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https://hdl.handle.net/2142/46532
Description
Title
Silicon Nitride Waveguide Smoothing Techniques
Author(s)
Lu, Ching-Ying
Contributor(s)
Goddard, Lynford
Issue Date
2011-12
Keyword(s)
waveguides
silicon nitride waveguides
smoothing techniques
distributed Bragg reflectors
microring resonators
diode lasers
Abstract
Integrating a distributed Bragg reflector (DBR) inside a microring resonator (MRR) provides several advantages over linear DBRs such as compact size, suppressed side mode ripples, and narrower linewidth. However, sidewall roughness created during fabrication would cause reflection at unwanted resonance wavelength and introduce additional scattering loss to the devices. In this work, wet etching by hot phosphoric acid was implemented on photolithography defined Si3N4 strip waveguides that have widths similar as actual DBR-MRR devices patterned by e-beam lithography. The strategy is based on the difference in reaction rates between peaks and troughs of a rough surface. To characterize the devices, images of waveguide cores were taken by scanning electron microscope (SEM) from the top and side. In addition, the propagation losses of the waveguides were measured by coupling light from a tunable laser in and out of the waveguide with tapered fibers. After the smoothing was implemented, the image results showed a significant reduction in sidewall roughness and the propagation loss was decreased. In the future, the smoothing technique will be used to improve the performance of the microring mirror. In addition, smoothing techniques for other waveguide materials will be investigated. Finally, the ultimate goal is intergrating DBR-MRRs as in-line mirrors to make low threshold, narrow linewidth diode lasers.
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