Background
The optical helico-conical beams (HCBs) can be generated from a product of helical and conical phase function, which leads to a spiral intensity distribution at the focal plane when experiencing a Fourier transform. Recently, the propagation characteristics and fabrication methods of HCBs were reported. However, most of the existing manipulating work has limited flexibility. In addition, the fine structures of optical fields represented by optical vortex arrays have not been further studied in the field of helico-conical beams.
Highlights
In response to the current research status, the team of Professor Bo Liu from Nankai University has proposed a reconfigurable interference-pattern HCB. The HCBs with elaborate fringe structures are generated based on tuning of complex amplitude and optical interference. Furthermore, by introducing initial phase tuning, the optical field pattern on the focal plane could be reconfigured. The relevant research findings were published in the journal Chinese Optics Letters, Volume 22, Issue 9, 2024 (D. Xu, et al., Generation and reconfiguration of interference-pattern helico-conical beams), and were selected as the cover article for that issue. Shaoxiang Duan, a lecturer at the Institute of Modern Optics of Nankai University, is the corresponding author of the paper, and Dongye Xu, a doctoral student, is the first author.
The cover illustrates the design and generation process of the conbined-type interference pattern helico-conical optical field. The helico-conical phase components carrying different orbital angular momenta are superimposed and loaded onto a spatial light modulator (SLM). The modulated beam then propagates forward and undergoes Fourier transformation by a lens, ultimately presenting the desired optical field on the focal plane.
The generation process of HCBs is shown in Fig.1(a). The trajectory of traditional HCBs mostly exhibits sharp and slender characteristics, which limits its ability to carry fine structures. Inspired by Fourier optics, by adding Gaussian-type diaphragms to the incident beams on the initial plane, the spiral trajectory of the optical field on the target plane can be widened, providing a probability for further constructing fine structures. As one of the most basic optical phenomena, interference usually brings rich characteristics to beams, such as bright and dark fringes. By interfering with beam components carrying different orbital angular momentum factors, different HCBs with fine interference patterns could be obtained. By tuning the angular phase components on the initial plane, the optical field pattern on the focal plane will be reconstructed. In addition, the HCBs with different interference modes can also be combined and superimposed to achieve more complex optical field distributions. The experimental setup for optical field generation is shown in Fig. 1(b).
Fig. 1 (a) Schematic diagram for the generation of HCBs, (b) schematic diagram of the experimental setup.
The simulation and experimental results are illustrated in Fig. 2. Figure 2(a) demonstrates the optical field intensity distributions for interference components with the same and opposite topological charge numbers. One can see that the fringes formed by interference with the same topological charge numbers are rougher, resembling "breakpoints," while those formed by interference with opposite topological charge numbers are finer and denser. The interference pattern HCBs reconstructed through initial angular phase modulation are shown in Fig. 2(b). Obviously that the optical fields could be tuned into more diverse shapes, significantly enhancing the flexibility of control. Figure 2(c) demonstrates the combined interference pattern spiral conical beams, further enhancing the flexibility of their optical fields.
Summary
In conclusion, the reconfigurable interference pattern helico-conical beams have been proposed in this work. The first author of the paper, Dongye Xu, said: This study deepens our knowledge about spiral-like optical patterns and paves a new avenue for potential applications, especially in the fields of optical metrology and optical tweezers. In the future, the research team will continue to explore structured light fields and their potential applications in related fields.
