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A successful implementation of optics into printed circuit boards
requires a precise passive alignment of optical elements (optical
transceivers, optical connectors) relative to the optical waveguides
in the board. We tackled this challenge with a novel concept that
allows the passive alignment with a precision of a few micrometers.
Markers, structured into a copper layer during manufacturing,
are used as a position reference for the polymer waveguide fabrication
and for the formation of mechanical alignment features. These are
formed by laser ablation, a standard process for via formation in
printed circuit boards. Thereby, we exploit the fact that the laser
light is reflected at the copper surface, such that the copper marker
acts as a mask for the laser beam. An opening in the copper marker
can then be used to define an accurately positioned alignment slot,
independently of the low positioning accuracy of the drilling laser.
In order to provide a standardized interface to the optical printed
circuit board, we realized MT adapters that snap into the alignment
slots. We measured a standard deviation < 4 µm for the
in-plane and out-of-plane misalignments of the MT adapter with respect
to the optical waveguides.
The passive alignment concept is based on established printed
circuit board manufacturing processes, which is crucial for the
development of a low-cost optical interconnect technology platform.
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