Controllable split polarization singularities for ultra-precise displacement sensing

• jiakang zhou, Haixiang Ma, Shuoshuo Zhang, Wu Yuan, Changjun Min, Xiaocong Yuan, and Yuquan Zhang
• received 02/01/2024; accepted 05/10/2024; posted 05/10/2024; Doc. ID 520675
• Abstract: The topic of optical precise displacement measurement has garnered significant attention and generated widespread interest recently. The use of optical singularity offers a potential solution for this purpose, although effectively manipulating the singularity in an ideal manner remains challenging. In this work, we demonstrate a precisely controlled pair of C-point polarization singularities in the focal plane, whose spatial position can be easily modulated by adjusting the relative off-axial index β of an azimuthal polarization beam, while the interval and orientation of the C-points can be flexibly regulated. Notably, the chiral polarization state undergoes a distinct reversal along the link-line connecting the two C-points, thereby providing a promising approach for accurate displacement sensing. To evaluate its sensing characteristics, scattering properties of the C-points are monitored by sweeping a gold helix and nanoparticle along the link-line. The simulation quality index results verify that the equilibrium factor of the scattering field possesses an obvious linear relationship with the displacement, signifying a precise sub-nano-metric sensitivity. This research introduces new methods for the flexible control of polarization singularities in tightly focused fields, thereby enhancing the utilization of circular polarization properties near C-points for displacement sensing. These findings not only enrich the field of nanometer measurement technology but also pave the way for new avenues of research in this domain.