Tellurium (Te) semiconductor core optical fibers with silicate glass cladding were drawn by the molten core method. The as-drawn precursor fiber has a large core diameter of about 123 µm, which was found to be polycrystalline. What is more, a Bridgman-type fiber postprocessing technique was constructed and used for the first time to anneal the polycrystalline Te semiconductor core optical fibers. The Te core in precursor fiber was melted and recrystallized to single crystal Te with c-axis orientation parallel to fiber axis, which was confirmed by X-ray diffraction, single crystal X-ray diffraction, micro-Raman spectra, and transmission electron microscope measurement results. Enhanced conductivities were observed in single crystal Te semiconductor core optical fibers under illuminated and stress states, respectively. This work demonstrates that the Bridgman-type fiber postprocessing technique could be an effective way to fabricate single crystal semiconductor core optical fibers with large core diameters (∼ 100 µm) and long lengths (a few centimeters).

In the field of multimaterial optical fibers, the demand for high-performance single-crystal core glass-clad multimaterial optical fibers is increasing. However, the applications of single-crystal fibers are restricted by the complex fabrication processes and the slow growth of single-crystal materials. Here, a two-step method is demonstrated to achieve single-crystal tellurium (Te) core fibers with high crystal quality over the length of the fiber. This method starts with the thermal drawing of a fiber preform into polycrystalline Te core multimaterial fibers (precursor fibers) that are long and mechanically stable. A 532-nm continuous laser is then employed to recrystallize the Te core in the precursor fiber into a single crystal state along the entire length of the fiber. Experimental studies of these single-crystal fibers demonstrate that the single-crystal Te core fibers possess high transmittance (>90% at 2-10 μm) and high thermoelectric performance (ZT values from 0.03 to 0.13 at 300 K temperature). They are superior to previous reports and our previous work. This method works for fabricating various single-crystal fibers and has important applications in the field of optical fibers, functional fibers, and their integrated devices.

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