Optical interconnections on PCBs: a killer application for VCSELs

As a result of the constant improvement of performances and reliability of VCSEL-fabrication, parallel short distance optical interconnections are becoming more and more important. Integrating optical interconnections on a board level, covering distances from a few centimeters to a few meters, is however very challenging as the optical interconnection and mounting technology has to be integrated in existing printed circuit board manufacturing technology. Fiber based interconnections, using technologies as Fiber-In-Board and Fiber-based optical backpanels are already available, but new solutions for integrating a guided-wave based optical interconnection layer in a standard FR4-based electrical printed circuit board are emerging. These technologies are based on either organic materials or glass sheets integrated in the FR4-stack. Examples of both technologies will be presented and optical interconnections showing the feasibility of both technologies will be described. The interconnections will be realized using VCSEL-arrays and photodetector arrays which are flip-chip, mounted on the printed circuit boards. The coupling of light in and out of the optical layer in the FR4-stack is done using deflecting micro-optics realized in the optical layer, e.g. using laser-ablation.

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