The attenuation properties of Tm3+ -doped fluorozirconate optical fibers at 632.8 nm induced by a signal at 1175 nm are investigated for the first time. We believe this approach has potential applications in Q-switching of fiber lasers. A red-guided signal is gradually attenuated up to 14.7 dB by increasingly applying a copropagating 1175-nm signal. This value is obtained in 12.5-cm samples. Fibers with different concentrations (1000, 2000, and 20,000 ppm wt) are characterized. For example, the most efficient, the 20,000-ppm wt fiber, requires ~120 mW to exhibit complete attenuation, although 30 mW would be sufficient for a smaller core. In general, low concentration is related to fast response and high concentration to high efficiency. In the fiber with the best performance, the 2000 ppm wt, a red signal is 13.5% modulated up to 130 Hz with a theoretical limit of 266 Hz.