Restoration of blurred images based on phase conjugation by using single second-order nonlinear parametric processes

Abstract

We review our previous result: backward difference-frequency generation can be exploited to achieve phase conjugation in a second-order nonlinear medium. The backward configuration can be utilized to achieve broadband quasi-phasematching, compared with the forward counterpart. Our calculation shows that a nonlinear reflectivity of close to 100% is achievable from a laser emitting an output power of ≈ 1 mW. Such an efficient phase conjugator is made feasible by placing the nonlinear medium inside a pump laser cavity. In addition, a Fabry-Perot cavity at the input frequency is used to significantly improve the nonlinear reflectivity. In our previous experimental result, we demonstrated that broadband and polarization-insensitive phase conjugation, achieved based on difference-frequency generation in a second-order nonlinear composite consisting of stacked KTP plates, was exploited to restore blurred images due to phase distortion as a novel scheme. Due to the quasi-phase matching in the stacked KTP crystals, our result reveals that the image restoration is insensitive to the polarization direction and wavelength of the input beam.