Intensity dependence of the transient two-wave mixing by population grating in Er-doped fiber

Theoretical analysis of the transient two-wave mixing (TWM) of two continuous waves with rectangular phase modulation counter-propagating through the Er-doped optical fiber is presented. Approximate analytic solutions obtained for undepleted interacting waves of low power (neglecting large-scale saturation of the fiber optical absorption) and of high power (with significant spatially uniform large-scale absorption saturation) are complemented by numerical simulation for a broad region of the recording light power. The experimental dependence of the TWM efficiency on the recording power obtained for a single-mode fiber with ≃640 ppm erbium concentration and with initial optical density ≈8.4 at λ = 1526 nm demonstrated the initial, growing and decaying parts predicted theoretically. The maximum experimentally observed relative TWM signal amplitude proved to be approximately 3 times lower than expected.