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As the Bragg fiber can guide light by tuning the structure parameters of claddings, it is possible to improve the ability of laser-power transmission in the mid-infrared with effective omnidirectional reflection, but it usually suffers from the disturbance of the air core and functional bandgap. Here, the structural parameters of three pairs of periodic cladding layers were optimized by the plane wave expansion method, and the thickness of each layer is 3.36 µm, consisting of Ge20As20Se15Te45 and As2S3 glasses with a refractive index contrast of Δn = 0.8. The simulation results showed that a wide bandgap of 1.2 µm can be realized in the fiber after structural optimization. Then, a fiber preform was prepared via an improved stacked extrusion based on seven thickness-compensated glass plates. The experimental results show that the all-solid Bragg fiber has three pairs of uniform periodic cladding and an extra-large core. The superior optical fiber structure can also be well maintained in the whole fiber length, and the average ratio of each cladding thickness to the fiber diameter is kept nearly at 3:100. Finally, the fiber loss at 1.55 µm and 2.94 µm is 12 dB/m and 18 dB/m, respectively. In all, such a well-structured all-solid chalcogenide Bragg fiber would pave a new way to develop high-quality laser transmission or optical sensors in mid-infrared.

The difficulty in the preparation of high-quality rare-earth-doped double-clad chalcogenide glass fiber with high absorption of pumping energy is one of the major issues in the development of mid-infrared fiber lasers. In this study, we solve this problem by changing the inner cladding structure of the fiber. The absorption efficiencies of several typical inner cladding shapes were compared and analyzed by the ray tracing method. The result shows that the hexagonal inner cladding fiber has the best absorption efficiency. For the first time, we developed an Er3+-doped Ge-Ga-Sb-S double-clad chalcogenide glass fiber with a hexagonal inner cladding via the fiber extrusion method, and experimentally demonstrated a higher absorption efficiency in the fiber compared with those in the traditional circular double-clad fibers. Such a hexagonal double-clad chalcogenide glass fiber possesses the potentials for developing high-efficiency mid-infrared fiber lasers.

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