Page 50 - Chip Scale Review_January February_2023-digital

loads. We studied the fiber stress
response on the ribbon array for various
boot materials and geometries, and
presented some of the results of design
optimization performed on a simplified
quasi-2D model to take advantage of the
boot-fiber system uniformity along its
middle section to minimize fiber stress
under a side pull force.
Preliminary studies showed the
benef its of a boot with a tapered
Figure 12: Description of the loading conditions used for boot optimization. shape using softer material—it tends
to distribute the stress. The loading
of the bending control of the fibers to act condition is applied sequentially as
as a strain relief mechanism. However, we described in Figure 12, with a first
must be careful that the fiber curvature and axial load before an imposed rotation
anchoring forces do not exceed the allowable of 90 degrees to reproduce the side pull
thresholds. The benefit of the initial bend test on the fiber. The initially applied
of the fibers are demonstrated [1], and an tensile axial force prevents local bending
optimization was performed to balance and excessive unbalanced forces,
the stress for the optimal strain relieving both of which improve the stability
effect. The fiber bends and radii are the best of the simulation. A morphing model
indicators to track the fiber loads and ensure was used as a strategy to optimize
that they are within our specification. All the boot geometric parameter, where
these values need to be below the long-term the finite element mesh is deformed
and short-term bending radius thresholds for using a combination of six smooth and
all loading conditions, to ensure robustness. continuous perturbations as shown
in Figure 13 in the computational
Boot optimization for ribbon pull domain. In our model, the material’s
It’s possible to add a boot at the point elastic modulus is varied during the
where optical fibers exit the module optimization process, but the length of
to prevent fibers failures when loads the boot is kept constant at the minimal
are applied to them. This feature is size to achieve an acceptable radius
commonly used on all kinds of cables of curvature for the side pull test. The
to mitigate the bending force and morphology of the boot is optimized
stresses. A gradual change of shape toward minimization of the fiber’s
enables stiffness control to redistribute maximal principal stress. The boot shape
and reduce stress concentrations and morphology optimization experimental
Figure 13: Shape perturbations used for boot therefore, to improve the overall cable results suggested that there should be
geometric optimization. strength when it is subjected to external an increase in the root base of 27% in
the thickness and an increase of 32% in
the elastic modulus with respect to the
original values. The combination of these
two modifications leads to a reduction
in fiber stress by 33% in our model as
shown in Figure 14. Also, the location
of the maximum stress has moved out
from the root attachment to one fifth
inside the boot length, indicating that the
boot is able to distribute the fiber stress
over a wider area, thereby decreasing the
maximum stress level and improving the
robustness of the fibers under this type
of loading.
Several boot shapes have been tested
in lateral load in Figure 15 with the
objective of improving the resistance of
the fibers when subjected to lateral loads.
Figure 14: Morphologic optimization of the tapered boot. The initial and optimal shapes for such a boot are Those boots add stiffness around the fiber
presented along with the resulting fiber stress in the side pull test load application. The shape did reduce by ribbon at the edge discontinuity and the
33% the stress in the fiber used in our model.

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