Chirality, the absence of mirror symmetry, is predominant in nature. The chiral nature of the electromagnetic field behaves differently with chiral matter for left circularly polarized and right circularly polarized light. The chiroptical behavior in the sensing of naturally occurring chiral objects is weak, and improving the chiroptical response enhances the chiral sensing platform. This review covers the fundamental concepts of chiral metasurfaces and various types of single- and multi-layered chiral metasurfaces. In addition, we discuss tunable and deep-learning-based chiral metasurfaces. Tunability is achieved by manipulating the meta-atom’s property in response to external stimuli for applications such as optical modulation, chiral photonics, advanced sensing, and adaptive optics. Deep-learning modeling techniques, such as CNNs and GANs, offer efficient learning of the complex relationships in data, enabling the optimization and accurate prediction of chiral metasurface properties. The challenges in the design and fabrication of chiral metasurface include achieving broadband performance and scalability and addressing material limitations. Chiral metasurface performance is evaluated by optical rotation, circular dichroism enhancement, and tunability, which are quantified through the spectroscopic measurement of circular dichroism and optical rotation. Chiral metasurface progress enables applications, including metaholography, metalenses, and chiral sensing. Chiral sensing improves the detection of pharmaceuticals and biomolecules, increasing the sensitivity and accuracy of analytical diagnostics.

Chiral metasurfaces exploit structural asymmetry to control circular polarized light, presenting new possibilities for the design of optical devices, specifically in the dynamic control of light and enhanced optical sensing fields. This study employed theoretical and computational methods to examine the chiroptical properties of a bilayer crescent chiral metasurface, demonstrating the effect of the angle of rotation on the chiroptical response. We particularly investigated the changes in transmittance, electric field distribution, and circular dichroism (CD) across various rotation angles. The crescent chiral metasurface demonstrated the maximum CD and showed significant control over the CD and electric field distribution across different rotation angles in the near-infrared region. The highest CD value was observed at a 23° rotation angle, where the chiroptical response reached its maximum. In addition, the left circular polarized light showed a stronger intensity of the electric field along the crescent metasurface edge relative to the right circular polarized light, underscoring the significant difference in the intensity and field localization. It was also shown that the configuration with a 2 by 2-unit cell, compared with a single-unit cell, exhibited significantly enhanced CD, thus underlining the importance of the unit cell arrangement in optimizing the chiroptical properties of metasurfaces for advanced photonic applications. These results prove that the 2 by 2 bilayer crescent chiral metasurface can be tailored to a fine degree for specific applications such as improved biosensing, enhanced optical communications, and precise polarization control by optimizing the configuration. The insight presented by this theoretical and computational study will contribute to the broad understanding of chiroptical phenomena as well as pave the way for potential applications in developing advanced optical devices with tuned chiroptical interactions.