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• Chinese Optics Letters
• Vol. 20, Issue 1, 012601 (2022)
Yihua Bai, Haoran Lv, Xin Fu, and Yuanjie Yang*
Author Affiliations
• School of Physics, University of Electronic Science and Technology of China, Chengdu 611731, China
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Yihua Bai, Haoran Lv, Xin Fu, Yuanjie Yang. Vortex beam: generation and detection of orbital angular momentum [Invited][J]. Chinese Optics Letters, 2022, 20(1): 012601 Copy Citation Text show less

Abstract

Recent advances in the research of vortex beams, structured beams carrying orbital angular momentum (OAM), have revolutionized the applications of light beams, such as advanced optical manipulations, high-capacity optical communications, and super-resolution imaging. Undoubtedly, the methods for generation of a vortex beam and detection of its OAM are of vital importance for the applications of vortex beams. In this review, we first introduce the fundamental concepts of vortex beams briefly and then summarize approaches to generating and detecting the vortex beams separately, from bulky diffractive elements to planar elements. Finally, we make a concise conclusion and outline that is yet to be explored.

1. Introduction

Light beams, as electromagnetic waves, can carry both energy and momentum. Meanwhile, we know that momentum can be classified into linear and angular momentum, and there are two particular kinds of angular momenta: spin angular momentum (SAM) and orbital angular momentum (OAM). More than a century ago, Poynting proposed that the SAM is related to the photon spin, namely, the circularly polarized light carries an SAM of $±ℏ$ per photon[1], whereas linearly polarized light carries no SAM, as illustrated in Fig. 1(a). In 1932, Darwin realized the photon can carry both SAM and OAM, and he even obtained the expression for each one[2]. But, it was not until 1992 that Allen et al. revealed the OAM of a light beam clearly[3]. It was shown that vortex beams with an azimuthal phase factor $exp(ilθ)$ can carry OAM of $lℏ$ per photon, where $l$ can be any integer number, named topological charge. The discovery of OAM of light has changed the way in which we understand and employ light. Different from traditional Gaussian beams, vortex beams exhibit a phase singularity in the center, which leads a doughnut-shaped intensity profile, as shown in Fig. 1(b). Figure 1(b) shows vortex beams with helical wavefronts, in which the number of intertwined helices and the handedness are dependent on the topological charge $l$.

Copy Citation Text
Yihua Bai, Haoran Lv, Xin Fu, Yuanjie Yang. Vortex beam: generation and detection of orbital angular momentum [Invited][J]. Chinese Optics Letters, 2022, 20(1): 012601