Chip-to-chip communication by optical routing inside a thin glass substrate

Abstract

Most optical waveguide technologies on board level are using polymer materials. The drawback for these approaches are issues with post packaging processes because of thermal instabilities under thermal load, high optical loss in the infrared wavelength range and process challenges in case of single mode waveguide geometries. A planar gradient index glass waveguide, optical mirror and refractive optic integration technology on wafer level will be presented here. 3D optical interconnects result inside a commercial available thin glass sheet. The waveguides are single mode and processed by a two step thermal ion-exchange technology. The propagation loss at 1310 nm is 0.2 dB/cm. The waveguides characterize a symmetric gradient index profile. Low coupling loss results between the waveguide and single mode optical fibers as well as optoelectronic components because of excellent mode matching. Different refractive optics are implemented by a field-assisted ion-exchange technology. An optical mirror is processed by laser ablation technology. The integration of waveguides, lenses and mirrors into an optical material like thin glass benefits of very high integration density and reliability. Processing thin glass by wafer level techniques in a planar way makes it compatible with post processes (e.g. thin film and assembling processes). In this approach thin glass is the platform for photonic integrated circuits, VCSELs and photodetectors. Thus flip-chip mounted photonic devices become optically interconnected directly by 3D optical pathways inside the thin glass substrate. For this approach different building blocks and interfaces in between are designed and proofed by optical simulations. Building blocks are VCSEL waveguide coupling, waveguide detector interface, beam collimation for interposer board interface and PIC waveguide coupling. The concept is verified by experimental results. The glass based packaging concept, the design of each building block and the technologies for waveguide, mirror and lens integration are presented in this paper.