The index of refraction of pseudomorphic Si_1-xGe_x layers grown on si has been deter-mined at wavelengths lambda =1330 nm and lambda =1550 nm, for Ge concentrations between x=0.01 and x=0.1. The refractive indexs values were obtained from mode profile measurements on a series of Si_1-xGe_x waveguides. The index of refraction is significantly larger for light polarized parallel to the growth direction than for light polarized in the plane of the epilayer. This birefringence is consistent with the anisotropic index change predicted using photoelelastic theory, given the biaxial strain present in the pesudomorphic Si_1-xGe_x layers.
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