Fiber amplifier system for suppression of modal instabilities and method

摘要

Apparatus and method for suppressing modal instabilities (MI) in fiber-amplifier systems. In some embodiments, thermal effects drive the MI process, and in some such embodiments, the present invention provides a plurality of options for mitigating these thermal effects. In some embodiments, the present invention provides a hybrid fiber with a smaller core in the initial length where the thermal loads are highest, followed by a larger-core fiber. In some embodiments the length of the smaller-core section is chosen to keep the core heat-per-unit-length of the second section below a critical value for the onset of MI. In some embodiments, the hybrid fiber of the present invention avoids modal instabilities while yielding almost the same performance as compared to conventional fibers with regard to minimizing fiber nonlinearities such as Stimulated Brillouin Scattering (SBS). In some embodiments, the hybrid fiber outputs a signal beam with at least 1 kW of power.

主权项

1. An apparatus comprising:
an optical-fiber amplifier having a plurality of optically coupled gain-fiber segments including a first gain-fiber segment and a second gain-fiber segment, wherein pump light is guided into the optical-fiber amplifier, wherein the first gain-fiber segment has a first core that has a first core diameter, wherein the first core is surrounded by a first cladding layer having a first outer diameter, wherein the first gain-fiber segment has a first end, a second end, and a first length, wherein signal light of a signal-light wavelength propagates in the first core, wherein the first gain-fiber segment has a first thermal load due, at least in part, to absorption of the pump light over the first length, wherein the second gain-fiber segment has a second core that has a second core diameter, wherein the second core diameter is larger than the first core diameter, wherein the second core is surrounded by a second cladding layer having a second outer diameter, wherein the second gain-fiber segment has a first end, a second end, and a second length, wherein the first end of the second gain-fiber segment is connected to the second end of the first gain-fiber segment, wherein a first amplified version of the signal light is coupled into the second core from the first core in a first direction, wherein the second gain-fiber segment has a second thermal load due, at least in part, to absorption of the pump light over the second length, wherein a second amplified version of the signal light is coupled out of the second core as an output signal beam, and wherein the first and second lengths are configured such that the second thermal load stays below a value at which a modal-instability occurs.