Single-frequency low-threshold linearly polarized DFB Raman fiber lasers.

Distributed feedback (DFB) fiber lasers have been demonstrated to be excellent narrow-linewidth (kilohertz range) single-frequency laser sources. However, this type of laser is normally limited to rare-earth-doped fibers. Raman gain offers an alternative, operating at any arbitrary wavelength.

Frequency-modulated, tunable, semiconductor-optical-amplifier-based fiber ring laser for linewidth and line shape control.

We report how the linewidth and line shape of a tunable semiconductor-optical-amplifier-based fiber ring laser can be actively adjusted by applying an intracavity frequency modulation to the laser. Frequency-modulated laser operation is achieved by driving the phase modulator frequency close to the cavity axial-mode spacing, leading to a constant-amplitude laser output having a periodically varying instantaneous frequency. The resulting linewidth varies proportionally with the inverse of the frequency detuning, and it is adjustable from submegahertz to over more than 5 GHz.