Optical RAM and flip-flops using bit-input wavelength diversity and SOA-XGM switches

In this paper, we demonstrate a novel RAM cell based only on three traveling waveguide semiconductor optical amplifier-cross gain modulation (SOA-XGM) switches. The RAM cell features wavelength diversity in the incoming bit signals and provides Read/Write operation capability with true random access exclusively in the optical domain. Two of the SOA-XGM switches are coupled together through an 70/30 coupler to form an asynchronous flip-flop, which serves as the memory unit. Random access to the memory unit is granted by a third SOA-ON/OFF switch and all three SOAs together form the proposed RAM cell. Proof-of-principle operation is experimentally demonstrated at 8 Mb/s using commercial fiber-pigtailed components. The distinctive simplicity of the proposed RAM cell architecture suggests reduced footprint. The proposed flip-flop layout holds all the credentials for reaching multi-Gb/s operational speeds, if photonic integration technologies are employed to obtain wavelength-scale waveguides and ultrashort coupling lengths. This is numerically confirmed for 10 Gb/s using a simulation model based on the transfer matrix method and a wideband steady-state material gain coefficient.