Polarisation Applications In Remote Sensing

We report the first experimental generation of high-order Mathieu beams and confirm their propagation invariance over a limited range. In our experiment we use a computer-generated phase hologram. The peculiar behaviour of the vortices in Mathieu beams gives rise to questions about their orbital-angular-momentum content, which we calculate by performing a decomposition in terms of Bessel beams.

Holographic generation and orbital angular momentum of high-order Mathieu beams : Special issue on atoms and angular momentum of light

P Hariharan 1984 Cambridge: Cambridge University Press xii + 319 pp price £35 ISBN 0 521 24348 3 It is the declared aim of the author of this book to provide a 'self-contained treatment of the principles, techniques and applications of optical holography with particular emphasis on recent developments'. He has covered a wide range of topics in this expanding field at a level which is suitable for both the student and research worker.

https://iopscience.iop.org/article/10.1088/0031-9112/36/4/047/pdf

Optical Holography: Principles, Techniques and Applications

A quantitative analysis of optical fields is essential, particularly when the light is structured in some desired manner, or when there is perhaps an undesired structure that must be corrected for. A ubiquitous procedure in the optical community is that of optical mode projections—a modal analysis of light—for the unveiling of amplitude and phase information of a light field. When correctly performed, all the salient features of the field can be deduced with high fidelity, including its orbital angular momentum, vectorial properties, wavefront, and Poynting vector. Here, we present a practical tutorial on how to perform an efficient and effective optical modal decomposition, with emphasis on holographic approaches using spatial light modulators, highlighting the care required at each step of the process.

Modal analysis of structured light with spatial light modulators: a practical tutorial.

Polarization singularities are superpositions of orbital angular momentum (OAM) states in orthogonal circular polarization basis. The intrinsic OAM of light beams arises due to the helical wavefronts of phase singularities. In phase singularities, circulating phase gradients and, in polarization singularities, circulating Stokes phase gradients are present. At the phase and polarization singularities, undefined quantities are the phase and Stokes phase, respectively. Conversion of circulating phase gradient into circulating Stokes phase gradient reveals the connection between phase (scalar) and polarization (vector) singularities. We demonstrate this by theoretically and experimentally generating polarization singularities using phase singularities. Furthermore, the relation between scalar fields and Stokes fields and the singularities in each of them is discussed. This paper is written as a tutorial-cum-review-type article keeping in mind the beginners and researchers in other areas, yet many of the concepts are given novel explanations by adopting different approaches from the available literature on this subject.

Phase Singularities to Polarization Singularities

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

Stokes polarimetry is widely used to extract the polarization structure of optical fields, typically from six measurements, although it can be extracted from only four. To measure the required intensities, most approaches are based on optical polarization components. In this work, we present an all-digital approach that enables a rapid measure of all four intensities without any moving components. Our method employs a polarization grating (PG) to simultaneously project the incoming mode into left- and right-circular polarized states, followed by a polarization-insensitive digital micromirror device (DMD), which digitally introduces a phase retardance for the acquisition of the remaining two polarization states. We demonstrate how this technique can be applied to measuring the SoP, vectorness, and intramodal phase of optical fields, without any moving components, and shows excellent agreement with theory, illustrating fast, real-time polarimetry.

All-digital Stokes polarimetry with a digital micromirror device.

Stokes polarimetry is widely used to extract the polarisation structure of optical fields, typically from six measurements, although it can be extracted from only four. To measure the required intensities, most approaches are based on optical polarisation components. In this work, we present an all-digital approach that enables a rapid measure of all four intensities without any moving components. Our method employs a Polarisation Grating (PG) to simultaneously project the incoming mode into left- and right-circular polarised states, followed by a polarisation-insensitive Digital Micromirror Device (DMD), which digitally introduces a phase retardance for the acquisition of the remaining two polarisation states. We demonstrate how this technique can be applied to measuring the SoP, vectorness and intra-modal phase of optical fields, without any moving components and shows excellent agreement with theory, illustrating fast, real-time polarimetry.

All-Digital Stokes Polarimetry with a Digital Micro-mirror Device

In this work, Stokes polarimetery is used to extract the polarization structure of optical fields from only four measurements as opposed to the usual six measurements. Here, instead of using static polarization optics, we develop an all-digital technique by implementing a Polarization Grating (PG) which projects a mode into left- and right-circular states which are subsequently directed to a Digital Micromirror Device (DMD) which imparts a phase retardance for full polarization acquisition. We apply our approach in real-time to reconstruct the State of Polarization (SoP) and intra-modal phase of optical modes.

Amogh Manthalkar

Papers

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

All-digital Stokes polarimetry with a digital micromirror device.

All-Digital Stokes Polarimetry with a Digital Micro-mirror Device

Polarization reconstruction with a digital micro-mirror device