Optical data storage has had a major impact on daily life since its introduction to the market in 1982. Compact discs (CDs), digital versatile discs (DVDs), and Blu-ray discs (BDs) are universal data-storage formats with the advantage that the reading and writing of the digital data does not require contact and is therefore wear-free. These formats allow convenient and fast data access, high transfer rates, and electricity-free data storage with low overall archiving costs. The driving force for development in this area is the constant need for increased data-storage capacity and transfer rate. The use of holographic principles for optical data storage is an elegant way to increase the storage capacity and the transfer rate, because by this technique the data can be stored in the volume of the storage material and, moreover, it can be optically processed in parallel. This Review describes the fundamental requirements for holographic data-storage materials and compares the general concepts for the materials used. An overview of the performance of current read-write devices shows how far holographic data storage has already been developed.

From the surface to volume: concepts for the next generation of optical-holographic data-storage materials.

Orbital angular momentum (OAM), one of the most recently discovered degrees of freedom of light beam field has fundamentally revolutionized optical physics and its technological capabilities. Optical beams with OAM have enabled a large variety of applications, including super-resolution imaging, optical trapping, classical and quantum optical communication, and quantum computing, to mention a few. To enable these and several other emerging applications, optical beams with OAM have been generated using a variety of methods and technologies, such as a simple astigmatic lens pair, one-/two-dimensional holographic optical elements, three-dimensional spiral phase plates, optical fibers, and recent entrants such as metasurfaces. All these techniques achieve spatial light modulation and can be implemented with either passive elements or active devices, such as liquid crystal on silicon and digital micromirror devices. Many of these devices and technologies are not only used for the generation of amplitude phase-polarization structured light beams but are also capable of analyzing them. We have attempted to encompass a wide variety of such technologies as well as a few emerging methodologies, broadly categorized into generation and detection protocols. We address the needs of scientists and engineers who desire to generate/detect OAM modes and are looking for the technique (active or passive) best suited for their application.

/pdf/generation-and-decomposition-of-scalar-and-vector-modes-4gpcle709y.pdf

Generation and decomposition of scalar and vector modes carrying orbital angular momentum: a review

Light-Directed Soft Mass Migration for Micro/Nanophotonics

The results of studies that have been performed over the last decade in the field of development of silver halide and nonsilver holographic recording media of organic and inorganic origin are analyzed. It is shown that previously developed materials mainly allow the development of holographic investigations. Among irreversible materials, considerable progress has been made in improving the characteristics of photopolymerizable recording media, which has allowed their use in color image holography and 3D optical archive-type memory, as well as for fabricating holographic optical elements. In the field of improving the properties of reversible holographic recording media, practically significant results have been obtained for the creation of photoanisotropic materials based on azo dyes experiencing cis–trans photoisomerization, which allow the recording of polarization holograms. The needs of dynamic holography have been satisfied by lightsensitive doped inorganic crystals and polymer layers that have been created with nonlinear optical properties.

The Current Status of the Development of Light-Sensitive Media for Holography (a Review)

The realization of spiral phase optical elements on the cleaved end of an optical fiber by focused ion beam milling is presented. A focused Ga+ ion beam with an acceleration voltage of 30 keV is used to etch continuous spiral phase plates and fork gratings directly on the tip of the fiber. The phase characteristics of the output beam generated by the fabricated structures measured via an interference experiment confirmed the presence of phase singularity in the output beam. The devices are expected to be promising candidates for all-fiber beam shaping and optical trapping applications.

Direct patterning of vortex generators on a fiber tip using a focused ion beam

Incorporation of silver ions into a dye-sensitized poly(vinyl alcohol)/acrylamide photopolymer is observed to give better performance compared to other metal-ion-doped photopolymer holographic recording media. Plane-wave transmission gratings were recorded in the photopolymer films using a He-Ne laser, and various holographic parameters were optimized so as to explore maximum potential of the material for various holographic applications. Silver-doped films showed good energy sensitivity, and gratings recorded in optimized film exhibited a diffraction efficiency of more than 75%. The potential of the material for holographic data storage applications is also studied using peristrophic multiplexing.

/pdf/silver-doped-photopolymer-media-for-holographic-recording-3k1ikh9r19.pdf

Silver-doped photopolymer media for holographic recording

High efficiency panchromatic photopolymer recording material for holographic data storage systems

Holographic grating with good storage life in poly(vinyl alcohol) based photopolymer film, pre- pared by gravity settling method, with reduced concen- tration of the dye was found to give good diffraction efficiency without crosslinking. The material was found to show good diffraction efficiency and sensitivity (75% diffraction efficiency at exposure energy of 80 mJ/cm 2 ). The shelf life of the photopolymer solution could be improved by storage at a temperature � 4 � C in refriger- ator. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125: 1238-1243, 2012

https://dyuthi.cusat.ac.in/xmlui/bitstream/handle/purl/4720/Effect%20of%20Concentration%20of%20DYE%20on%20the%20Storage%20Life%20ofPlane%20Wave%20Gratings%20on%20Photopolymer%20Film.pdf?sequence=1

Effect of Concentration of DYE on the Storage Life of Plane Wave Gratings on Photopolymer Film

In the past, UV lithography has been used extensively for the fabrication of diffractive optical elements (DOEs). The advantage of this technique is that the entire structure can be written at one time, however, the minimum feature size is limited to about 1 μm. Many 1-d and 2-d periodic grating structures may not need such fine details but it is essential for diffractive optics with circular structures. This is because the spacing between features typically decreases towards the edge of the element resulting in the smallest feature falling well below 1 μm. 1-d structures such as sub-wavelength gratings will also have smaller feature sizes throughout the structure. In such cases, advanced techniques such as Focused Ion Beam and Electron-beam Lithography are required for the fabrication of finer structures. In this paper, we present results of DOEs fabricated with a focused ion beam system (Nova Nanolab 600 from FEI) directly on a single mode fibre tip. The ability to write DOEs directly on fibre tip is of great importance in fields such as endoscopy and optical trapping. The DOE itself, transforms the laser beam to a phase and intensity profile that matches the requirement. Because it is located directly on the fibre, no extra alignment is required. In addition, the system becomes more compact, which is especially important for applications in the field of endoscopy. The main goal of the present work was to develop the most accurate method for creating the desired pattern (that is, the DOE structure) into an actually working element. Different exposure strategies for writing test structures directly with the ion beam on the fibre tip have been tested and carefully evaluated. The paper will present in detail the initial fabrication and optical test results for blazed and binary structures of 1-d and circularly symmetric Fresnel axicons on optical fibres.

Optimizing the fabrication of diffractive optical elements using a focused ion beam system

The peristrophic multiplexing technique with rotation of the film in a plane normal to the bisector of the incident beams was employed for recording plane-wave transmission gratings at the same location of silver doped acrylamide photopolymer film. Both constant and variable exposure scheduling methods were adopted for storing gratings using a 632.8 nm HeNe laser. The diffraction efficiency (DE) and M number (M/#) obtained from both methods were compared to determine which method enabled the greatest number of gratings to be recorded with uniform diffraction efficiencies. By the variable exposure energy scheduling method, 30 nearly uniform plane wave gratings with M/# equal to 4.7, could be recorded in a 130 µm thick photopolymer layer.

V. Pramitha

Papers

Silver-doped photopolymer media for holographic recording

High efficiency panchromatic photopolymer recording material for holographic data storage systems

Effect of Concentration of DYE on the Storage Life of Plane Wave Gratings on Photopolymer Film

Optimizing the fabrication of diffractive optical elements using a focused ion beam system

Peristrophic multiplexing studies in silver doped photopolymer film