The Center for Freeform Optics
An Industry/University Cooperative Research Center

Angular scan optical coherence tomography imaging and metrology of spherical gradient refractive index preforms

Jianing Yao, Panomsak Meemon, Michael Ponting, and Jannick P. Rolland

in Opt. Express 23(5), 6428-6443 (2015)

The fabrication of high-performance spherical gradient refractive index (S-GRIN) optics requires nondestructive metrology techniques to inspect the samples. We have developed an angular-scan, swept-source-based, Fourier-domain optical coherence tomography (OCT) system centered at 1318 nm with 5 mm imaging depth capable of 180° polar scan and 360° azimuthal scan to investigate polymeric S-GRIN preforms. We demonstrate a method that enables simultaneous mapping of the group optical thickness, physical thickness, the radially-averaged group refractive index, and the transmitted wavefront of the S-GRIN preforms. The angular scan OCT imaging and metrology enables direct visualization, molding uniformity characterization, and optical property evaluations of the preforms. The results on two generations of S-GRIN preforms are discussed that showcase the evolution of the manufacturing process in response to the OCT metrology feedback.