Smart responsive lasing signals for high-security optical encryption

August 21, 2020

Information security has drawn considerable attention as the exponential growth of information communication in the era of big data. The stimuli-responsive photoluminescent materials that can quickly switch among different states have been an effective approach to increasing the data security and storage density of such devices. Some smart photoluminescent materials (e.g., transitionmetal complexes, fluorescent supermolecules and dyes), capable of responding to external stimuli with reversible changes in chemical constitutions or superstructures, have been intensively explored as optical data storage media and document encryption systems. However, most of them can only provide broad band photoluminescence (PL) from limited luminescent states, resulting in a relatively low security level and limited coding capacity.

In comparison with broad band PL, stimulated emission with narrow linewidth for easily distinguishable readout, is promising in coding field as a novel cryptographic primitive. Nevertheless, owing to the limitation of the Franck-Condon principle, it has been a great challenge to broadly tailor the lasing wavelength, which is unable to generate multiple lasing states, and thus restricting their applications in high-density information storage and high-security optical encryption.

Very recently, Professor Yong Sheng Zhao's group in the Institute of Chemistry, Chinese Academy of Sciences propose a strategy to achieve multiple responsive lasing emission states for high-security optical encryption by modulating the competition between radiative rate of donor and the rate of energy transfer in FRET microlasers, which is published in National Science Review.

The competitive lasing from the donor and acceptor were reversibly switched by modulating the competition between radiative rate of donor and the rate of energy transfer (Figure 1). At a low pump fluence, there is no lasing emission as a result of insufficient gain. Because the KET is larger than Kr, FRET dominates the deexcitation processes, leading to spontaneous emission from the acceptor. When the pump fluence exceeds the acceptor lasing threshold, majority of the excitation energy captured by donor transfers to the acceptor and lasing from acceptor occurs when population inversion is created. Further increasing of pump fluence induce simultaneous lasing emissions from the donor and acceptor as a result of the approaching of Kr to KET. At an even higher pump fluence, the Kr outpaces the KET and radiative decay from donor begins to dominate the deexcitation processes, resulting in lasing from donor when corresponding population inversion is build-up. Consequently, energy transfer to the acceptor is suppressed and lasing emission from the acceptor disappears due to the inefficient gain. Dynamic lasing action could be well controlled through tailoring the balance between radiative rate of donor and the rate of energy transfer, thus resulting in multiple distinguishable lasing states.

On this basis, the authors realized a novel quaternary coding platform and a proof-of-concept demonstration of cryptographic application was exhibited with an inkjet-printed microlaser array (Figure 2). Data encryption and extraction were demonstrated using a 4×4 microlaser array, showing vast prospect in avoiding the disclosure of security information. The results not only offer a comprehensive understanding of the function-oriented construction of organic composite materials, but also open up a new way to the fabrication of flexible photonic components that can be used for optical recording and information encryption.
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See the article:

Smart Responsive Organic Microlasers with Multiple Emission States for High-Security Optical Encryption
https://doi.org/10.1093/nsr/nwaa162

Science China Press

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