Infrared circuits using silicon photonics

Abstract

In this thesis, a complete design of silicon-on-silica integrated optical sensor for carbon dioxide is proposed. Carbon dioxide sensing is vital for many industrial processes and indoor air quality monitoring. Unlike formerly proposed sensors, this design does not replace the buried silica by other materials. The presented work push-es the utilization of the mature complementary metal oxide semiconductor technology more into mid infrared applications. The proposed design relies on the confinement of the mode in the waveguide to overcome silica absorption losses. The design is based on optimizing the dimensions of the waveguide to minimize the absorption losses, then making a grating coupler matches the waveguide to reduce the losses. . The pro-posed grating coupler offering 3.5 dB coupling efficiency with incident Gaussian beam from InF3 single mode fiber. The sensing is based on the interaction between the evanescent mode and the gas, consequently the length of the waveguide is optimized to get the highest detection sensitivity. The sensor operates at a wavelength of 4.28 μm, at which carbon dioxide has an absorption coefficient of 260 cm-1. The sensor features a detection sensitivity of 6.37 ppm and a sensor length of 4.68 cm. A ring resonator is introduced to avoid using this long waveguide, the circumference of the ring is 442.2 µm and the minimum detectable concentration is 6.5 ppm. The study shows both analytical and numerical calculations with good agreement.