Ter Hoe Loh

Design and Analysis of Optical Coupling Between Silicon Nanophotonic Waveguide and Standard Single-Mode Fiber Using an Integrated Asymmetric Super-GRIN Lens

Comprehensive design and analysis of optical coupling between silicon nanophotonic waveguide and standard single-mode fiber is presented. The coupling structure employs an integrated asymmetric graded refractive index (GRIN) lens deposited at the end of the tapered waveguide, and the GRIN lens has an optimized refractive index profile with a super high numerical aperture for aberration-free subwavelength focusing/collimating. The influence of end-facet reflection of the GRIN lens on the coupling efficiency is investigated. The optimized GRIN lens with a proper antireflection coating shows a coupling efficiency of ~90% between a 300-nm-thick silicon nanophotonic waveguide and a standard single-mode fiber. A 3-D modeling and simulation of the GRIN lens is carried out. The influences of fiber displacement and angular misalignment on the coupling efficiency are analyzed. The overall systematic design and analysis indicate that this integrated GRIN-lens-based optical coupler offers a compact and efficient solution for nanophotonic waveguide coupling with a good alignment tolerance.

Ultra-compact multilayer Si/SiO 2 GRIN lens mode-size converter for coupling single-mode fiber to Si-wire waveguide

We report on the fabrication and experimental demonstration of optical mode size transformation between standard single-mode fiber and 0.26 μm-thick Si-waveguide by 12 μm-thick Si/SiO(2) multilayer on-chip GRIN lens of lengths 16 μm or 24 μm butt-joint to 10 μm-wide terminated Si-waveguide. The overall coupling loss of the coupler was measured to be 3.45 dB in which the Fresnel reflection loss is estimated to be 2dB at the GRIN-lens/air interface. The on-chip integrated GRIN lens opens up the feasibility of a low cost passive aligned fiber-pigtailed electronic-photonics integrated circuits platform.

Heterogeneously integrated III-V laser on thin SOI with compact optical vertical interconnect access.

A new heterogeneously integrated III-V/Si laser structure is reported in this report that consists of a III-V ridge waveguide gain section on silicon, III-V/Si optical vertical interconnect accesses (VIAs), and silicon-on-insulator (SOI) nanophotonic waveguide sections. The III-V semiconductor layers are introduced on top of the 300-nm-thick SOI layer through low temperature, plasma-assisted direct wafer-bonding and etched to form a III-V ridge waveguide on silicon as the gain section. The optical VIA is formed by tapering the III-V and the beneath SOI in the same direction with a length of 50 μm for efficient coupling of light down to the 600 nm wide silicon nanophotonic waveguide or vice versa. Fabrication details and specification characterizations of this heterogeneous III-V/Si Fabry-Perot (FP) laser are given. The fabricated FP laser shows a continuous-wave lasing with a threshold current of 65 mA at room temperature, and the slope efficiency from single facet is 144  mW/A. The maximal single facet emitting power is about 4.5 mW at a current of 100 mA, and the side-mode suppression ratio is ∼30  dB. This new heterogeneously integrated III-V/Si laser structure demonstrated enables more complex laser configuration with a sub-system on-chip for various applications.

CMOS compatible integration of Si/SiO2 multilayer GRIN lens optical mode size converter to Si wire waveguide

We present a CMOS compatible mass manufacturable, compact Si/SiO(2) multilayer GRIN lens mode size converter from standard single mode fiber to 300 nm-thick Si waveguide. The fiber-to-GRIN lens coupling loss is 2.6 ± 0.3 dB (coupling efficiency: 51~60%) with optimized focal length of 11.6~11.8 μm and Si/SiO(2) multilayer thickness of 7.4 μm.

CMOS Compatible Integration of Si/SiO2 Multilayer GRIN Lens Optical Mode Size Converter to SOI-Based Waveguide

Vertical mode size conversion from 300nmthick Siwaveguide to 6to7um, coupling to singlemode fiber was demonstrated using CMOS-compatible onchip GRIN lens (length:11.5um). GRIN lens to fiber coupling loss of 2.9dB was achieved.

Design, fabrication and demonstration of heterogeneously III-V/Si laser with a compact optical vertical interconnect access

A new heterogeneously integrated III-V/Si laser structure is reported in this letter, which consists of a III-V ridge waveguide gain section on silicon, III-V/Si optical vertical interconnect accesses (VIAs) and silicon-oninsulator (SOI) nanophotonic waveguide sections. The III-V semiconductor layers are introduced on top of the 300 nm thick SOI layer through low temperature, plasma assisted direct wafer-bonding and etched to form III-V ridge waveguide on silicon as the gain section. The optical VIA is formed by tapering the III-V and the beneath SOI in the same direction with a length of 50 μm for efficient coupling of light down to the 600 nm wide silicon nanophotonic waveguide or vice versa. Fabrication details and specification characterizations of this heterogeneous III-V/Si Fabry–Pérot (FP) laser are given. The fabricated FP laser shows a continuous-wave lasing with a threshold current of 65 mA at room temperature and the slope efficiency from single facet is 144 mW/A. The maximal single facet emitting power is about 4.5 mW at a current of 100 mA and the side-mode suppression ratio is ~30 dB. This new heterogeneously integrated III-V/Si laser structure demonstrated enables more complex laser configuration with a sub-system on-chip for various applications.

Integration of Si/SiO 2 multilayer GRIN lens optical mode-size converter on SOI-based waveguides

A low cost and CMOS-process compatible solution capable of passive-alignment coupling of singlemode optical fiber (SMF) to silicon-on-insulator (SOI) based photonic waveguide (size: sub-μm) is critical for realization and acceptance of fiber-pigtailed SOI-based electronics/photonics integrated circuits (EPIC) chips for mass applications in optical interconnects, optical information processing and sensing. In this work, we propose and demonstrate monolithic integration of an ultra-compact Si/SiO2 multilayer super-high numerical-aperture (NA) graded-index (MLS-GRIN) lens mode-size converter on SOI-based waveguide platform. The MLS-GRIN lens, with longitudinal focal-length of 20μm, total stack height of 8μm, and simulated NA better than 3, converts optical mode size vertically from SMF (core-φ ∼9μm) to 300nm-thick SOI waveguide by an engineered near-parabolic refractive index profile formed by varying the thickness ratio of alternating Si/SiO2 layers, while keeping the thicknesses of Si and SiO2 less than quarter of optical wavelength in the medium. The horizontal mode size conversion is performed by lateral up-taper of Si-waveguide prior to MLS-GRIN lens on the chip.

Realization of multilayer Si/SiO 2 super-high N.A. GRIN lens on Si-waveguide coupling to single-mode optical fibre

Vertical optical mode-size transformation from 260nm-thick Si-nanowaveguide to 10∼12µm matching the single-mode-fibre-core has been demonstrated using compact multilayer Si/SiO<inf>2</inf> asymmetric GRIN lens (length:∼24µm). GRIN lens to single-mode-fibre practical coupling loss of −3.45 dB was achieved.

Design and Fabrication of Multilayer Si/SiO 2 Super-High N.A. GRIN Lens for Nanowaveguide to Optical Fiber Coupling

Compact multilayer Si/SiO 2 asymmetric GRIN lens (length:10~20?m) for vertical optical mode-size transformation from sub-0.5?m of nanowaveguide to ~10?m of single-mode-fiber, is proposed and designed. We report success in deposition and etching of 6~8?m multilayer Si/SiO 2 .