Effects of inhomogeneities on nonlinear integrated optics components

Calculations are presented showing how small index inhomogeneities, of a size likely to occur in real devices, limit the useful length of all-optical waveguide switches. The author derives scaling rules, showing the effects of device length and of the magnitude and correlation length of the inhomogeneities, and calculates the relative sensitivity of interferometers and directional couplers. The device lengths and index variations used in the calculations were typical of those expected in devices fabricated on planar substrates. Scaling indicates that similar effects will be seen with the greater lengths and smaller index inhomogeneities typical of all-fiber devices. Long all-fiber nonlinear couplers have been observed to behave in ways that can only be explained by index mismatches. Even short, i.e. 5 mm, couplers have been seen to deteriorate when the presence of light induces permanent index changes