Probing vortex beams based on Talbot effect with two overlapping gratings

In a prior report the optical vortex was characterized using the near-field Talbot effect [1, 2]. This near-field technique can resolve both order and charge of the orbital angular momentum state of the vortex beam. We have proposed before that a small open fraction of the grating in the Talbot configuration can improve the image contrast [3]. In this study, we combine these previously reported techniques, i.e. the Talbot effect for probing an optical vortex and overlapping gratings to manipulate the open fraction. Both theoretical simulation and experimental demonstration are presented here. We believe that our technique can be an alternative method for optical vortex imaging, and could be useful in optical applications.

Recovery and Characterization of Orbital Angular Momentum Modes with Ghost Diffraction Holography

Orbital angular momentum (OAM) of optical vortex beams has been regarded as an independent physical dimension of light with predominant information-carrying potential. However, the presence of scattering environment and turbulent atmosphere scrambles the helical wavefront and destroys the orthogonality of modes in vortex beam propagation. Here, we propose and experimentally demonstrate a new basis for the recovery of the OAM mode using a holographic ghost diffraction scheme. The technique utilizes the speckle field generated from a rotating diffuser for optical vortex mode encoding, and the fourth-order correlation of the speckle field for the efficient recovery of the associated modes. Furthermore, we successfully demonstrate the complex-field recovery of OAM modes by the adoption of a holography scheme in combination with the ghost diffraction system. We evaluate the feasibility of the approach by simulation and followed by experimental demonstration for the recovery of various sequentially encoded OAM modes. Finally, the efficacy of the recovered modes was quantitatively analyzed by an OAM mode analysis utilizing orthogonal projection scheme.

Quantifying the quality of optical vortices by evaluating their intensity distributions

Optical vortices are widely used in optics and photonics, ranging from microscopy and communications to astronomy. However, little work has been done to quantify the quality of scalar optical vortices. Since the quality of an optical vortex affects measurements and conclusions derived from their use, development of tools to evaluate the vortex quality is crucial. Moreover, the quality of a vortex strongly depends on the application. Therefore, this work aims to establish metrics for the evaluation of optical vortex quality. We propose to evaluate vortex quality using the following intensity parameters: eccentricity of the intensity distribution, cross-sectional peak-to-valley measurements, cross-sectional peak difference, and the ratio of the ring width to the vortex core diameter (doughnut-ratio). These parameters can be used as a guide for the quality of optical vortices depending on their implementation for specific optical technologies.