An electro-refraction modulator includes a series of layers with different doping levels surrounding a single-crystal regrown p-n junction implemented in a silicon-on-insulator (SOI) technology. The regrown p-n junction is spatially abrupt and precisely defined, which significantly increases the tuning efficiency of the electro-refraction modulator while maintaining acceptable insertion loss. Consequently, the electro-refraction modulator (such as a resonator modulator or a Mach-Zehnder interferometer modulator) can have high bandwidth, compact size and reduced drive voltage. The improved performance of the electro-refraction modulator may facilitate silicon-photonic links for use in applications such as wavelength-division multiplexing.