Near-Field Vortex Beams Diffraction on Surface Micro-Defects and Diffractive Axicons for Polarization State Recognition

Abstract

The diffraction of vortex Gaussian laser beams by elementary objects of micro-optics (surface micro-defects) to recognize the type of polarization (linear, circular, radial, azimuthal) of the input radiation was investigated in this paper. We considered two main types of defects (protrusion and depression in the form of a circle and a square) with different sizes (the radius and height were varied). Light propagation (3D) through the proposed micro-defects was modeled using the finite difference time domain (FDTD) method. The possibility of recognizing (including size change) of surface micro-defects (protrusions and depressions) and all the above types of polarization are shown. Thus, micro-defects act as sensors for the polarization state of the illuminating beam. The focusing properties of micro-defects are compared with diffractive axicons with different numerical apertures (NAs). The possibility of sub-wavelength focusing with element height change is demonstrated. In particular, it is numerically shown that a silicon cylinder (protrusion) forms a light spot with a minimum size of the all intensity FWHM of 0.28λ.

The comparison of the optical vortices focusing by silicon diffraction axicons and ring gratings with variable relief heights using high-performance computer systems

“…The results are shown in figure 3. As previously shown 32,42 , the following is true for optical vortices of the first order: a zero value of the central focal spot indicates "+" circular polarization, and a nonzero one indicates "-" circular polarization. Similarly, for radial polarization there will be a zero value at the central focal point, and a non-zero value means azimuthal polarization 42 .…”

“…Previous studies have shown that under certain conditions, a conventional round protrusion can be used to recognize polarization and focusing, and the focusing will be better than for a diffractive axicon with a similar grating size 32,43 . But the relief height also plays a key role 44,45 .…”

Peculiarities of focusing circularly and radially polarized super-Gaussian beams using ring gratings with varying relief height

“…При таком типе круговой поляризации, как было показано ранее [13,39], наблюдается перераспределение энергии между компонентами электромагнитного поля, выраженное в усилении продольной компоненты электрического поля на оптической оси.…”

“…Для формирования протяженного светового отрезка вдоль оптической оси достаточно часто используются аксиконы [34 -38], в том числе их дифракционные аналоги (кольцевые решетки) [39,40]. Изменение высоты рельефа оптического элемента существенным образом влияет на картину дифракции лазерного излучения [36, 39 -42].…”

Narrow-Bandpass One-Step Leapfrog Hybrid Implicit-Explicit Algorithm with Convolutional Boundary Condition for Its Applications in Sensors

“…With the development of the electronic industry, sensors have become more important than ever before. Large numbers of sensors work in narrow bandpass circumstances or individual frequency [1,2]. Although the finite-difference time-domain (FDTD) algorithm has been extensively employed in many applications, sensor simulation by the FDTD algorithm is severely limited by the inefficient bandpass calculation.…”