Active chiral plasmonics have attracted a considerable amount of research interest for their power to switch the handedness of chiral metamaterials and the potential applications in highly integrated polarization sensitive devices, stereo display fields, and so on. In this work, we propose a kind of active chiral metamaterial absorber (ACMA) composed by planar anisotropic chiral metamaterials (PACMs) and a metal layer. Our in-depth theoretical analysis indicates that the circular conversion dichroism (CCD) from PACMs plays a crucial role to achieve the active chiroptical effect. The CCD effect can enable a differentiated microcavity-interference effect between the left and right circular incident lights and results in a chiroptical effect related to the equivalent optical length between the PACMs and the metal layer. In simulations, a high-performance ACMA, which are composed by the ‘Z’-shaped PACMs, is designed, and the maximum reflection $C{D}_R$ from ACMA can reach 0.882. Meanwhile, the minimum reflection $C{D}_R$ can reach to 0, resulting a very large adjustable range of from 0 to 0.882. The maximum modulation sensitivity, which is defined as $M_n=\partial C{D}_R/\partial n$ and $M_d=\partial C{D}_R/\partial d$, can reach to about 1368.252 for $d=100$um and 0.06157 nm⁻¹ for $n=4.5,$respectively. In addition to the active chiroptical effect, the designed ACMA also shows excellent performance as a sensor, such as when it is being used as a highly-sensitive temperature sensor. In that case, the minimum detected precision can reach approximately 3.067 * 10⁻⁸ °C, if VO₂ is used to fill the FP cavity.

Optical diode-like effect has sparked growing interest in recent years due to its potential applications in integrated photonic systems. In this paper, we propose and numerically demonstrate a new type of easy-processing metal/dielectric cylinder composite grating on semi-sphere substrate, which can achieve high-contrast asymmetric transmission of unpolarized light for the sum of all diffraction modes in the entire visible region, and effectively guide the diffraction light transmitting out the substrate. The asymmetric light transmission (ALT) ratio is larger than 2 dB in the waveband from 380 nm to 780 nm and the maximum ALT ratio can reach to 13 dB at specified wavelengths. The thorough theoretical research reveals that the proposed metal/dielectric pillar composite grating structure, together with the substrate, can effectively excite localized surface plasmonic resonance (LSPR) effect and waveguide mode (WGM), and enlarge the diffraction difference between forward and backward transmission spaces, including both number of diffraction orders and diffraction efficiency, thus resulting in high-contrast broadband ALT phenomenon. In particular, lowering the symmetry of the grating can achieve polarization-dependent ALT. Such a type of easy-processing ALT device with high performance for both polarized and unpolarized light can be regarded as suitable candidates in practical applications.

Large-area and high-performance chiral metamaterials are highly desired for practical applications, such as controlling the polarization state of an electromagnetic wave and enhancing the sensor sensitivity of chiral molecules. In this work, cavity-enhanced chiral metamaterials (CECMs) with a large area (1 cm²) have been fabricated by the convenient angle-dependent material deposition technique. The optimal chiral signal (g factor) resonance in the visible waveband can reach about 0.94 with a figure of merit (FOM) of about 5.2, which is about ten times larger than that of chiral metamaterials (CMs) without a cavity (i.e., a g factor of 0.094 with the FOM of about 1.12). Both the theoretical and experimental results demonstrate that the circular conversion components from the anisotropic geometry of CMs play a crucial role in the final chiroptical effect of CECM, which together with the cavity effect enhance both the chiroptical resonance intensity and FOM. Choosing the appropriate deposition parameters can effectively modify the geometric anisotropy of CM and thus the chiroptical effect of CECM. The geometric nanoscale morphology, electromagnetic properties and sensor performance were investigated carefully in this work. The fabricated CECM working in the visible waveband together with the cavity-enhanced scheme provides a competitive candidate for enhancing the performance and the practical applications of CMs.