All-Optical Tag Comparison for Hit/Miss Decision in Optical Cache Memories

An all optical multi-wavelength tag comparator unit followed by a semiconductor optical amplifier-read access gate (SOA-RAG) is presented for all-optical cache memory architectures. Proof-of-principle operation of the Tag Comparison (TC) circuit as a dual-bit tag-comparison stage is presented by exploiting cross-phase modulation-based XOR logic gates based on SOA-Mach-Zehnder interferometers (SOA-MZIs), in order to decide upon a cache hit or cache miss operation, while the two SOA-MZI outputs control the ON/OFF cross-gain-modulation of the SOA-RAG unit. Experimental error free operation is demonstrated for a 8 × 10-Gb/s wavelength division multiplexing (WDM) formatted optical word signal and a 4 × 10-Gb/s WDM tag.