An optical fiber operating in the mid-infrared wavelength range is fabricated using ZrF
4-based fluoride glass. Material purification, the fiber fabrication process, and transmission properties are presented. The starting materials, ZrF
4, BaF
2, GdF
3, AlF
3, and SbF
3are carefully purified by sublimation techniques. The "built-in" casting technique, specially developed for fluoride glass fiber, is used for preparing cladded type fiber with a smooth core-cladding interface. Spectral loss is measured in the 0.7- to 5.5-μm wavelength region, and a minimum loss of 12 dB/km is attained at 2.55 μm. Based on the refractive-index spectrum measured in the

m range, material dispersion characteristics are also investigated. It is indicated that material dispersion falls to zero at 1.52 μm and exhibits a gentle wavelength dependence in the present glass system.