Cavity-Enhanced Nanophotonic Spectroscopy In Optofluidic Devices

The devices fabricated and explored in this thesis belong to an emergent research field referred to as optofluidics. Research innovations in the areas of integrated optics and microfluidics have brought forth this new and exciting area of study which combines photonics with fluid handling on the microscale. By taking advantage of tools designed for the microelectronics industry, optofluidics promises new innovations which may revolutionize the areas of diagnostic medicine, drug discovery, and environmental monitoring. In this thesis, I have explored how one of the main building blocks of photonics-the optical cavity- can be combined with microfluidic handling capabilities to perform spectroscopic measurements for life science applications. This dissertation is divided into seven chapters with the following organization. In Chapter 1, I introduce the research field of optofluidics and its application in lab-on-a-chip technologies. Chapter 2 includes a motivation for the use of optical microcavities in biomedical sensing applications. I discuss the relevant parameters which describe the behavior of microring resonators and derive the equations governing their operation. Chapter 3 describes an experiment where polystyrene microspheres were optically trapped by the evanescent field from high index contrast silicon nitride waveguides. The use of a high-power broadband light source enables the simultaneous trapping, transport, and characterization of these microspheres by using their resonant properties. Chapter 4 discusses the use of optical microcavities to perform integrated laser absorption spectroscopy on nanoliter volumes of fluid. Relying on the cavity enhancement of light by silicon microrings, I demonstrate a sensitive and compact device which measures optical absorption in the near infrared regime. In Chapter 5 I demonstrate spectrophotometry measurements at visible wavelengths using microring resonators. Absorption products catalyzed by enzymes commonly used in bioassays are measured with microring resonator sensitive to the activity of individual enzymes. Chapter 6 builds on the work of the previous chapters to demonstrate microring measurements of optical absorption generated by bacteria growth. Results show the platform can be useful for fundamental studies on single bacteria. The final chapter includes a summary of the work and an outlook on the future of lab-on-a-chip devices