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, threedimensional 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. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Bessel beams (BBs) appear to be immune to diffraction over finite propagation distances due to the conical nature of light propagation along the optical axis. This offers promising advantages in laser fabrication. However, BBs exhibit a significant intensity variation along the direction of propagation. We present a simple technique to engineer the axial intensity of the BBs over centimeter-long propagation distances without expansion of the incoming laser beam. This method uses two diffractive optical elements (DOEs), one converts the input Gaussian intensity profile to an intermediate intensity distribution, which illuminates the second DOE, a binary axicon. BBs of a desired axial intensity distribution over a few centimeters length can be generated.

Metasurfaces are engineered thin surfaces comprising two dimensional (2D) arrays of sub-wavelength spaced and sub-wavelength sized resonators. Metasurfaces

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Metasurfaces have recently emerged as a promising technology to realize flat and ultra-thin optical elements that can manipulate light at sub-wavelength scale. The typical design flow of a metasurface involves tedious Finite Difference Time Domain (FDTD) simulations followed by creation of a GDSII layout of the metasurface phase profile, the latter being essential for fabrication purposes. Both these steps can be time-consuming and involve the usage of expensive software. To make the design process more straightforward, we have developed an open-source software called MetaOptics built using Python for designing a generic metasurface optical element. MetaOptics uses the FDTD simulated phase response data of a set of meta-atoms and converts the phase profile of any given optical element into a metasurface GDSII layout. MetaOptics comes with in-built FDTD data for most commonly used wavelengths in the visible and infrared spectrum. It also has an option to upload user-specific dimension versus transmission phase data for any choice of wavelength. In this work we describe the software’s framework and provide details to guide users to design a metasurface layout using MetaOptics.

Herein, we report the chemiresistive gas and humidity sensing properties of pristine and nickel-doped tin oxide (Ni-SnO2) gas sensors prepared by a microwave-assisted wet chemical method.

Recently, metasurfaces have gained popularity due to their ability to offer a spatially varying phase response, low intrinsic losses and high transmittance. Here, we demonstrate numerically and experimentally a silicon metasurface at THz frequencies that converts a Gaussian beam into a Vortex beam independent of the polarization of the incident beam. The metasurface consists of an array of sub-wavelength silicon cross resonators made of a high refractive index material on substrates such as sapphire and CaF 2 that are transparent at IR-THz spectral range. With these substrates, it is possible to create phase elements for a specific spectral range including at the molecular finger printing around 10 µm as well as at longer THz wavelengths where secondary molecular structures can be revealed. This device offers high transmittance and a phase coverage of 0 to 2π. The transmittance phase is tuned by varying the dimensions of the meta-atoms. To demonstrate wavefront engineering, we used a discretized spiraling phase profile to convert the incident Gaussian beam to vortex beam. To realize this, we divided the metasurface surface into eight angular sectors and chose eight different dimensions for the crosses providing successive phase shifts spaced by π/4 radians for each of these sectors. Photolithography and reactive ion etching (RIE) were used to fabricate these silicon crosses as the dimensions of these cylinders range up to few hundreds of micrometers. Large 1-cm-diameter optical elements were successfully fabricated and characterised by optical profilometry.

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