The optical field enhanced nonlinear optical (NLO) absorption of spin-coated 10-layer and 20-layer 1D photonic crystal structures is demonstrated. A significant 2.5 fold increase in the two-photon absorption coefficient is reported for multilayer structures as compared to a single layer of semiconductor nanocomposite (NC) having a comparable thickness. Under high-intensity illuminance, increased nonlinear absorption could be accredited to the confinement of the optical field due to the localization of intensity. The carefully engineered multilayer structures embedded with semiconductor NCs can provide an attractive approach to designing practical NLO limiters and switches.
A watermarking scheme is proposed based on optical asymmetric cryptography using double random phase encoding in
the gyrator transform domain. It is based on the phase and amplitude truncation during the encryption process. The
scheme is validated through computer simulations showing the scheme's sensitivity to decryption keys and orders of the
gyrator transform. The occlusion and noise attacks have also been analysed. The proposed scheme is significantly
resistant to both these attacks.
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