Spectral dependence of two-wave mixing efficiency in saturable erbium-doped fibers

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Detailed experimental data on the efficiency of two-wave mixing via population dynamic grating in erbium-doped fiber (EDF) with saturable optical absorption are presented. The measurements were performed for spectral region 1490–1560 nm of the EDF absorption/gain spectrum, both for absorption and for phase (refractive index) components of the dynamic grating. The reported data confirm the earlier results published for some particular recording wavelengths. In particular, the amplitude gratings recorded in EDF in the central part of this region (1520–1560 nm) are significantly less efficient (by more than 1 order of magnitude) than it can be estimated from measurements of a spatially uniform fiber absorption saturation. It is shown, however, that this effect cannot be explained by spatial migration of the Er3+ excited state. At the short-wavelength spectrum side around 1490 nm, the disagreement between the experimentally observed and the evaluated grating amplitude is minimum (∼0.3) and can, probably, be attributed to the polarization mismatch in the counterpropagating recording waves.