Bismuth (Bi)-doped glasses and fibers have been regarded as the most promising gain medium for broadband optical amplifiers. However, the Bi-doped glasses and fibers still meet low gain and insufficient efficiency due to the volatilization, uneven distribution, and uncontrollable valence states of Bi ions in the high-temperature (~2000°C) modified chemical vapor deposition process. Herein, we modified the sol-gel method and synthesized uniform Bi-doped glass with a doping concentration of 0.5wt.% Bi ions at 1300°C. Employing an 808nm LD as a pump, the Bi-doped glass showed a broadband fluorescence with the emission peak at 1413nm and a FWHM of 112nm. On this basis, the Bi-doped fibers were fabricated by rod-in-tube method. The background loss was measured to be 0.27dB/m at 1550nm. A 40m Bi-doped fiber amplifier was constructed by 808nm backward pumping. The maximum on-off gain at 1395nm reached 36dB, heralding the potential of our modified sol-gel method for high-gain Bi-doped glass and fiber fabrication.
Flexible and wearable fiber-based triboelectric nanogenerators (FTENGs) have gained much attention in the wearable field due to their ability to convert waste mechanical energy from human motion into electrical energy. However, due to the limitation of preparation technology, FTENG still has the problems of poor flexibility and low electrical output performance. Herein, we prepared super-elastic microstructure triboelectric fibers (SMTFs) by using an extrusion combined with the thermal drawing process. The thermoplastic elastomer was drawn as the cladding, and filled with liquid metal EGaIn as the conductive electrode. The SMTFs show a superior stretchability (1900 % strain), and excellent conductivity. Utilizing a 5 cm long fiber to contact with PMMA medium, the average open circuit voltage was up to 10 V. Moreover, the SMTFs have a stable electrical output performance over 2000 s. The SMTFs were further woven into 8×8 cm2 textiles for energy harvesting. The maximum electrical outputs were 150 V, 10 μA, and 33 nC, respectively. Our results indicate that the SMTFs fabricated by extrusion method combined with the thermal drawing process have the potential in wearable energy devices, intelligent textiles, and human-machine interaction.
The layered van der Waals materials γ-InSe showed great potential in integrated photonic devices and microlasers due to the high electron mobility, wide tunable direct bandgap, and high lattice compressibility. However, γ-InSe crystal has weak stability and dissociation tendency in ambient conditions, which hampers its applications. Herein, we proposed a novel method for single-crystal InSe. By thermal stretching combined with photothermal processing, ultralong and layered single-crystal InSe fibers were obtained. The InSe fiber core was effectively restrained and protected, improving the mechanical properties and stability of the device. Moreover, by using a 532 nm nanosecond pulse laser as the pump source, the WGM microlaser operating at 1107.33 nm was obtained. This work provides a convenient approach for van der Waals materials preparation and paves the pathways for the development of light sources for layered van der Waals materials.
Bismuth (Bi)-doped silica-based glasses and fibers are attractive materials for the new optical amplifiers and tunable lasers. In this paper, Bi/Al co-doped silica glass with a relatively high Bi concentration (0.552 wt.%) were prepared by using the optimized sol-gel method. Hydrofluoric acid (HF) was used as a catalyst in the reaction, which reduced the hydroxyl to lower than 5ppm in the final glass. After the process of drying and sintering, the gel was turned into the transparent glass at low temperature (~1300 °C). The optical properties of Bi/Al co-doped silica glass were also investigated. Excited by a 980 nm laser diode, broadband fluorescence centered at 1114 nm was obtained, which was ascribed to the Bi-Al active center (BAC-Al). The emission cross-section (𝜎𝑒𝑚) was calculated to be 7.4 × 10−21 cm2 for BAC-Al. In addition, ultra-broadband emission ranging from 850 nm to 1700 nm was also obtained excited by the 808 nm LD, which might be ascribed to BAC-P overlapped by other BACs. After the gaussian separation of fluorescence peak, the emission cross-section for BAC-P was 13.4×10−21 cm2. Our results confirmed the potentialities of the optimized sol-gel method in Bi-doped glass fabrication. The Bi/Al co-doped silica glass prepared in this work were promising to develop Bi-doped fibers and relative devices.
Due to the strong light–matter interactions, van der Waals semiconducting materials have shown their great potential in the development of high-performance photodetectors. However, the van der Waals semiconducting devices via conventional growth method often introduce defects or are in the form of isolated flakes, which hinders the optoelectronics from widespread applications. In this paper, van der Waals semiconductor indium selenide (InSe) fibers for photodetection were developed based on thermal drawing. Meters level length of InSe fibers have been fabricated through thermal drawing, and the problem of easy cracking of InSe is solved. The InSe fibers have high crystallinity, and it is found that the cleavage planes have a preferential orientation. The InSe fibers show a high-speed response to modulated 639 nm laser irradiation with up to 10 kHz repetition rate. In addition, the photoelectric response of the fibers were further improved through annealing by CO2 laser.
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