In this paper we discuss free carrier generation by pulsed laser fields as a mechanism to switch the optical properties of semiconductor photonic crystals and bulk semiconductors on an ultrafast timescale. Requirements are set for the switching magnitude, the time-scale, the induced absorption, as well as the spatial homogeneity, in particular for silicon at lambda= 1550 nm. Using a nonlinear absorption model, we calculate carrier depth profiles and define a homogeneity length lhom.Homogeneity length contours are visualized in a plane spanned by the linear and two-photon absorption coefficients. Such a generalized homogeneity plot allows us to find optimum switching conditions at pump frequencies nu/c= 5000 cm−1 (lambda= 2000 nm). We discuss the effect of scattering in photonic crystals on the homogeneity. We experimentally demonstrate a 10% refractive index switch in bulk silicon within 230 fs with a lateral homogeneity of more than 30mm. Our results are relevant for switching of modulators in the absence of photonic crystals.

T. G. Euser and W. L. Vos

2005

01/2005

J. Appl. Phys.

97

043102: 1-7

10.1063/1.1846949

3D silicon photonics, semiconductor, silicon photonics, spatial homogeneity, ultrafast optics