**3. Brief Overview of the Contributions to This Special Issue**

Tikhonravov et al. [1] presented a computational approach for comparing various broadband monitoring strategies, taking into account the positive and negative effects associated with the correlation of thickness errors caused by the monitoring procedure. The presented computational approach is general and can be applied to check the prospects of the production of various types of optical coatings. Stenzel et al. [2] studied linear and non-linear optical properties of titanium dioxide films prepared by plasma ion-assisted electron beam evaporation. Linear optical properties were investigated in terms of spectrophotometry using the beta-distributed oscillator model as a parametrized dispersion law. The nonlinear two-photon absorption coefficient of titanium dioxide was determined by means of the laser-induced deflection technique at a wavelength of 800 nm. Dimitrov et al. [3] demonstrated transparent and conductive aluminum-doped zinc oxide (AZO) thin films deposited on rigid and transparent substrates through atomic layer deposition. Applications as transparent conductive layers in AZO/glass-supported liquid crystal displays and flexible polymer-dispersed liquid crystal devices were discussed. Akhmedov et al. [4] investigated the structural, electrical, and optical performances of Ga-doped ZnO/Ag/Ga-doped ZnO (GZO/Ag/GZO) multilayered structures deposited on glass substrates by direct current (DC) magnetron sputtering in a pure Argon medium without any substrate heating. Highly transparent and conductive samples were obtained. Liu et al. [5] investigated Ti-doped SnO2 transparent conductive oxide thin films deposited on glass substrates using radio frequency (RF) magnetron sputtering and postdeposition annealing at temperatures in the range of 200–500 ◦C for 30 min. The effects of the annealing temperature on the structural properties, surface roughness, electrical properties, and optical transmittance of the thin films are then systematically explored. Cody et al. [6] demonstrated a possibility of optical sensing of copper ions in water using Linde Type L (LTL) zeolite thin films. Both single wavelength and spectroscopic ellipsometry were used for characterization of the changes in optical constants and thickness of films in the presence of heavy metal ions. Lazarova et al. [7] demonstrated a possible approach for enhancement of Poly(vinyl alcohol) (PVA) humidity-sensing ability using poly(vinylalcohol-*co*-vinylacetal) copolymers of different acetal content. Further enhancement through preparation of polymer–silica hybrids was demonstrated. The possibility of color sensing of humidity was also discussed. Eerdekens et al. [8] demonstrated organic, diamagnetic materials based on structurally simple (hetero-)tolane derivatives that form crystalline thin-film aggregates suitable for Faraday rotation spectroscopy. Huang at al. [9] studied the impact of vacuum annealing on CrWN glass molding coatings deposited by plasma enhanced magnetron sputtering. The vacuum annealing induced surface coarsening and spinodal decomposition accompanied by the formation of nm-sized c-CrN, c-W2N, and h-WN domains. The large volume fraction of the last one seriously weakened the coating strength and caused a drop in hardness. Shang et al. [10] used a theoretical/experimental combinative model for investigation of the waveguide sidewall roughness (SWR) and its impact on the optical propagation losses in silicon-on-insulator waveguides.
