Unique nonlinear wave mixing effects in photorefractive waveguides and bulks

The authors have been studying unidirectional mode coupling effects in planar waveguides based on photorefractive wave mixing. For example, in a funnellike process the high-order modes of a guided beam are converted into the lower modes. The opposite coupling process is also possible in an antifunneling device. Amplification of a guided beam by laterally pumping the waveguide from the outside by another beam (a leaky mode) and polarization effects are other applications. All these effects do not depend on the total beam intensities (except for their time response) and can be achieved with very low light power densities. The authors recently demonstrated two new photorefractive oscillators: the double-phase conjugate mirror and the double color-pumped oscillator. They allow the interaction of two beams that are mutually incoherent and have different colors. These processes allow many new applications.