Polarization insensitive quasi-phase-matched frequency conversion in a periodically poled lithium niobate

Periodically poled Lithium Niobate (PPLN) is a promising material for wavelength conversion and switching in an all optical network. However, current PPLN based network elements are normally polarization sensitive, which is not convenient for telecom applications. We proposed a polarization insensitive frequency conversion approach in a PPLN. The second harmonic generation (SHG) studied as an example. The PPLN consists of four sections. External electric fields could be selectively applied to them to induce polarization rotation between the ordinary and extraordinary waves. If the domain structure is well designed, the fundamental wave with an arbitrary polarization state can be frequency doubled efficiently in this special PPLN.