Tri-layer gradient and polarization-selective vertical couplers for interlayer transition

High density vertical optical interconnects for passive assembly

The co-packaging of optics and electronics provides a potential path forward to achieving beyond 50 Tbps top of rack switch packages. In a co-packaged design, the scaling of bandwidth, cost, and energy is governed by the number of optical transceivers (TxRx) per package as opposed to transistor shrink. Due to the large footprint of optical components relative to their electronic counterparts, the vertical stacking of optical TxRx chips in a co-packaged optics design will become a necessity. As a result, development of efficient, dense, and wide alignment tolerance chip-to-chip optical couplers will be an enabling technology for continued TxRx scaling. In this paper, we propose a novel scheme to vertically couple into standard 220 nm silicon on insulator waveguides from 220 nm silicon nitride on glass waveguides using overlapping, inverse double tapers. Simulation results using Lumerical's 3D Finite Difference Time Domain solver are presented, demonstrating insertion losses below -0.13 dB for an inter-chip spacing of 1 µm; 1 dB vertical and lateral alignment tolerances of approximately 2.6 µm and ± 2.8 µm, respectively; a greater than 300 nm 1 dB bandwidth; and 1 dB twist and tilt tolerances of approximately ± 2.3 degrees and 0.4 degrees, respectively. These results demonstrate the potential of our coupler for use in co-packaged designs requiring high performance, high density, CMOS compatible out of plane optical connections.

Interlayer Slope Waveguide Coupler for Multilayer Chalcogenide Photonics

The interlayer coupler is one of the critical building blocks for optical interconnect based on multilayer photonic integration to realize light coupling between stacked optical waveguides. However, commonly used coupling strategies, such as evanescent field coupling, usually require a close distance, which could cause undesired interlayer crosstalk. This work presents a novel interlayer slope waveguide coupler based on a multilayer chalcogenide glass photonic platform, enabling light to be directly guided from one layer to another with a large interlayer gap (1 µm), a small footprint (6 × 1 × 0.8 µm3), low propagation loss (0.2 dB at 1520 nm), low device processing temperature, and a high bandwidth, similar to that in a straight waveguide. The proposed interlayer slope waveguide coupler could further promote the development of advanced multilayer integration in 3D optical communications systems.