A. Logistics
The goal of the project was to design a Mach-Zehnder interferometer (fig. 1) using silicon photonics for the purpose of detecting COVID-19 proteins in a given sample. The interferometer consists of two Y-branches (A splitter and a combiner) and two waveguides of differing lengths to create a specified Free Spectral Range (FSR). The project was conducted using LUMERICAL photonic simulation software.

B. Description
The interferometer operates around a specified Free Spectral Range (FSR), which was designed to be 10nm. When a sine wave is propagated into the splitter Y-Branch, it will split off into either branch, go through one of the two waveguides, and be recombined at the combiner Y-Branch. If the signal coming from one waveguide does not reach the combiner Y-Branch at the same time as the opposite waveguide, then there will be a phase shift in the two sine waves which creates an interference pattern of peaks and valleys when the two waves combine. The interference pattern is characterized by its FSR, which is the distance between two peaks of the resulting sine wave at the combiner Y-branch. If there is a change in the length of one waveguide, or a change in its effective index, then the FSR will change as a result. This is the effect observed when a COVID-19 protein is present in the sample. As the number of proteins increases, so too will the change in the FSR. As such, the interferometer can be used to estimate the viral load in a sample. This is significant, as current diagnostic tools are only able to identify whether there is any viral load to begin with.