Graded-index silver chlorobromide fibers for the mid-infrared

We have developed and characterized graded-index optical fibers for the mid-IR spectral range, based on silver chlorobromide (AgClBr) crystals. A preform was fabricated by inserting a cylindrical rod made of AgCl_0.1Br_0.9 into a tube made of AgCl_0.9Br_0.1. The preform was heated in an oven, causing diffusion of Cl into the outer layer of the rod, thus reducing its index of refraction. The rod was removed from the tube and was then extruded through a die to form a graded-index fiber. Such a fiber was analyzed, investigated, and compared with a step-index fiber made of AgClBr. The attenuation of a 0.9-mm-diameter graded-index fiber was found to be 2.4 dB/m, and the attenuation of a 1.2-mm-diameter graded-index fiber was 4 dB/m at 10.6 (mu)m.