Security-enhanced optical voice encryption in various domains and comparative analysis

Optical voice encryption based on digital holography (DH), which uses the double random phase encoding (DRPE) in the Fourier transform domain, has been proposed [Opt. Lett.42, 4619 (2017)OPLEDP0146-959210.1364/OL.42.004619]. In the present work, we propose optical voice encryption in other optical domains such as fractional Fourier, Fresnel, and gyrator transform, which convert input information into different mixed space-frequency domains. We also analyze the recording conditions of human voice and some security aspects of the scheme. An optical setup based on off-axis DH is used to record the time-series of holograms, and these holograms can visualize the sound wave propagation. Then, the different encryption domains in double random phase encoding (DRPE) are used to encrypt voice information with enhanced security. With the numerical reconstruction and decryption procedure of DRPE with all correct keys and correct orders of optical domains, the original voice information can be retrieved. The extension of voice encryption in different domains will enhance the security level and analysis of recording, and security aspects will explore the possibilities and challenges of the optical voice encryption scheme. We present simulation results for encryption of an experimentally recorded human voice in various domains.