Frozen-in electrical field in thermally poled fibers

have experimentally verified existence of the frozen-in field in thermally poled fiber devices using a Mach-Zehnder interferometer. This technique can be used to measure both the magnitude and the direction of the frozen-in f ield. This same technique can also be used to measure the third-order nonli nearity chi((3)) of unpoled fibers and poled fibers. We find out that chi(( 3)) of fibers has increased by a factor of similar to 2 after thermal polin g. (C) 1999 Academic Press.