Optik mikroçınlaçlar ile opto-akışkan algılamaları

In this thesis, detection of various fluids using optical microresonators is described. As optical microresonators, different geometries are used such as microdisks, microrings, microspheres, and microcylinders. The sensing mechanism relies on the change of optical properties, when there is a change in the amount of quantity of interest. Modes of optical microresonators, also known as whispering gallery modes (WGMs), are analyzed for the changes, and their spectral positions or quality factors are tracked, and employed as sensitive indicators of the changes. Sensing of air humidity and hydrogen gas, liquid refractometry, and contamination detection in liquid microspheres are demonstrated in the context of this thesis. In humidity sensing work, air humidity is sensitively detected using SU-8 polymer microdisk resonators. These resonators are produced with a single-step fabrication, and they provide a repeatable and long-term-stable sensing platform. When these SU-8 microresonators are coated with Pd, they can also operate as hydrogen sensors. Using this idea, hydrogen gas sensing using Pd-coated SU-8 microdisk resonators is presented in the hydrogen concentrations well below its flammable limit of 4%. Apart from gas sensing, detection in a liquid environment is also studied in two studies. In the first study, the refractive index of the liquid environment is detected using optical fiber resonators (OFRs). These OFRs are easily fabricated from standard optical fibers, and they provide refractive index sensitivity in the order of 10-5 RIU. Refractive index detection results, as well as the analytical calculations of the expected response of OFR sensors, are discussed. In the second study, contamination of the oil droplets is investigated for sunflower seed oil-olive oil mixtures. In addition, benzyl benzoate (BB) droplets are investigated. WGM shifts due to dissolution of the BB droplets, as well as incoming and outgoing small particles are discussed. The experiments performed in microfluidic chips and the droplets are held in position using optical trapping. Based on the Q-factors of the droplets, the material contained inside the droplets can be predicted. Finally, hydrogen gas sensing using polymer and Pd-coated OFRs is presented. These OFRs present even higher sensitivity than the Pd-coated SU-8 microdisk resonators. OFR sensors are easier to prepare and more flexible than the SU-8 microdisk sensors. Hydrogen concentrations down to 1000 ppm are successfully detected, with a potential detection limit less than 100 ppm. For all these sensing applications, detection results and underlying sensing mechanisms are presented, and they are compared with the state-of-the-art WGM-based sensors.