Two-wave mixing by means of dynamic Bragg gratings recorded by saturation of absorption in erbium-doped fibers

We present experimental results of two-wave mixing in single-mode Er-doped optical fibers for which dynamic Bragg reflectance gratings are formed as a result of saturation of fiber-optic absorption (i.e., by means of the effect of spatial hole burning). The gratings are probed by the same recording waves at lambda approximately = 1549 nm and are detected as periodic changes of the intensity of light reflected from a Sagnac interferometer (with a piece of the doped fiber included) observed when periodic phase modulation is induced in one of the waves. Both rectangular and sinusoidal modulation were used, which permitted evaluation of the grating recording time (tau(g) approximately = 3 ms for OFS-Fitel EDF-HG980 fiber) and the grating amplitude, which proved to be approximately 6-7 times lower than expected from measurements of saturation of fiber-optic absorption by one wave only.