The MuseLearn Platform: Personalized Content for Museum Visitors Assisted by Vision-Based Recognition and 3D Pose Estimation of Exhibits

MuseLearn is a platform that enhances the presentation of the exhibits of a museum with multimedia-rich content that is adapted and recommended for certain visitor profiles and playbacks on their mobile devices. The platform consists mainly of a content management system that stores and prepares multimedia material for the presentation of exhibits; a recommender system that monitors objectively the visitor’s behavior so that it can further adapt the content to their needs; and a pose estimation system that identifies an exhibit and links it to the additional content that is prepared for it. We present the systems and the initial results for a selected set of exhibits in Herakleidon Museum, a museum holding temporary exhibitions mainly about ancient Greek technology. The initial evaluation that we presented is encouraging for all systems. Thus, the plan is to use the developed systems for all museum exhibits as well as to enhance their functionality.

Flexible tube lattice fibers for terahertz applications

In this paper a flexible hollow core waveguide for the terahertz spectral range is demonstrated. Its cladding is composed of a circular arrangement of dielectric tubes surrounded by a heat-shrink jacket that allows the fiber to be flexible. Characterization of straight samples shows that the hollow core allows the absorption caused by the polymethylmethacrylate tubes of the cladding to be reduced by 31 times at 0.375 THz and 272 times at 0.828 THz with respect to the bulk material, achieving losses of 0.3 and 0.16 dB/cm respectively. Bending loss is also experimentally measured and compared to numerical results. For large bending radii bending loss scales as Rb-2, whereas for small bending radii additional resonances between core and cladding appear. The transmission window bandwidth is also shown to shrink as the bending radius is reduced. An analytical model is proposed to predict and quantify both of these bending effects.

Pure chiral optical fibres

We investigate the properties of optical fibres made from chiral materials, in which a contrast in optical activity forms the waveguide, rather than a contrast in the refractive index; we refer to such structures as pure chiral fibres. We present a mathematical formulation for solving the modes of circularly symmetric examples of such fibres and examine the guidance and polarisation properties of pure chiral step-index, Bragg and photonic crystal fibre designs. Their behaviour is shown to differ for left- and right-hand circular polarisation, allowing circular polarisations to be isolated and/or guided by different mechanisms, as well as differing from equivalent non-chiral fibres. The strength of optical activity required in each case is quantified.

Stable imprinting of long-period gratings in microstructured polymer optical fibre

A simple heat imprinting method for producing stable long-period gratings (LPGs) in microstructured polymer optical fibre (mPOF) is presented as well as the examination of their lifetime and the modelling results of these gratings. Writing LPGs in mPOF presents opportunities for sensors in fibre that can withstand greater bending and strain and are adaptable to specific applications through modification of the cladding structure.

Liquid-filled hollow core microstructured polymer optical fiber

Guidance in a liquid core is possible with microstructured optical fibers, opening up many possibilities for chemical and biochemical fiber-optic sensing. In this work we demonstrate how the bandgaps of a hollow core microstructured polymer optical fiber scale with the refractive index of liquid introduced into the holes of the microstructure. Such a fiber is then filled with an aqueous solution of (-)-fructose, and the resulting optical rotation measured. Hence, we show that hollow core microstructured polymer optical fibers can be used for sensing, whilst also fabricating a chiral optical fiber based on material chirality, which has many applications in its own right.

Guidance properties of low-contrast photonic bandgap fibres

We investigate the guidance properties of low-contrast photonic band gap fibres. As predicted by the antiresonant reflecting optical waveguide (ARROW) picture, band gaps were observed between wavelengths where modes of the high-index rods in the cladding are cutoff. At these wavelengths, leakage from the core by coupling to higher-order modes of the rods was observed directly. The low index contrast allowed for bend loss to be investigated; unlike in index-guiding fibres, anomalous "centripetal" light leakage through the inside of the bend can occur.

Photonic bandgap with an index step of one percent

Early work suggested that very large refractive index contrasts would be needed to create photonic bandgaps in two or three dimensionally periodic photonic crystals. It was then shown that in two-dimensionally periodic structures (such as photonic crystal fibres) a non-zero wavevector component in the axial direction permits photonic bandgaps for much smaller index contrasts. Here we experimentally demonstrate a photonic bandgap fibre made from two glasses with a relative index step of only 1%.

Solution doping of microstructured polymer optical fibres

Solution doping of microstructured polymer optical fibres [mPOF] is demonstrated, a technique which allows dopants to be introduced after polymerisation through the microstructure. Controlled diffusion is used to disperse the dopant uniformly across the fibre core, and the final concentration can be systematically varied by appropriate choice of conditions. We use this technique to produce a fibre doped with Rhodamine 6G and characterize its loss and fluorescence behavior.

Microstructured optical fiber for single-polarization air guidance

An air-core microstructured fiber design that supports a single-polarization, circularly symmetric nondegenerate mode is presented. The fiber design is modeled directly, and the microstructured cladding is analyzed by use of band diagrams to elucidate the mechanism through which polarization nondegeneracy is achieved.

Electron tomography and computer visualisation of a three-dimensional 'photonic' crystal in a butterfly wing-scale

A combination of transmission electron tomography and computer modelling has been used to determine the three-dimensional structure of the photonic crystals found in the wing-scales of the Kaiser-I-Hind butterfly (Teinopalpus imperialis). These scales presented challenges for electron microscopy because the periodicity of the structure was comparable to the thickness of a section and because of the complex connectivity of the object. The structure obtained has been confirmed by taking slices of the three-dimensional computer model constructed from the tomography and comparing these with transmission electron microscope (TEM) images of microtomed sections of the actual scale. The crystal was found to have chiral tetrahedral repeating units packed in a triclinic lattice.

Ring structures in microstructured polymer optical fibres

Recent developments in polymer microstructured optical fibres allow for the realisation of microstructures in fibres that would be problematic to fabricate using glass-based capillary stacking. We present one class of such structures, where the holes lie on circular rings. A fibre of this type is fabricated and shown to be single moded for relatively long lengths of fibre, whereas shorter lengths are multimoded. An average index model for these fibres is developed. Comparison of its predictions to the calculated properties of the exact structure indicates that the ring structures emulate homogeneous rings of lower refractive index resulting in the ring structured fibres behaving approximately as cylindrically layered fibres.

Microstructured polymer optical fibre

The first microstructured polymer optical fibre is described. Both experimental and theoretical evidence is presented to establish that the fibre is effectively single moded at optical wavelengths. Polymer-based microstructured optical fibres offer key advantages over both conventional polymer optical fibres and glass microstructured fibres. The low-cost manufacturability and the chemical flexibility of the polymers provide great potential for applications in data communication networks and for the development of a range of new polymer-based fibre-optic components.