Subwavelength focusing of all-dielectric surface waves

TL;DR

This paper demonstrates a method to achieve subwavelength focusing of all-dielectric surface waves using Bloch surface waves, enabling nano-scale manipulation and sensing in integrated optical systems.

Contribution

It introduces a novel all-dielectric approach for subwavelength focusing of surface waves, overcoming limitations of plasmonic methods in integrated photonics.

Findings

Achieved a 0.66λ spot size experimentally.

Theoretically and numerically validated the focusing mechanism.

Enabled potential applications in nano-particle manipulation and sensing.

Abstract

Micro-sized spheres can focus light into subwavelength spatial domains: a phenomena called photonic nanojet. Even though well studied in three-dimensional (3D) configurations, only a few attempts have been reported to observe similar phenomena in two-dimensional (2D) systems. This, however, is important to take advantage of photonic nanojets in integrated optical systems. Usually, surface plasmon polaritons are suggested for this purpose, but they suffer notoriously from the rather low propagation lengths due to intrinsic absorption. Here, we solve this problem and explore, theoretically, numerically, and experimentally, the use of Bloch surface waves sustained by a suitably structured all-dielectric media to enable subwavelength focusing in an integrated planar optical system. Since only a low index contrast can be achieved while relying on Bloch surface waves, we perceive a new functional element that allows a tight focusing and the observation of a photonic nanojet on top of the surface. We experimentally demonstrate a spot size of 0.66{\lambda} in the effective medium. Our approach paves the way to 2D all-dielectric photonic chips for nano-particle manipulation in fluidic devices and sensing applications.