This paper reports all optical switching in a fully integrated Mach-Zehnder interferometer due to the cascaded second order nonlinearities with a switching ratio of 8:1. Along with the lithium niobate directional coupler, these represent the first integrated all-optical switching devices using cascaded second order nonlinearities. By using a higher X2 material and/or quasiphase-matching techniques independently for each channel, the switching power can be reduced by orders of magnitude.
Baek, Y., Schiek, R., Stegeman, G. I., Krijnen, G., Baumann, I., & Sohler, W. (1996). All-optical integrated Mach-Zehnder switching due to cascaded nonlinearities. Applied physics letters, 68(15), 2055-2057. https://doi.org/10.1063/1.116301