Effect of Thermal Expansion Mismatch on the Optical Coupling Stability of Fiber Array Units

{'en': 'Fiber array units (FAUs) are key components for fiber-to-chip coupling in silicon photonics and optical interconnection systems, and their coupling stability under temperature variation directly determines system reliability. This paper analyzes the mechanism by which thermal expansion mismatch among the optical fiber, substrate, and adhesive in an FAU induces deformation of the fiber end faces and consequently degrades optical coupling. On the basis of the structure of the unit and the mismatch in coefficients of thermal expansion, an analytical model of thermal deformation and coupling loss is established that covers lateral offset, pitch mismatch, axial separation, and angular misalignment. The effects of temperature cycling, adhesive creep, and hysteresis on coupling stability are discussed. Numerical estimation shows that within a broad temperature range the coupling loss introduced by the differential expansion between substrate and fibers and by adhesive strain can reach several tenths of a decibel and may even exceed 1 dB, which is by no means negligible for multi-channel coupling. Accordingly, design and mitigation measures are proposed from the aspects of CTE-matched materials, adhesive engineering, structural compensation, and packaging, providing a reference for improving the temperature stability of fiber array units.'}