Plasmonic nanorings provide the unique advantage of a pronounced plasmonic field enhancement inside their core. If filled with a polarizable medium, it may significantly enhance its optical effects. Here, we demonstrate this proposition by filling gold nanorings with lithium niobate. The generated second harmonic signal is compared to the signal originating from an unpatterned lithium niobate surface. Measurements and simulation confirm an enhancement of about 20. Applications requiring nanoscopic localized light sources like fluorescence spectroscopy or quantum communication will benefit from our findings.

Structural modifications induced by femtosecond laser pulses in LiNbO3 were studied. The influence of the processing and focusing parameters was investigated. Two different types of modifications could be identified. High laser fluences cause a refractive index decrease, material damage and stresses in the surrounding crystalline lattice. At low laser fluences, an extraordinary index increase was observed that allows for optical waveguiding. This kind of modification is thermally unstable and correlates to a weak distortion of the lattice. The electrooptic coefficient measured in a waveguide was found to be substantially reduced. The mechanisms underlying the structural modifications are discussed

In this letter a "quasi-incoherent" propagation in waveguide arrays is theoretically derived and experimentally verified. Depending on the initial light distribution the propagation in a waveguide array after multiwaveguide excitation exhibits an interference pattern or not. For the experimental verification the waveguide array is realized in OH rich fused silica by femtosecond laser direct writing. The light propagation within the array is directly visible due to the fluorescence of the created color centers. A precise excitation of different waveguides is achieved using a phase grating

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We report on the light propagation in a one-line-defect photonic crystal waveguide (W1 PhC WG) patterned into a 450 nm thick free-standing lithium niobate membrane by ion-beam enhanced etching. The Bloch wave vectors and transmission spectrum of this PhC WG were retrieved from optical near-field images. The experimental data show good agreement with simulations performed with the three-dimensional (3D) finite-element method and the 3D finite-difference time-domain method. Those results are promising for the development of integrated optics devices operating at telecom wavelengths and based on free-standing lithium niobate PhC membranes.