Ball Lens Embedded Through-Package Via To Enable Backside Coupling Between Silicon Photonics Interposer and Board-Level Interconnects

Abstract

Development of an efficient and densely integrated optical coupling interface for silicon photonics based board-level optical interconnects is one of the key challenges in the domain of 2.5D/3D electro-optic integration. Enabling high-speed onchip electro-optic conversion and efficient optical transmission across package/board-level short-reach interconnections can help overcome the limitations of a conventional electrical I/O in terms of bandwidth density and power consumption in a highperformance computing environment. In this context, we have demonstrated a novel optical coupling interface to integrate silicon photonics with board-level optical interconnects. We show that by integrating a ball lens in a via drilled in an organic package substrate, the optical beam diffracted from a downward directionality grating on a photonics chip can be coupled to a board-level polymer multimode waveguide with a good alignment tolerance. A key result from the experiment was a 14 µm chipto-package 1-dB lateral alignment tolerance for coupling into a polymer waveguide with a cross-section of 20×25 µm 2 . An in-depth analysis of loss distribution across several interfaces was done and a -3.4 dB coupling efficiency was measured between the optical interface comprising of output grating, ball lens and polymer waveguide. Furthermore, it is shown that an efficiency better than -2 dB can be achieved by tweaking few parameters in the coupling interface. The fabrication of the optical interfaces and related measurements are reported and verified with simulation results.

Compact packaged silicon photonic Bragg grating sensor based on a ball lens interface

“…After the validation experiments, a robust optical interface was realized which involved fabricating a suitable holder in which a commercial ball lens can be mounted and precisely aligned with respect to both the interfacing fiber and the PIC. Here, we propose a conically-shaped cavity as ball lens holder, drastically improving the ball lens positioning accuracy compared to a laser-ablated through-via realized in previous work [14]. By controlling the slope and dimensions of the conical cavity, the ball lens can be positioned at the desired x, y and z coordinates as dictated by the design.…”

Design, fabrication, and characterization of integrated optical through-silicon waveguides for 3D photonic interconnections

“…OTSWs can be integrated on SOI photonics platforms by performing localized backside etching, where the waveguide lands either on an optoelectronic component such as a VCSEL or a photodetector, or a passive component such as an integrated grating coupler that can steer the incoming radiation into a planar silicon nanowaveguide [19,20]. However, for the initial purpose of characterizing only the waveguides, a pure silicon wafer patterned with a 4 µm SiO2 mask was chosen.…”

Laser Written Glass Interposer for Fiber Coupling to Silicon Photonic Integrated Circuits

“…3D electro-optic integration [6]. Edge coupling provides a relatively high coupling efficiency of -2 dB to lensed fibers, a 1 dB bandwidth of more than 100 nm, and a low polarization dependent loss (< 0.5 dB) [3].…”