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 on-chip 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 high-performance 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 $\mu$m chip-to-package 1-dB lateral alignment tolerance for coupling into a polymer waveguide with a cross-section of 20 × 25 $\mu$m$^2$. 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.

中文翻译：

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球透镜嵌入式贯穿封装通孔可实现硅光子中介层和板级互连之间的背面耦合

为基于硅光子学的板级光互连开发高效且密集集成的光耦合接口是 2.5D/3D 电光集成领域的关键挑战之一。实现跨封装/板级短距离互连的高速片上电光转换和高效光传输可以帮助克服传统电气 I/O 在带宽密度和功耗方面的限制，以实现高性能计算环境。在这种情况下，我们展示了一种新颖的光耦合接口，可将硅光子学与板级光互连集成在一起。我们表明，通过在有机封装基板上钻出的通孔中集成球透镜，从光子芯片上向下的方向性光栅衍射的光束可以耦合到具有良好对准公差的板级聚合物多模波导。实验的一个关键结果是 14 $\mu$m 芯片到封装 1-dB 横向对准公差，用于耦合到横截面为 20 × 25 的聚合物波导 $\mu$米$^2$. 对多个界面上的损耗分布进行了深入分析，并在由输出光栅、球透镜和聚合物波导组成的光学界面之间测量了 -3.4 dB 的耦合效率。此外，还表明通过调整耦合接口中的几个参数可以实现优于 -2 dB 的效率。报告了光学接口的制造和相关测量，并通过模拟结果进行了验证。