Electroabsorption optical modulators integrated with passive waveguides have been fabricated on GaAs/AlGaAs multiquantum well material using the impurity-free vacancy diffusion technique with SrF2 and SiO2 capping layers. At a wavelength of 861.6nm, devices with a 400 mu m long modulator section showed ON/OFF ratios greater than 35dB for a reverse bias voltage of 3V.