Low loss and high tolerance out-of-plane single-mode optical interconnections in glass interposers

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Chou, Chia Te
Tummala, Rao R.
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The specific focus of this dissertation research is to design and demonstrate low loss and high tolerance out-of-plane single-mode fiber-to-chip optical interconnections in glass to address three challenges in performance, density, and cost: 1) high fiber-to-chip coupling loss, 2) lack of high density fiber-to-chip coupling solutions, and 3) high cost active fiber alignment. Four research tasks are defined, one task each to address each challenge, and a fourth task focused on a demonstration test vehicle. The optimized optical interconnection is able to achieve < 2 dB of coupling loss at fiber-like alignment tolerance. It includes a parallel-processed 45° turning mirror using moving mask lithography. The novel moving mask process ensures that the turning mirror and the pads for chip assembly are planar aligned with only micron level offset. In addition, fiber alignment u-grooves are fabricated in glass with aims to allow passive fiber assembly. Although the research results did not meet the passive alignment criterion, future direction has been defined based on these results. A co-design process flow has been developed to optimize the demonstration test vehicle, which emulates a 400 Gbps optical transceiver module. The test vehicle features optimized electrical interconnects at < 0.1 dB/mm insertion loss, thermal vias to keep laser temperature under 80 °C, as well as the low loss and high tolerance out-of-plane optical interconnections as discussed. The results demonstrate compelling evidences in the cost, performance, and density advantages of glass interposer technology for photonics applications.
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