Creation of Sub-diffraction Longitudinally Polarized Spot by Focusing Radially Polarized Light with Binary Phase Lens

Abstract

The generation of a sub-diffraction longitudinally polarized spot is of great interest in various applications, such as optical tweezers, super-resolution microscopy, high-resolution Raman spectroscopy, and high-density optical data storage. Many theoretical investigations have been conducted into the tight focusing of a longitudinally polarized spot with high-numerical-aperture aplanatic lenses in combination with optical filters. Optical super-oscillation provides a new approach to focusing light beyond the diffraction limit. Here, we propose a planar binary phase lens and experimentally demonstrate the generation of a longitudinally polarized sub-diffraction focal spot by focusing radially polarized light. The lens has a numerical aperture of 0.93 and a long focal length of 200λ for wavelength λ = 632.8 nm, and the generated focal spot has a full-width-at-half-maximum of about 0.456λ, which is smaller than the diffraction limit, 0.54λ. A 5λ-long longitudinally polarized optical needle with sub-diffraction size is also observed near the designed focal point.

Superoscillation: from physics to optical applications

“…To avoid SPP loss, an SOL based on a BA 86,87 and BP 66 annular ring belt array can be designed for the superoscillation focusing of radially polarized waves. A BP SOL fabricated with a Si 3 N 4 concentric ring array that exhibits a subdiffraction longitudinally polarized focal spot with an average FWHM of 0.456λ and a depth of focus (DOF) of 5λ has been demonstrated 88 . Sharper focal spots were expected using higher-order radially polarized waves 89,90 .…”

“…95 Copyright 2016, NPG, d – f ref. 88 Copyright 2016, NPG, under a Creative Commons license (https://creativecommons.org/licenses/by/4.0/)…”

“…Using an SPP lens, a longitudinally polarized optical needle with a transverse size of 0.44λ and a length of 2.65λ was demonstrated at a meso-field distance by numerical simulation 120 . With an optimized SOL based on a BP mask, a 5λ-long longitudinally polarized optical needle was experimentally obtained with a transverse FWHM of 0.456λ (0.424λ/NA) at an ultralong working distance of 200λ 88 .…”

Sub-wavelength annular-slit-assisted superoscillatory lens for longitudinally-polarized super-resolution focusing

“…LP foci also improve SR focusing, thus LP-SR focusing is an essential tool in nano-applications such as particle trapping, particle acceleration, and high-resolution imaging 22,23 . Recently, sub-diffraction longitudinally polarized focusing using binary phase lenses and RP input has been reported 24,25 .…”

An Investigation of Influencing Factors on Practical Sub-Diffraction-Limit Focusing of Planar Super-Oscillation Lenses

“…Note that the high-quality fabrication of nanoscale devices still remains a worldwide challenge, and the fabrication imperfections more or less work on the performance of the micro/nano devices. Furthermore, it has been a common phenomenon that the experimental results do not always come out the same as the theoretical ones; we just summarize the deviation between the theoretical results and the measured ones from the recent publications [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], as shown in Figure 1 . What we can clearly observe in Figure 1 is that most of the deviation is above 6%, while the relatively high deviation may impose a certain restriction on the practical application of the devices.…”