Manipulating Bloch surface waves in 2D: a platform concept-based flat lens

Abstract

At the end of the 1970s, it was confirmed that dielectric multilayers can sustain Bloch surface waves (BSWs). However, BSWs were not widely studied until more recently. Taking advantage of their high-quality factor, sensing applications have focused on BSWs. Thus far, no work has been performed to manipulate and control the natural surface propagations in terms of defined functions with two-dimensional (2D) components, targeting the realization of a 2D system. In this study, we demonstrate that 2D photonic components can be implemented by coating an in-plane shaped ultrathin ( l/15) polymer layer on the dielectric multilayer. The presence of the polymer modifies the local effective refractive index, enabling direct manipulation of the BSW. By locally shaping the geometries of the 2D components, the BSW can be deflected, diffracted, focused and coupled with 2D freedom. Enabling BSW manipulation in 2D, the dielectric multilayer can play a new role as a robust platform for 2D optics, which can pave the way for integration in photonic chips. Multiheterodyne near-field measurements are used to study light propagation through micro-and nano-optical components. We demonstrate that a lens-shaped polymer layer can be considered as a 2D component based on the agreement between near-field measurements and theoretical calculations. Both the focal shift and the resolution of a 2D BSW lens are measured for the first time. The proposed platform enables the design of 2D all-optical integrated systems, which have numerous potential applications, including molecular sensing and photonic circuits. Keywords: Bloch surface wave; 2D optics; manipulation; micro-and nano-optics; nanophotonics; platform INTRODUCTION One or several elements are considered to comprise a two-dimensional (2D) optical system if they fulfill two conditions. First, the in-plane light propagation must have two spatial non-imaginary propagation constants. Second, the corresponding optical elements should have a 2D degree of freedom in shape. The previous statements may appear to imply that the reduction from three-dimensional (3D) to 2D is primarily a reduction in the degree of freedom. However, one of the main advantages is that 2D elements can have arbitrary shapes, which is difficult to achieve in 3D.There are various methods for addressing a 2D optical environment. One approach is represented by the use of wave-guiding media wherein the light is confined and propagated in a sandwiched structure. However, in the case of slab waveguides, the light is almost completely buried in the inner layers of the waveguide; thus, direct spatial mapping remains difficult or impossible. As an alternative to waveguides, a second route for 2D optics is represented by surface plasmons (SPPs) on smooth planar or structured metallic films. SPPs are electronic-electromagnetic modes sustained at an appropriate metallic/dielectric interface wherein the field reaches its maximum intensity at the surface of the metal.

Bloch surface waves based platform for integrated optics

“…(b) . For 15 nm thickness of TiO 2 , we achieved a propagation length of around 2.5 millimeters in near field, which is ~ 30 times longer than the recently obtained "Long-Range SPPs" studied by Lin et al [3] and ~ 4 times longer than the one studied by L. Yu [4]. Effective refractive index (n eff ) is introduced by propagation constant of surface waves.…”

Two-dimensional polymer grating and prism on Bloch surface waves platform

“…By fitting this curve by an exponential law, we experimentally obtained a decay length of 628 µm [4], 7 times greater than the value recently obtained for the long-range SPPs studied by Lin et al [23]. This corresponds to a propagation loss of 60dB/cm.…”

“…However, the propagation length of SPPs is limited by high absorption losses in metals. A novel low-cost platform suitable for fundamental investigations of light propagation through micro-and nano-structures has been recently proposed [4]. The presented 2D concept based on Bloch Surface Waves (BSWs) is a strong candidate to realize fundamental experiments, as well as entire photonic systems.…”

“…Furthermore, Sfez et al [15] studied the refraction of surface waves at thin waveguide structures. The vision of the dielectric multilayer as a platform for two-dimensional integrated optics has been studied and demonstrated by studying a 2D lens [4] or simulating high-Q ring resonators [16].…”

Optical Effects Induced by Bloch Surface Waves in One-Dimensional Photonic Crystals

“…In several further works, the possibilities of BSW guiding using diffraction gratings of different geometries and visualization of the BSW by leakage radiation microscopy techniques are shown [18][19][20]. The prospect of the BSWs in photonic crystals for the development of flat optics elements was recently demonstrated in two-dimensional lens [21] and planar triangles [7].…”