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.