This paper discusses 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 time scale. 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 l_hom. 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 near v/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 30 micrometers. Our results are relevant for switching of modulators in absence of photonic crystals.
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机译：本文讨论了脉冲激光场产生的自由载流子，作为一种以超快的时间尺度切换半导体光子晶体和体半导体的光学特性的机制。设置了开关量，时间尺度，感应吸收以及空间均匀性的要求，特别是对于λ= 1550 nm的硅。使用非线性吸收模型，我们计算载流子深度轮廓并定义均匀长度l_hom。均质长度轮廓在由线性和双光子吸收系数跨越的平面中可视化。这种通用的均匀性图使我们能够在泵频率接近v / c = 5000 cm ^ {-1}（λ= 2000 nm）时找到最佳开关条件。我们讨论了光子晶体中的散射对均匀性的影响。我们通过实验证明了在230 fs内的块状硅中有10％的折射率转换，其横向均匀性超过30微米。我们的结果与在没有光子晶体的情况下切换调制器有关。
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