Ray tracing through a two ball uniaxial sapphire lens system in a single mode fiber-to-fiber coupler

A worst case ray trace analysis is presented for a two ball uniaxial lens system in a single mode fiber-to-fiber coupler. The purpose is to determine if the e-wave Poynting vector walkoff effect contributes adversely to coupling loss due to beam offset. Sapphire ball lenses with radii of 250 /spl mu/m separated by 500 /spl mu/m are used to produce numerical results at /spl lambda/=1.3 /spl mu/m. A worst case offset of 4.302 /spl mu/m is calculated at the coupler exit. In addition, aberration due to birefringent focusing is examined; uniaxial ball lenses focus the o-wave and e-wave at different points.