ABSTRACT
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. We demonstrate here linearly polarized, single-frequency, DFB fiber Bragg grating Raman lasers with, to the best of our knowledge, the lowest pump threshold of 350 mW, an output power of up to 50 mW at 1120 nm, an 8.5% slope efficiency, and 300 mW of output power at 1178 nm. In the high-power regime, stimulated Brillouin scattering plays an important role in the laser dynamics. We also report the characterization of the power profile inside the fiber along its axis through a novel side-scatter technique.
ABSTRACT
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. By appropriate selection of the modulating waveform we have synthesized a near-Gaussian output line shape; other line shapes can be produced by modifying the modulating waveform. Experimental observations are in good agreement with a simple model.
