Symmetry breaking in fiber optic connector endface geometry: correction via controlled manual polishing

The performance of fiber optic networks critically depends on the physical contact between mating connector endfaces. The three-dimensional geometry of the ferrule endface—particularly the radius of curvature (ROC), apex offset, and fiber height—dictates the quality of this contact. Symmetrical geometry ensures uniform pressure distribution and low insertion loss (IL), while asymmetrical defects lead to increased signal attenuation and back-reflection.

This study investigates the effectiveness of secondary manual polishing techniques in restoring the symmetry of the polished surface. Multimode patch cords with FC/PC connectors (OM2 fiber, 50 µm core) were divided into control groups exhibiting either excessive apex offset (mean 304 µm) or surface damage. An interferometer (Data-Pixel DAISI V2) was used to quantify the 3D surface parameters before and after polishing.

A novel combined polishing technique, employing circular motion with a deliberately biased pressure vector, was developed to induce localized abrasive wear. This method acts directly against the vector of the observed apex offset, effectively “re-centering” the spherical surface of the ferrule. The physical mechanism relies on the controlled breakdown of geometric symmetry to re-establish a uniform contact pressure profile.

The combined method demonstrated superior efficiency. In 80% of cases, the median apex offset was reduced from 304 µm to 41 µm. For samples with surface damage, the mean IL decreased by a factor of 4.5 (from 0.18 dB to 0.041 dB). The study reveals that while the technique is highly effective, it cannot correct defects originating from glue or fiber breakage, confirming that such flaws are fundamental limitations set by manufacturing processes and can be identified through 360° mechanical rotation tests.