Prototyping of pluggable out-of-plane coupling components for multilayer board-level optical interconnections

Board-level optical interconnects offer a possible solution to the bandwidth problems that electrical interconnects are facing in the near future. The integration of the optical interconnection to the board level is done by integrating one or more optical layers on a printed circuit board (PCB). We present Deep Proton Writing (DPW) as a generic rapid prototyping technology for the fabrication of a micro-optical coupling component incorporating a 45° micro-mirror that can be readily inserted into a multilayer optical waveguiding structure integrated on a PCB. Micro-cavities are ablated into the optical layers to accommodate the discrete out-of-plane coupler. The advantage of using a discrete component is that micro-lenses can be incorporated to increase the coupling efficiency with a guaranteed perfect alignment of the lens and the micro-mirror. In case lenses are integrated in the coupling component, the layer thickness of top and bottom optical layer has to be in accordance with the designed value and the alignment of the component with respect to the waveguide is critical. In the case the lenses are not used and a metallized mirror facet is used for out-of-plane coupling, there is quite a large tolerance on the thickness of the layers and the alignment accuracy of the component. The surface quality of the fabricated components was characterized and the coupling efficiency of the out-of-plane coupling components was be measured in a fiber-to-fiber coupling scheme. The coupling component is prototyped in PMMA material, which is not compatible with standard PCB manufacturing. This should however not be considered as a limiting factor since the DPW process is compatible with mass replication technologies such as hot embossing or micro-injection moulding and the master as such can be replicated in a variety of hightech plastics.