The laser comprising an optical fiber having two ends of which a first whereby the light is to be received, and a doped section for absorbing at least part of the light received via the first end and emitting light, the method includes: applying a torsion angle to the optical fiber; supplying light having a pump power at the first end of the optical fiber; checking that the Polarization Extinction Ratio of the light output from the first end of the optical fiber remains greater than a predetermined value throughout a predetermined range of the pump power; and, if the Polarization Extinction Ratio remains greater than the predetermined value throughout the predetermined range of the pump power, attaching the optical fiber to a mechanical mount at two attachment points of the optical fiber situated on either side of the doped section, with the torsion angle applied to the optical fiber.