Metasurface-mediated bound states in the continuum (BIC) provides a versatile platform for light manipulation at the subwavelength dimension with diverging radiative quality factor and extreme optical localization. In this work, we theoretically propose the magnetic dipole quasi-BIC resonance in asymmetric silicon nanobar metasurfaces to realize giant Goos-Hänchen (GH) shift enhancement by more than three orders of wavelength. In sharp contrast to GH shift based on the Brewster dip or transmission-type resonance, the maximum GH shift here is located at the reflection peak with unity reflectance, which can be conveniently detected in the experiment. By adjusting the asymmetric parameter of metasurfaces, the Q-factor and GH shift can be modulated accordingly. More interestingly, it is found that GH shift exhibits an inverse quadratic dependence on the asymmetric parameter. Furthermore, we theoretically design an ultrasensitive environmental refractive index sensor based on the quasi-BIC enhanced GH shift, with a maximum sensitivity of 1.5×107 μ m/RIU. Our work not only reveals the essential role of BIC in engineering the basic optical phenomena but also suggests the way for pushing the performance limits of optical communication devices, information storage, wavelength division de/multiplexers, and ultrasensitive sensors.

Alginate fiber, a kind of bio-based fiber, is a type of inherently flame retardant material. Can the addition of alginate fiber to cotton fiber improve flame retardancy of prepared cotton/alginate fabric? To solve this question, in the present work, flammability and thermal degradation properties of the cotton and cotton/alginate fabrics were studied by thermogravimetric analysis (TG), microscale combustion calorimetry (MCC), cone calorimeter (cone) and thermogravimetric analysis coupled with Fourier transform infrared analysis. Compared to cotton fabric, TG results showed that the addition of alginate fiber decreased initial degradation temperature (T initial ) and maximum-rate degradation temperatures (T max ) of cotton/alginate fabric; however, the addition of alginate fiber improved the char residual amount at higher temperature. MCC and cone results indicated that the addition of alginate fiber reduced the peak heat release rate value and total heat release, showing improvement on flame retardant properties of cotton/alginate fabric. The release amounts of inflammable gases, such as H 2 O, for cotton/alginate fabric, were almost the same as cotton fabric in the thermal degradation process; however, compared to cotton fabric, the release amounts of flammable gases, such as compounds containing -C-H groups, alcohol, compounds containing carbonyl groups and ethers, were reduced. On the basis of the results mentioned above, the flame retardant properties of cotton/alginate fabric were enhanced. The results obtained in the present study can supply a flame retardant method by the addition of inherently bio-based flame retardant alginate fiber to flame-retard cotton fabric and enlarge the applied fields of alginate fiber.

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transmit data [1] and has attracted considerable interest in optical local area networks and photonic integrated circuits. Plastic optical fibers (POF) are typically employed to transmit optical signals in VLC systems. [2,3] Although POF have low absorption losses in the visible wavelength window, it is still necessary to use optical waveguide amplifiers to compensate for the propagation loss. Moreover, there is a growing demand for chip-level monolithic photonic systems that integrate optical devices with various functions, such as optical multiplexing, switching, modulation, and amplification. These systems should employ waveguide amplifiers operating across the visible and near-infrared spectral ranges to compensate for the optical losses.Owing to their low absorption loss, simple processing, and being low cost, optical waveguide amplifiers based on polymer materials exhibit great potential in the visible wavelength region in photonic integrated circuits. For optical amplification in the red region, ongoing research mainly focused on the organic dyedoped [4][5][6] and rare-earth Eu 3+ ions or Er 3+ ion-doped polymer waveguide amplifiers. [7][8][9][10] The organic dye-doped optical amplifier pumped with a 575 nm pulsed laser achieved a relative gain of 9.3 dB cm −1 at 650 nm in a waveguide with a cross-section of 7 µm × 100 µm. [11] The rare-earth Eu 3+ ions-doped waveguide amplifier pumped with a 351 nm laser showed a gain of 8.6 dB cm −1 at 612 nm with a cross-section of 2.7 µm × 100 µm. [7] For Er 3+ ion-doped polymer amplifiers, a relative optical gain of 2.0 dB cm −1 at 650 nm, based on the up-conversion of Er 3+ ions, was obtained upon the excitation of a 976 nm laser diode (LD). [9] In addition to the waveguide amplifiers mentioned above, almost all waveguide amplifiers, such as Er 3+ -doped inorganic materials, [12][13][14] Nd 3+ -doped polymer [15][16][17] frequently select LDs as pump sources. In the pumping mode, either light-beam spatial coupling [7,10,17] or a wavelength division multiplexer (WDM) [12,18,19] is generally used to combine the signal laser with a pump laser. The light beam spatial coupling possess the disadvantage of limiting the amplifier to a 1D axial space, as shown in Figure 1a, which is not conducive to the application of Optical gains at 637 nm wavelength using light-emitting diodes (LEDs) instead of traditional semiconductor lasers as pumping sources are demonstrated in the organic molecule 2,6-bis[4-(diphenylamino)phenyl]-9,10-anthracenedione (AQ(PhDPA) 2 )-doped polymethylmethacrylate (PMMA) and SU-8 polymer waveguides. Under excitation of four blue-violet LEDs with different central wavelengths, fluorescence in the red band is observed owing to the transition of AQ(PhDPA) 2 from the excited states to the ground state based on the thermally activated delayed fluorescence (TADF) mechanism. Channel waveguides with a cross-section of 6 µm × 5 µm are fabricated. The relative gains of 5.0 and 4.0 dB cm −1 are obtained in rectangular waveguides with active core layers as AQ(PhDPA) ...

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