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Sub-wavelength chiral resonators formed from artificial structures exhibit exceedingly large chiroptical responses compared to those observed in natural media. Owing to resonant excitation, chiral near fields can be significantly enhanced for these resonators, holding great promise for developing enantioselective photonic components such as biochemical sensors based on circular dichroism (CD) and spin-dependent nonlinear imaging. In the present work, strong linear and nonlinear chiroptical responses (scattering CD > 0.15 and nonlinear differential CDs > 0.4) at visible and near infrared frequencies are reported for the first time for individual micrometer-scale plasmonic and dielectric helical structures. By leveraging dark-field spectroscopy and nonlinear optical microscopy, the circular-polarization-selective scattering behavior and nonlinear optical responses (e.g., second harmonic generation and two-photon photoluminescence) of 3D printed micro-helices with feature sizes comparable to the wavelength (total length is ∼5λ) are demonstrated. These micro-helices provide potential for readily accessible photonic platforms, facilitating an enantiomeric analysis of chiral materials. One such example is the opportunity to explore ultracompact photonic devices based on single, complex meta-atoms enabled by state-of-the-art 3D fabrication techniques. [ABSTRACT FROM AUTHOR]

The resonance based strong light-matter interaction in metamaterials offers unprecedented opportunities to manipulate polarization of electromagnetic waves. In this work, we fabricate a three-dimensional (3D) metamaterial consisting of 90°-twisted split-tube resonators using a 3D printing technique and demonstrate the corresponding asymmetric transmission for linearly polarized electromagnetic waves in the Ku band with near-unity polarization conversion efficiency. Experimental results reveal a 90° polarization rotation and an incident polarization angle dependent asymmetric transmission at a frequency around 15.2 GHz. The experimental results are in good agreement with simulations. Possessing the merits of both flexibility of response tailoring and ease of fabrication, the proposed 3D-printed metamaterials have great potential for compact polarization-control devices exhibiting unidirectional transmission at both microwave and terahertz frequencies. [ABSTRACT FROM AUTHOR]