UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Silicon photonic components using sub-wavelength gratings and other periodic structures Yun, Han


Sub-wavelength gratings (SWGs) and periodic waveguides play important roles in integrated optics. These periodic structures have been employed in integrated optical power couplers and wavelength filters which are key components for optical communication and sensing systems. This dissertation is a theoretical and experimental study of high performance silicon photonic SWG-based adiabatic couplers, SWG contra-directional couplers (SWG CDCs), and polarization-rotating Bragg grating (PRBG) filters that use these periodic structures. Mode-evolution-based couplers, also known as adiabatic couplers, are fundamental building blocks for optical communications applications such as broadband optical switches and electro-optic modulators. In this thesis, to begin with, adiabatic 3 dB couplers using conventional silicon-on-insulator (SOI) ridge and strip waveguides are studied and demonstrated for 100-mm-long mode-evolution regions and 100 nm operating bandwidths with splitting imbalances <0.5 dB. Next, SWG waveguides are explored and employed to design and demonstrate a compact, broadband SWG 3 dB adiabatic coupler with a 20-mm-long mode-evolution region, a 130 nm bandwidth, and a splitting imbalance <0.4 dB. Finally, SWG-assisted strip waveguides are studied and utilized for a compact, ultra-broadband, adiabatic 3 dB coupler that has a 15-mm-long mode-evolution region, a 185 nm bandwidth, a splitting imbalance <0.3 dB, low insertion losses (ILs) <0.11 dB, and high fabrication tolerances. The SWG-assisted adiabatic 3 dB couplers have smaller footprints with much wider operating bandwidths and much lower ILs than their alternatives, i.e., directional couplers and multi-mode interference couplers. SWG CDCs are proposed and demonstrated to provide broadband wavelength filtering for applications such as add-drop filters and bandwidth-tunable filters. These devices provide square-shaped, drop-port responses with 3 dB bandwidths >30 nm and sidelobe suppression ratios >50 dB. PRBGs are proposed and demonstrated using periodic corner corrugations on single-mode SOI strip waveguides for polarization-insensitive wavelength filtering. A PRBG band-rejection filter is demonstrated with a 3 dB bandwidth of 2.63 nm, an extinction ratio (ER)>27 dB, and a low IL<1 dB for both the transverse electric and transverse magnetic modes. A PRBG band-pass filter is also demonstrated using phase-shifted PRBGs and achieves a 3 dB bandwidth of 0.26 nm and an ER of 19 dB for both modes.

Item Media

Item Citations and Data


Attribution-NonCommercial-NoDerivatives 4.0 International