A controllable variable optical buffer is one of the most critically sought after components in optical communications and signal processing. In such a buffer, optical data would be kept in optical format throughout the storage time without being converted into electronic format. The buffer must be able to turn on to store and off to release optical data at a very rapid rate by an external command. It is generally believed that an optical buffer would enable many new optical systems such as packet-switched networks [1-4], optical signal processing, phase-arrayed antennas, and nonlinear optics.
An ideal optical buffer needs to be compact, have low-power consumption, have variable buffering time, and most importantly, provide enough buffering capacity and bandwidth. We propose the first semiconductor all-optical buffer  based on the electromagnetically-induced transparency (EIT) effect  in QDs (quantum dots). We establish the conditions and formulation necessary to achieve a large slow-down factor. The light pulses can slow down significantly with negligible dispersion, making it desirable for making optical buffers with an adjustable storage. Narrow linewidth QD fabrication is found to be critical to the overall device performance. Figure 1 shows the schematics of the device and Figure 2 shows the simulation results of signal packet buffering.
Figure 1: Schematics of a semiconductor all-optical buffer based on quantum dot waveguide structures. Signal and pump copropagate (or counterpropagate) in the same waveguide. Signal slow down is induced by the pump via electromagnetically-induced transparency (EIT).
Figure 2: (a) Signal propagation through a quantum dot waveguide with the length of 1 cm. (b) Control of the slow-down factor with the pump power density.