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IEEE Photonics Technology Letters

Arbitrary Vector Beam Encoding Using Single Modulation for Information Security Applications

Praveen Kumar, Areeba Fatima, Naveen Kumar Nishchal

Published Feb 2, 2021• 30 citations
Publisher

Abstract

Features of vector beam such as its spatial degree of freedom and intensity-based measurements are useful in information encoding but often require a complex optical-setup. In this letter, the concept of modulating a single-polarization component for encoding in arbitrary vector field through a non-interferometric approach has been introduced. Utilizing this concept, an efficient information security scheme has been demonstrated. The experimental results verify the feasibility of a practical system.

DOI
10.1109/lpt.2021.3052571

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Features of vector beam such as its spatial degree of freedom and intensity-based measurements are useful in information encoding but often require a complex optical-setup. In this letter, the concept of modulating a single-polarization component for encoding in arbitrary vector field through a non-interferometric approach has been introduced. Utilizing this concept, an efficient information security scheme has been demonstrated. The experimental results verify the feasibility of a practical system.
In this work, it is experimentally demonstrated that the nonseparability of vector beams (e.g., radial and azimuthal polarization) can be used to encode information for optical communication. By exploiting the nonseparability of a vector beam's space and polarization degrees of freedom using conventional wave plates, it is shown that 2 bits of information can be encoded when applying the identity and three Pauli operators to its polarization degree of freedom. It is also shown that vector beams can be efficiently decoded with as low as 2.7% cross talk using a Mach-Zehnder interferometer that exploits a higher-order Pancharatnam-Berry phase and liquid crystal q-plates.
The complex vector beams yield up an abundance of polarization information that has not yet been well utilized in information encoding. In this paper, we propose a polarization encoding scheme with the non-orthogonal polarization states using a stationary vector beam. Recognizing those non-orthogonal polarization states is assisted by the structured patterns of the single vector beams under different polarization projections. We show that one can achieve different capacities of encoding bits by changing the step of the polarization angle with the single vector beam. We also demonstrate the non-orthogonal polarization encoding scheme can be well decoded with the machine learning classification algorithm. A 64×64 gray image is successfully transmitted by using 4 bits/symbol encoding-decoding scheme with 99.94 % transmission accuracy. Besides, by extending the encoding-decoding scheme to 8 bits/symbol based on the same single vector beam, we achieve a higher transmission rate with 65.58% transmission accuracy. Our work holds promise for small-angle non-orthogonal polarization encoding for free-space optical communications.
Vector vortex beams, featuring independent spatial modes in orthogonal polarization components, offer an increase in information density for emerging applications in both classical and quantum communication technology. Recent advances in optical instrumentation have led to the ability of generating and manipulating such beams. Their tomography is generally accomplished by projection measurements to identify polarization as well as spatial modes. In this paper we demonstrate spatially resolved generalized measurements of arbitrary vector vortex beams. We perform positive operator valued measurements (POVMs) in an interferometric setup that characterizes the vector light mode in a single-shot. This offers superior data acquisition speed compared to conventional Stokes tomography techniques, with potential benefits for communication protocols as well as dynamic polarization microscopy of materials.
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.
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.
Abstract Optical encryption strategies utilizing fully coherent light have been widely explored but often face challenges such as speckle noise and beam instabilities. In this work, we introduce a novel protocol for multi-channel optical information encoding and encryption using vectorial spatial coherence engineering of a partially coherent light beam. By characterizing the beam’s spatial coherence structure with a 2×22 \times 22×2 2 × 2 coherence matrix, we demonstrate independent control over the three components of the coherence Stokes vector. This allows for three-channel optical information encoding and encryption, with applications in color image representation. Unlike existing methods based on fully coherent light modulations, our approach utilizes a two-point dependent coherence Stokes vector, proving resilient to random noise in experimental scenarios. Our findings provide a robust foundation for higher-dimensional optical encoding and encryption, addressing limitations associated with partially coherent light in complex environments.