High-power, single-mode fiber sources
An optical apparatus includes one or more pump sources situated to provide laser pump light, and a gain fiber optically coupled to the one or more pump sources, the gain fiber including an actively doped core situated to produce an output beam, an inner cladding and outer cladding surrounding the doped core and situated to propagate pump light, and a polymer cladding surrounding the outer cladding and situated to guide a selected portion of the pump light coupled into the inner and outer claddings of the gain fiber. Methods of pumping a fiber sources include generating pump light from one or more pump sources, coupling the pump light into a glass inner cladding and a glass outer cladding of a gain fiber of the fiber source such that a portion of the pump light is guided by a polymer cladding surrounding the glass outer cladding, and generating a single-mode output beam from the gain fiber.
1. A method of pumping a high power fiber source, comprising:
generating pump light at a pump wavelength from one or more pump sources;
coupling the pump light into a glass inner cladding surrounding an actively doped core and a glass outer cladding surrounding the glass inner cladding of a gain fiber such that a portion of the pump light is guided by a polymer cladding surrounding the glass outer cladding;
wherein a length of the gain fiber corresponds to deferred onset of out-of-band optical nonlinearities until reaching an output power of 1 kW or greater and wherein the length correlates to a proportion of the pump light that is guided by the polymer cladding; and
generating a single-mode output beam from the gain fiber.
2. The method of claim 1 , wherein the proportion of the pump light guided by the polymer cladding correlates further to the glass outer cladding diameter and pump light absorption in the actively doped core.
3. The method of claim 1 , wherein the pump light wavelength has a relatively large quantum defect with respect to an output wavelength.
4. The method of claim 1 , wherein the length of the gain fiber limits generation of out of band optical nonlinearities to 20% or less than the power of the output beam.