Event
Ph.D. Dissertation Defense: Tiecheng Zhu
Wednesday, December 14, 2016
10:00 a.m.
AVW 2460
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: Ph.D. Dissertation Defense
Name: Tiecheng Zhu
Committee:
Professor Mario Dagenais (Chair)
Professor Chris Davis
Professor Martin Peckerar
Professor Thomas Murphy
Professor Sylvain Veilleux (Dean's Representative)
Date/Time: Wed, December 14, 2016 at 10:00 am
Location: AVW 2460
Title: Layer Peeling/Adding Algorithm and Complex Waveguide Bragg Grating For Any Spectrum Regeneration & Fiber-to-Waveguide Coupler With Ultra High Coupling Efficiency
Abstract:
A Layer Peeling/Adding algorithm for designing optical filters is not only developed theoretically but also demonstrated experimentally. Unlike the conventional design approaches which can handle only limited spectral profiles, the algorithm presented here is capable of regenerating transmission/reflection spectra of any shape. As a proof of demonstration, Complex Waveguide Bragg Gratings (CWBG) are designed, fabricated and characterized using the algorithm. The CWBG, which is implemented as a single-mode Si3N4/SiO2 waveguide grating with aperodic varying waveguide widths, is capable of removing a large number of randomly-distributed wavelengths simultaneously. Two generations of CWBGs are shown to remove 20 and 47 notches, with spectral precision better than +-0.1 nm, suppression ratios larger than 15 dB, and 3-dB width of 0.3 nm. Among the CWBG's various potential applications, we highlight its use for eliminating the OH emission lines from the Earth's atmosphere for ground-based astronomical observations.
An easy-to-fabricate but very efficient fiber-to-waveguide coupler is theoretically analyzed and experimentally demonstrated. In this design, light from a single-mode fiber can be butt-coupled into a single-mode high-index-contrast Si3N4/SiO2 waveguide with a measured coupling efficiency of 96 % at the wavelength of 1550 nm, and > 90 % in the spectral range from 1450 nm to 1650 nm. Large horizontal and vertical alignment tolerances of 3.8 um and 3.6 um respectively are obtained between the fiber and the waveguide coupler. All these experimental results agree well with simulations. The waveguide coupler also features ease of end-facet cleaving, and can be used in ultra-broadband high coupling efficiency applications.
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