Abstract
In this paper, we develop the methodology, including the refraction correction, geometrical thickness correction, coordinate transformation, and layer segmentation algorithms, for 3D rendering and metrology of a layered spherical gradient refractive index (S-GRIN) lens based on the imaging data collected by an angular scan optical coherence tomography (OCT) system. The 3D mapping and rendering enables direct 3D visualization and internal defect inspection of the lens. The metrology provides assessment of the surface geometry, the lens thickness, the radii of curvature of the internal layer interfaces, and the misalignment of the internal S-GRIN distribution with respect to the lens surface. The OCT metrology results identify the manufacturing defects, and enable targeted process development for optimizing the manufacturing parameters. The newly fabricated S-GRIN lenses show up to a 7x spherical aberration reduction that allows a significantly increased utilizable effective aperture.
Highlights
The rapid expansion of modern optical components towards light weight, compact volume yet efficient aberration correction stimulates the investigation of gradient refractive index (GRIN) materials [1,2,3]
We demonstrated the development of a swept-source optical coherence tomography (OCT) (SS-OCT) system for the inspection of flat axial GRIN optics [8,20,21] and an angular-scan OCT system for the metrology of curved spherical GRIN (S-GRIN) preforms [4] that serve as the precursors to the final lenses
We report on the investigation of the 3D metrology and image rendering methodology developed for nondestructive, volumetric characterization and visualization of final S-GRIN lenses based on the angular-scan OCT system
Summary
The rapid expansion of modern optical components towards light weight, compact volume yet efficient aberration correction stimulates the investigation of gradient refractive index (GRIN) materials [1,2,3]. By tuning the volumetric ratio of the co-polymers, a library of films with varying refractive indices can be produced. Through the compression-molding of a film stack arranged to meet a GRIN prescription, a flat axial GRIN sheet may be formed and subsequently thermoformed into a curved S-GRIN preform, which is diamond-turned into an S-GRIN lens [8]. This SGRIN manufacturing approach enables a widely expanded range of achievable internal refractive index distribution compared to traditional interdiffusion [9], deposition [10], or solgel GRIN fabrication techniques [11]
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Published Version
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