Optical phase erasure and its application to format conversion through cascaded second-order processes in periodically poled lithium niobate

We describe a new optical phase erasure characteristic of periodically poled lithium niobate (PPLN) by using cascaded second-harmonic generation and difference-frequency generation with the signal set at the quasi- phase-matching wavelength. A simple analytical expression is derived clearly explaining the operation principle. It is interesting that the optical phase erasure feature enables an all-optical format conversion from carrier-suppressed return to zero (CSRZ) to return to zero (RZ). We experimentally and theoretically demonstrate a PPLN-based 40 Gbits / s all-optical CSRZ-to-RZ format conversion. Moreover, tunable and multi- casting CSRZ-to-RZ format conversions are also verified in the experiment.