Abstract
Information encryption with optical technologies has become increasingly important due to remarkable multidimensional capabilities of light fields. However, the optical encryption protocols proposed to date have been primarily based on the first-order field characteristics, which are strongly affected by interference effects and make the systems become quite unstable during light–matter interaction. Here, we introduce an alternative optical encryption protocol whereby the information is encoded into the second-order spatial coherence distribution of a structured random light beam via a generalized van Cittert–Zernike theorem. We show that the proposed approach has two key advantages over its conventional counterparts. First, the complexity of measuring the spatial coherence distribution of light enhances the encryption protocol security. Second, the relative insensitivity of the second-order statistical characteristics of light to environmental noise makes the protocol robust against the environmental fluctuations, e.g, the atmospheric turbulence. We carry out experiments to demonstrate the feasibility of the coherence-based encryption method with the aid of a fractional Fourier transform. Our results open up a promising avenue for further research into optical encryption in complex environments.
Highlights
As a fundamental attribute that describes statistical properties of random light fields, optical coherence has played an important role in understanding and tailoring lightmatter interactions [1, 2]
We have presented a protocol for optical information encryption into the second-order correlations of random light fields expressed in terms of the cross-spectral density of the field
We have verified the feasibility of our protocol by carrying out a proof-of-principle experiment by encoding an optical image into the cross-spectral density of a random light beam with the aid of a fractional Fourier transform encoding system and decoding the plaintext through the measurement of the said cross-spectral density with the help of the recently introduced generalized Hanbury Brown–Twiss technique [40]
Summary
As a fundamental attribute that describes statistical properties of random light fields, optical coherence has played an important role in understanding and tailoring lightmatter interactions [1, 2]. The early theoretical [8, 9] and experimental [10] work on light beams with nonuniform spatial coherence has triggered research into engineering spatial coherence structure of random sources. A rich repertoire of propagation scenarios induced by the spatial coherence engineering enables a host of promising applications to photovoltaics [38], diffractive imaging with low-coherence light [39], optical target tracking [40, 41], and particle trapping [42, 43] among others
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