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Journal of the Optical Society of America A

Binary image encryption with a QR code-encoded optical beam having an array of vortices

Allarakha Shikder, Sonu Kumar Rao, Praveen Kumar, Naveen Kumar Nishchal

Published Jan 22, 2024• 27 citations
Publisher

Abstract

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.

DOI
10.1364/josaa.507046

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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.
Structured light carrying optical vortices have gained significant attention in information security as they offer high-dimensional orthogonal states for encoding. These states are usually associated with the orbital angular momentum of light. In this letter, we demonstrate a novel method for binary image encryption using structured phase encoding. The structured phase is obtained by multiple lattices of spatially distributed phase singularity points with varying azimuthal indices. It has been shown that data encoding using orthogonal sets of optical vortex modes enable noise-free decryption and provide robustness against atmospheric turbulence in short propagation distance.
Vortex beams carrying orbital angular momentum (OAM) modes hold the promise of facilitating high-dimensional symbol mappings for information encryption. However, challenges persist in achieving both high-security and high-capacity encryption with OAM modes, mainly due to limitations in encoding degrees of freedom and compatible decoding methods. Herein, we present an encryption scheme that integrates truncated OAM modes with phase encoding. Truncated OAM modes are hybrid modes that emerges from mode dispersion caused by the absence of amplitude modulation during generation. By combining the generation function with phase encoding, we can modulate the mode dispersion, creating a discrete set of truncated modes. This introduces a phase degree of freedom for encoding information onto the mode spectrum, achieving high-security encryption. The exponential expansion of the phase factors enables the construction of higher-order symbol maps, thereby increasing encryption capacity. As a proof-of-concept, we implemented an optical information encrypting link using 4 OAM modes and 32-order phase encoding, resulting in over 3×104 modulation orders. The neural network successfully decoded the encryption information with 100% accuracy. This scheme offers the potential to incorporate additional OAM modes in the generating function and further partition the phase encoding, enabling even higher-dimensional symbol mapping. These advancements open up new possibilities for advancing high-security and high-capacity information encryption based on OAM modes.
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.
Optical vortices carrying orbital angular momentum have drawn much attention because they provide high-dimensional encoding. Employing an array of optical vortices, we demonstrate an authentication verification system. For security authentication, an exclusive-OR logic operation has been implemented employing a light beam consisting of an array of vortices. A liquid crystal spatial light modulator has been used to generate orthogonal states of optical vortices. The proposed technique can provide a secure method of authentication with straightforward implementation. We have presented simulation and experimental results to verify the proposed scheme.
Multi-ring optical vortices are a kind of structured beams that carry orbital angular momentum (OAM) and have concentrical doughnut intensity distributions. In this Letter, we present both theoretically and experimentally a scheme that employs the dimensions of both the OAM states and radial index of multi-ring optical vortices simultaneously to accomplish high-dimensional free-space data coding/decoding transmissions. Such a scheme can further improve the coding efficiency when limited OAM states are available. In the proof-of-concept experiment, 64-ary coding/decoding employing 16 OAM states and four radial indices are present. Also, the coding/decoding performance when facing various atmosphere turbulences is evaluated. Furthermore, a 64 × 64 gray image (totally, 32,768 bits) is also transmitted through multi-ring optical vortices coding in free-space successfully, showing good transmission performance.