides, the crescent-shaped high-index nanocap leads to modified light tunneling channels and inflected far-field emission angle. It is envisioned that such a localized deposition-assisted technique for adjusting the structural deformation of 3D optical microcavities will be highly useful for understanding rich insights in non-Hermitian photonics and unfolding exotic properties on lasing, sensing, and cavity quantum electrodynamics.