We report on a broad-band all-optical switch that exhibits high linearity (>30 dB), high switching contrast (>25 dB), and large data wavelength tunability (100 nm). The switching principle is based on four-wave mixing. Two control pulse trains are placed in the gain wavelength region of a 1300-nm semiconductor-optical amplifier. The data signal, however, is at 1550 nm in the transparent wavelength region where four-wave mixing sidebands are generated due to index modulations. The switch is used to sample a 160-Gb/s data signal with a temporal resolution of approximately 1.7 ps.