TE-polarized design for metallic slit lenses: a way to deep-subwavelength focusing over a broad wavelength range

Controlled Dispersion and Transmission-Absorption of Optical Energy through Scaled Metallic Plate Structures

The dispersive feature of metals at higher frequencies has opened up a plethora of applications in plasmonics. Besides, Extraordinary Optical Transmission (EOT) reported by Ebbesen et al. in the late 90's has sparked particular interest among the scientific community through the unprecedented and singular way to steer and enhance optical energies. The purpose of the present paper is to shed light on the effect of the scaling parameter over the whole structure, to cover the range from the near-infrared to the visible, on the transmission and the absorption properties. We further bring specific attention to the dispersive properties, easily extractable from the resonance frequency of the drilled tiny slits within the structure. A perfect matching between the analytical Rigorous Coupled Wave Analysis (RCWA), and the numerical Finite Elements Method (FEM) to describe the underlying mechanisms is obtained.

Retrieving the subwavelength cross-section of dielectric nanowires with asymmetric excitation of Bloch surface waves

Optical microscopy with a diffraction limit cannot distinguish nanowires with sectional dimensions close to or smaller than the optical resolution. Here, we propose a scheme to retrieve the subwavelength cross-section of nanowires based on the asymmetric excitation of Bloch surface waves (BSWs). Leakage radiation microscopy is used to observe the propagation of BSWs at the surface and to collect far-field scattering patterns in the substrate. A model of linear dipoles induced by tilted incident light is built to explain the directional imbalance of BSWs. It shows the potential capability in precisely resolving the subwavelength cross-section of nanowires from far-field scattering without the need for complex algorithms. Through comparing the nanowire widths measured by this method and those measured by scanning electron microscopy (SEM), the transverse resolutions of the widths of two series of nanowires with heights 55 nm and 80 nm are about 4.38 nm and 6.83 nm. All results in this work demonstrate that the new non-resonant far-field optical technology has potential application in metrology measurements with high precision by taking care of the inverse process of light-matter interaction.

Optically levitated conveyor belt based on polarization-dependent metasurface lens arrays

In this Letter, we have proposed an optically levitated conveyor belt based on periodic arrays of a polarization-dependent nanoslit-based metasurface lens (NBML) that is capable of realizing far-field capture, transport, and sorting. The NBML in arrays can be lit up in a relay way by rotating the polarization angle of the excitation beam and thereby provide a better stiffness for transporting particles. When excited at the wavelength of 1064 nm and power density of 0.3 mW/µm², the particles will follow the directional movement of hot spots with an alternative switch of polarization angle and the success ratio of transport can be up to 97.0% with the consideration of Brownian motion. Furthermore, the influence of polarization switching time and incident optical power densities on the efficiency of transport are investigated numerically from a statistical point of view. The sorting of particles with different sizes has also been proved in a given power density. With the analysis of numerical results, our research provides a new approach, to the best of our knowledge, for particle trapping and transport, which is beneficial to on-chip optofluidic applications.

Application of the Metal Reflector for Redistributing the Focusing Intensity of SPPs

The near-field photolithography system has attracted increasing attention in the micro- and nano-manufacturing field, due to the high efficiency, high resolution, and the low cost of the scheme. Nevertheless, the low quality of the nano-patterns significantly limits the industrial application of this technology. Theoretical calculations showed that the reason for the poor nano-patterns is the sharp attenuation of the surface plasmon polaritons (SPPs) in the photoresist layer. The calculation results suggest that the waveguide mode, which is composed of the chromium-equivalent dielectric layer-aluminum, can facilitate the energy flux density distribution in the photoresist layer, resulting in the enhancement of the field intensity of SPPs in the photoresist layer. This reduces the linewidth of nano-patterns, while it enhances the pattern steepness. Eventually, the focusing energy of the photoresist layer can be improved. The finite-difference time-domain method was employed to simulate and verify the theoretical results. It is found that for the rotational near-field photolithography with 355 nm laser illumination, the linewidths of the nano-patterns with and without the aluminum reflector are 17.54 nm and 65.51 nm, respectively. The robustness of the experimental results implies that the application of the aluminum reflector enhances the focusing effect in the photoresist, which can broaden the application of the near-field photolithography.

Polarization Controlled Dual Functional Reflective Planar Metalens in Near Infrared Regime

The metalens has been a hotspot in scientific communications in recent years. The polarization-controlled functional metalens is appealing in metalens investigation. We propose a metalens with dual functions that are controlled by polarization states. In the first design, when applied with x- and y-polarized light, two focal spots with different focal lengths are acquired, respectively. The proposed metalens performs well when illuminated with adjacent wavelengths. In the second design, the reflected light is focused when applied with x-polarized light, and when applied with y-polarized light, the reflected light is split into two oblique paths. We believe that the results will provide a new method in light manipulation.

Investigation on Super-Resolution Focusing Performance of a TE-Polarized Nanoslit-Based Two-Dimensional Lens

Conventional optics suffer from the diffraction limit. Our recent work has predicted a nanoslit-based two-dimensional (2D) lens with transverse-electric (TE) polarized design that is capable of realizing the super-resolution focusing of light beyond the diffraction limit in the quasi-far field. Furthermore, the super-resolution capability can be kept in a high-refractive-index dielectric over a wide wavelength range from ultraviolet to visible light. Here, we systematically investigate the influence of various factors on the super-resolution focusing performance of the lens. Factors such as lens aperture, focal length and nanoslit length are considered. In particular, the influence of nanoslit length on lens focusing was ignored in the previous reports about nanoslit-based 2D lenses, since nanoslit length was assumed to be infinite. The numerical results using the finite-difference time-domain (FDTD) method demonstrate that the super-resolution focusing capability of a nanoslit-based 2D lens increases with the lens aperture and reduces with the increase of the lens focal length. On the other hand, it is notable that the length of the lens focus is not equal to but smaller than that of the nanoslits. Therefore, in order to achieve a desired focus length, a lens should be designed with longer nanoslits.

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

Planar super-oscillation lenses (SOLs) can fulfill super-resolution focusing and nanoscopic imaging in the far field without the contribution of evanescent waves. Nevertheless, the existing deviations between the design and experimental results have been seldomly investigated, leaving the practical applications of SOLs unpredictable and uncontrollable. In this paper, some application-oriented issues are taken into consideration, such as the inevitable fabrication errors and the size effect of the designed SOLs, with the aim of providing an engineering reference to elaborately customize the demanded focusing light field. It turned out that a thicker structural film makes the focal spots enlarged, while the sloped sidewalls just weaken the intensity of the focal hotspot. Furthermore, the focal lengths are diminished with the decrease of device size, while the focal spots are enlarged. This research will promote the wide-spread applications of SOLs for sub-diffraction-limit far-field focusing in the areas of nanoscopy and high-density optical storage.