Single-frequency and single-polarization Er/sup 3+/-doped fiber ring laser with less than 0.7 kHz linewidth

Reports the results of a single-mode single-polarization operation of an Er/sup 3+/-doped fiber (EDF) ring laser with narrow linewidth in a compact configuration using a circulator and a fiber Bragg grating (FBG), where the FBG also functions as an output coupler. The laser cavity was constructed with all polarization-maintaining fibers to eliminate the detrimental polarization instability and to maintain single polarization and the unidirectional travelling wave operation eliminated the spatial hole burning effect.