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APL Photonics

Audio encryption using polarized light beam

Allarakha Shikder, Sudheesh K. Rajput, Naveen Kumar Nishchal, Osamu Matoba, Yasuhiro Awatsuji

Published Mar 1, 2025• 9 citations
Publisher

Abstract

In recent years, the security of audio data has become paramount in terms of personal information, national security, and forensic evidence. However, most reported systems use digital algorithms and lack their implementation in the optical domain, which can provide better security due to the use of physical keys and high speed. In addition, recently developed phase-encoded audio encryption schemes in the optical domain have quality limitations due to precise wavefront measurement and control. Perfect experimental alignment to achieve good quality retrieved data is very challenging, due to which no optical implementation of voice security has been reported. This work introduces a robust audio encryption scheme using the polarization property of a light beam. Initially, one-dimensional (1D) audio combined with a random dataset acts as an encryption key and converts it to 1D cipher audio, which is transformed into a two-dimensional (2D) cipher-audio map. Subsequently, this is fragmented into several 2D segments, which are then encoded into the light beam using binary polarization states. An arbitrary sequence is maintained during encoding of the 2D segments into binary polarization states. The demonstrated technique is a non-interferometric method, and the decryption can be achieved through intensity recording only.

DOI
10.1063/5.0234393

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In recent years, the security of audio data has become paramount in terms of personal information, national security, and forensic evidence. However, most reported systems use digital algorithms and lack their implementation in the optical domain, which can provide better security due to the use of physical keys and high speed. In addition, recently developed phase-encoded audio encryption schemes in the optical domain have quality limitations due to precise wavefront measurement and control. Perfect experimental alignment to achieve good quality retrieved data is very challenging, due to which no optical implementation of voice security has been reported. This work introduces a robust audio encryption scheme using the polarization property of a light beam. Initially, one-dimensional (1D) audio combined with a random dataset acts as an encryption key and converts it to 1D cipher audio, which is transformed into a two-dimensional (2D) cipher-audio map. Subsequently, this is fragmented into several 2D segments, which are then encoded into the light beam using binary polarization states. An arbitrary sequence is maintained during encoding of the 2D segments into binary polarization states. The demonstrated technique is a non-interferometric method, and the decryption can be achieved through intensity recording only.
In recent years, optical information processing has become increasingly important due to its ability to handle large amounts of data efficiently. Amplitude, phase, spatial frequency, wavelength, and polarization are the physical dimensions used for information encoding into the light beam. Information encoding using orbital angular momentum (OAM) carried by a vortex beam is gaining interest in this regard. Such beams provide high-dimensional orthogonal states for encoding and have shown more stability in turbulent media than Gaussian beams, especially in the case of free space propagation. This study demonstrates an image encryption method utilizing an array of OAM light modes. The approach uses a non-interferometric intensity recording-based encoding scheme, which offers ease of implementation. Quick response codes have been utilized for encoding to avoid information loss from non-uniform distribution of light and aberrations. The encryption scheme is highly secure because the encrypted light beam contains only partial information about the object, preventing complete information retrieval without proper key information.
Information security has attracted much current attention due to the rapid development of modern technologies, such as computer and internet. We propose a novel method for optical image encryption using multilevel Arnold transform and rotatable-phase-mask noninterferometric imaging. An optical image encryption scheme is developed in the gyrator transform domain, and one phase-only mask (i.e., phase grating) is rotated and updated during image encryption. For the decryption, an iterative retrieval algorithm is proposed to extract high-quality plaintexts. Conventional encoding methods (such as digital holography) have been proven vulnerably to the attacks, and the proposed optical encoding scheme can effectively eliminate security deficiency and significantly enhance cryptosystem security. The proposed strategy based on the rotatable phase-only mask can provide a new alternative for data/image encryption in the noninterferometric imaging.
A technique that combines the high speed and the high security of optical encryption with the advantages of electronic transmission, storage, and decryption is introduced. Digital phase-shifting interferometry is used for efficient recording of phase and amplitude information with an intensity recording device. The encryption is performed by use of two random phase codes, one in the object plane and another in the Fresnel domain, providing high security in the encrypted image and a key with many degrees of freedom. We describe how our technique can be adapted to encrypt either the Fraunhofer or the Fresnel diffraction pattern of the input. Electronic decryption can be performed with a one-step fast Fourier transform reconstruction procedure. Experimental results for both systems including a lensless setup are shown.
Data proliferation in the digital age necessitates robust encryption techniques to protect information privacy. Optical encryption leverages the multiple degrees of freedom inherent in light waves to encode information with parallel processing and enhanced security features. However, implementations of large-scale, high-security optical encryption have largely remained theoretical or limited to digital simulations due to hardware constraints, signal-to-noise ratio challenges, and precision fabrication of encoding elements. Here, we present an optical encryption platform utilizing scattering multiplexing ptychography, simultaneously enhancing security and throughput. Unlike optical encoders which rely on computer-generated randomness, our approach leverages the inherent complexity of light scattering as a natural unclonable function. This enables multi-dimensional encoding with superior randomness. Furthermore, the ptychographic configuration expands encryption throughput beyond hardware limitations through spatial multiplexing of different scatterer regions. We propose a hybrid decryption algorithm integrating model- and data-driven strategies, ensuring robust decryption against various sources of measurement noise and communication interference. We achieved optical encryption at a scale of ten-megapixel pixels with 1.23 µm resolution. Communication experiments validate the resilience of our decryption algorithm, yielding high-fidelity results even under extreme transmission conditions characterized by a 20% bit error rate. Our encryption platform offers a holistic solution for large-scale, high-security, and cost-effective cryptography.
The optical network supporting emerging bandwidth-intensive services has become the cornerstone of the 5G era. However, the development of optical fiber eavesdropping and quantum computing has brought huge security challenges to traditional cryptography. As an effective approach to improving optical layer transmission security, all-optical logic gate encryption has important research significance. This paper proposes a high-speed coherent optical encryption and decryption system based on phase encoding with all-optical logic gates. The system ingeniously designs the phase encoding and decoding scheme between two quadrature phase-shift keying (QPSK) signals, which doubles the encryption and decryption efficiency. In addition, the integration of physical-layer key distribution (PLKD) and physical-layer encryption (PLE) contributes to a reduction in overall system complexity. By adopting real-time signal processing in an all-optical domain, the single-wavelength rate of system security communication can reach 100 Gbps. The system is also applicable to other phase-modulated signals and provides a feasible scheme to enhance transmission security in wavelength division multiplexing (WDM) optical networks featuring high speed, low latency, and high flexibility.