Abstract
Multimode polymer waveguides are promising for use in board-level optical
interconnects. In recent years, various on-board optical interconnection architectures
have been demonstrated making use of passive routing waveguide components.
In particular, 90° bends have played important roles in complex waveguide layouts
enabling interconnection between non co-linear points on a board. Due to the
dimensions and index step of the waveguides typically used in on-board optical
interconnects, low-loss bends are typically limited to a radius of ~ 10 mm. This
paper therefore presents the design and fabrication of compact low-loss waveguide
bends with reduced radii of curvature, offering significant reductions in
the required areas for on-board optical circuits. The proposed design relies
on the exposure of the bend section to the air, achieving tighter light confinement
along the bend and reduced bending losses. Simulation studies carried out
with ray tracing tools and experimental results from polymer samples fabricated
on FR4 are presented. Low bending losses are achieved from the air-exposed
bends up to 4 mm of radius of curvature, while an improvement of 14 μm in the 1 dB
alignment tolerances at the input of these devices (fibre to waveguide coupling)
is also obtained. Finally, the air-exposed bends are employed in an optical
bus structure, offering reductions in insertion loss of up to 3.8 dB.
© 2013 IEEE
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