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.
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.
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.
With the increasing output power of lasers, the problem of poor beam quality in most of them also arises. Therefore, we design, simulate and fabricate a hollow-core antiresonant fiber that can reduce high-order modes loss. The fabricated fiber has a rod structure (710 μm outer diameter) to resist the influence of bending, and its cladding is composed of ten noncontact capillaries. The fiber has a 128 μm core inscribed circle diameter, an average 40 μm cladding capillary inner diameter, and a tube wall thickness of about 650 nm. The test results of this fiber show that the transmission loss at 1 μm and 1.5 μm is close to 0.1 dB/m and in 2.6-4 μm band is mostly below 0.5 dB/m (except molecular absorption peak). The beam quality test results of this fiber show that its M2 is basically inversely proportional to the wavelength at 2.6-4 μm, and M2 below 3 μm is about 2. By observing the output spot of this fiber at 1 μm and 1.5 μm wavelength with a CCD camera, we can intuitively see its multimode transmission characteristics.
In this work, we report the fabrication and characterization of a 5-tubes nested hollow-core anti-resonant fiber (Nested HC-ARF), which exhibits outstanding optical performance in terms of a record attenuation value of 0.85 dB/km at 2 μm wavelength and excellent modal. The power handling capability of Nested HC-ARF is also firstly demonstrated in this work. The maximum average power of 60.5 W at 2 μm has been transmitted through the fabricated Nested HC-ARF in robustly single-mode fashion without introducing any damage to the input and output fiber end-faces, which represent the highest average power delivered by HCF in this wavelength, to the best of our knowledge.
Er/Yb co-doped YAG nanopowders-derived silica fibers (YNDSFs) are fabricated from UV-curable composites and achieve 1550-nm laser generation with active fiber length of 1 cm. The UV-curable nanocomposites are consisted of 40 wt% home-made Er:YAG/Yb:YAG nanopowders and 60 wt% polymer resins. The Er:YAG/Yb:YAG nanopowders are fabricated by coprecipitation method with diameters in the range of 25 - 165 nm. An Er:YAG/Yb:YAG–polymer hybrid core rod was polymerized using high power UV-lamps, and was drawn to Er/Yb co-doped fiber in silica cladding by melting-in-tube method after debound process to remove organics. The absorption coefficients of the Er/Yb co-doped fiber were measured to be 17 dB cm-1 and 3.2 dB cm-1 at 976 nm and 1530 nm, respectively. The background loss was 0.05 dB cm-1 at 1200 nm. A linear fiber laser cavity was constructed with different length of Er/Yb co-doped fiber and a pair of FBGs (reflectivity: 99 % and 94 %) to quantify the laser performance. The maximum output powers were 7.5 mW and 1.5 mW with active fiber length of 6 cm and 1 cm, respectively. This scheme is expected to be an effective approach for obtaining Er:Yb co-doped fiber with high pump absorption for the generation of 1550-nm single-frequency fiber lasers.
High-power fiber lasers have experienced a dramatic development over the last decade. Further increasing the output power needs an upscaling of the fiber mode area, while maintaining a single-mode output. Here, we propose an all-solid anti-resonant fiber (ARF) structure, which ensures single mode operation in broadband by resonantly coupling high order modes (HOMs) into the cladding. A series of fibers with core sizes ranging from 40 to 100 μm are proposed exhibiting maximum mode area exceeding 5000 μm2. Numerical simulations show this resonant coupling scheme provides a HOMs suppression ratio more than 20 dB, while keeping the fundamental mode loss lower than 1 dB/m. The proposed structure also exhibits high tolerance for core index depression.
A silica leakage channel microstructured optical fiber (LCMOF) is firstly drawn from a 3D printed preform. The LCMOF realized the optical signal transmission of supercontinuum spectrum from 600 nm to 1650 nm and the measured propagation loss is 15 dB/m at 632 nm and 19.5 dB/m at 1064 nm. The bending loss is 5 dB/m with 15 cm radius and 7.3 dB/m with 5 cm radius. The refractive index fluctuation is less than 7×10-4 in the fiber core region. The structure of LCMOF can be adjusted effectively by altering the pre-designed preform and optimizing drawing temperature, which result in the less defects and lower loss.
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