On-chip implementation of Mach-Zehnder Interferometer (MZI) photonic circuits: Design, simulation and characterization

As the limitations of integrated electronics start to appear, it becomes important to look for potential alternatives. Silicon photonics holds a lot of promise in this regard. It cannot only provide superior performance to traditional integrated electronics in many aspects, but also co-exist in harmony with it through the realization of electro-optic devices. The focus of this paper is on Photonic Integrated Circuits (PICs) only. A theoretical understanding of Mach-Zehnder Interferometer (MZI) circuits has been developed. Computational design tools have been employed to model photonic waveguides. The design of optical waveguides has been numerically investigated in MATLAB through the Effective Index Method (EIM). The material properties of silicon and silicon dioxide, used in the simulations, have been presented. The properties include the refractive indices, group refractive indices and effective indices. Waveguide geometrical parameters have been explored and a 500 nm x 220 nm silicon waveguide structure has been finalized for experimental work. The schematics for four MZI optical circuits have been prepared in KLayout. Interoperability of KLayout and Ansys Lumerical Interconnect allows for spectral response to be obtained through simulations. The circuits consist of grating couplers, Y-branch splitters and bidirectional couplers. The input signal is split into two waveguide paths. Both waveguide paths culminate into grating couplers connected to photodetectors. The signals from both the channels have been recorded. The fabrication of the chip has been carried out at Applied Nanotools Inc. through Electron Beam Lithography (EBL). The characterization of the devices has been done at 25oC. A decent conformity can be observed between simulation and experimental results.