Page 48 - Chip Scale Review_January February_2023-digital

The experimental measure of the fiber attach retention force
to the PIC V-groove depends on the direction of the applied
force as shown in Table 2. Naturally, the axial pulling force
is the strongest one, while the shear force out of the V-groove
is lower. The strength measurements are also obtained for
the ribbon pull at the anchoring points – either the lid or the
stiffener depending on the configuration. Table 3 shows the
typical axial pull force at failure for an array of 12 fibers for
different configurations. Those experimental values are used as
limits to guide our model optimization.
Table 2: Experimental measures or retention forces of the fibers attached to the
V-groove. Model results
The variation of the fiber free length between the attach
point on the maximal fiber axial stress in the pigtail
configuration is presented in Figure 9. In general, stress
decreases with increasing length, which is expected because
longer fibers require less force and curvature to accommodate
the thermal strain. The environmental stress test with low-
temperature loading creates the maximum thermal stress
condition, as the thermal shrinkage with respect to the
adhesive curing temperature induces the most bending in
Table 3: Experimental retention force pull data of ribbons of 12 optical fibers the fibers. A similar effect is observed in the minimum fiber
(typical sample size of 12) on a metallic surface.
axial stress for the fiber length range studied. It is noted that
the stress of the optical fiber for the pre-stress condition is
nonzero because we applied an initial fiber bending from an
initial offset and exiting angle when placed and attached in the
package. The bending of the fiber is illustrated in Figure 10
and shows the evolution of fiber curvature for various fiber free
lengths. If the fiber bend radius gets too small, the integrity of
the fiber may be at risk. We have traced lines showing common
minimum radius thresholds of 15 and 25 millimeters. Modules
with shorter free fibers exhibit more curvature and stress.

Figure 9: a) Maximum and b) minimum fiber stresses vs. the fiber free length for Figure 10: Maximum fiber curvature of various fiber free lengths of the pigtail
the pigtail configuration. latching within the module.

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