Design and Demonstration of Integrated Silicon Devices for Optical Sensing and Optical Communications

Abstract

In recent years, gas sensors at a micro-and-nano scale have gained a lot of attention especially in critical areas such as environmental and medical fields. The development of such sensors is accompanied by advances in micro-and-nano fabrication as well as through exploration of new materials, which has led to enhanced gas sensing performance. The focus is to achieve a realtime, highly sensitive and selective integrated gas sensors while overcoming the fundamental challenges such as device footprint, cost and temperature fluctuations that influence the sensor's behavior. The presented work is a theoretical and experimental analysis of different optical gas sensors based on the Mach-Zehnder interferometer (MZI) design, created on silicon-on-insulator platform. The proposed sensors have enhanced the possibility of gas detection with high sensitivity and low detection limit in the optical domain. The sensors are susceptible to the undesired effect of temperature change which originates from the subjection of different gases. Therefore, a detailed description on a simple approach to counteract this change via the use of microring resonator is introduced. Two MZI configurations were studied: a partially exposed and a suspended interferometer, for which the estimated sensitivities were 2071 nm/RIU and 5500 nm/RIU, respectively. The sensing experiment was conducted using: Helium and Nitrogen gases. Finally, an integrated optical readout system is introduced via the use of Arrayed waveguide grating (AWG) and Multi-mode Interferometers (MMIs). The integrated spectrometer eliminates the need for expensive off-chip bulky systems. AWG devices are typically used for wavelength division multiplexing (WDM) in the optical telecommunication field. However, the same concept may also apply for spectroscopic intents. In this work a 4×4 MMI was designed and fabricated with efforts directed to secure a 100 GHz channel spacing in 4-channel WDM, a 3-dB optical bandwidth of about 100 GHz, high uniformity and excess loss less than 1 dB for the MMI couplers.

Date of Award	Dec 2020
Original language	American English
Supervisor	Jaime Viegas (Supervisor)