Slow and fast light enables key functionality in various rf applications and all-optical networks. Semiconductor-based schemes offer electrical control of velocity at very high bandwidths in an extremely compact device. Furthermore, they operate at room temperature and can be easily integrated into various optical systems. Ultrafast nonlinear processes in semiconductor optical amplifiers (SOAs) have been used to achieve tunable slow and fast light in the terahertz bandwidth. For a pulse, we show an electrically and optically controllable advance of corresponding to an advance–bandwidth product (ABP) of 2.5. Furthermore, by leveraging self-phase modulation in these devices, we extend the performance to an ABP of 3.7. We develop comprehensive theory using a density matrix approach to explain the experimental results. Our results show that an ultrashort pulse propagating through the SOA experiences nonlinear index change due to spectral-hole burning and wave mixing between different spectral components. We derive analytical expressions for the nonlinear index induced by these ultrafast processes and numerically solve the propagation of an ultrashort pulse through the SOA. Our theoretical predictions agree very well with our experimental results. Finally, we show fast light for two ultrashort pulses separated by , which demonstrates the feasibility of this scheme at high bit rates.
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