A STUDY ON DESIGNING ALL-OPTICAL MULTIPLIERS AND OPTICAL CHANNEL ROUTING IN PHOTONIC INTEGRATED CIRCUITS

Abstract

In the past few decades, the very-large-scale integration (VLSI) industry has witnessed rapid growth in semiconductor technology. Due to the continuous need for high performance, low power, and smaller-size transistors, this VLSI industry is reaching its limit. As a result, nontransistor technologies are being investigated as alternatives to traditional technology. Among these alternatives, silicon photonics is a promising candidate for next-generation computing due to the benefits of low power, high bandwidth and complementary metal-oxide semiconductor (CMOS) compatibility. Therefore, the design of optical circuits has spurred great attention among researchers in the domain of electronic design automation. With this motivation, the design and synthesis of photonic integrated circuits (PICs) have been explored in recent times. The logic and architectural circuit design is the first step in the synthesis of PICs, where combinational and sequential circuits such as adders, multiplexers, multipliers and flip-flops are designed with the help of basic optical components/switches. However, in order to develop full-fledge efficient optical systems, the need for optimized physical design automation arises. The basic optical combinational logic circuits like adders, subtractors, and multiplexers have been designed with the help of semiconductor optical amplifier (SOA) based Mach-Zender interferometers (MZIs), which can be used to design an all-optical arithmetic and logic unit (ALU). However, an all-optical ALU will also need to have an all-optical multiplier. In this thesis, we investigate different all-optical multiplier designs, where the complexity of these designs is analyzed with respect to the optical circuit design parameters such as optical cost, delay, number of ancilla inputs and garbage outputs. At first, we design two different all-optical multipliers, namely array multiplier and carry save adder (CSA)-based multiplier, using SOA-based MZIs. The time and space complexity of these designs are analyzed for generalized n-bit multipliers. The performance evaluation of optical parameters shows that all-optical CSA multipliers perform better in terms of both optical cost and delay compared to those of all-optical array multipliers. Next, we have explored the designs of three different types of all-optical parallel multipliers (Wallace tree multiplier, Dadda multiplier and reduced area multiplier). The basic MZI switch, full adder and 2-bit multiplier have been simulated to analyze the power loss due to the presence of beam splitters along the optical path. Furthermore, an all-optical merged multiplier has been designed, which is often used in digital signal processors. In comparison with other designed multipliers, it is evident from the simulation results that the MZI-based reduced area multiplier has the highest performance in terms of speed, while the MZI-based carry save adder (CSA) multiplier has the least optical cost. On the physical layout of the optical circuits, it is a challenging task to obtain the optimal routing of optical waveguides while minimizing all the parameters like the number of tracks, total bend loss, worst signal loss, total propagation loss and total crossing loss. This thesis proposes two non-Manhattan grid-based methods for optical waveguide channel routing to reduce the bend loss, worst signal loss, and tracks in optical channel routing. First, we propose a scalable heuristic called reducing bend loss (RBL), which reduces the total bend loss (TBL) and tracks (T) by using a restricted horizontal routing. This restricted horizontal routing helps to eliminate such bends that cause the highest bend loss. Simulation results confirm the trade-off between the bend loss and track reduction. Lastly, we propose a 0-1 integer linear programming (ILP) based algorithm called minimizing bend loss (MBL). MBL is a multi-objective optimization method that minimizes the TBL, the worst signal loss (WSL) and T in optical waveguide channel routing. The comparative simulation results show the efficacy of MBL over RBL. However, the execution time of MBL for larger testcases is very high. Hence, for the large testcases when time is the constraint, then RBL can be chosen over MBL; however, for smaller testcases MBL is preferred over RBL. The optical multiplier design and all-optical channel routing presented in this thesis would help develop optical circuits and a full-fledged optical system in the future. The presented optical multipliers design and optical channel routing methods can play a substantial role in the architectural design and design automation, respectively, for the PICs.