Development of 3D Microstructures for the Formation of a Set of Optical Traps on the Optical Axis

Three-dimensional (3D) microstructures used in the formation of optical traps on the optical axis in the near diffraction zone are calculated and studied. Subwavelength, variable-height annular gratings (a lattice period of 1.05λ) with a standard and graded-index (GRIN) substrate are considered as microstructures. Two scenarios are examined for changing the refractive index n of the GRIN substrate: from a maximum n in the center to a minimum n at the edges (direct GRIN) and, conversely, from a minimum n in the center to a maximum n at the edges (reverse GRIN). The propagation of light through the proposed 3D microstructures is simulated using the finite-difference time-domain (FDTD) method. The possibility of obtaining not only single but also a set of optical traps on the optical axis is demonstrated. It is also shown that compared to the results obtained with a diffractive axicon, the size of the focal spot can be reduced by 21.6% when use is made of the proposed 3D microstructures and the light needle is increased by 2.86 times

Wavefront Aberration Sensor Based on a Multichannel Diffractive Optical Element

We propose a new type of a wavefront aberration sensor, that is, a Zernike matched multichannel diffractive optical filter, which performs consistent filtering of phase distributions corresponding to Zernike polynomials. The sensitivity of the new sensor is theoretically estimated. Based on the theory, we develop recommendations for its application. Test wavefronts formed using a spatial light modulator are experimentally investigated. The applicability of the new sensor for the fine-tuning of a laser collimator is assessed

Spatial-Light-Modulator-Based Multichannel Data Transmission by Vortex Beams of Various Orders

We report an atmospheric multichannel data transmission system with channel separation by vortex beams of various orders, including half-integer values. For the demultiplexing of the communication channels, a multichannel diffractive optical element (DOE) is proposed, being matched with the used vortex beams. The considered approach may be realized without digital processing of the output images, but only based on the numbers of informative diffraction orders, similar to sorting. The system is implemented based on two spatial light modulators (SLMs), one of which forms a multiplexed signal on the transmitting side, and the other implements a multichannel DOE for separating the vortex beams on the receiving side. The stability of the communication channel to atmospheric interference and the crosstalk between the channels are investigated

Simple Method of Light Field Calculation for Shaping of 3D Light Curves

We propose a method for generating three-dimensional light fields with given intensity and phase distributions using purely phase transmission functions. The method is based on a generalization of the well-known approach to the design of diffractive optical elements that focus an incident laser beam into an array of light spots in space. To calculate purely phase transmission functions, we use amplitude encoding, which made it possible to implement the designed elements using a single spatial light modulator. The generation of light beams in the form of rings, spirals, Lissajous figures, and multi-petal “rose” distributions uniformly elongated along the optical axis in the required segment is demonstrated. It is also possible to control the three-dimensional structure of the intensity and phase of the shaped light fields along the propagation axis. The experimentally generated intensity distributions are in good agreement with the numerically obtained results and show high potential for the application of the proposed method in laser manipulation with nano- and microparticles, as well as in laser material processing

Holographic Writing of Forked Diffraction Gratings on the Surface of a Chalcogenide Glass Semiconductor

We consider the formation of forked diffraction gratings on the surface of a multilayer structure based on chalcogenide glass semiconductors As2S3 and a-Se is. The distribution of electric field components upon interference of beams with different polarization states is analyzed theoretically. The possibility of direct holographic writing of diffraction gratings with a “forked” structure is demonstrated. The parameters of vortex laser beams generated by the microrelief formed are examined

Analysis of the Polarization Distribution and Spin Angular Momentum of the Interference Field Obtained by Co-Planar Beams with Linear and Circular Polarization

Interference of two and four light beams with linear or circular polarization is studied analytically and numerically based on the Richards–Wolf formalism. We consider such characteristics of the interference fields as the distribution of intensity, polarization, and spin angular momentum density. The generation of light fields with 1D and 2D periodic structure of both intensity and polarization is demonstrated. We can control the periodic structure both by changing the polarization state of the interfering beams and by changing the numerical aperture of focusing. We consider examples with a basic configuration, as well as those with a certain symmetry in the polarization state of the interfering beams. In some cases, increasing the numerical aperture of the focusing system significantly affects the generated distributions of both intensity and polarization. Experimental results, obtained using a polarization video camera, are in good agreement with the simulation results. The considered light fields can be used in laser processing of thin films of photosensitive (as well as polarization-sensitive) materials in order to create arrays of various ordered nano- and microstructures

Holographic Writing of Forked Diffraction Gratings on the Surface of a Chalcogenide Glass Semiconductor

We consider the formation of forked diffraction gratings on the surface of a multilayer structure based on chalcogenide glass semiconductors As2S3 and a-Se is. The distribution of electric field components upon interference of beams with different polarization states is analyzed theoretically. The possibility of direct holographic writing of diffraction gratings with a “forked” structure is demonstrated. The parameters of vortex laser beams generated by the microrelief formed are examined

Free-Space Transmission and Detection of Variously Polarized Near-IR Beams Using Standard Communication Systems with Embedded Singular Phase Structures

We propose to achieve multichannel information transmission in free space by means of variously polarized beams. The interaction of vortex beams of various orders with the main polarization states is theoretically analyzed. The passage of beams with different polarization states through multi-order diffractive optical elements (DOEs) is simulated numerically. Using the simulation results, tables of code correspondence of diffraction order numbers to the presence of phase vortices in the analyzed beams are constructed, which allow one to determine diffraction orders that carry information about various polarization states. The performed experiment made it possible to study the recognition of the first order cylindrical polarization state formed by a Q-plate converter using a phase DOE. In the experiment, these elements were built into a commercial fiber-optic communication system operating at the near-IR frequencies. After detecting the beam polarization state, beams of the required diffraction orders are efficiently coupled into optical fiber using an additional phase element. The developed optical detection system also provides channel suppression of homogeneously polarized components, which are supposed to be used for transmission of other channels

Polarization-Sensitive Patterning of Azopolymer Thin Films Using Multiple Structured Laser Beams

The polarization sensitivity of azopolymers is well known. Therefore, these materials are actively used in many applications of photonics. Recently, the unique possibilities of processing such materials using a structured laser beam were demonstrated, which revealed the key role of the distribution of polarization and the longitudinal component of light in determining the shape of the nano- and microstructures formed on the surfaces of thin azopolymer films. Here, we present numerical and experimental results demonstrating the high polarization sensitivity of thin azopolymer films to the local polarization state of an illuminating structured laser beam consisting of a set of light spots. To form such arrays of spots with a controlled distribution of polarization, different polarization states of laser beams, both homogeneous and locally inhomogeneous, were used. The results obtained show the possibility of implementing a parallel non-uniform patterning of thin azopolymer films depending on the polarization distribution of the illuminating laser beam. We believe that the demonstrated results will not only make it possible to implement the simultaneous detection of local polarization states of complex-shaped light fields but will also be used for the high-performance fabrication of diffractive optical elements and metasurfaces