Experimental Identification of the Failure Modes and Failure Mechanisms of Fiber to Waveguide Couplings Under Cyclic Tensile Loading

The need for a lifetime prediction methodology for optoelectronic devices has become a necessity as they become more widely used. The development of such a methodology first requires the identification of the most relevant failure modes and mechanisms activated in service. This paper reports on an experimental investigation of the failure modes and failure mechanisms of fiber-to-waveguide coupling (FWC) under tensile cycling loading. Samples with a geometry similar to an industrial silicon photonic chip with V-groove alignment features were fabricated for ribbons of 12 single mode fibers. A cyclic tensile loading with a constant amplitude between 10 and 35 N in the direction of the free end of the ribbon and a frequency of one load cycle per 10 seconds was used. The insertion loss for all 12 fibers was continuously monitored. Three failure modes were observed during tensile cycling reliability tests: slow interference cycles on the optical power (mode I) that accumulated over tensile cycles, fast cycles (mode II) that were in phase with the tensile load cycles, and a sudden power drop due to fiber breakage (mode III). Mode I occurred when a fiber accumulated irreversible displacement under tensile cycles due to slippage in a fully delaminated strain relief (SR). Failure Mode II was observed when the ribbon was only partially detached from the SR and the fiber was disconnected from the V-groove, resulting in reversible displacement cycles under tensile loading. This study contributes to a first step towards the development of a lifetime prediction methodology for optoelectronic devices, by identifying failure modes and mechanisms that can be accelerated and related to service conditions with a lifetime model like the Coffin-Manson model.