A Caltech Library Service

High-Q Microresonators as Lasing Elements for Silicon Photonics


Borselli, Matthew Gregory (2006) High-Q Microresonators as Lasing Elements for Silicon Photonics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2EF5-QD36.


Although the concept of constructing active optical waveguides in crystalline silicon has existed for over twenty years, it is only in the past few years that silicon photonics has been given serious attention as a displacing technology. Fueled by the predicted saturation of "Moore's Law" within the next decade, universities and industries from all over the world are exploring the possibilities of creating truly integrated silicon opto-electronic devices in a cost effective manner. Some of the most promising silicon photonics technologies are chip-to-chip and intra-chip optical interconnects. Now that compact high-speed modulators in silicon have been achieved, the limiting factor in the widespread adoption of optical interconnects is the lack of practical on-chip optical sources. These sources are critical for the generation of the many wavelengths of light necessary for high-speed communication between the logical elements between and within microprocessors. Unfortunately, crystalline silicon is widely known as a poor emitter because of its indirect bandgap.

This thesis focuses on the many challenges in generating silicon-based laser sources. As most CMOS compatible gain materials possess at most 1 dB/cm of gain, much of our work has been devoted to minimizing the optical losses in silicon optical microresonators. Silicon microdisk resonators fabricated from silicon-on-insulator wafers were employed to study and minimize the different sources of scattering and absorption present in high-index contrast Si microcavities. These microdisks supported whispering-gallery modes with quality factors as high as 5 x 10^6, close to the bulk limit of lightly doped silicon wafers. An external silica fiber taper probe was developed to test the microcavities in a rapid wafer-scale manner. Analytic theory and numerical simulation aided in the optimization of the cavity design and interpretation of experimental results. After successfully developing surface chemistry treatments and passivation layers, erbium-doped glasses were deposited over undercut microdisks and planar microrings. Single-mode laser oscillation was observed and carefully characterized for heavily oxidized silicon microdisks. Dropped power thresholds of 690 nW, corresponding to 170 nW of absorbed power, were measured from gain-spectra and Light in-Light out curves. In addition, quantum efficiencies for these lasers were as high as 24%, indicating that this technology may be ready for further development into real-world devices.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:lasers; microdisks; quality factor; surfaces
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Painter, Oskar J.
Thesis Committee:
  • Painter, Oskar J. (chair)
  • Yariv, Amnon
  • Scherer, Axel
  • Vahala, Kerry J.
  • Gyure, Mark F.
Defense Date:17 May 2006
Record Number:CaltechETD:etd-05242006-085503
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2008
Deposited By: Imported from ETD-db
Deposited On:30 May 2006
Last Modified:17 Apr 2020 22:27

Thesis Files

PDF (MGB_thesis_v1_double_sided.pdf) - Final Version
See Usage Policy.

PDF (MGB_thesis_v1_single_sided.pdf) - Final Version
See Usage Policy.


Repository Staff Only: item control page