A new gradient-index lens with high numerical aperture has been fabricated by a new ion-exchange technique. In this treatment, a glass rod doped with a highly polarizable ion (dopant A) is immersed into KNO3 salt doped with a medium polarizability ion (dopant B). Dopant B penetrates into the rod and modifies the refractive-index profile of the lens. This new lens has 0.6 N.A. and gives a 1.18-μm spot diam in the light-focusing system. This lens gives good results also in a light source coupling system and is useful in microoptic devices.
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