Compact C-band random fiber laser with localized feedback from a graphene/TiO₂ composite droplet

We demonstrate a compact C-band random fiber laser (RFL) using a graphene/TiO₂ composite droplet as a localized feedback interface on a flat-cleaved single-mode fiber endface. This endface configuration avoids long passive feedback fibers and random-grating fabrication. Compared with bare-fiber, water, graphene-only, and TiO₂-only controls, the composite yields denser random lasing peaks, stronger spectral modulation, and higher slope efficiency. The RFL shows an estimated lasing threshold of 59 mW and an optical signal-to-noise ratio of 26.81 dB at 189 mW. Diameter-dependent performance is nonmonotonic; among the tested diameters, the 7.5 mm droplet provides the strongest spectral concentration and background suppression and the lowest measured low-frequency relative intensity noise (-76.61 dB/Hz at 122 mW).