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• 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 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]