Optical fiber pigtails integration in co-package

Abstract

Fiber ribbons exiting a silicon photonic device (referred to as pigtail herein) need an appropriate fastening method within the package to protect the light coupling interface they are secured to. Co-packaged components that rely on automated self-alignment to assemble pigtails to V/U grooves provide a cost-effective solution to interface single mode fibers to silicon photonic integrated circuits. A strain relief element must be designed to isolate the light coupling interface from deformation due to thermal expansion during downstream assembly processes, thermo cycles experienced during normal device lifetime, as well as handling stresses applied to the pigtail. A parametric model evaluates latching configurations that use fiber bending as a strategy to accommodate the thermal and mechanical strain that the ribbons must support. This model helps to design optimal geometries to control the stress at both anchoring points: the photonics interconnect and the ribbon strain relief area. We demonstrate the benefits of using a free-fiber length of 8mm or more to incorporate the bends on our selected layouts. A fiber ribbon exit angle of a few degrees can provide advantages in controlling the fiber bending and buckling direction and in reducing fiber pistoning. Finally, the use of boots where the ribbon exits the component are shown to provide a significant benefit in controlling the radius of curvature and stress of the ribbon during side pull stress tests, and morphology can reduce stress up to 33%. These results provide guidance for optimizing the layout of fibers ribbons inside a package and how to strain relief the photonic interconnect through fiber bend designs.