AbstractWe discuss high‐speed waveguide modulators for optical fiber communications that employ semiconductor quantum wells, with emphasis on electrorefractive devices. The prime advantages of quantum‐well material in this application are provided by enhanced electro‐optic effects that allow ultracompact devices with low drive voltage requirements. The small size is particularly important for low‐cost monolithic integration with other components for guided‐wave photonic integrated circuits. In our devices, compactness is also key for obtaining high electrical modulation bandwidth. © 1993 John Wiley