Ytterbium-doped all glass leakage channel fibers with highly fluorine-doped silica pump cladding.

All glass leakage channel fibers have been demonstrated to be a potential practical solution for power scaling in fiber lasers beyond the nonlinear limits in conventional large mode area fibers. The all glass nature with absence of any air holes is especially useful for allowing the fibers to be used and fabricated much like conventional fibers. Previously, double clad active all glass leakage channel fibers used low index polymer as a pump guide with the drawbacks of being less reliable at high pump powers and not being able to change fiber outer diameter independent of pump guide dimension. In this work, we demonstrate, for the first time, ytterbium-doped double clad all glass leakage channel fibers with highly fluorine-doped silica as pump cladding. The new all glass leakage channel fibers have no polymer in the pump path and have independent control of fiber outer diameters and pump cladding dimension, and, therefore, enable designs with smaller pump guide for high pump absorption and, at the same time, with large fiber diameters to minimize micro and macro bending effects, a much desired features for large core fibers where intermodal coupling can be an issue due to a much increased mode density. An ytterbium-doped double clad PM fiber with core diameter of 80 microm is also reported, which can be coiled in 76 cm diameter coils.