Simultaneous effects of gain and loss anisotropies on the thresholds of a bipolarization fiber laser.

We study, both experimentally and theoretically, the threshold properties of the polarized modes in Nd(3+)-doped fiber lasers. We demonstrate the influence of the gain anisotropy induced by the pump polarization and of the loss anisotropy induced by the cavity mirror tilt. An understanding of these two phenomena reveals the microscopic anisotropies of the ion for both the pump and laser transitions.

Channeled spectrum of a fiber laser.

We describe the polarization properties of a long Nd(3+)-doped optical fiber laser. An intracavity prism acts as a dichroic element and fixes the polarization of the laser beam essentially in its plane of incidence. The slight birefringence of the fiber makes a wavelength-dependent phase plate that modifies the state of the polarization. In the laser output spectrum, the azimuth for the elliptically polarized field can thus rotate by several times pi/2 if the fiber is long enough. This gives a channeled spectrum when observed through a polarizer.