Mr. Yu-Chia Chang

Abstract:

Perfect vortex beams (PVBs) represent a compelling advancement in the field of structured light due to their unique property of maintaining a constant annular intensity ring diameter across different topological charges (TCs). This distinct feature contrasts with conventional optical vortex beams, whose ring diameters vary with TC, making PVBs particularly advantageous for multiplexed beam applications. The uniform ring size facilitates efficient spatial coupling of multiple vortex beams with different TCs simultaneously, which is crucial for high-dimensional optical communication systems, parallel optical trapping, and quantum photonic networks. Despite these advantages, practical deployment of PVBs remains constrained by the bulky and often complex optical setups required to generate them. Conventional PVB generation relies on interferometric arrangements or combinations of axicons and spiral phase plates, which are not compatible with compact or integrated platforms. These limitations hinder their integration into on-chip photonic devices or CMOS-compatible systems, particularly when high-order TCs are required. To overcome these challenges, this work presents a novel approach to realizing perfect vortex beams using flat, subwavelength-structured optical components—specifically, metasurfaces [1]. We experimentally demonstrate metasurface-generated perfect vortex beams (MPVBs) with TCs as high as +16 and −32 in the visible spectrum [2]. These MPVBs exhibit annular intensity distributions that remain largely invariant with respect to their TC, confirming the generation of perfect vortex beam profiles. In addition to their compactness and integrability, these metasurfaces show broadband functionality, enabling consistent performance across a range of visible wavelengths. The metasurfaces are carefully engineered to encode both the radial and azimuthal phase profiles necessary to form the PVBs. By manipulating the local phase delay through nano-resonators with spatially varying orientations and geometries, we achieve the desired field distribution without the need for bulk optics. The result is a highly efficient and compact optical device capable of generating complex vortex beam states with topological diversity and spatial uniformity. A particularly innovative aspect of this study is the integration of the optical eraser concept with the MPVBs. The optical eraser technique involves the interference of two vortex beams with opposite or different TCs, producing flower-like interference patterns that can be used to selectively suppress or modulate specific spatial modes. In our experiments, the interference of MPVBs with carefully chosen TCs results in helicity switching, a phenomenon in which the angular momentum characteristics of the beam are inverted or neutralized. This effect leads to the uniformization of the ring-shaped intensity distributions, helping to stabilize and homogenize the output for a range of topological charges. This ability to erase or modify the intensity profiles of high-order vortex beams has far-reaching implications. It provides a powerful method for dynamically controlling structured light fields, which is of particular interest in areas such as quantum optics, where phase coherence and modal purity are essential. The helicity switching observed in the flower-like interference patterns could also offer a new pathway to study spin–orbit interactions and quantum entanglement phenomena in optical fields. Moreover, the compact, CMOS-compatible nature of these metasurface-based devices makes them highly suitable for integration into lab-on-chip systems, high-density optical interconnects, and adaptive optics platforms. Their robustness, tunability, and high-resolution phase control position MPVBs as a scalable and versatile solution for future optical technologies. In conclusion, this work not only demonstrates the generation of high-order, broadband, and spatially uniform perfect vortex beams using metasurfaces but also introduces a novel method for their dynamic modulation through interference-based helicity control. These findings pave the way for miniaturized, multifunctional vortex beam generators with applications ranging from quantum information processing to next-generation optical sensing and beam shaping.