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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.