Offset and Tilt Loss in Optical Fiber Splices

Fiber transmission lines will frequently have more than 10 splices between terminal points; to estimate the overall line loss, we need a reliable figure for the splice loss to be expected under varying line conditions. The loss in multimode fiber splices depends on the power distribution among the modes in the fiber. The difficulty of correctly simulating line conditions in laboratory measurements or computations has so far prevented the establishment of a reliable splice-loss estimate. Calculations have predicted as much as 0.4 dB for a 10percent relative offset (offset divided by the core radius). These calculations assumed an equal or uniform power distribution in all modes.1 Techniques used to measure the offset loss have attempted to simulate the equal-power condition by illuminating the full numerical aperture of the input fiber by a coherent source,1,2 but the resulting loss values were between 0.1 and 0.2 dB for a 10-percent offset. The question has been raised whether some of the discrepancies are attributable to leaky rays. The following study considers lateral offset and angular misalignment (tilt) of splices made from perfectly similar fibers by joining them without air gap. As an introduction to the subject, we derive simplified offset-loss formulae for power-law profiles, considering both the absence and presence of leaky rays. We find that leaky rays are 905