Birefringence in gradient-index rod lenses: a direct measurement method and interferometric polarization effects

Gradient-index (GRIN) media can contain stress birefringence resulting from the variation in material composition. Anisotropy in a GRIN rod lens affec ts ray propagation and can degrade image quality. A technique, believed to be new, for measuring birefringence in GRIN rod lenses has been developed. The change in optical path difference (OPD) for orthogonal polarizations is measured directly. With this method, effects on OPD from standard imaging aberrations are excluded. Birefringence measurements for various GRIN rod s amples are presented. The data are compared with results obtained previousl y by use of a Twyman-Green measurement method. Also, the polarization effec ts on tilt fringes observed with the direct measurement method and the Twym an-Green method are presented and modeled theoretically. Tilt fringes for l arge birefringence test cases are also modeled. (C) 2001 Optical Society of America.