Synthesis of Circuits based on All-Optical Mach-Zehnder Interferometers Using Binary Decision Diagrams

The advancement of fabrication technology in VLSI (Very Large Scale Integration) and photonic industry has gained significant interest due to the feasibility of performing functional computations on-chip using ultra-high speed optical devices and low-power interconnects. Here, the necessity of optical circuits arises as they are inevitable components in developing optical Integrated Circuits (ICs). In this conjuncture, methodologies to design highly scalable optical circuits and their synthesis schemes have received interest. In recent years, several works and their findings have been reported in various research articles where researchers have mainly designed combinational and sequential memory elements using optical devices. The use of Binary Decision Diagrams (BDDs) to construct optical circuits has been reported recently. However, the costs of the resulting circuits are still rather high. Furthermore, they include a substantial amount of splitters, which is a significant drawback as they degrade the signal strength in the circuits. In this paper, we propose an improved design technique where we use BDDs to construct optical circuits. Rather than generating a single graph for multi-output functions, we consider individual graphs for each output separately which, afterwards are combined to realize the entire function. In our experiments, we find that this approach performs better in comparison to related techniques – a cost improvement of approx. 34% is observed on average. As these optical circuits are mainly designed with MZIs, beam combiners and beam splitters, the use of beam splitters in the circuit degrades the signal quality at the receiver end. To address this concern, in a second phase of our design, we make all the circuits free from splitters. Experimental results for both the design schemes are given and analyzed.