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• We have demonstrated a mid-infrared (MIR) device exhibiting exceptional circular dichroism (CD), utilizing multilayer films composed of α-phase molybdenum trioxide (α-MoO 3) and BaF 2. • It is found that the proposed structure achieves a remarkable absorption efficiency of 0.99 for left circularly polarized light at 12 μm, accompanied by a maximum CD in reflection of 0.93 and a resonant Q-factor of 111. • The strong chirality originates from the symmetry breaking of the structure. • The proposed chiral structure demonstrated exceptional responses across a broad range of wavelengths, highlighting its remarkable adaptability and versatility to accommodate various optical frequencies. As an emerging natural biaxial hyperbolic material, α-phase molybdenum trioxide (α-MoO 3) exhibits the excellent anisotropy and unique electromagnetic manipulation properties, which further stimulates the potential for polarization manipulation. Here, a Fabry-Perot cavity chiral structure based on multilayer films of α-MoO 3 and BaF 2 is presented, which exhibits excellent circular dichroism (CD) by displaying different reflectance properties for left-hand circular polarization and right-hand circular polarization light in the mid-infrared range. The numerical simulation results demonstrate that the chiral structure exhibits a remarkable absorption efficiency of 0.99 for left circularly polarized light at a wavelength of 12 μm, accompanied by a maximum CD in reflection of 0.93 and a resonant quality factor (Q-factor) of 111. This exceptional performance arises from the relative twist between α-MoO 3 and the underlying BaF 2 thin film, which simultaneously breaks the rotational and mirror symmetries of the chiral structure. To gain a deeper understanding, we further investigate the influence of film thickness and relative rotation angle on the optical properties of the chiral structure. By adjusting the geometric parameters of the chiral structure, it becomes possible to tune the chiral resonance wavelength and the corresponding CD value, providing a novel approach for the development of tunable chiral optical devices. This study offers new insights into the fabrication of low-cost chiral structures with high-Q resonances and their potential applications in the mid-infrared range, laying the foundation for the development of more powerful and controllable chiral optical devices. [ABSTRACT FROM AUTHOR]

• A novel optical BIC classified as the mirror-coupled toroidal dipole mode is demonstrate in a dielectric metasurface on a lossless reflecting mirror. • Such the mode is characteristic by both the symmetry-protect BIC and accidental BIC, and thus its radiative lifetime can be controlled by two typical geometric parameters. • The unique loss engineering capability of the mode allows us to design metasurfaces critically-coupled to graphene, producing resonances with unity absorbance. • The platform holds for multiple tuning knobs to accurately control the coupling condition. Metasurfaces have received a significant amount of attention in recent years as they offer novel ways for wave front control, subwavelength light focusing, and flat optics. Here, we employ sharp resonances in metasurfaces originated from the physics of bound states in the continuum (BICs) for both engineering and enhancing the absorption of light. Specifically, using temporal coupled-mode theory and numerical simulations, we demonstrate that an all-dielectric metasurface, of which the meta -atom consists of narrow-gap Si dimers with a monolayer graphene, can perfectly absorb the incident near-infrared light through critical coupling to the mirror-coupled toroidal dipole BIC. Due to unique loss engineering capabilities of the mode, multiple tuning knobs, including the narrow gap, meta -atom–mirror distance, and geometrical scaling factor, can be utilized for control over the coupling condition and the electric-field enhancement at the critical coupling condition. These results suggest that our platform could promise in on-chip optoelectronic applications. [ABSTRACT FROM AUTHOR]

• The absorber exhibits high absorption, the remarkable anisotropy and flexible tunability characteristics. • The absorption reach nearly 100 % thought bound states in the continuum even at electronic doping of n s = 0.1 × 1013 cm−2. • The quality factor can achieve a value of 611.2. Black phosphorus (BP) is a promising two-dimensional (2D) material with direct band gap and distinctive lattice structure. Control over its bandgap can be achieved through physical or chemical methods, enabling selective light absorption within specific wavelength ranges. This study designed a narrow-bandwidth perfect absorber with highly quality (Q) factor, anisotropy and flexible tunability based on BP. The proposed structure comprises a monolayer BP sheet on the square array of Si hollow nanodisks placed on a SiO 2 spacer with a gold substrate backing. We numerically demonstrate the narrowband perfect absorption, which is achieved through bound states in the continuum resonance supported by metasurfaces critically coupled to BP monolayer. Notably, simulation results show that the absorption magnitude can reach nearly 100 % even at low electronic doping of n s = 0.1 × 1013 cm−2, and the Q factor can achieve a value of 611.2. The absorption peak and the resonance wavelength can be flexibly tuned by adjusting the electron doping of BP, the geometrical parameters of the structure and the angles of incident. Additionally, due to the inherent in-plane anisotropic feature of BP, the proposed structure exhibits high polarization-dependence. These results make our design a promising candidate for polarization-selective and tunable high performance mid-infrared devices, including polarizers, modulators, and photodetectors. [ABSTRACT FROM AUTHOR]

• The effect of protective layer on the performance of smart radiation devices is comprehensively evaluated. • The emission regulation can be enhanced to 0.65, while the solar absorption can be decreased to 0.18. • The performance of the proposed SRD meets the requirement of the spacecraft thermal control devices. • This work provides a theoretical basis for the design of more reasonable spacecraft thermal control devices. With the arrival of the space economy, the miniaturization of spacecraft and their multi-functional trends have put a greater demand on space thermal control systems. Smart radiation devices (SRDs) are gaining attention as a low-cost, light-weight material for the thermal control of spacecraft. Previous works have focused on how to enhance IR emittance tunability of SRDs. In fact, the SRDs performance and lifetime may be affected by the external space environment. Thus, researchers proposed to cover the SRDs with a protective layer to resist oxidation and other problems. However, the influence of protective layer on the performance of SRDs, including IR emittance tunability Δ ε and solar absorption α s , has not been studied systematically yet. In this paper, the impact of protective layer on the performance of SRDs is comprehensively evaluated in theory. Firstly, a three-layer SRD is composed of a vanadium dioxide (VO 2) film, BaF 2 , and a silver (Ag) substrate, which is optimized using the transfer matrix method. The IR emittance tunability and solar absorption can reach 0.64 and 0.29, respectively. Secondly, the smart thermal control device with three protection materials (BaF 2 , Al 2 O 3 and Si) is investigated. The results show that the performance of SRD can be enhanced or deteriorated, depending on the types of protection materials and the thickness. When the protection material is Si, the IR emittance tunability can be enhanced to 0.65, while the solar absorption can be decreased to 0.18. The performance of the proposed SRD meets the requirement of the spacecraft thermal control devices. We believe that this work provides a theoretical basis for the design of more reasonable spacecraft thermal control devices. [ABSTRACT FROM AUTHOR]

An optical fiber sensor based on the single-mode/no-core/single-mode (SNS) core-offset technology along with a Faraday rotator mirror structure has been proposed and experimentally demonstrated. A transverse optical field distribution of self-imaging has been simulated and experimental parameters have been selected under theoretical guidance. Results of the experiments demonstrate that the temperature sensitivity of the sensor is 0.0551 nm/°C for temperatures between 25 and 80 °C, and the correlation coefficient is 0.99582. The concentration sensitivity of the device for sucrose and glucose solutions was found to be as high as 12.5416 and 6.02248 nm/(g/ml), respectively. Curves demonstrating a linear fit between wavelength shift and solution concentration for three different heavy metal solutions have also been derived on the basis of experimental results. The proposed fiber-optic sensor design provides valuable guidance for the measurement of concentration and temperature. [ABSTRACT FROM AUTHOR]

• The sensor is constituted by multimode interferometer and Mach-Zehnder interferometer. • Simultaneous measurement of refractive index (RI) and temperature can be achieved. • The sensitivity of RI reach to 1191.27 nm/RIU in the low RI range. • It has the advantages of cost effectiveness, high sensitivity and easy fabrication. In this paper, a refractive index (RI) and temperature sensor based on a folded-tapered multimode-no-core (FTMN) fiber structure is proposed and experimentally demonstrated. The FTMN has an additional Mach-Zehnder interferometer (MZI), which is introduced in the folded-tapered multimode (FTM) fiber. And with the inherent multimode interference (MMI) and the previously mentioned MZI as foundation, a composite interference is successfully established. This synthetic composite interference greatly improves the performance of traditional optical fiber RI sensing in the low RI range. The experimental results demonstrate that a maximum sensitivity of 1191.5 nm/RIU within a linear RI ranging from 1.3405 to 1.3497 can be achieved, which is greater than the traditional modal interferometer structure. Furthermore, the temperature sensitivities at interference dips A and B are 0.0648 nm/°C and 0.0598 nm/°C, respectively. By monitoring the wavelength shifts of interference dips A and B, the sensor can simultaneously measure RI and temperature to overcome the temperature induced cross-sensitivity. [ABSTRACT FROM AUTHOR]