Chip-Integrated Photonic Interferometer for in Situ Film Thickness Characterization in Silicon Photonic Waveguides

Date of Award

5-9-2026

Degree Name

M.S. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Swapnajit Chakravarty

Abstract

Over the past few years, on chip interferometric sensors have become very common, particularly in label free detection in the healthcare sector. However, their sensitivity is influenced by the conformality of thin film deposition and surface functionalization processes. Understanding the coverage of these films across the involved waveguides is essential to ensure consistent precision in device specifications. Conventional single polarization using TE mode alone provides limited insights into these parameters and thus the exploration of polarization dependent strategies is desired. The primary objective of this work is to further exploit polarization-dependent modal behavior in silicon photonic waveguides to evaluate the conformality of thin-film deposition methods. This will further enhance the sensitivity of chip-based, label-free biosensors by promoting uniform binding interactions across the waveguide surface. To achieve this a dual-polarization device was designed leveraging the response of Transverse Electric (TE) and Transverse Magnetic (TM) modes to surface induced films. A theoretical framework is developed to describe polarization-dependent modal propagation, interferometric phase evolution, and sensing arm thin-film perturbation effects arising from evanescent field interactions. Optical thin-film model and look up table motivated by spectroscopic ellipsometry is incorporated to parameterize film thickness and refractive index, thus serving as a reference for determining the actual thin film thickness and refractive index. Experimentally, dual-polarization transmission spectra are acquired for different thicknesses of thin-films coated on silicon photonic waveguide devices and processed using Fourier-based fringe isolation techniques to extract polarization-resolved wavelength and phase shifts. Measurements are then made to determine the exact thicknesses of the thin films. The model developed will help to determine the film thickness of functionalization layers and subsequent surface biomarker attachments to accurately determine the thickness of the probe biomarkers attached to their conjugate biomarkers in the biosensing process. Broadly, this work establishes a compact, highly sensitive method for in-situ thin-film characterization and three-dimensional process control in silicon integrated circuits. The results demonstrate clear and repeatable differences between TE and TM mode responses to thin-film coatings, indicating sensitivity to film conformality and surface coverage.

Keywords

Engineering

Comments

OCLC No. 1591829354

Rights Statement

Copyright 2026, author.

Link to Full Text

Share

COinS
 
 
 

Links