Chiroptical resonances inspired by bound states in the continuum (BICs) open a new, to the best of our knowledge, avenue to enhance chiral light-matter interaction. Symmetry breaking is the widely employed way, wherein the circularly polarized states (CPSs) arise from BIC splitting. Here, we utilize a far-field interference mechanism to create ultrahigh-Q (typically, 2.36 × 106) chiroptical resonance beyond BIC splitting, in which CPSs coexist with BICs in the momentum space. Accordingly, the spin-selective absorption with ultranarrow linewidth is achieved at the CPS points, which can be regulated by monolayer transition metal dichalcogenides (TMDCs). In addition, the chiral response of our scheme exhibits the incident-direction robustness and flexible tunability. Our findings may facilitate potential applications in light manipulation, spin-valley interaction, and chiral sensing.
Photoelectric imaging systems typically employ a focal plane detector structure, rendering them vulnerable to laser damage. Laser damage can severely impair or even completely deprive the information acquisition capability of photoelectric imaging systems. A laser damage protection method based on a microlens array light field imaging system is proposed to prevent photoelectric imaging systems from laser damage. The technique utilizes the light field modulation effect of the microlens array to homogenize the spot energy, thereby reducing the maximum single-pixel receiving power at the image sensor. The method's effectiveness has been verified through numerical simulations and experimental validation. First, the laser transmission theoretical model of light field imaging is proposed. Then an experimental setup is established, and measurements are conducted to capture the spot profiles and intensity distributions on the imaging plane across various defocus distances. Finally, the impact of the propagation distance on the maximum single-pixel receiving power and suppression ratio of the light field imaging system is experimentally measured. The simulation and experimental results indicate that, with the proposed method, the energy suppression ratio can easily reach two orders of magnitude, significantly reducing the probability of laser damage in photoelectric imaging systems.
Due to the diffraction limit, subwavelength nanoslits (whose width is strictly smaller than λ/2) are hard to resolve by optical microscopy. Here, we overcome the diffraction limit by measuring the full Stokes parameters of the scattered field of the subwavelength nanoslits with varying width under the illumination of a linearly-polarized laser with a 45° polarization orientation angle. Because of the depolarization effect arising from the different phase delay and amplitude transmittance for TM polarization (perpendicular to the long axis of slit) and TE polarization (parallel to the long axis of slit), the state of polarization (SOP) of the scattered light strongly depends on the slit width for subwavelength nanoslits. After correcting for residual background light, the nanoslit width measured by the SOP of scattered light is consistent with the scanning electron microscopy (SEM) measurement. The simulation and experiment in this work demonstrate a new far-field optical technique to determine the width of subwavelength nanoslits by studying the SOP of the scattered light.
The guided-modes of Bloch surface waves, such as the transverse electric modes (TE00 and TE01 modes), can simultaneously exist in a low-refractive-index ridge waveguide with subwavelength thickness that are deposited on an all dielectric one-dimension photonic crystal. By using the finite difference frequency domain method, coupled mode theory and finite-difference time-domain method, the conversion between the guided-modes has been investigated. This conversion can be realized in a broadband wavelength with surface pattern of this low-index ridge. This conversion is useful for developing lab-on-a-chip photonic devices, such as a mode converter that can maintain the output mode purity over 90% with working wavelength ranging from 590 to 680 nm, and a power splitter that can maintain the splitting ratio over 8:2 with wavelength ranging from 530 to 710 nm.
