Realization of Flattened Structural Luneburg Lens Based on Quasi-Conformal Transformation

Ultralong Wave Focusing via Generalized Luneburg Lens

In this paper, a novel gradient index (GRIN) structural lens based on the concept of generalized Luneburg lens (GLL) is proposed. This lens allows for the realization of double foci and localization of energy flow between the two focal spots, thereby achieving ultralong focusing. The double-foci GRIN lens consists of two concentric circular regions with varying thickness defined in a thin plate structure. The two concentric circular regions are designed to realize continuous change of refractive indices with different profiles. Numerical simulations and experimental studies are performed to ob…

Bi-functional Structural Luneburg Lens for Broadband Structural Wave Cloaking and Waveguide

In this paper, we explore the concept of structural Luneburg Lens (SLL) as a design framework for performing dynamic structural tailoring to obtain a structural wave cloak and a structural waveguide. The SLL is a graded refractive index lens, which is realized by using a variable thickness structure defined in a thin plate. Due to the thickness variation of the plate, the refractive index decreases radially from the centre to the outer surface of the lens. By taking advantage of the unique capabilities of SLL for flexural wave focusing and collimation, we develop a structural wave cloak and wa…

Multi-Functional Variable Thickness Structure for Broadband and Omnidirectional Focusing and Collimation

Luneburg lens is a symmetric gradient-index lens with a refractive index that increases from the outer surface to the center in a radial manner. It has the ability to focus and collimate waves, which makes it useful for energy harvesting, waveguiding and as a component in transducers. An ideal Luneburg lens should be easy to fabricate, has broadband and omnidirectional characteristics, as well as a focal length that can be easily tuned. However, existing structural Luneburg lenses based on phononic crystals can hardly achieve these requirements. Here, we propose an alternative structural Luneb…

A Luneburg lens for spin waves

We report on the theory of a Luneburg lens for forward-volume magnetostatic spin waves, and verify its operation via micromagnetic modelling. The lens converts a plane wave to a point source (and vice versa) by a designed graded index, realised here by either modulating the thickness or the saturation magnetization in a circular region. We find that the lens enhances the wave amplitude by 5 times at the lens focus, and 47% of the incident energy arrives in the focus region. Furthermore, small deviations in the profile can still result in good focusing, if the lens index is graded smoothly.

Ultrashort waveguide tapers based on Luneburg lens

In integrated photonic circuits, silicon-on-insulator waveguides with different geometries have been employed to realize a variety of components. Therefore, efficient coupling of two different waveguides is crucial. In this paper, focusing property of the Luneburg lens is exploited to design waveguide tapers. The Luneburg lens, truncated in a shape of a parabolic taper with reduced footprint, is utilized to connect a 10 $μ$m-wide waveguide to a 0.5 $μ$m one with the same thickness with an average coupling loss of 0.35 dB in the entire O, E, S, C, L, and U bands of optical communications. The p…

Coupling silica waveguides to photonic crystal waveguides through multilayered Luneburg lens

We present a detailed analysis of a coupler based on the Luneburg lens to couple a silica waveguide to a photonic crystal waveguide. The dependence of coupling efficiency on the lens's truncation, cut position of the photonic crystal structure, coupler tip width, and misalignment are investigated with two-dimensional finite element method. We implement the lens with a concentric ring-based multilayer structure. We also present a method to replace layers with very narrow widths by layers of predetermined minimum widths in the structure of the lens. The coupling loss of the designed 2.7 $μm$-lon…

Analytical, numerical and experimental investigation of Luneburg lens system for directional cloaking

In this study, the design of a directional cloaking based on the Luneburg lens system is proposed and its operating principle is experimentally verified. The cloaking concept is analytically investigated via geometrical optics and numerically realized with the help of the finite-difference time-domain method. In order to benefit from its unique focusing and/or collimating characteristics of light, the Luneburg lens is used. We show that by the proper combination of Luneburg lenses in an array form, incident light bypasses the region between junctions of the lenses, i.e., the "dark zone." Hence…

采用各向异性降低与阻抗失配优化的变换光学方法的平面双极化毫米波龙伯透镜天线

A Flat Dual-Polarized Millimeter-Wave Luneburg Lens Antenna Using Transformation Optics with Reduced Anisotropy and Impedance Mismatch

本研究基于变换光学设计了Ka波段低各向异性、阻抗匹配优化的平面双极化毫米波龙伯透镜天线，搭配超表面相控阵馈源，兼具高增益、宽频带、大扫描角等优势，适用于B5G与雷达感知的机载系统。

Acoustic Metamaterial Beam Splitter

This paper proposes an acoustic beam splitter based on acoustic Luneburg lens. A two-dimensional acoustic Luneburg lens with gradient refractive index is achieved to provide a practical realization for the acoustic beam splitter. The acoustic wave propagation through the beam splitter was explored theoretically, numerically and experimentally. Results show that three output channels can be achieved using a point source on the edge of the beam splitter in a broadband frequency range. Furthermore, the output channel directions can be tuned via changing the design parameter.

Coupling $Si_3N_4$ waveguide to SOI waveguide using transformation optics

Silicon nitride ($Si_3N_4$) planar waveguide platform combined with silicon-on-insulator (SOI) devices offer a whole new generation of system-on-chip applications. Therefore, efficient coupling of an $Si_3N_4$ waveguide to an SOI waveguide is essential. We present a coupler to interface a 1.8 $μm$-wide $Si_3N_4$ waveguide to a 0.5 $μm$-wide SOI waveguide based on the focusing property of the Luneburg lens. In order to match the refractive indices of the waveguides with the edges of the lens, one side of the lens is flattened with quasi-conformal transformation optics. The designed coupler is i…