Polarization-insensitive wavelength conversion in a lithium niobate waveguide by the cascading technique

In this letter, we present a polarization-insensitive wavelength conversion scheme based on the cascading of two second-order processes. The nonlinear device exploits a double pass configuration in a titanium indiffused waveguide realized on a periodically poled lithium-niobate substrate. Polarization-independent conversion efficiency is obtained by rotating the signal polarization state by means of a Faraday mirror. A polarization sensitivity lower than 0.8 dB is experimentally demonstrated.