The third-order nonlinear optical coefficients of Si, Ge, and Si1-xGex in the midwave and longwave infrared

Using a combination of semiconductor theory and experimental results from the scientific literature, we have compiled and plotted the key third-order nonlinear optical coefficients of bulk crystalline Si and Ge as a function of wavelength (1.5-6.7 mu m for Si and 2-14.7 mu m for Ge). The real part of third-order nonlinear dielectric susceptibility (chi((3))'), the two-photon absorption coefficient (beta(TPA)), and the Raman gain coefficient (g(R)), have been investigated. Theoretical predictions were used to curve-fit the experimental data. For a spectral range in which no experimental data exists, we estimate and fill in the missing knowledge. Generally, these coefficient-values appear quite useful for a host of device applications, both Si and Ge offer large chi((3))' and g(R) with Ge offering the stronger nonlinearity. In addition, we use the same theory to predict the third-order nonlinear optical coefficients of Si1-xGex alloy. By alloying Si and Ge, device designers can gain flexibility in tuning desired optical coefficients in between the two fundamental components based upon their application requirements. (C) 2011 American Institute of Physics. [doi:10.1063/1.3592270]