Angle-Selective Optical Resonance and Circular Radial Lasing from a Chiral Polymeric Microsphere

Spheres are inherently isotropic in structure, while their optical isotropy can be broken when the refractive index distribution is not isotropic. For microspheres made of molecules, spheres with bipolar or twisted-bipolar molecular configuration exhibit distinctive birefringence inside the sphere. However, impacts of the molecular arrangement on the spherical surface to optical functions have not yet been elaborated. Herein, we present optical sphere resonators exhibiting angular-selective resonance and lasing derived from its topological and chiral surface. Self-assembly of chiral π-conjugated polymers forms microspheres, whose surface is featured with the swirl molecular arrangement arising from diametrical topological defects. Despite its spherical morphology, the microsphere shows angular-selective whispering gallery mode (WGM) resonance emission, which is predominantly localized along the particular circular orbits. Furthermore, upon strong photoexcitation, the microsphere exhibits WGM laser oscillation with a distinct azimuthal direction. This work demonstrates the impacts of the textured spherical surface on optical properties and provides the virtues of the chiral sphere resonators as spatio-selective light amplifiers and directional lasers without shape change.