Photonic hooks from Janus microcylinders

TL;DR

This paper introduces a novel method to generate and control photonic hooks using Janus microcylinders with broken symmetry in material composition, demonstrating smaller beam width and tunability through simple mechanical operations.

Contribution

The study presents a new approach utilizing material composition asymmetry in Janus microcylinders to produce and modulate photonic hooks, expanding the capabilities of beam shaping.

Findings

Photonic hooks have a smaller FWHM (~0.29λ) than photonic nanojets (~0.35λ).

Refractive index contrast and rotation modulate PH shape profiles.

Stretching or compressing Janus microcylinders tunes PHs effectively.

Abstract

Recently, a type of curved light beams, photonic hooks (PHs), was theoretically predicted and experimentally observed. The production of photonic hook (PH) is due to the breaking of structural symmetry of a plane-wave illuminated microparticle. Herein, we presented and implemented a new approach, of utilizing the symmetry-broken of the microparticles in material composition, for the generation of PHs from Janus microcylinders. Finite element method based numerical simulation and energy flow diagram represented theoretical analysis were used to investigate the field distribution characteristics and formation mechanism of the PHs. The full width at half-maximum (FWHM) of the PH (~0.29$\lambda$) is smaller than the FWHM of the photonic nanojet (~0.35$\lambda$) formed from a circular microcylinder with the same geometric radius. By changing the refractive index contrasts between upper and lower half-cylinders, or rotating the Janus microcylinder relative to the central axis, the shape profiles of the PHs can be efficiently modulated. The tunability of the PHs through simple stretching or compression operations, for the Janus microcylinder constituted by one solid inorganic half-cylinder and the other flexible polymer half-cylinder, was studied and discussed as well.