SINGLE-MODE FIBER COUPLING EFFICIENCY WITH GRADED-INDEX ROD LENSES

Losses are calculated for the single-mode graded-index- (GRIN-) lens c oupler. The main advantage of this coupling system is large separation between fibers with small power loss. The excess loss of the GRIN-len s coupler is due primarily to the misalignments of the GRIN lenses and is most sensitive to angular tilt rather than lateral offset or end s eparation. The excess loss is calculated from the overlap of two diffe rently sized or misaligned Gaussian beams. Experimental results show t hat this method is adequate for predicting losses that are due to misa lignments of the GRIN lenses.