Submicrometer all-optical digital memory and integration of nanoscale photonic devices without isolators

In this paper, the authors introduce multibit all-optical memory devices in nanostructured photonic-crystal circuits using only intrinsic nonresonant optical nonlinearities of semiconductors. Introduced devices can record incoming pulses at speeds of 10 Gb/s using power levels less than 1 mW or at speeds approaching 70 Gb/s using power levels of 10 mW. The incoming pulses are recorded in high-contrast digital output levels independent of the input bit format. The devices exhibit tunable gain for fan-out with negligible reflection and low dissipation and can provide signal regeneration, including reshaping and retiming. Separate signal, clock and reset inputs, and memory outputs coexist without any crosstalk. Input, clock, and output operating frequencies can be independently tuned. By simulating the operation of such all-optical memory devices, it is also shown that nanoscale optical devices can be cascaded to construct densely integrated systems without any isolators or amplifiers, even in the presence of reflections.