Two-wave coupling in LiNbO3:Fe:Ru crystals

Two-wave coupling in LiNbO3:Fe:Ru crystals is investigated experimentally and theoretically in this paper. The dependence of gain coefficient on doped concentration, as well as the light intensity ratio between pump beam and signal is experimentally investigated, the maximal gain coefficient 9.2cm-1 is found while the ratio is 2.2, light gain cannot be observed in the reduced sample because of fan effect. Effect of phase difference between light modulation and the refractive index grating on two-wave coupling is investigated based on jointly solving the two-center material equations and the coupled wave equations, the variation of phase difference is obvious in the crystals with reduced process or high doped concentration.