Abstract
We designed and demonstrated a tri-layer Si3N4/SiO2 photonic integrated circuit capable of vertical interlayer coupling with arbitrary splitting ratios. Based on this multilayer photonic integrated circuit platform with each layer thicknesses of 150 nm, 50 nm, and 150 nm, we designed and simulated the vertical Y-junctions and 3D couplers with arbitrary power splitting ratios between 1:10 and 10:1 and with negligible(< -50 dB) reflection. Based on the design, we fabricated and demonstrated tri-layer vertical Y-junctions with the splitting ratios of 1:1 and 3:2 with excess optical losses of 0.230 dB. Further, we fabricated and demonstrated the 1 × 3 3D couplers with the splitting ratio of 1:1:4 for symmetric structures and variable splitting ratio for asymmetric structures.
Highlights
Si3N4(core) and SiO2(cladding) based optical waveguides are attractive because of its relatively low propagation loss [1] than silicon waveguides and small footprints [2] compared to silica waveguides
We designed and demonstrated a tri-layer Si3N4/SiO2 photonic integrated circuit capable of vertical interlayer coupling with arbitrary splitting ratios
Acknowledgments Fabrication of the devices utilized the facilities at the Marvell Nanofabrication Laboratory (Berkeley, CA) and at the Center for Nano-MicroManufacturing (Davis, CA)
Summary
Si3N4(core) and SiO2(cladding) based optical waveguides are attractive because of its relatively low propagation loss [1] than silicon waveguides and small footprints [2] compared to silica waveguides. By repeating the optimized Si3N4 deposition and waveguide fabrication [2] while maintaining reasonable wafer bowing, we introduce additional Si3N4 layers to further reduce crosstalk and losses when multiple waveguides need to cross and intersect inevitably in single layer photonic integrated circuits. We design non-identical layer thicknesses to utilize the variable confinement factor and mode sizes of Si3N4 for functional purposes, such as large mode size for optical gyroscope with ultra-low propagation loss [12] and small mode size for compact arrayed waveguide grating with tight bending [13]. The proposed tri-layer Si3N4 3D couplers are more attractive because of its simplified design for low loss couplers compared to the traditional silicon Y-junctions [14] and 2D asymmetric Y-junctions [15], as well as the good fabrication tolerance compared to the photonic crystal Y-junctions [16]
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