Features of the application of a novel optical filter with angular selectivity of the light transmission to architectural glazing are considered. The filter consists of a sheet transparent substrate with thin-film grating layers on both surfaces. The gratings formed by directionally transmissive strips, alternating with absorptive, reflective, or scattering strips. Their relative position on the input and output surfaces provides angular selectivity of the directional light transmission – as the incidence angle changes, the proportion of radiation that passes through both gratings of the filter also changes. Chromogenic materials currently used in the laminated smart windows, providing control over the intensity and spectrum of the transmitted solar radiation, cannot achieve the selective regulation on the ranges of incidence angles. Such a regulation requires the use of additional daylight-redirecting devices, especially blinds, to dynamically adapt to the position of the sun. The grating optical filter provides angular selectivity of the light transmission of a window without such devices. The features of using this filter in the single and double glazed windows are described. A graphic analytical calculation method is proposed for estimating the effect of geometrical and optical parameters of the filter on the angular characteristics of the light transmission. An algorithm to optimize filtering solar radiation taking into account the geographical coordinates of terrain, time of day and year and the orientation of the window to the cardinal is set. An algorithm to calculating geometrical parameters of the filter with pre-specified characteristics of the light transmission is obtained.
Classical multilayer filters are optically homogeneous in each layer of the surface coatings. Diffraction gratings and photonic crystals used in the filters have micro- and nanoscale inhomogeneities. An optical filter consisting of sheet transparent substrate with thin-film grating layers on both surfaces is developed. Macroscopic gratings of submillimeter widths are formed by directionally transmissive strips, alternating with absorptive, reflective, or scattering strips. Their relative position on input and output surfaces provides angular selectivity of light transmission – part of the radiation that has passed through input gratings is blocked additionally by output gratings depending on incidence angle. Graphicanalytical calculation method determines the influence of optical and geometric parameters of alternating strips on angular characteristics of transmission. Characteristics are broken lines with areas of decreasing or increasing transmission, which practically linear for the angles up to approximately 60°, with further increase in the angles, the lines are curved more because of sinusoidal dependence under Snell's law. Results of graphic-analytical calculations are confirmed experimentally. Preset the desired dependence of transmission is adjusted considering reflection (Fresnel formulas) and absorption (Bouguer-Lambert law). The adjusted dependence is approximated to a broken line taking into account obtained regularities. Finally, all parameters of alternating strips of gratings are chosen. Thus at pre-known trajectory of light source relative to the filter pre-adapted angular selective regulation of its light transmission is provided. Architectural glazing to control the transmitted solar radiation without special redirecting devices and provide invisibility through window at predetermined angles is the most promising area of application.