Towards reference-grade multi-mode fiber connectors: Impact of fiber geometry on attenuation and encircled flux

The connection attenuation for perfectly aligned graded-index multi-mode fiber connections with dissimilar core diameter (CD) and numerical aperture (NA) is derived in analytical form for spatially large intensity patterns that include target encircled-flux (EF) compliant launches and overfilled (OF) launches. The launches are spatially stable in that it is possible to describe the ray density distribution (and hence the EF), the intrinsic connection attenuation and the redistribution of the rays in the receiving fiber by means of the ray turning points. This has enabled us to derive the analytical formulation. Although imposing an EF compliant launch significantly reduces the sensitivity of the attenuation due to fiber geometry mismatch by about a factor of three for the NA and a factor of six for the CD as compared to an OF launch, we show that tightening the tolerance of the CD to 50±0.5μm (instead of ±2.5μm) and the tolerance of the NA to 0.2±0.002 (instead of ±0.015) is necessary to ensure <0.1 dB attenuation among reference-grade connectors (instead of ≤1.2 dB).