We present a study of optical modulation by the effect of temperature-induced insulator-to-metal phase transition of vanadium dioxide (VO2) nanocrystals deposited in an antiresonance hollow-core fiber (AR-HCF). We fabricate such a VO2-coated fiber by embedding alkylsilane functionalized VO2 nanocrystals into the air holes of an AR-HCF. With this fiber, we achieve an optical loss modulation of ∼60% at a temperature above ∼53∘C over an ultrabroad spectral range that encompasses the S+C+L band.