An optical apparatus comprises segments of a GRIN optical medium mounted on a substrate in at least one groove thereon. The GRIN segments are longitudinally spaced apart from one another on the substrate, and are arranged so that a free-space optical beam received through the distal end face of the first GRIN segment is transmitted through the proximal end face of the first GRIN segment, propagates to the proximal end face of the second GRIN segment, is received through the proximal end face of the second GRIN segment, and is transmitted as a free-space optical beam through the distal end face of the second GRIN segment. The GRIN segments can be derived from a single GRIN optical medium mounted on the substrate.