Focus modulation of cylindrical vector beams by using 1D photonic crystal lens with negative refraction effect

Super-oscillatory spots with different inhomogeneous linear polarized states

We present the formation of super-oscillatory (SO) spots by tightly focusing the inhomogeneous linear polarized beam of different polarization states. At the entrance pupil of the focusing lens, a suitable phase manipulation in the incident beam results in a small super-oscillatory spot. Our numerical study based on the vectorial diffraction theory shows that SO spots of controllable size and various polarization combinations are possible. We also discuss the effect of the different polarization patterns of the incident beam on the size and energy distribution of the generated SO spots, which are potentially valuable for the orientation determination of single molecules and polarization-resolved imaging. This study reveals more influence of polarization states on the different components of the focused beam under the utilization of the proposed method rather than the usual tight focusing conditions.

Creation of pure longitudinal super-oscillatory spot

We present a method that creates a super-oscillatory focal spot of a tightly focused radially polarized beam using the concept of a phase mask. Using vector diffraction theory, we report a super-oscillatory focal spot that is much smaller than the diffraction limit and the super-oscillation criterion. The proposed mask works as a special polarization filter that enhances the longitudinal component and filters out the transverse component of radial polarization at focus, permitting the creation of a pure longitudinal super-oscillatory focal spot.

Focusing characteristics of cylindrical vector beams through a multi-focal all-dielectric grating lens

A novel, to the best of our knowledge, type of multi-focal all-dielectric grating lens is proposed in this work, and focusing characteristics of cylindrical vector beams through the lens are investigated in detail. Based on the negative refraction mechanism of negative-first-order diffraction and Fermat's principle, a multi-focal lens is designed. By analyzing the diffraction effect of the grating, the essential factor that affects the focus quality is found. Through a two-step optimization process, secondary foci and the focal displacement of primary foci caused by high-order diffractions are overcome, and the quality of the focal field is significantly improved. This work provides a reference for micro-lens design for focus modulation, and the research results also have potential applications in the fields of light-field manipulation and optical tweezers.

TM01 mode in a cylindrical hybrid plasmonic waveguide with large propagation length

This study reports on a cylindrical hybrid plasmonic waveguide (CHPW) consisting of a high-index dielectric core, a sandwiched low-index dielectric layer, and a metal cladding. The CHPW supports the TM₀₁ mode with a radially polarized transverse component of the electric field. Optical fields can be significantly enhanced in the sandwiched low-index dielectric region with nanoscale thickness down to 5 nm, and tight mode confinement with the same order of the normalized mode area compared with that of the plasmonic waveguide is achieved. Moreover, the mode propagation loss is well compensated by adjusting dimensions of the waveguide to obtain a longer propagation distance. The calculated figure of merit reaches a value several times greater than that in the similarly reported structure. The results indicate that this novel type of hybrid structure can support the limited propagation of a radially polarized mode with good confinement and low loss, consummate the whole system of manipulating the cylindrical vector beams, and show great potential of applications for various integrated nano-photonic devices.