Elsie Barakat

Focusing and Extraction of Light mediated by Bloch Surface Waves

The control of emission from localized light sources is an objective of outstanding relevance in nanophotonics. In a recent past, a large number of metallic nanostructures has been proposed to this end, wherein plasmonic modes are exploited as energy carriers on a subwavelength scale. As an interesting alternative, we present here the use of surface modes on patterned dielectric multilayers to deliver electromagnetic power from free-space to localized volumes and vice versa. Thanks to this low-loss energy transfer, proper periodic ring structures are shown to provide a subwavelength focusing of an external radiation onto the multilayer surface. By reciprocity, the radiated power from emitters within the ring center is shown to be efficiently beamed in the free-space, with a well-controlled angular divergence. This mechanism overcomes some important limitations involved in the all-plasmonic approach, while opening new opportunities for hybrid devices in photon management applications such as optical sensing and lighting.

Near-field characterization of a Bloch-surface-wave-based 2D disk resonator.

We present, to the best of our knowledge, the first experimental investigation of a two-dimensional disk resonator on a dielectric multilayer platform sustaining Bloch surface waves. The disk resonator has been patterned into a few tens of nanometer thin (∼λ/25) titanium dioxide layer deposited on the top of the platform. We characterize the disk resonator by multi-heterodyne scanning near-field optical microscopy. The low loss characteristics of Bloch surface waves allowed us to reach a measured quality factor of 2×103 for a disk radius of 100 μm.

Leakage radiation interference microscopy

We present a proof of principle for a new imaging technique combining leakage radiation microscopy with high-resolution interference microscopy. By using oil immersion optics it is demonstrated that amplitude and phase can be retrieved from optical fields, which are evanescent in air. This technique is illustratively applied for mapping a surface mode propagating onto a planar dielectric multilayer on a thin glass substrate. The surface mode propagation constant estimated after Fourier transformation of the measured complex field is well matched with an independent measurement based on back focal plane imaging.

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

A one-dimensional photonic crystal sustaining Bloch Surface Waves (BSWs) is used as a platform for two-dimensional integrated optics. The dielectric platform shows low loss, long propagation distance and high surface field enhancement. In order to study the potential of the platform for future photonic chips, polymer ultra-thin prisms and gratings (~100 nm) are engineered on the top of the platform. This polymer layer modifies the BSWs effective index enabling a direct manipulation of light. The BSW deflection effects caused by surface prisms are observed in the near-field and Snells law is verified; then the BSW diffractions through surface gratings are experimentally and theoretically characterized. The results show a robust platform that can be used for integrated optics that includes different optical components. One of the main advantages is that these 2D photonic devices can have arbitrary shapes, which is difficult to obtain in 3D.

Vertically coupled plasmonic slot waveguide cavity for localized biosensing applications

We propose and study an integrated refractive index sensor which is based on a plasmonic slot waveguide cavity. In this device, a guided mode supported by a silicon photonic wire waveguide is vertically coupled to a metal-dielectric-metal cavity separated by a silicon oxide spacer. We perform an in-depth study that links the geometrical parameters of the sensor to the coupling mechanism and sensitivity of the plasmonic slot waveguide cavity. Simulation results promise that local changes of refractive index can be measured with a high sensitivity of around 600 nm/RIU in a femto-liter volume. These results are obtained with three-dimensional time and frequency domain simulations. Thanks to the high field enhancement in the slot of the plasmonic cavity, a high local sensitivity to changes of refractive index is obtained. Moreover, the high level of achieved decoupling between the bulk and the local sensitivity complies well with the requirements of biomolecular sensing.

Near-field investigation of Bloch surface wave based 2D optical components

We study the Bloch surface wave based nano-thin 2D optical components. The 2D elements are fabricated on the dielectric multilayer platform which sustains the Bloch surface waves. Such a platform is considered as a novel foundation for planar integrated optics. We exploit the total internal reflection configuration to achieve the phase matching condition for BSW excitation. Because of the evanescent behavior of the BSW, we use a scanning near field optical microscope to characterize the near-field properties of in-plane components. The 2D optical components include Disk resonators and Bessel-like beams.

Bloch surface waves, a 2D platform for planar optical integration

A novel platform suitable for fundamental investigations of light propagation through micro- and nano-structures will be discussed. This platform is based on a dielectric multilayer that sustains Bloch surface waves (BSWs). BSWs are electromagnetic surface waves excited at the interface between a truncated periodic dielectric multilayer and a surrounding media. The modification of the top surface to customize a complete 2D micro-system can be produced using e-beam writing, optical lithography or other patterning techniques. The results obtained confirm the possibility of developing a robust multilayer platform that would pave the way for integration of photonic components in photonic chips using standard wafer-scale production.

Optics in 2D, Bloch surface wave phenomena and applications

Nano-photonics, where optical structures can manipulate light at the sub-wavelength scale, is making important advances towards optical communications, imaging and sensing. A novel platform suitable for fundamental investigations of light propagation through micro- and nano-structures will be discussed. This platform is based on a dielectric multilayer that sustains Bloch surface waves (BSWs). We experimentally and theoretically investigate components including a disk resonator and a photonic nanojet, which are fabricated on a Bloch surface wave platform.

Nano-thin 2D axicon generating nondiffracting surface waves

We investigate nondiffracting surface waves. On top of the Bloch surface wave platform, a 60-nm-thick TiO2 isosceles triangle serves as a 2D axicon. Scanning near-field microscopy measurements verify nondiffracting surface beam properties.

Nondiffracting Bloch surface wave: 2D quasi-Bessel-Gauss beam

2D Bessel-Gauss beam, which is known as nondiffracting beams in 3D space, is demonstrated in the domain of Bloch surface wave. Its self-healing capacity is verified by using cylindrical obstacles in the diffraction-free beam path.