A typical Nonlinear Directional Coupler NLDC permits power dependent energy transfer between two adjacent waveguides. The output of the device can be controlled by the input power solely for high energy signals. For weak fields NLDC works like a linear coupler with the output dependent only on the device design. NLDC working with weak modes and controlled by a strong field at a different frequency guided by the central region of the coupler was proposed by Lederer.
This article is from 'OSA Proceedings of the Topical Meeting on Nonlinear Guided-Wave Phenomena Held in 2-4 September 1991. Cambridge, England United Kingdom. Volume 15', AD-A253 471, p329-332.