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In seeking to promote cycling in wintertime, it is desirable to understand how important the winter maintenance service level is in people's decision to cycle or not, and methods to compare different road conditions on cycleways are therefore needed. By measuring friction, an assessment of the service level can be achieved, but methods available often involve the use of large vehicles, which can lead to overloading damage on cycleways, and constitute a safety risk for cyclists and pedestrians. A portable friction tester (PFT), originally designed to measure friction on road markings, was thought to be an appropriate instrument for cycleways and was, therefore, tested on different winter road conditions, and on different cycleway pavement materials. In this study, it was found that the PFT is a valuable tool for measuring friction on cycleways. Different winter road conditions, as well as different pavement materials, can be distinguished from each other through PFT measurements. The PFT provides a good complement to visual inspections of cycleways in winter maintenance evaluation and can, for example, be used to determine if desired service levels have been achieved. CE Database keywords: Bicycles; Friction; Measurement; Roads; Maintenance.

The properties of guided-mode resonance reflection filters constructed with multiple thin-film layers are addressed. Greatly improved filter characteristics are shown to follow by the incorporation of multiple homogeneous layers with the spatially modulated layer. Calculated results for single-layer, double-layer, and triple-layer filter structures are presented. Whereas good filter characteristics are obtainable with single layers that are half-resonance-wavelength thick, there remains a residual reflection in the sidebands unless the cover and the substrate permittivities are equal. With double-layer and triple-layer designs, extensive wavelength ranges with low sideband-reflectance values are shown to be possible without requiring equal cover and substrate permittivities. The antireflection properties of the layer stack can be understood if the modulated layer is modeled as a homogeneous layer characterized by its average relative permittivity. However, as the grating-modulation index increases, this approximation deteriorates. In particular it is found that, for a given high modulation index, the double-layer antireflection thin-film approximation fails, whereas for the same modulation in a triple-layer system it holds firmly. Multilayer designs can thus have significantly large filter passbands, as they may contain heavily modulated resonant gratings without corruption of the ideal filter characteristics.

The guided-mode resonance properties of planar dielectric waveguide gratings are presented and explained. It is shown that these structures function as filters that produce complete exchange of energy between forward- and backward-propagating diffracted waves with smooth line shapes and arbitrarily narrow filter linewidths. Simple expressions based on rigorous coupled-wave theory and on classical slab waveguide theory give a clear view and quantification of the inherent TE/TM polarization separation and the free spectral ranges of the filters. Furthermore, the resonance regimes, defining the parametric regions of the guided-mode resonances, can be directly visualized. It is shown that the linewidths of the resonances can be controlled by the grating modulation amplitude and by the degree of mode confinement (refractive-index difference at the boundaries). Examples presented of potential uses for these elements include a narrow-line polarized laser, a tunable polarized laser, a photorefractive tunable filter, and an electro-optic switch. The guided-mode resonance filter represents a basic new optical element with significant potential for practical applications.

Experimental results on real-time holographic interferometry using photorefractive iron-doped lithium niobate crystals to store the reference holograms are presented. Since the crystals are self-developing, precise repositioning of the reference hologram or in situ wet processing is not needed. With proper choice of experimental parameters it is found that the same reference hologram can be used for real-time processing of long sequences (approximately 10 min.) of input data with minimal degradation. The results obtained on visualization of heat-flow patterns from electronic chips illustrate the utility of this approach.

Experimental results on holographic subtraction interferometry in photorefractive lithium niobate crystals are presented. The dependence of the subtraction operation on the hologram diffraction efficiency has been measured for both single holograms and angularly multiplexed holograms. Example results from heat transfer and acoustics are presented. Key words: Holographic subtraction, interferometry, photorefractive materials.

Fundamental effects in nanophotonic resonance systems focused on singular states and their properties are presented. Strongly related to lattice geometry and material composition, there appear resonant bright channels and non-resonant dark channels in the spectra. The bright state corresponds to high reflectivity guided-mode resonance (GMR) whereas the dark channel represents a bound state in the continuum (BIC). Even in simple systems, singular states with tunable bandwidth appear as isolated spectral lines that are widely separated from other resonance features. Under moderate lattice modulation, there ensues leaky-band metamorphosis, merging modal bands and resulting in offset dark states and reflective BICs along with transmissive BICs within a high-reflectance wideband. Rytov-type effective medium theory (EMT) is shown to be a powerful means to describe, formulate, and understand the collective GMR/BIC fundamentals in resonant photonic systems. Particularly, the discarded Rytov analytical solution for asymmetric fields is shown here to predict the dark BIC states essentially exactly for considerable modulation levels. The propagation constant of an equivalent EMT homogeneous film provides a quantitative evaluation of the eminent, oft-cited embedded BIC eigenvalue. The work concludes with experimental verification of key effects.

The guided-mode resonance characteristics of dielectric waveguide gratings are presented. The sharp resonance features predicted theoretically are experimentally observed in the microwave region (4-18 GHz) and are shown to be in agreement with theory.