Whispering gallery modes in layered microspheres: mode structure, thermal response, and reactive sensing

• Author / Creator

  Zhi, Yanyan

• This thesis focuses on the physics of the whispering gallery modes (WGMs) of silica microspheres coated with a layer of fluorescent silicon quantum dots (Si QDs). The basic theory associated with these structures was explored, and we showed how the important physical parameters such as the quality factor (Q factor), resonance wavelengths, electric field profile, and thermal properties can be straightforwardly calculated. The QD coating plays a major role in controlling each of these key parameters. The QDs also provide a fluorescent source which can couple to the WGMs of the microsphere, avoiding the complexity and fragility associated with coupling via an “evanescent” field. After a thorough discussion of the experimental issues associated with the fabrication and measurement of these structures, we next showed how the cold-cavity modes are related to the WGMs observed in the fluorescence spectrum. Then we examined theoretically the basic properties of the WGMs, their thermal response, and the sensing capabilities associated with these structures. Based on the theory, a microsphere demonstrated extreme stability against local temperature fluctuations. Finally, the refractometric sensor response of the coated microsphere devices was studied. This required the design of different fluidic environments to test the sensor response. The detection limits approached 10^{-5} refractive index units, which appeared to be limited mainly by the wavelength shift resolution of the analysis method and by mechanical drift. Finally, outstanding issues and potential future directions were discussed.

• Subjects / Keywords

  • Whispering gallery modes
  • Microsphere
  • Silicon quantum dots
  • Mode structure
  • Thermal stability
  • Refractometric sensing

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3J95T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.