A rod lens made of a transparent cylindrical medium having a refractive index distribution in the radial direction is used as a graded index lens. An object surface and an image surface are arranged on both sides of the rod lens. A first surface of the lens is a convex spherical surface, and a second...http://www.google.com/patents/US6078431?utm_source=gb-gplus-sharePatent US6078431 - Object lens system
