All-Optical Wavelength Selective Switching Exploiting the Nonlinear Phase Shift Induced by Cascaded Sum and Difference Frequency Generation (cSFG/DFG) in a Ti:PPLN Channel Waveguide

The predicted growth of broadband services, has led to extensive research for high capacity systems and networks. Current efforts are concentrated on the investigation of optical time-division multiplexing (OTDM) techniques combined with wavelength-division multiplexing (WDM) in order to fully utilize the potential of the installed fibers. All-optical switches, which can route a signal spatially, are one of the fundamental building blocks for the realization of broadband WDM/OTDM systems. Cascaded sum and difference frequency generation (cSFG/DFG) provides a challenging possibility to realize ultrafast all-optical switching operations. A large nonlinear phase shift of π can be obtained with a moderate optical pump power of less than 1W at exact phase matching for SFG. Since there is no essential time limit for operation of all-optical devices based on nonlinear parametric interactions, even THz switching can be achieved. Recently, an all-optical gating device of a LiNbO3 waveguide Mach-Zehnder interferometer with cSFG/DFG section was demonstrated by T. Suhara et al. [1]. However it showed very poor switching efficiency. G. S. Kanter et al. investigated ultrafast all-optical switching of 5 ps pulses in a proton exchanged periodically poled LiNbO3 channel waveguide [2]. Since the proton exchanged LiNbO3 guide only sustains TM mode, a complicated interferometer structure was used to demonstrate a switching operation based on a cSFG/DFG induced nonlinear phase shift. In this contribution, we report the demonstrated of all-optical switching based on π-phase shift induced by cSFG/DFG. The device configuration is a polarization interferometer with a Tiindiffused periodically poled (Ti:PPLN) channel waveguide as the core element for cSFG/DFG. Moreover, wavelength selective switching was demonstrated for the first time. Compared with the previous works, our device is very compact and easily extended to an all-optical 2×2 spatial switch. In the following sections, experimental and numerical results of optical switch will be presented together with linear and nonlinear optical characterizations of the Ti:PPLN channel waveguide.