Physical-Optics Tolerance and Compensation Design for a Dual-Lens Single-Mode Fiber Coupler

Alignment errors in a dual-lens single-mode fiber coupler are coupled. We separate first-order transport from full-field effects by comparing independent Gaussian/ABCD and paraxial ray-transfer models with scalar physical optics. For Lens-2 decenter, the dimensionless physical-optics compensation slope is 1.14677, close to the first-order prediction, while direct calculations in both transverse directions confirm the same compensation behavior. Manufacturing-distribution tests support surrogate use for screening rather than threshold certification. Parameter-transfer studies confirm system specificity. The study is entirely computational and provides design guidance requiring experimental calibration before deployment.