Sculpting Light in Three Dimensions: Advances in Longitudinal Control of Optical Vortex Beams

The precise longitudinal control of structured light, particularly the class of helical beams known as optical vortices, represents a significant and rapidly advancing frontier in modern photonics. By strategically and intricately modulating the core properties of light, including amplitude, phase, and polarization, in the transverse plane, their unique and complex spatial structures can be meticulously engineered to exhibit remarkable and highly useful behaviors as they propagate through space. This review is dedicated to systematically summarizing and contextualizing the pivotal progress achieved over the past five years within the expansive and dynamic field of the longitudinal engineering of vortex light fields. We categorize and analyze the field's most impactful advancements through the four key technological platforms, each with a unique profile of capabilities: metasurfaces, which offer unprecedented, subwavelength-resolution control over the wavefront; spiral phase plates, providing robust and high-fidelity static phase control; structured optical arrays, which masterfully utilize the principles of diffraction and interference; and liquid-crystal spatial light modulators (LC-SLMs), which grant unparalleled capabilities for dynamic, real-time beam shaping. For each of these distinct platforms, we delve deeply into their fundamental operating principles, examine their sophisticated and often computationally intensive design methodologies, and highlight their most salient and impactful applications. This is accompanied by a critical and balanced discussion of their respective advantages, such as efficiency, compactness, or tunability, and their inherent limitations. To conclude, we project our view forward, outlining the most promising future research directions, identifying the key technological and scientific challenges that must be overcome, and speculating on the potential for paradigm-shifting breakthroughs. This work aims to provide a comprehensive, detailed, and didactic reference for both the fundamental physics and the burgeoning applications of longitudinal optical control, thereby inspiring and catalyzing further innovation in fields such as multi-plane super-resolution imaging, coordinated multi-particle optical micromanipulation, ultra-high-capacity optical communications, robust quantum information science, and other emerging technological arenas.