Integrated photonic devices for spectroscopic chemical detection

Abstract

Chemical sensing systems realized with photonic components integrated on traditional semiconductor substrates have emerged as a promising technology for remote sensing applications that require low cost, low power consumption, light weight, small size, and high-performance. In this thesis, I discuss methods and systems for practical implementations of chip-scale integrated photonic chemical sensors and spectromeƯters. The work focuses on solutions to a variety of obstacles that have hindered real-world implementations of microphotonic chemical sensors. First, a new chip arƯchitecture capable of acquiring high channel count, high resolution optical spectra (200 pm resolution in the telecommunications C-band) is presented both theoretically and experimentally, along with a new 'elastic-D₁' regularized regression method for spectrum reconstruction. Next, evanescent field sensing using dielectric waveguides is studied theoretically and numerically, with a special emphasis on sensing perforƯmance in the presence of random, fabrication-induced waveguide sidewall roughness. I demonstrate that a locally flat perturbation approximation is valid for typical experƯimental roughness in silicon-on-insulator platforms, and use a volume-current method to explicitly compute scattering loss rates for a variety of three-dimensional wavegƯuide structures. To then experimentally realize photonic sensing systems, I developed a low-loss (0.36 ± 0.11 dB/cm), quick-turn (16.4 day turnaround) fabrication process for inexpensively prototyping silicon nitride photonic integrated circuits with heaters, etched edge couplers, and opened sensing windows. Using this fabrication process, I present a successful experimental demonstration of a fiber-packaged, waveguideƯenhanced Raman spectroscopic sensor used for detecting liquids in contact with the surface of the chip via measured Raman peaks from 500 - 3500 cm⁻¹.