Double clad optical fiber having ring core surrounding core for high power operation

Abstract

An optical fiber apparatus having a wavelength of operation comprises an optical fiber comprising a core; a pump cladding disposed about the core for receiving pump optical energy having a pump wavelength; and a second cladding disposed about for tending to confine pump optical energy to the pump cladding. The core can comprise a rare earth material for providing optical energy having the wavelength of operation responsive to the optical fiber receiving the pump optical energy, and the fiber can further comprise at least one ring core spaced from the core, the ring core defined by inner and outer diameters and comprising the cross sectional area therebetween. The ring core can comprise an absorbing material for absorbing optical energy having the wavelength of operation. At the wavelength of operation the optical fiber can comprise a fundamental mode that is primarily a mode of the core and at least one higher order mode (HOM) that is a mixed mode of a selected mode of the core and of a selected mode of the ring core, the selected modes being of the same azimuthal order. The mixed mode can be suppressed relative to the fundamental mode.