Generation of optical orbital angular momentum light by an azimuthally-graded refractive index plate

Abstract

We propose and numerically demonstrate a method to generate orbital angular momentum (OAM) light by using an azimuthally graded index (AGI) plate of uniform subwavelength thickness. We illustrate, theoretically, through numerical simulations, how a plane polarized fundamental gaussian beam incident onto such an AGI plate acquires a nonzero orbital angular momentum, and exhibits an annular far-field intensity profile with a phase singularity line along its axis. We further confirm the OAM property of the output beam by calculations of the overlap integral between its far-field and the paraxial Laguerre Gaussian modes of nonzero OAM. We also highlight the advantages of the proposed AGI plate over existing methods to generate OAM light.