HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The roughness of shallow or deep metallic diffraction gratings modifies the propagation of surface plasmon mode along the metallic-air interface. The scattering losses lead to a spectral or angular broadening of the surface plasmon resonance (SPR) and to a shift of the resonance wavelength and coupling angle. This mechanism is deeply analyzed both experimentally and theoretically to overcome these effects when such structures, in particular deep ones, are used as SPR-based sensors.

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 phasemask transverse to the tube axis under axial beam exposure onto a photoresist-coated TiO 2 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 o 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.

In this work, we report on the design of a one-dimensional subwavelength resonant grating comprised of a fused silica substrate and a bi-layer waveguide, consisting of a solgel synthetized anatase TiO2 layer followed by a thin VO2 layer that is applied using pulsed laser deposition and rapid thermal annealing. A TE waveguide mode is excited under normal incidence in the VO2/TiO2 bi-layer via a positive photoresist based grating printed on top, leading to high resonant reflection at room temperature. Increasing the temperature to about 68°C causes the VO2 to undergo a dielectric to metallic transition accompanied by optical modifications in the IR region, canceling the resonance effect. This thermally triggered absorber/emitter tunable configuration enabling the on and off switching of optical resonant excitation in a reversible manner is proposed for passive Q-switching self-protecting devices for high power lasers in the IR wavelength range. Modeling of the optimized temperature dependent resonant waveguide and preliminary experimental results are presented.

No abstract

No abstract

The insulator‐to‐metal transition (IMT) of vanadium dioxide (VO2) at ≈68 °C enables a variety of optical applications, including switching and modulation, and tuning of optical resonators. This work designs and demonstrates a novel thermally activated optical switch consisting of a SiN/VO2/SiN multilayer sandwich structure with an AMONIL‐based grating with a reduced transition temperature of 47 °C. The optical switching in the multilayer is due to the IMT of the VO2‐embedded layer. Here, the asymmetrical TE1 mode exhibiting a quasi‐zero electric field in the center of the multilayer waveguide is excited in the resonant waveguide grating (RWG) structure under normal incidence via the AMONIL‐based grating printed on top, leading to high resonant transmittance (75%) at room temperature. Increasing the temperature to more than 47 °C causes VO2 to undergo an insulator‐to‐metal transition accompanied by optical modifications in the IR region, completely canceling the resonance effect, while reducing the transmittance to 30%. Further, the modeling results aimed at optimizing the design of the experimental structure. These results demonstrate good performance of the proposed design and pave the way to fabricate VO2‐based optical switches for photonics applications including lasers, sensors, and detectors, in which external stimuli such as heat affect the transmittance or reflectance spectrum.