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The strain relief allows some deformation to accommodate   to the top of the module lid cover plate or to the stiffener ring
        pulls and thermal loads, as well as to protect the tight sub-  that surrounds the module. The ribbon attachment and latching
        micron level alignment at the photonic die. In our case, the   within the module relies on the dispense of a hard ultraviolet
        assembly can rely on the self-aligning V-grooves to provide   (UV) adhesive that holds the ribbon jackets in place. As the
        strong anchoring points for the fibers and accommodate fiber   attach solution needs to be compatible with microelectronic
        bending caused by package deformations.              environmental stressing and solder reflow [9,10], we will use
                                                             those load cases in the simulation. Furthermore, we use the
        Methodology                                          ribbons’ axial and lateral pulls to analyze how the package
          A multi-fibers ribbon integration inside a photonic co-  design around the fiber can help to relieve strain for the
        package is studied here in which the strain and stress   package integrity.
        distribution against various fiber layout geometries within   The pigtail strain relief on the lid configuration is shown in
        the module are compared [1]. We will evaluate how the strain   Figure 2. This architecture connects the fibers at the PIC and at a
        relieving structure affects the stress with different load cases   supplemental anchoring location for the fiber ribbon near the edge
        (thermal and mechanical) and how the optical fiber can bend   of the module. In the test module studied, the fibers are attached
        within the package to reduce stress. The resulting forces at   using an adhesive bridge that is in contact with both the substrate
        the fiber connections to the PIC are compared to experimental   and the lid, while in a second configuration studied, the anchoring
        fiber pull data. The module includes an array of optical   is done on a stiffener. Constraining the fibers in this configuration
        communication fibers aligned with V-grooves and secured   induces thermal stresses due to differences in thermal expansion
        to the photonic die using an adhesive that inherently creates   coefficients of the materials as they are exposed to curing, solder
        a fillet with the fibers at the die’s edge. The fibers are then   reflow and environmental conditions. It is, therefore, necessary to
        encased within a ribbon coating (either flat or bundled) that   evaluate how the fibers behave under these conditions, especially
        is itself anchored inside the photonic module at a specified   in terms of stress, curvature, and internal force as they are
        location where bending can be induced by changing the height   transferred to the PIC V-groove interface. With both architectures,
        of the ribbon. A typical arrangement is shown in Figure 1.   it is possible to drastically affect the fiber ribbon exit angle by
                                                             bending or machining an angle where the fibers are attached, as
                                                             shown in Figure 3. The lid cover plate or stiffener helps to limit
                                                             module warpage, and also provides flexibility to attach different
                                                             parts using fastening methods, and can even be extended to
                                                             accommodate further lengths.






        Figure 1: Photo of a co-package photonic module [6] with two pigtails, where the
        ribbon strain relief is created with adhesive on the package stiffener.
        The advantages of using transition boots and ribbon sleeves
        surrounding the fibers in the pigtail retention solution will also
        be evaluated.
          The stress at interfaces and bending radii control are some
        of the critical aspects of the optical fiber layout inside the
        package [8]. Two attachment approaches are compared and
        shown in Figures 2 and 3, where the ribbon can be secured
                                                             Figure 3: Photonic device with pigtail strain relief is the attachment on the
                                                             module’s stiffener.

                                                               We propose to track the fibers’ bending and the forces
                                                             applied at the photonic die coupler for various lengths and
                                                             geometries. The initial bending will help transfer the thermal
                                                             strain from axial strain in the fibers to a bending that accepts
                                                             deformation and strains that occur with the ribbon. The
                                                             bending also allows the accommodation of the strain relief
                                                             deformation that occurs when pulling the ribbons. We did
                                                             examine the effects of the following geometric parameters: the
                                                             free fiber length, vertical offset of anchoring height, exiting
                                                             angle, and boot shape and location. Figure 4 shows how the
                                                             variable geometric parameters are defined. We will compare
                                                             the benefits of various cases and track radii of curvature of the
        Figure 2: Photonic device with three pigtail ribbons exiting the module; also   ribbon and the stresses at the interface.
        shown is the ribbon strain relief between the lid and substrate.

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