Temporal coherence of a low-power erbium-doped fiber laser with spectrally broadened output

The temporal coherence of spectrally selected output from a CW broadband erbium-doped fiber ring laser (EDFRL) based on four wave mixing is characterized using a fiber-optic Mach-Zehnder interferometer. The visibility is found to be comparable to that of a standard narrow-linewidth tunable laser when their spectral widths are matched using an intracavity filter in EDFRL. But its visibility is distinctly higher than two other broadband sources (superluminescent diode and amplified spontaneous source) even when their spectral widths are matched, establishing that the cavity effect aids the coherence in EDFRL by mitigating the phase noise from four wave mixing.