Continuous-wave laser oscillation with an ultralong optical-fiber resonator

Continuous-wave laser oscillation with a long optical-fiber resonator has been observed. The fiber resonators that were examined were 1.65, 11.3, and 101 m long, and longitudinal self-beat spectra of laser oscillations were confirmed with a 1.15-μm He–Ne laser; the observed frequencies were in good agreement with the calculated ones. By using a spectrum analyzer, the spectral amplitude was found to be modulated, which is attributable to the fact that a complex Fabry–Perot resonator was formed by reflections on a lens and an input portion of the optical fiber.