An optical memory cell based on erbium-doped fiber

The optical packet switching (OPS) paradigm, where optical packets flow in the network within the optical layer, has the potential to solve the mismatch between the ever increasing link transmission capacity and the node switching capacity, limited by electronics constraints. Anyway, to make this solution feasible and cost-effective, some technological issues must be faced. In particular OPS network nodes, in analogy with current electronic packet network nodes, require some buffering capability to store the optical packets. Since optical random access memories (RAM) are not available, current solutions exploit fiber delay lines (FDL), whose drawbacks are the fixed and finite memorization time and the sequential access. In this paper we propose a novel approach for optical memories, which exploits erbium-doped fiber fluorescence. In particular, an erbium-doped fiber span serves as a one-bit all-optical memory cell associating the bit 1 to the fiber transparency state induced by a strong writing signal, and the bit 0 to the fiber absorption state without excitation. The memory state can be probed injecting a low power reading signal in the fiber span: if it reaches the output port the stored bit is 1, if it is completely absorbed the stored bit is 0. The advantages of this architecture are a long memorization time (up to millisecond range) and the possibility to read the cell at any time (rather than at fixed instants, as happens with FDL). If the memory needs to be reset, a proper erasing signal is sent to speed up the memory cleaning. Experimental results have shown the feasibility of the proposed approach: a one-bit optical memory cell with 2.5 ms refresh time, 752 μJ writing energy, 316 μJ erasing energy, and contrast ratio up to 21 dB is experimentally demonstrated.