Published/Posted: July 18, 2015
Authors: Li; S.; Kumar, G.; Murphy, T. E.
The interaction of terahertz waves with silicon is usually explained using a linear model of conduction in which free carriers respond to the oscillating electric field, leading to absorption. Here we employ a silicon dielectric waveguide to confine and concentrate terahertz pulses, and observe that the absorption saturates under strong terahertz fields. By comparing the response between lightly-doped and intrinsic silicon waveguides, we confirm the role of hot carriers in this saturable absorption. We introduce a nonlinear dynamical model of Drude conductivity that, when incorporated into a wave propagation equation, predicts a comparable field-induced transparency and elucidates the physical mechanism underlying this nonlinear effect: velocity saturation—an effect that fundamentally limits the speed of most semiconductor devices. The results are numerically confirmed by Monte Carlo simulations of the Boltzmann transport equation, coupled with split-step nonlinear wave propagation. The results reported here could have significance in understanding and designing a variety of emerging and future terahertz devices, such as waveguides, mixers, detectors, and oscillators.
S. Li, G. Kumar and T. E. Murphy, "Terahertz nonlinear conduction and absorption saturation in silicon waveguides", Optica 2(6) 553-557 (2015)
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