Image restoration based on phase conjugation in second-order nonlinear materials under reflection configuration

We have demonstrated the recovery of the distorted images by a phase plate to nearly their original qualities under a refection configuration. This is made possible by utilizing difference-frequency generation in a bulk KTiOPO(4) (KTP) crystal and an AFB-KTP crystal composite. In such a geometry, both input and phase-conjugated waves propagate through the distorted phase plate for a round trip. They are reflected by the object, which can be far away from the imaging system, and captured by the cameras. Therefore, such a configuration is much more practical for eventually deploying our imaging system for realizing practical applications. We have demonstrated the advantages of the imaging system such as polarization insensitivity and broadband capability.