Femtosecond direct laser writing on bi-layer gold-silicon films for hidden data storage and random key generation

To keep up with the growing needs for data storage, new-generation nanophotonic devices are being actively developed, as they have a high potential to meet all the essential industrial requirements. In addition to the high stability and capacity of such systems, it is highly desirable to provide them with additional security features that would protect data from unauthorized reading. However, this usually leads to inevitable and critical complications of existing recording techniques. This work presents a novel and facile technology for hidden data storage, based on femtosecond laser processing of bilayer gold-silicon films at low energy densities. It is shown that the recorded data can be successfully extracted using photoluminescence signal mapping, while remaining completely invisible in an optical microscope. Furthemore, the use of the investigated procedure for the optical random key generation is also demonstrated. The proposed technology stands out for its simplicity and reliability and, thus, has the potential to be an excellent choice for industrial use in the upcoming era of secure optical communication.