LAYER PEELING/ADDING ALGORITHM AND COMPLEX WAVEGUIDE BRAGG GRATING FOR ANY SPECTRUM GENERATION & FIBER-TO-WAVEGUIDE COUPLER WITH ULTRA HIGH COUPLING EFFICIENCY
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Abstract
Part 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.