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

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.