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

We have presented a polarization insensitive wavelength converter device based on the cascading of two second order processes. The scheme is based on a double pass gain in a periodically poled LiNbO₃ waveguide and exploits the signal nonreciprocal polarization rotation obtained by a Faraday mirror. The experimentally implemented device shows a polarization sensitivity lower than 0.8 dB. A further improvement can be obtained by an optimized design of the experimental set-up.