Gradient‐Index polymer materials and their optical devices

A gradient‐index (GRIN) plastic optical fiber was prepared by a heat‐drawing process of the GRIN preform rod obtained by a new interfacial‐gel copolymerization technique. The attenuation loss of the GRIN fiber was 179 kB/km at 650‐nm wave‐length and its numerical aperture was 0.20‐0.25. To attain low loss and highly dense integrated circuits, steric radial‐GRIN optical waveguide components such as GRIN branching, star coupler, multi‐coupler, and a 2‐D GRIN lens array, were monolithically fabricated by this technique. A novel spherical GRIN sphere lens, whose index function is symmetrical about the center of the sphere, with a low spherical aberration, was prepared by a modified suspension polymerization technique. A W‐shaped GRIN sphere has been newly proposed to further reduce the spherical aberration, compared with the parabolic GRIN sphere previously proposed.