Photo-isomerization enabled reversible wavelength switching in fiber random laser for color image encryption.

Random lasers owing the functionality of generating random spectra facilitate the chaotic encrypted systems essential for cryptography in the current information epoch. Nevertheless, single wavelength bands of random lasers provide an unsuitable key for image encryption that causes outline interpretation and a fragile complex dual chaotic encryption demanding secured image encryption. This research presents an inevitable development of a reversible switchable wavelength fiber random laser composed of the mixture of highly polarized intramolecular charge transfer dye molecules and the optimum concentration of titanium dioxide acting as gain and efficient scattering mediums respectively within a polyvinyl alcohol matrix. This mixture with a certain ratio is coated on a fiber employing a dip coated method, followed by a layer of polydimethylsiloxane to facilitate with high coefficient of thermal expansion. Random laser emission is enabled with dynamically switchable wavelengths obeying the excited state intramolecular proton transfer phenomenon under the photo-isomerization. The optimum scatters concentration yields a lower threshold of 32 µJ/cm with full width at half maximum of 0.4 nm and dual emission reversible switchable wavelength bands centered around 443 nm and 464 nm attributed to inter charge transfer feature of the dye molecules. Thereby, the dual reversible switchable wavelength bands feed as input for a dual chaotic color image encryption system. Further, in this integrated system, beam divergence of random laser emissions remains less than 20° during both situations of with- and without irradiation. This delicate approach paves the way in laying the foundation about the applicability of fiber random lasers in an information security system.