Fiber-optic interferometers are one of the most sensitive components of optical meters of physical fields, mechanical strains and movements. The greatest efficiency is shown when such devices are used together with semiconductor sources - lasers, LED and SRD. Until very recently nonlinear effects in optical instruments and devices were thought to play an obvious role only with emissions having comparatively great power (from some units up to some tens mW ) in quartz fibers. The results of the most recent researches show that non-linear effects in fiber-interferometers with the length of baselines up to some kilometers with small emission power in the fiber (deciles mW ) play an important role.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.