Ultrabroad Bandwidth Slow Light in Semiconductor Nanostructures

摘要

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. Further they operate at room temperature and can be easily integrated into various optical systems. Ultra-fast non-linear processes in semiconductor optical amplifiers (SOAs) have been used to achieve tunable advance and delay at THz bandwidth. For a 700 fs pulse, we show electrically and optically controllable advance of 1.9 ps corresponding to an advance-bandwidth product (ABP) of 2.5. Further, by leveraging self-phase modulation in these devices we extend the performance to an ABP of 3.7. We develop comprehensive theory using density matrix approach to explain the experimental results. Our results show that an ultra-short pulse propagating through the SOA experiences non-linear index change due to spectral-hole burning and wave mixing between different spectral components. We derive analytical expressions for nonlinear index induced by these ultra-fast processes and numerically solve the propagation of an ultra-short pulse through the SOA. Our theoretical predictions agree very well with our experimental results. Finally, we show fast light for two ultra- short pulses separated by 7.2ps which demonstrates the feasibility of this scheme at high bit-rates.