Transformation optics (TO) (aka, transformation electromagnetics) provides the mathematical framework for representing the behavior of electromagnetic radiation in a given geometry by transforming it to an alternative, usually more desirable, geometry through an appropriate mapping of the constituent material parameters. TO has enabled the design of previously unachievable electromagnetic structures including those more often associated with science fiction than reality, such as cloaking. CEARL researchers are world experts in TO-enabled optical and EM designs including lens antennas, illusions optics, cloaks, and gradient-index photonic components.  

Beyond lithography-based nanofabrication techniques, recent advances in 3D fabrication technology (such as 3D printing) offer a path toward fabrication of highly-complex 3D structures with micrometer-scale characteristic dimensions. Incorporating advanced inverse design methods and state-of-art fabrication techniques provides a promising route for exploiting 3D metamaterials with sophisticated functionalities via effectively exploring the high-dimensional parametric space offered by true 3D meta-atoms. An example is the 3D metamaterial for broadband asymmetric transmission of linearly polarized mid-infrared light, which is based on a combination of a genetic algorithm (GA) based optimization method and a membrane projection lithography (MPL) fabrication approach.

Chirality is ubiquitous, especially in the organic world. Chiroptical response (optical enantioselectivity) not only enables a unique quantitative approach to examine chiral property of materials but also offers an extra degree of freedom to manipulate light. As circularly polarized light (CPL) intrinsically possesses 3D structure, 3D nanoarchitectures are usually required to achieve a pronounced chiroptical response. Chiral meta-mirrors with broken 2D-chiral symmetry offer a unique possibility to explore strong chiroptical response with just a single 2D patterned layer. A hybrid chiral meta-mirror has been demonstrated as a feasible platform for picosecond all-optical polarization switching of near-infrared light.

Metamaterials that derive their properties from the subwavelength structure of meta-atoms offer unprecedented flexibility for manipulating light-matter interaction, while practical examples of versatile metamaterials remain exceedingly rare. Considerable efforts have been made to achieve photonic metamaterials that exhibit an active response under external stimuli. The primary strategy is to incorporate active materials that possess variable refractive index into the design of metamaterials. Phase-change materials have recently attracted particular attention due to their variation of material properties in a broad frequency band. Active photonics metadevices based on phase transition of vanadium dioxide (VO2) can enable applications ranging from electro-optical information process and storage to energy-efficient display.

Time-varying materials (TVMs) provide an unprecedented opportunity to control the propagation of electromagnetic (EM) waves with greater flexibility. It is observed that if the material’s properties (ε,μ) change abruptly in time, the wave would split into two parts at this moment. This phenomena is usually called ‘temporal boundary (TB)’. The energy distribution between the two waves can be calculated using the continuities of  D and B fields in time. CEARL researchers have developed a rigorous matrix formalism to calculate the wave propagation in the media with multiple TBs, for both anisotropic and bi-isotropic case. Several interesting applications have been demonstrated based on our theory, including real-time polarization conversion, anti-reflection temporal coating, and re-direction of energy propagation. They are usually unachievable by conventional materials.