UV LED Curable Perfluoropolyether (PFPE)-Urethane Methacrylate Transparent Coatings for Photonic Applications: Synthesis and Characterization.

The contribution aims to bring forth a novel synthesis route in developing transparent UV LED-curable coatings accounting for various exposure options. A selection of perfluoropolyether (PFPE)-urethane methacrylate and acrylate resins, free-radical photo-initiator Omnirad 2100, and two distinct silane-based crosslinking agents were blended under a weight ratio of 75:20:5 (without crosslinker) and 70:15:5:10, respectively. The coatings were cured under a UV LED 4 × 3 matrix light emitting source, in a chamber under a controlled atmosphere, by means of an in-house developed conveyor belt type platform, at different conveyor belt speeds (5, 50, 150, 250, and 500 mm/s). The morphologies of fabricated coatings were characterized by FTIR revealing high conversion rates (e.g., from 98 to 100%) for increased exposure time as a result of the 5 or 50 mm/s values, on all combinations. Dynamic-mechanical and optical properties of UV LED-cured transparent coatings were also investigated. A negative shift of the glass transition temperature values with a decrease in exposure time, in all combinations, from about 60 °C to 30 °C, along with storage moduli lowering in the glassy plateau further favors higher exposure times for curing. The refractive indices of poly-mers were from 1.38 to 1.40, whereas the thermo-optic coefficients are showing minor changes around the value of 2.55∙10-4 K-1.

SiO2 Nanoparticles-Acrylate Formulations for Core and Cladding in Planar Optical Waveguides.

A combination of acrylate formulations and SiO2 nanoparticles is investigated with the aim to improve the optical properties of low-refractive index polymers that are used for the fabrication of planar optical waveguides. A decrease in refractive index and also in the thermo-optic coefficient of nanocomposite materials is clearly demonstrated, while some formulations exhibit an increase in the glass transition temperature. The possibility of using these nanocomposite materials to fabricate waveguiding layers with low optical propagation losses at telecommunication wavelengths around 1550 nm is also shown. The nanomaterials can be applied in optical microchips on polymer platforms.

Single step optical fabrication of a DFB laser device in fluorescent azobenzene-containing materials.

Distributed feedback (DFB) lasers are produced directly in fluorescent azobenzene-containing materials using a single holographic optical step. Surface relief grating capable of producing images in fluorescence microscopy can be holographically formed in a number of materials.

Efficient single-beam light manipulation of 3D microstructures in azobenzene-containing materials.

Large aspect ratio 3D microstructures (arrays of square posts and linear rectangular gratings) fabricated in a number of azobenzene-containing materials by soft lithography were manipulated by a single beam of polarized light. The materials exhibited different response to the beam orientation and the direction of light polarization. An elongation of the square posts both along and perpendicular to the polarization plane was observed depending on material. Reversibility of the deformation has been demonstrated. Broadening of the hills, amplitude and shape changing were observed for linear gratings. A slanted expose led to the blazed asymmetric structures. Some aspects of light-induced deformation mechanisms in azobenzene-containing materials are discussed. The approach developed in the paper can be useful both for the understanding of mass transport mechanism in azobenzene-containing materials and for the fabrication of diffracted optical structures.

Phenomenology of photoinduced processes in the ionic sol-gel-based azobenzene materials.

Very recently, supramolecular azobenzene-containing materials have been demonstrated to be effective for holographic inscription of surface relief gratings. High efficiency of grating formation in these materials is advantageously combined with easy material preparation because of the supramolecular principle of building blocs combination, availability of chemical components, and good film-forming properties. The materials show great promise for wide optical applications. Here, one type of material formulation based on ionic complexes of poly(aminosiloxane) is experimentally investigated concerning the induction of birefringence, efficiency of relief formation, and thermal stability of surface structures. Properties of the material were changed on the molecular level by varying the azobenzene content and on the macro level by varying chemical processing conditions. The results are discussed in terms of cross-linking and plasticizing effects caused by residual solvent and the low-molecular-weight azobenzene component. An improvement of both the efficiency of grating formation and their thermal stability by these means has been demonstrated. The results can be adapted to other azobenzene-containing materials. In addition, a drastic change of films solubility has been observed upon irradiation.

Three-dimensional planarized diffraction structures based on surface relief gratings in azobenzene materials.

The method of step-by-step formation of correlated 3D phase optical structures is presented. Surface relief gratings (SRG) recorded in azobenzene polymer layers are alternated with layers of a spacer polymer with a different refractive index. A pair of azobenzene and spacer polymers with excellent compatibility makes it possible to prepare layers of good optical quality in a stack without destruction of SRG in the previous layer. A correlated stack of six layers (three active and three spacer layers) with 2D structures of different types (linear, tetragonal, and hexagonal) were built. In this way hierarchical 3D structures with different grating periods or different shapes of SRG can be also produced, resulting in full flexibility of the structure type and grating parameters.

Large-scale synthesis of organophilic zirconia nanoparticles and their application in organic-inorganic nanocomposites for efficient volume holography.

We present a multigram scale, one-step nonaqueous synthesis route to monodisperse, highly crystalline ZrO(2) nanoparticles. The nanoparticles can be stabilized in nonpolar solvents via a simple functionalization procedure using only minute amounts of organic stabilizers. Their great potential in materials applications is demonstrated by the fabrication of organic-inorganic nanocomposites that can be selectively photopolymerized to inscribe extremely effective and volume holographic gratings with the highest refractive index contrast (n(1) of up to 0.024) achieved so far.

Thermally stable holographic surface relief gratings and switchable optical anisotropy in films of an azobenzene-containing polyelectrolyte.

In a search for effective polymer film material for holographic surface patterning, commercially available azobenzene polyelectrolyte has been employed. Films of good optical quality in a wide range of thickness were produced. Optical dichroism up to 0.19 was induced upon irradiation with linearly polarized light. Surface relief gratings with amplitudes up to 630 nm and diffraction efficiency of 37% were inscribed by holographic exposure to the light of 488 nm. Due to the ionic nature of the material, the relief was stable at least up to the temperature of decomposition (ca. 200 degrees C) but could be erased and inscribed again by light.