Applications of optical micro-ring and micro-disk resonators as physical, chemical, and biological sensors

This dissertation presents the applications of optical micro-ring and micro-disk resonators as various sensors in physical, chemical, and biological applications. This work describes the functioning of 5 different sensors and suggests ways for optimizing the performance of each of them. All of these sensors work on the principle of shift in the resonance wavelength of the micro-ring or the micro-disk in response to an external physical, chemical or biological perturbation.; The first portion describes the functioning of a ring resonator device and details the various parameters which are important in sensing applications. Then a strain sensor, an accelerometer, and a humidity sensor based on polymer micro-ring resonator are described. The strain sensor has a sensitivity of 0.32pm/mu&egr; and a dynamic range of 17000mu&egr;, the accelerometer has a sensitivity of 31pm/g and a dynamic range of +/-7g, whereas, the humidity sensor has a sensitivity of 16pm/%RH and a dynamic range of 72%. The dependency of each of their sensitivities and dynamic ranges on various geometrical parameters are also discussed. The response time of the humidity sensor was reduced to less than 200ms which enables us to utilize this device as a human breathing monitor in hospitals.; The second portion of the thesis, discusses the possible incorporation of ultra-high-Q silica micro-disk resonators, developed at the Jet Propulsion Laboratory by Mr. Thanh M. Le, into various sensing devices. This device is first proposed as a biosensor for detecting trace amounts of specific biomolecules. The first experiments are performed for developing the silica micro-disk as a biosensor. In this experiment, the sensitivity of the micro-disk as a function of change in refractive index of the surrounding medium is demonstrated. The observed sensitivity is 11.82nm/RIU (Refractive Index Units). Then, the possibility of using this device as a specific biosensor is explored. The method for surface functionalization of the micro-disk is also outlined. From the calculations, this device can sense biomolecules with concentrations as low as 10 6cm-2. Finally, the silica microdisk resonator is proposed as a sensitive hydrogen gas sensor based on the expansion of palladium metal on absorbing hydrogen gas. This sensor has a calculated sensitivity of 0.227pm/%H2 concentration and it can detect hydrogen concentration down to 5ppm. Its sensitivity as a function of various geometrical parameters is also studied.; All the above described sensors are also sensitive to temperature changes. Various techniques for eliminating this temperature sensitivity are also discussed.; Finally, in the conclusions, various methods of multiplexing these sensors for multi-point sensing are also outlined.