A new plasmonic configuration is proposed for application in a sensor and demonstrated for the detection of variations in the bulk refractive index of solutions. The configuration consists of monitoring two diffracted orders resulting from the interaction of a TM-polarized optical beam incident on a grating coupler, operating based on an effect termed the “optical switch”. The two monitored diffracted orders enable differential measurements which cancel the drift and perturbations common to both, leading to an improved detection limit, as demonstrated experimentally. The measured switch pattern associated with the grating coupler is in good agreement with theory. Bulk sensing is demonstrated under intensity interrogation via the sequential injection of solutions comprised of glycerol in water into a fluidic cell. A limit of detection of about ${10}^{-6}$ RIU was achieved. The optical switch configuration is easy to implement and is cost-effective, yielding a highly promising approach for the sensing and the real-time detection of biological species.

A single-step sol-gel technological approach combining sol-gel layer development and UV lithography is demonstrated for the fabrication of resonant waveguide gratings (RWG) on planar and cylindrical substrates. The aim of this article is the demonstration of a resonant reflection in TE and TM polarization in the near-infrared region (NIR) in a planar and in cylindrical-based resonant waveguide gratings (RWG). In this work, we start with a planar corrugated waveguide structure excited by a planar wave and demonstrate this concept to a circularly symmetrical waveguide applied to the inside wall of an 8 mm diameter tube, excited by a cylindrical wave. For both configurations, the same TiO₂ sol-gel layer is used for the high index waveguide layer and for the grating printing thanks to the UV photosensitivity property of the sol-gel layers, avoiding any etching processes. The reflection spectrum was measured in the near-infrared range and compared to the modeling, showing the expected resonant behavior.

Zirconium oxide (ZrO₂) is a well-studied and promising material due to its remarkable chemical and physical properties. It is used, for example, in coatings for corrosion protection layer, wear and oxidation, in optical applications (mirror, filters), for decorative components, for anti-counterfeiting solutions and for medical applications. ZrO₂ can be obtained as a thin film using different deposition methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). These techniques are mastered but they do not allow easy micro-nanostructuring of these coatings due to the intrinsic properties (high melting point, mechanical and chemical resistance). An alternative approach described in this paper is the sol-gel method, which allows direct micro-nanostructuring of the ZrO₂ layers without physical or chemical etching processes, using optical or nano-imprint lithography. In this paper, the authors present a complete and suitable ZrO₂ sol-gel method allowing to achieve complex micro-nanostructures by optical or nano-imprint lithography on substrates of different nature and shape (especially non-planar and foil-based substrates). The synthesis of the ZrO₂ sol-gel is presented as well as the micro-nanostructuring process by masking, colloidal lithography and nano-imprint lithography on glass and plastic substrates as well as on plane and curved substrates.

Surface micro-nanostructuring can provide new functionalities and properties to coatings. For example, it can improve the absorption efficiency, hydrophobicity and/or tribology properties. In this context, we studied the influence of micro-nanostructuring on the photocatalytic efficiency of sol-gel TiO₂ coatings during formic acid degradation under UV illumination. The micro-nanostructuring was performed using the UV illumination of microspheres deposited on a photopatternable sol-gel layer, leading to a hexagonal arrangement of micropillars after development. The structures and coatings were characterized using Raman spectroscopy, ellipsometry, atomic force microscopy and scanning electron microscopy. When the sol-gel TiO₂ films were unstructured and untreated at 500 °C, their effect on formic acid’s degradation under UV light was negligible. However, when the films were annealed at 500 °C, they crystallized in the anatase phase and affected the degradation of formic acid under UV light, also depending on the thickness of the layer. Finally, we demonstrated that surface micro-nanostructuring in the form of nanopillars can significantly increase the photocatalytic efficiency of a coating during the degradation of formic acid under UV light.

Surface plasmon resonance is an effect widely used for biosensing. Biosensors based on this effect operate in different configurations, including the use of diffraction gratings as couplers. Gratings are highly tunable and are easy to integrate into a fluidic system due to their planar configuration. We discuss the optimization of plasmonic grating couplers for use in a specific sensor configuration based on the optical switch. These gratings present a sinusoidal profile with a high depth/period ratio. Their interaction with a p-polarized light beam results in two significant diffracted orders (the 0th and the −1st), which enable differential measurements cancelling noise due to common fluctuations. The gratings are fabricated by combining laser interference lithography with nanoimprinting in a process that is aligned with the challenges of low-cost mass production. The effects of different grating parameters such as the period, depth and profile are theoretically and experimentally investigated.

The phenomenon of resonant reflection from a grating-coupled waveguide mode is conceptually, technologically, and experimentally transposed from a planar corrugated waveguide structure under plane wave excitation to a circularly symmetrical waveguide at the inner wall of a tube under cylindrical wave excitation. The mode coupling element is an azimuthally periodic wall corrugation having an integer number of lines parallel to the tube axis. The grating is defined by diffractive coordinate transform of a radial grating phase-mask transverse to the tube axis under axial beam exposure onto a photoresist-coated TiO2 sol-gel wall-waveguide. The holistic excitation of a waveguide mode is achieved by transforming a broad spectrum, centered axial incident beam into a cylindrical wave by a centered, 90° apex reflective cone. The expected resonantly reflected cylindrical wave at the mode-coupling wavelength is in turn transformed back into an axial beam by the cone. TE resonant reflection is demonstrated experimentally.