High power optical apparatus employing large-mode-area, multimode, gain-producing optical fibers

Abstract

Optical apparatus includes a multimode, gain-producing fiber for providing gain to signal light propagating in the core of the fiber, and a pump source for providing pump light that is absorbed in the core, characterized in that (i) the pump source illustratively comprises a low brightness array of laser diodes and a converter for increasing the brightness of the pump light, (ii) the pump light is coupled directly into the core, and (iii) the area of the core exceeds approximately 350 μm. In one embodiment, the signal light propagates in a single mode, and the pump light co-propagates in at least the same, single mode, both in a standard input fiber before entering the gain-producing fiber, and a mode expander is disposed between the input fiber and the gain-producing fiber. In another embodiment, multiple pumps are coupled into the core of the gain-producing fiber. The pumps may generate light of the same wavelength or of different wavelengths. In accordance with a particular embodiment of our invention, we have demonstrated amplification of nanosecond optical pulses at 1545 nm in a single clad Er-doped fiber having a core area of 875 μm; the core was pumped by a high brightness Raman laser at 1480 nm; and the pulses had a record peak power of several hundred kW.