All-fiber microheater with attenuation-controlled hot-zone based on metal-doped silica fibers

We propose and experimentally demonstrate an optical microheater based on metal-doped optical fibers (MDFs) that exploits the intrinsic 1480 nm absorption of Co²⁺ and Fe²⁺/Fe³⁺ ions co-doped in an aluminosilicate core. Three MDFs with attenuation coefficients of 9.45, 12.58, and 32.43 dB/cm are fusion-spliced to single-mode fibers to form 10-mm-long heaters. Under 367 mW pumping, the peak surface temperatures reach 166, 268, and 478 °C, while the corresponding hot-zone lengths (FWHM) decrease from 10.6 to 2.8 mm, demonstrating that the attenuation coefficient is a single design parameter that simultaneously controls both temperature and spatial confinement. A Beer-Lambert distributed heat source coupled with a cylindrical fin model predicts the peak temperatures of the remaining samples within 5-21% from a single calibration point. Independent fiber Bragg grating measurements verify the thermographic results within 18 °C, and optically induced carbonization of an acrylate recoating confirms the practical heating capability. Unlike conventional coating-based fiber microheaters, the proposed device requires no external photothermal layer, is directly fusion-spliceable to standard SMFs, and enables attenuation-controlled tailoring of both the peak temperature and hot-zone length.