A numerical Kramers-Kronig analysis is used to predict the refractive-index perturbations produced in crystalline silicon by applied electric fields or by charge carriers. Results are obtained over the

m optical wavelength range. The analysis makes use of experimental electroabsorption spectra and impurity-doping spectra taken from the literature. For electrorefraction at the indirect gap, we find

at

m when

V/cm, while the Kerr effect gives

at that field strength. The charge-carrier effects are larger, and a depletion or injection of 10
18carriers/cm
3produces an index change of

at

m.