Self Pumped Phase Conjugation and Optical Light Oscillation in Fe Doped KNbO3

In recent years, self-pumped phase conjugation and self-induced photorefractive light oscillation have been reported, using different photorefractive materials. The main photorefractive materials used in these experiments are BaTiO3 and Bi12SiO20. In ferroelectric BaTiO3 the high electro-optic coefficients give rise to large reflectivities. In photoconductive and paraelectric Bi12SiO20 phase shifting techniques lead to enhanced self-diffracted intensities and phase conjugate reflectivities. KNbO3 is such a material which in addition to its high photorefractive sensitivity3 and large beam coupling gain4, has been shown to become highly photoconductive if prepared properly, leading to optimized response speed5 down to 100 μs. In a degenerate four wave mixing configuration, maximum phase conjugate reflectivities up to 25% with an applied electric field have been observed several years ago6. In a previous paper7 and for the first time, the possibility of using KNbO3 crystals for self-induced optical resonators has been reported. Both an unidirectional ring and a linear resonator configurations were realized and coherent light oscillations observed. Build up time constants of milliseconds were reported when an undoped reduced KNbO3 crystal was employed. However the measured phase conjugate reflectivity for these configurations were very small. Later on self-pumped phase conjugation in KNbO3 has been reported at 124°C8. In this paper we report on self-pumped phase conjugation experiments, performed with an iron doped KNbO3 crystal at room temperature in both a linear and a passive ring resonator configuration. We also report on self-pumped phase conjugation in a configuration requiring no external optical elements. Results deriving from degenerate four-wave mixing are also presented.