Evanescent Field Coupled Microdisk Cavities
Open Access
- Author:
- Li, Xia
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 02, 2007
- Committee Members:
- Nitin Samarth, Committee Chair/Co-Chair
Richard Wallace Robinett, Committee Member
Vincent Henry Crespi, Committee Member
Venkatraman Gopalan, Committee Member
Jayanth R Banavar, Committee Member - Keywords:
- photonic molecules
photonics
microdisk
laser
semiconductor
microcavity
cavity quantum electrodynamics - Abstract:
- This dissertation focuses on studies of spontaneous and stimulated emissions from whispering gallery mode (WGM) (Ga, Al)As/GaAs based microdisk cavities that are evanescent field coupled with each other. Microdisks are of great interest as test beds to demonstrate concepts in the fields of cavity quantum electrodynamics (CQED) and novel optoelectronics devices. We employ molecular beam epitaxy (MBE) to prepare the samples that have epitaxial heterostructures of (Ga, Al)As/GaAs. Then we use cleanroom processing techniques to fabricate the microdisk devices. We then perform static and dynamic optical spectroscopy measurements to investigate their optical properties. The first experiment in this thesis describes external strain engineering of the microdisk lasers to lower the lasing thresholds. A stressed silicon nitride (SiNx) thin film was deposited on the microdisk surfaces to provide an external compressive strain. Lasing thresholds were decided with static light-in light-out intensity plot and charge life time dynamics. The second and third experiment are both about evanescent field coupled microdisk cavities. We fabricated three types of twin coupled microdisk cavities: twin circular ones, twin elliptical ones coupled along the long axis and twin elliptical ones coupled along the short axis. Normal mode splitting was observed in these coupled cavities with a lower energy bonding mode and a higher energy antibonding mode. The second experiment characterizes the mode energy splitting as a function of different geometrical layout, excitation power and ambient temperature. We observed a clear correlation between the mode energy splitting and the splitting mode intensities. The mode splitting increases as the intensities increase, and vice versa. This correlation is a result of the evanescent field coupling. In the third experiement, we simulated the electromagnetic field patterns inside and outside the twin coupled microdisk cavities. In the simulation, we used a four-classe of symmetry to construct two nearly-degenerate bonding modes and two nearly-degenerate antibonding modes. The simulations predict directional and in-plane polarized emission from the bonding and the antibonding modes in the twin circular coupled microdisks. These predictions were confirmed by experiment. We also observed in-plane polarized emission patterns from the twin elliptical microdisks. However, these observations are not consistent with simulations. The fourth experiment uses a new method to measure the cavity quality factor of the microdisk. We prepared optical fiber tapers that have a few micron diameter and placed the tapers in the vicinity of the microdisk rim so that they are coupled through evanescent field. We passed a white light spectrum through the taper coupled with the microdisk. The transmission spectra clear show dips caused by the absorption from the microdisk cavity modes. Linewidth of the dips are limited by the spectrometer resolution, but this still gives a lower limit of the microdisk cavity quality factor, which is around 1.9×104.