Temporal coherence study of four-wave mixing products with and without the laser cavity effect.

In this work, we have studied the temporal coherence property of a four-wave mixing (FWM)-assisted continuous-wave erbium-doped fiber ring laser source. To understand the temporal coherence characteristics of FWM, we have analyzed the visibility of their interference pattern with the help of a Mach-Zehnder-based fiber interferometer. The visibility of FWM sidebands is compared with respect to the input pumps, with and without the cavity effect. The stand-alone FWM without any cavity effect has a visibility comparable to its input coherent pumps, while the FWM in the presence of the cavity effect has a poorer visibility due to the intra-cavity noise arising from the amplified spontaneous emission, which is not entirely annulled in broadband lasers. The study also confirms that the visibility/temporal coherence property of FWM sidebands does not depend on the efficiency of their generation.