Er3+-doped fibers have been widely investigated to offer convenient laser sources  and optical amplifiers ,  operating at the 1.5 µm region. To apply these lasers to optical coherent communications, especially for homodyne detection, much effort to narrow their linewidths has been made by using fiber-gratings in Fabry-Perot fiber cavities-. So far, the linewidths were more than 1MHz mainly restricted by the rather low quality factor of the cavities. On the contrary, all fiber-ring-cavity has the potential for achieving the high quality factor, since the cavity loss can be easely reduced by using low loss fibers.
© 1989 Optical Society of AmericaPDF Article