Investigation of Surface Electromagnetic Waves with Multi-Heterodyne Scanning Near-Field Optical Microscopy

In this thesis, we present the development of a tunable Multi-Heterodyne Scanning Near-Field Optical Microscope (MH-SNOM). This instrument has been built and evaluated for the investigation of optical near fields in amplitude, phase and polarization. With this microscope, the response of a structure illuminated with two orthogonally polarized beams can be simultaneously measured both in amplitude and phase. Moreover, the integral state of polarization at the surface of a specimen can be retrieved under specific conditions. We demonstrate the capabilities of the system through a series of measurements involving Surface Electromagnetic Waves (SEWs). We have mainly focused our attention on a particular class of SEWs known as Bloch Surface Waves (BSWs). The propagation of BSWs on the outer surface of a silicon nitride multilayer has been studied in detail. Furthermore, we show that this propagation is affected by the presence of shallow dielectric corrugations such as a subwavelength grating or at the straight interface with a coated portion of the multilayer. In particular, we demonstrate that ultra-thin (thickness < λ/10) dielectric ridges may act as BSW waveguides. Combining the detection capabilities of the MH-SNOM with a numerical treatment of the experimental data, we are able to separate the transverse and longitudinal field components of the three modes propagating within a specific BSW waveguide. This new structure provides interesting opportunities in waveguide-based biosensing schemes in which the ridge is realized with functionalized molecular layers of nanometric thickness. Finally, we investigate a structure sustaining another type of SEW: Surface Plasmon Polaritons (SPPs). This structure is designed for the asymmetrical coupling of SPPs at normal incidence. Through a detailed analysis of the spatial spectra, we show that, in addition to SPPs, the field contains other near-field components. All these experiments demonstrate the expected MH-SNOM capabilities of measuring the amplitude, phase and polarization of optical near fields. The MH-SNOM therefore serves as a powerful tool for the investigation with subwavelength resolution of optical near fields generated in structures such as integrated optics, photonic crystals, cavities, resonators, etc

Opportunities in microstructured photonics

The progress in novel light sources, detectors, materials and technology enable new opportunities and challenges for diffractive optics and nanoscale photonics. Important are also analysis tools, such as near-field imaging (SNOM). Only structures that can be characterized can be fabricate

2D Optics on Bloch Surface Waves (BSWs) Based Platform: Polymer Lens and Prism

In this work, we use a novel platform concept based on Bloch Surface Waves (BSWs) and manipulate the BSWs propagation with two-dimensional (2D) dielectric patterns deposited on it. The concept opens a way to realize 2D integrated all-optics systems including sensing functionalities

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

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 (similar to lambda/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

Concurrent polarization retrieval in multiheterodyne scanning near-field optical microscopy: validation on silicon formbirefringent grating

We demonstrate a concurrent polarization-retrieval algorithm based on a multi-heterodyne scanning near-field optical microscopy (MHSNOM) measurement system. This method relies on calibration of the polarization properties of the MH-SNOM using an isotropic region of the sample in the vicinity of the nanostructures of interest. We experimentally show the effectiveness of the method on a silicon form-birefringent grating (FBG) with significant polarization diversity. Three spatial dimensional near-field measurements are in agreement with theoretical predictions obtained with rigorous coupled-wave analysis (RCWA). Pseudo-far-field measurements are performed to obtain the effective refractive index of the FBG, emphasizing the validity of the proposed method. This reconstruction algorithm makes the MH-SNOM a powerful tool to analyze concurrently the polarization-dependent near-field optical response of nanostructures with sub wavelength resolution as long as a calibration area is available in close proximity

Asymmetrical excitation of surface plasmon polaritons on blazed gratings at normal incidence

We present results of numerical simulations and preliminary experiments to investigate and characterize the effect of asymmetrical coupling of normally incident light to surface plasmon polaritons (SPPs) on metallic blazed gratings. Two types of blazed gratings are investigated, a two-dimensional (2D) area-coded binary grating and a one-dimensional (1D) slanted sinusoidal grating. The 2D blazed grating, which can be fabricated with standard e-beam lithography, is shown to have the same ability as the classical 1D blazed grating to enhance the strength of the −1st(+1st) evanescent order over the +1st(−1st) counterpart, which leads to the asymmetrical excitation of two counterpropagating SPP modes on the grating surface. The 1D blazed grating, as a reference, is also studied experimentally to verify the previous theoretical predictions. In our first experiments, the observed asymmetrical coupling effect is relatively weak compared with the optimal designs due to many practical limitations. However, good agreement between theory and experiment has been obtained, and physical insight concerning the observed SPP coupling phenomena has been gained. Further measures to realize stronger asymmetrical excitation of SPPs on blazed gratings at normal incidence are discussed

Near-field polarization measurements based on two arbitrary, orthogonal optical field components

Using a multi-heterodyne scanning near-field optical microscope, we detect two arbitrary, orthogonal components of the near field. A numerical treatment of the experimental data allows the retrieval of the transverse and longitudinal components of the modes propagating in a waveguide for Bloch surface waves

Surface nanophotonics with Bloch waves on dielectric multilayers

Planar mutilayers sustaining either TE or TM polarized Bloch Surface Waves (BSWs) offer new opportunities for management of light at the nanoscale. We will discuss how BSWs can be exploited in guiding and confining light on nanometric relieves, enhancing fluorescence emission and providing additional features for plasmonic nano-antennas