A laser is fabricated from an optical transmission medium having a laser cavity with an rare earth (e.g. Erbium) doped portion. At least one longitudinal mode is suppressed using a plurality of series coupled Fabry-Perot cavities an optical grating, or a combination thereof. Ring lasers and linear structures...http://www.google.com/patents/US5151908?utm_source=gb-gplus-sharePatent US5151908 - Laser with longitudinal mode selection
