Layout- and variation-aware optimization of Mach-Zehnder interferometers

In this thesis, we address the fabrication process variation issue in Mach-Zehnder interferometers (MZIs) for silicon photonic integrated circuits. Three approaches were proposed. The first one is based on the conventional layout of MZI, in which we performed exhaustive search method by defining an optimization problem with a cost function of zero phase error and constraints on FSR and length of MZI’s arms to find an optimal structure for an MZI that is robust against FPVs. In the second approach we improved the first approach in a way that we can have any configuration with any number of curvatures in arms for an MZI apart from the conventional one based on the boundaries that defined by user for the first arm. The second arm of the MZI will be designed according to the design of the first arm. The third approach will be proposed as an upgrade for the second approach by allowing the user to design the second arm independent from the first arm in a way that we defined two separate searching regions for curvatures of arm1 and arm2. Matlab was used to implement algorithms coupled with finite-difference-time-domain (FDTD) simulations. In all three approaches, we showed that our framework works perfectly, as we do not see a shift of central wavelength in the results. Also, we demonstrated that by using the final results in MZI without variations, there is approximately 10 nm deviation for central wavelength which is because arms’ length differences are designed in approaches based on their effective index under variations.