An all-optical 8-bit RAM storage unit with 2×4-bit WDM-formatted data words

Abstract

During the past years, the processor-memory performance gap, also known as “Memory Wall” problem, has forced designers to allocate more than 50% of the chip real-estate for caching purposes to alleviate limited memory bandwidth. Optical technology holds the credentials of delivering high-bandwidth and energy-efficient photonic integrated memories that could revisit the traditional computing architectures. The migration, however, to fully functional and practical optical RAMs will require the exploitation of wavelength dimension as well as seamless cooperation between storage and peripheral decoding units, for efficient RAM architectural layouts. In this paper we present the first demonstration of an all-optical 8-bit RAM storage unit comprising WDM-enabled 2×4 Row and 1×4 Column Decoders and a 2×4-bit optical RAM Bank for storing a 20Gb/s 4-bit WDM-formatted optical data word per row. The proposed scheme incorporates a shared multi-λ SOA-MZI Access Gate (AG) per Word Line (WL) for granting access-control to the appropriate word line, WL “00” or WL “01”, and a passive Column Decoder that directs the incoming WDM-formatted data words to the respective RAM cells. Each RAM cell is in turn based on an elementary monolithically integrated InP photonic Flip-Flop (FF). The proposed architecture is experimentally verified for successful Write operation of a 4-bit WDM word to a selected 4-bit RAM row at 20Gb/s RAM throughput and a peak power penalty within the range of [7.8-10.7] dB, promising a 4× speed-up in memory-access throughput and paving the way for high-bandwidth multi-bit optical RAM-architectures that may relax the memory-bottleneck of computing architectures.