In this work, we demonstrate how a polarization switching technique can be used to create multiple fiber ends, and allow the radiation to pass twice through each amplifying section for more efficient energy extraction. The technique uses a polarizing beam splitter combined with polarization switching in each arm of the cavity to define a ring-like cavity with multiple gain sections that can be end pumped. Polarization-maintaining double-clad rare-earth-doped fiber with slightly multi-mode core was used as the gain sections. A laser system based on the in-cavity polarization switching design has been demonstrated with maximum measured 62% slope efficiency and close to 30W output. The relatively low output power is only limited by the available pump sources.
High energy laser systems, both pulsd and CW, have become of significant interst in the recent past. To achieve higher powers in a laser system, it is often necessary to consider means by which individual lasers can be made coherent with one another. This can be achieved through the use of a master oscillator concept, which can have problems with overall stability, or by monitoring the phases of each individual laser and using feedback technique that can be used to combine individual pumped fiber gain sources into a cavity with a single output and a single set of longitudinal modes. We discuss the advantages of end pumping of double clad fiber lasers and speculate on means by which an all-glass double clad fiber laser may be developed.