Accession Number : AD1012328


Title :   Power Scaling Fiber Amplifiers Using Very-Large-Mode-Area Fibers


Descriptive Note : Technical Report,24 Jul 2014,23 Feb 2016


Corporate Author : University of Rochester, Institute of Optics Rochester United States


Personal Author(s) : Marciante,John R


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/1012328.pdf


Report Date : 23 Feb 2016


Pagination or Media Count : 33


Abstract : DEW-class fiber lasers are limited to below 1kW due to limited mode size and thermal issues, particularly thermal mode instability (TMI). Two comprehensive models were developed for scaling the mode area of fiber amplifiers while inclusively addressing all relevant spatial and dynamic effects. The beam propagation model was found to be too computationally intensive for design purposes. A rate-equation/kinetics model was developed and validated for accurately modeling very large- mode-area fiber amplifiers while simultaneously including thermal lensing and TMI. This model was applied to investigate scaling to an effective 50m core diameter. Mode-area scaling using conventional large-mode-area fibers was found to be simply not possible since the TMI threshold decreases with increased core area. Modifications in pump geometry were found to provide a modest benefit, particularly when flattening out the temperature profile along the fiber. Confined gain was studied and found to provide exceptional resilience to TMI (at least 2x increase in TMI threshold), as was originally proposed. Two new promising fiber types were developed, and both were found to exhibit features with modeled and expected resilience to TMI.


Descriptors :   Power amplifiers , lasers , THERMAL INSTABILITY , fibers


Distribution Statement : APPROVED FOR PUBLIC RELEASE