Precision vertical drawing of diameter-gradient microfibers: cascaded geometries for tailored nonlinearity.

As nonlinearity is highly correlated with their geometric dimensions, precise fabrication of optical micro/nanofibers (MNFs) has been a longstanding pursuit. Existing MNFs fabrication systems typically adopt horizontal structures, which inherently introduce inaccuracy stem from asymmetry between fiber axis/geometry and chaotic environment due to high temperature airflow, vibration, etc., leading to deviations from the expected fiber morphology, especially for complex-structured MNFs. Here, we propose and manufacture a MNFs fabrication systems, effectively reducing fiber shape deviations during the fabrication process, enabling the fabrication of precise MNFs. To demonstrate the capability of our system in manufacturing precise structure MNFs, we design and fabricate diameter-gradient microfibers with four cascaded structures over a length of approximately 120 mm and a minimum diameter of about 1 μm for on-demand nonlinearity to generate supercontinuum spectrum. Eventually, we obtain supercontinuum spectrum covering 1463-1741 nm at the - 10 dB level with an efficiency of 264.62 $\text{nm}/\text{kW}$ , exhibiting good flatness and enabling efficient spectral broadening.