Radially polarized Bessel lens based on all-dielectric metasurface

Cylindrical vector beams are of significant value in high-resolution imaging, particle manipulation, material processing, etc. However, the study on the generation and manipulation of cylindrical vector beams, especially in a broadband range, is still challenging because simultaneously realization of the beam generation, wavefront manipulation and dispersion engineering with a single device, is limited by implemental mechanism and structure design.
    In the past few decades, cylindrical vector waves, especially radial polarized light (RPL), have received increasing attention due to their unique properties in focusing and imaging. RPL is the axis of polarization. The symmetrically distributed beam has a strong longitudinal component in the focal plane, which allows the RPL to focus a tighter focal spot. 
The metasurface is a new type of electromagnetic material, which not only can flexibly regulate the wavefront of electromagnetic waves, but also can achieve both miniaturization and integration. Nowadays, metasurface has high efficiency and small size when implementing optical devices such as polarization filter, focusing lens, optical holography, and vortex beam generator. 

    Professor Yu Honglin’s team, in Chongqing University, focuses on the generation and manipulation of vector beam based on metasurface in recent years. The team proposed the asymmetric photonic spin-orbit interactions (SOIs) in 2017 (Opto-Electronic Engineering, 2017, 44(3): 319–325), the key is multi-phase fusion, that is, the single-layer metasurface is proposed to independently control the spin-dependent geometric phase and the spin-independent waveguide propagation phase. The proposed asymmetric photonic SOIs will provide new ideas for vector beam generation, wavefront manipulation and dispersion control.

    Based on asymmetric SOIs, the research team proposed a single-layer all-dielectric metasurface for simultaneous circular asymmetric transmission and wavefront manipulation. This work has been published in Advanced Functional Materials as the cover paper (Advanced Functional Materials, 2017, 27(47): 1704295). 
    Based on multi-phase fusion, the team proposed the design method of multi-degree-of-freedom excitation and modulation of electromagnetic resonance. Through merging geometric phase and plasmonic retardation phase, broadband dispersion engineering (8~12 μm) can be realized with an efficiency of up to 60% (Applied Physics Express, 2018, 11(8): 082004).
    In view of the fact that the current metasurface-based photonic devices are fixed in function, the team proposed a method of combining phase change materials and metasurfaces to realize dynamic and tunable photonic devices, which was published in Advanced Science as the cover paper (Advanced Science, 2018, 5(10): 1800835).
    In view of the limited bandwidth of the terahertz absorption device, the team proposed the ultra-wideband terahertz absorption by using a double-layer metasurface by the dispersion engineering. This work was published in Nanophotonics (Accepted). 

    The recent project aims at the metasurfaces with asymmetric photonic spin-orbit interactions to realize the independent modulations for two spins of photons, and then generate high-quality vector beams with arbitrary wavefronts by photon spin recombination. With the methods proposed in this work, the researchers combine Bessel non-diffraction beam, finally realize a metalens breaking the diffraction limit. The work published in Opto-Electronic Engineering, Issue 11, 2018, has a great significance to promote the development of multiple disciplines, such as micro-nano photonics, materials science and condensed matter physics.

(a), (b) Intensity distribution of focal plane and xoz plane of Bessel focused x-polarized light; 
(c) B lens focal plane intensity distribution of Bessel focused radially polarized light; 
(d) The horizontal axis at y=0 in Figs. (a) and (c)

About the corresponding author
Professor Yu Honglin is the second-level professor and doctoral supervisor in Chongqing University. She is also the executive deputy director of the National Defense Key Discipline Laboratory of “New Micro-Nano Devices and System Technology”, and enjoys special government allowances from the State Council. With the core of the New Micro-Nano Devices and System Technology National Defense Key Discipline Laboratory and the Key Laboratory of Photoelectric Technology and Systems Ministry of Education, she has long been engaged in research on micro-nano optics, precision instruments and machinery, optoelectronic technology and systems. She has presided over the "Study on the Principle of Realizing the High Partition Rate of Small Photoelectric Encoders", "Study on the Principles of Optical Space Modulation and Optical Spatial Filter Torque Measurement", "Study on the Dynamic Characteristics of Hydraulic Turbine Mechanical Systems", "Study on the principle of AC-induced electromagnetic induction ring array based on spherical symmetry" and "Study on the principle of infrared polarization controller based on metamaterial",5 national natural science fund projects, and the national “863” project, and more than 20 national and provincial research projects. Among them, the “Study on the Principle of Realizing the High Partition Rate of Small Photoelectric Encoders” was rated as an excellent achievement by the National Fund. Professor Yu Honglin has won one second prize of National Science and Technology Progress Award, two second prizes for scientific and technological progress of the Ministry of Education, and one first prize for scientific and technological progress in Chongqing. Besides, she has published more than 60 related academic papers.

Chen Junyan, Zhang Fei, Zhang Ming, et al. Radially polarized Bessel lens based on all-dielectric metasurface[J]. Opto-Electronic Engineering, 2018, 45(11): 180124.