Abstract

One major problem when using the nonlinear optical loop mirror (NOLM) as an all-optical switch is that it is very sensitive to acoustic disturbances which affect the biasing condition due to changes in the propagation constant in the loop fibre. Since the two counter­propagating waves, in general, never are in the same physical location inside the fibre, they will experience different acoustical sound pressure and thus different refractive indices. This random change in refractive index gives rise to noise at the output of the NOLM which may seriously degrade the performance of the NOLM. This acoustic sensitivity becomes much stronger for long loop fibres and will in many cases limit the use of the device. This problem can, however, be virtually eliminated by spooling the fibre so the two counter-propagating signals always appear at about the same physical place along the fibre. Different winding geometries have previously been investigated to stabilize optical gyroscopes [1]. Here we demonstrate a winding technique where the fibre is folded and winded onto a drum starting with a bend from the middle and ending with both fibre ends on the outside of the drum.

© 1998 IEEE