Zhu, TiechengPart I: Layer Peeling/Adding Algorithm and Complex Waveguide Bragg Grating For Any Spectrum Generation A Layer Peeling/Adding algorithm for designing optical lters is not only de- veloped theoretically but also demonstrated experimentally. Unlike the conventional design approaches which can handle only limited spectral proles, the algorithm pre- sented here is capable of generating transmission/re ection spectrum 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 aperiodic varying waveguide widths, is capable of removing a large number of randomly-distributed wavelengths simultaneously. Two generations of CWBGs are designed and fabri- cated to remove 20 and 47 notches respectively, with spectral precision better than 0:1 nm, suppression ratios larger than 15 dB, and 3-dB widths of 0.3 nm. Among CWBG's various potential applications, we highlight its use for eliminating the mul- tiple OH emission lines from the Earth's atmosphere for ground-based astronomical observations. Part II: Fiber-to-Waveguide Coupler With Ultra High Coupling Efficiency An easy-to-fabricate but very efficient ber-to-waveguide coupler is theoreti- cally analyzed and experimentally demonstrated. In this design, light from a single- mode UHNA3 ber 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 m and 3.6 m respectively are obtained between the ber and the waveguide coupler. Coupling efficiencies are also characterized using Si3N4/SiO2 waveguides and both SMF28 ber and SM1500G80 ber. 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.enDissertationOptics