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As a three-dimensional topological phase of matter, Weyl semimetals possess extremely large gyrotropic optical response in the mid-infrared region, leading to the strong chiral anomaly. This study proposes a circular polarizer design with a double-WSM-layer structure. It is theoretically shown that the proposed polarizer possesses a high circular polarization efficiency and high average transmittance in the wavelength region from 9 µm to 15 µm at incidence angles up to 50°. The modified 4 × 4 matrix method is used to calculate the circularly polarized transmittance of Weyl semimetals in thin-film or multilayer structures. The temperature dependence on the transmittance is also examined to demonstrate the flexibility of the proposed polarizer in a varying temperature environment. This study reveals the technological prospect that Weyl semimetals are promising candidates for high-performance circular polarizers in infrared spectroscopy and polarimetry. 

Phase-change materials (PCMs) offer a compelling platform for active metaoptics, owing to their large index contrast and fast yet stable phase transition attributes. Despite recent advances in phase-change metasurfaces, a fully integrable solution that combines pronounced tuning measures, i.e., efficiency, dynamic range, speed, and power consumption, is still elusive. Here, we demonstrate an in situ electrically driven tunable metasurface by harnessing the full potential of a PCM alloy, Ge₂Sb₂Te₅(GST), to realize non-volatile, reversible, multilevel, fast, and remarkable optical modulation in the near-infrared spectral range. Such a reprogrammable platform presents a record eleven-fold change in the reflectance (absolute reflectance contrast reaching 80%), unprecedented quasi-continuous spectral tuning over 250 nm, and switching speed that can potentially reach a few kHz. Our scalable heterostructure architecture capitalizes on the integration of a robust resistive microheater decoupled from an optically smart metasurface enabling good modal overlap with an ultrathin layer of the largest index contrast PCM to sustain high scattering efficiency even after several reversible phase transitions. We further experimentally demonstrate an electrically reconfigurable phase-change gradient metasurface capable of steering an incident light beam into different diffraction orders. This work represents a critical advance towards the development of fully integrable dynamic metasurfaces and their potential for beamforming applications.

 

Ultrafast optical switching in plasmonic platforms relies on the third‐order Kerr nonlinearity, which is tightly linked to the dynamics of hot carriers in nanostructured metals. Although extensively utilized, a fundamental understanding on the dependence of the switching dynamics upon optical resonances has often been overlooked. Here, all‐optical control of resonance bands in a hybrid photonic‐plasmonic crystal is employed as an empowering technique for probing the resonance‐dependent switching dynamics upon hot carrier formation. Differential optical transmission measurements reveal an enhanced switching performance near the anti‐crossing point arising from strong coupling between local and nonlocal resonance modes. Furthermore, entangled with hot‐carrier dynamics, the nonlinear correspondence between optical resonances and refractive index change results in tailorable dispersion of recovery speeds which can notably deviate from the characteristic lifetime of hot carriers. The comprehensive understanding provides new protocols for optically characterizing hot‐carrier dynamics and optimizing resonance‐based all‐optical switches for operations across the visible spectrum.

 

A convenient method based on deep neural networks and an evolutionary algorithm is proposed for the inverse design of FinFET SRAM cells. Inverse design helps designers who have less device physics knowledge obtain cell configurations that provide the desired performance metrics under selected wearout conditions, such as a set specific stress time and use scenario that creates a specific activity level (duty cycle and transition rate). The cell configurations being considered consists of various process parameters, such as gate length and fin height, in the presence of variations due to process and wearout. The front-end mechanisms related to wearout include negative bias temperature instability (NBTI), hot carrier injection (HCI), and random telegraph noise (RTN). The process of inverse design is achieved quickly and at good accuracy. 

Enantiomers are chiral isomers in which the isomer's structure itself and its mirror image cannot be superimposed on each other. Enantiomer selective sensing is critical as enantiomers exhibit distinct functionalities to their mirror image. Discriminating between enantiomers by optical methods has been widely used as these techniques provide nondestructive characterization, however, they are constrained by the intrinsically small chirality of the molecules. Here, a method to effectively discriminate chiral analytes in the nonlinear regime is demonstrated, which is facilitated by an upconverting chiral plasmonic metamaterial. The different handedness of the chiral molecules interacts with the chiral metamaterial platform, which leads to a change in the circular dichroism of the chiral metamaterial in the near‐infrared region. The contrast of the circular dichroism is identified by the upconverted signal in the visible region.