Rigorous analysis of polarization-dependence loss (PDL) for equilateral 3×3 fused fiber couplers

A rigorous power coupling model for weakly fused 3×3 triangular fiber couplers is proposed to investigate the polarization-dependent loss (PDL) of the couplers. The accuracy of the power coupling model is checked by a comparison with the experimental results. The agreement between them is reasonably good. The effect of fabricating parameters of the coupler, fusion degree, and heated length on the PDL of the coupler is investigated by combining the Mueller matrix method into the proposed model. It is found that the fusion degree is the dominant factor to influence the PDL performance of the coupler. The PDL significantly increases as the coupler is fused in weakly fused condition and the fusion degree is suggested to be less than 0.95 for designing a low-PDL 3×3 coupler.