Slow and fast light using nonlinear processes in semiconductor optical amplifiers

Duill, Shumakher, Eisenstein

P. Kondratko, Akira Matsudaira, Shu‐Wei Chang +1 more

N. R. Brewer, Tian Li, K. M. Jones +1 more

Yin Zhang⋆, Xinliang Zhang, Xi Huang +1 more

Bala Pesala, Forrest G. Sedgwick, Alexander V. Uskov +1 more

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 700 fs pulse, we show an electrically and optically controllable advance of 1.9 ps 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 7.2 ps, which demonstrates the feasibility of this scheme at high bit rates.

Connie J. Chang-Hasnain, P. Bhattacharya, S. L. Chuang

Abstract : Slow and fast light schemes are attractive for many applications including optical signal processing and RF phased array antennas. 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. In this program, we used ultrafast nonlinearities in semiconductor optical amplifiers (SOAs) to achieve tunable time shifts at THz frequencies. In particular, we leveraged the spectral hole burning phenomena and demonstrated fast light in quantum well (QW) and quantum dot (QD) SOAs. The research included both theoretical and experimental efforts. Theoretical work was developed to understand and simulate experimental results and to optimize device designs. We introduced a novel pulse compression technique to reduce the pulse width to 100 fs to efficiently use ultra-fast nonlinearities in SOAs to achieve a large and cascadable delay. We implemented a novel chirped pulse scheme and obtained the largest advance-pulse-product of 10.7 with THz bandwidth. We demonstrated slow and fast light with GHz RF signal in QW/QD SOAs using coherent population oscillation and four-wave mixing. We also demonstrated cascaded SOAs in a loop to scale up the delay/advance.