The benefits obtained in terms of costs and applicability by the development of flexible and stretchable electronics, compared to its rigid counterpart, have fostered the quest for flexible photonic technologies and integrated platforms on suitable material systems. By adding mechanical flexibility to photonic structures, novel functionalities would be added to their already broad range of applications. In case of oxides, their typical qualifying properties in terms of transparency, high thermal and chemical resistance could be exploited in suitable material systems. Here it is presented two flexible SiO2/HfO2 1D photonic crystals, fabricated by radio frequency sputtering. As expected, the systems show a strong dependence of the optical features on the light incident angle. Nevertheless, the most interesting result is the experimental evidence that, even after the sample breakage, where the flexible glass shows naked-eye visible cracks, the multilayer structures generally maintain their integrity, resulting to be promising systems for flexible photonic applications thanks to their optical, thermal and mechanical stability.
For the development of flexible photonic devices, polymeric substrates are of capital importance due to their low cost and mechanical flexibility. However, they are sensitive to the environment’s influence on their durability. To overcome problems of polymeric substrates’ stability, we developed organically modified hybrid silica-titania coated PET (polyethylene terephthalate) films. The focus was put on the determination of the optical properties’ changes in dependence on the synthesis and materials processing parameters. Thanks to the application of the coatings, a protection effect on substrate and improvement in the transparency in comparison to the uncoated heat-treated polymeric material, was obtained.
Integration of photonic systems on deformable substrates has given rise to flexible photonics, a research field that has rapidly emerged in recent years. By adding mechanical flexibility to planar photonic structures, the spectrum of applications gains an incredible expansion. Flexible glassy photonic structures require a careful design and suitable fabrication protocols, in order to keep the optical and spectroscopic properties similar to their traditional rigid counterparts, even under mechanical deformation. Here, a radio frequency (RF) sputtering deposition protocol is developed for fabricating glass-based 1D photonic crystals on ultrathin flexible glass as well as on rigid substrates for comparison. Three different 1D multilayer structures, constituted by SiO2 and HfO2 layers, were first designed and modelled by Transfer Matrix Method to tailor targeted optical features (transmission windows, stopband ranges) and then fabricated by RF-sputtering technique. The structural, morphological, and optical features of the samples were investigated. In particular, the transmission spectra of the glass-based 1D photonic crystals, deposited on both flexible and rigid substrates, were acquired to highlight up to which extent the different nature of the substrates and the mechanical deformations (bending tests on the flexible structures) are not influencing the key spectral properties of the photonic crystals.
As already done in electronics, passive and active photonic devices demand integration on flexible substrates for a broad spectrum of application ranging from optical interconnection to sensors for civil infrastructure and environments, to coherent and uncoherent light sources and functionalized coatings for integration on biological tissue. In this communication we will present some recent results concerning the fabrication of novel flexible optical layers by sol-gel and radio frequency sputtering deposition techniques. The perspective is to give a technological way to transform intrinsically rigid or brittle materials into a highly mechanically flexible and optically functional systems
One of the current forefront in the field of photonic are flexible photonic research and development. The desired deliverable is to adjust the mechanical properties of materials to fabricate flexible photonic systems with various applications, e.g. gratings, channel waveguides, solar cells, protective coatings. It is well known that sol-gel metal oxide coatings may find applications as flexible coatings in photonics. Moreover, these materials can be easily functionalized to obtain materials with additional special, desired, properties like easy-to-clean, anti-fingerprint, anti-fogging and others, what is attractive for the potential of future commercialization of flexible photonic materials. In this work, we present the first step of research aimed to obtain silica-based coatings with appropriate adhesion on flexible substrates as poorly wettable surface – polymer PET and Ti-6Al-4V and 316L metallic thin foil as active oxide surface. The use of various types of substrates was aimed at presenting diversity in the possibilities of using the proposed coating materials. Nanoindentation, tensile test and scratch test of the investigated samples were studied. Measuring the mechanical properties of thin oxide films is difficult because it is usually impossible to detach of coating, not destroying its, from substrates. The thickness of coatings can range from a dozen to a few hundred nanometres, so complete methodology to determine a full set of mechanical properties is still lacking. In literature, the surface of samples is measured without a clear indication on coating properties, but on features which are the results of substrate-coating combinations.
We present the radio frequency sputtering fabrication protocols for the fabrication on flexible polymeric substrates of glass-based 1D photonic crystals and erbium activated planar waveguides. Various characterization techniques, such as atomic force microscopy and optical microscopy, are employed to put in evidence the good adhesion of the glass coating on the polymeric substrates. Transmittance measurements are performed on the multilayer structure and indicate that there are no differences between the samples deposited on the polymeric and SiO2 substrates, even after bending. Prism coupling technique is used to measure the optical parameter of the planar waveguide fabricated on flexible substrates. The 4I13/2 → 4I15/2 emission band, detected upon TE0 mode excitation at 514.5 nm, exhibits the spectral shape characteristic of Er3+ ions embedded in a crystalline environment.
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