Abstract
Recently, based on space-variant Pancharatnam-Berry (PB) phases, various flat devices allowing abrupt changes of beam parameters have been predicted and demonstrated to implement intriguing manipulation on spin states in three dimensions, including the efficient generation of vector beams, spin Hall effect of light and light-guiding confinement, and so on. Here, we report on the construction of independently controllable multiple focal spots with different inhomogeneous polarization states by utilizing segmented PB phases. Combining the phase shift approach with PB phases, we engineer fan-shaped segmented PB phases and encode them onto two spin components that compose a hybrid polarized vector beam in a modified common-path interferometer system. Experimental results demonstrate that the fan-shaped segmented PB phase enables the flexible manipulation of focal number, array structure and polarization state of each focal spot. Furthermore, we demonstrate that this fan-shaped approach enables to flexibly tailor the polarization state and the spin angular momentum distribution of a tightly focused field, which have potential applications in optical manipulation, tailored optical response and imaging etc.
Highlights
The Pancharatnam-Berry (PB) phase elements involving spin-orbit interaction for controlling and manipulating electromagnetic wave behaviors is currently an active research area[1,2,3,4,5,6,7,8,9]
We report on the creation and control of multiple focal spots from fan-shaped segmented PB phases
From the focusing model and PB phases described in Eq (2), we find that the parameters Δfx and Δfy, as well as lm and φ0m enable the possibility of independently steering each focus, including the transverse position and polarization state
Summary
The Pancharatnam-Berry (PB) phase elements involving spin-orbit interaction for controlling and manipulating electromagnetic wave behaviors is currently an active research area[1,2,3,4,5,6,7,8,9]. Considerable tightly focused fields with specific intensity, polarization and phase structures have been proposed toward promising applications for super-resolution imaging, optical trapping, and light micro-fabrication[15]. The PB phase-based multiple focus generation scheme has been exploited by using segmented metasurface[30], exhibiting unique potential in the simultaneous control of the spin angular momentum (SAM) and OAM of focal field. Experimental results demonstrate that the fan-segmented PB phases enable the flexible manipulation of focal number, array structure and polarization state of each focus. We propose ingenious focal fields by numerically analyzing the fan-shaped segmented vector fields based on vector diffraction theory These results can be extended to steer the polarization state and angular momentum distribution of tightly focused field and create topological structure such as Möbius ring[31]. According to the Fourier transform of lens, for a incident beam denoted as E0(x, y), the corresponding field in spectral domain can be expressed as
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