Optical logic has been a topic of vivid interest in recent years, due to its potential in eliminating the bottleneck currently associated with purely electronic information processing in ultra high-speed photonic networks. In order to properly function in a logic system, logic gates must adhere to basic properties such as logic functionality, bit restoration, gate fanout, and gate-to-gate isolation. In this work, we demonstrate the implementation of a programmable optical logic gate that may be multiply cascaded and reconfigured to create an optical logic chip.
The gate is composed of a linear front-end where Boolean optical inputs are combined with a reference signal which specifies the logic function (AND, NOR, XNOR...), followed by a nonlinear back-end that removes the signal phase, and is critical for the gate operation. With the frequency response limited only by the physical constraints of the nonlinear media, the optical gate may function at the high bit rates required by the telecommunications industry. In principle, our gate's inherent design flexibility allows its implementation in free-space optics, optical fibers or integrated optics at any bit rate. We experimentally demonstrate a low-bit rate two-gate cascade in an optical fiber system operating in the RF carrier (envelope) domain, satisfying the cascadability requirements and providing a proof-of-concept of this technology. We present this work in two parts: (i): the theory behind the reconfigurable logic gate, including an analysis of noise in the linear module and implementation options for the nonlinear module; (ii): the practical demonstration of a two-gate cascade.