TITLE:
Optimal VIA Placement in Under Filled Embedded Multimode Waveguides
AUTHORS:
Nicholas Riegel, Matthew Howard, Christopher Middlebrook
KEYWORDS:
Multimode Optical Waveguides; Optical Vertical Interconnect Assembly
JOURNAL NAME:
Optics and Photonics Journal,
Vol.3 No.6,
October
22,
2013
ABSTRACT: The self-imaging property of multimode waveguides creates
a challenging problem when finding the optimal placement position of an out-of-plane
coupler for embedded waveguides. This problem is compounded when the waveguides
are coupled using a small input such as a vertical cavity surface emitting laser
(VCSEL) or a single mode fiber where only some of the modes are generated. When
the waveguide system is under filled, the coupling efficiency for the optical vertical
interconnect assembly (VIA) can vary by as much as 6.2 dB depending on the length
of the proceeding waveguide due to different output fields from the self-imaging
property. This requires sweeping each individual VIA over the entire range of possible
coupler positions to find the total maximum coupling efficiency. This process increases
in complexity when a VIA supports several parallel channels all having a different
optical path length. If a VIA can be placed in a calculated position from the end
of a terminated embedded waveguide dependent upon the modal structure then blind
pick and place methods may be used. The optimal coupler placement was determined
based on smallest average VIA attenuation, smallest attenuation variance, and worse-case
alignment scenario.