Pump coupling of double clad fibers

Abstract

Apparatus for coupling light into a fiber, such as a double clad fiber (DCF) having a core having a refractive index n , surrounded by an inner cladding having refractive index n which is surrounded by an outer cladding having a refractive index n , where n >n >n . An optical coupler medium, referred to as a Fiber Space Division Multiplexor or FSDM, is formed on an exposed portion of the fiber inner cladding at a position along the length of the fiber without interfering with the continuity of its core and provides at, at least one position, the imaging of light external of the fiber into the inner cladding interface and its waveguiding with the inner cladding of the fiber. The FSDM coupler comprises an optical material in optical contact or integrated with the inner cladding and having a refractive index substantially equal to n . The coupler medium may also be employed with a fiber having no core and where the inner cladding would function as a multimode core. Also, disclosed are formed reflectors for reflecting back residual, unabsorbed pump light backward into the DCF inner cladding for absorption within the core doped with a rare earth active material. Other embodiments provided for the removal of pump light from the DCF inner cladding.