A UNIFIED MATERIALS APPROACH TO MITIGATING NONLINEARITIES IN HEL OPTICAL FIBERS
Abstract
A UNIFIED MATERIALS APPROACH TO MITIGATING NONLINEARITIES IN HEL OPTICAL FIBERSProject AbstractMost present approaches for reduci"ng the detrimental impact of parasitic phenomena, such as stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS""), on laser power scaling and performance have focused on fiber design (e.g., microstructured fibers) with the main goal being an ex""pansion of mode diameters to reduce nonlinearities. However, these ~effectively single mode~ fibers are naturally and inextricably m""ultimoded and other effects, such as higher order transverse mode instabilities (TMI), are now limiting factors. Further, while much"" has beenlearned in the development of the large mode area (LMA) designs, these fibers are highly complexand very difficult to man"ufacture; factors that conspire to make it difficult for the DoD to achieve its high energy laser (HEL) goals. All of these parasit"ic effects fundamentally originate from the light s interaction with the material from which the fibers are made. Accordingly, a mat"erials-related approach to novel high energy fiber lasers will permit the HEL community to move away from incrementally addressing these issues by jumping from design to design to directly attacking the underlying physical origins of these nonlinearities. Therefor"e, the objective of this program is to explore, model, fabricate,and test HEL optical fibers that mitigate SBS, SRS, and TMI all in" a single and simple core/clad fiber platform through designer yet practical and manufacturable materials.The program initially is" sub-divided into five (5) thrusts that address each central topic: (i) SBS, (ii) SRS, (iii) loss, (iv) modeling, and (v) TMI. These" thrusts merge to two (2) at Year 3 as the enabling materials commonly address multiple nonlinearities (such as SBS and SRS). By yea"r 5, a single active fiber is to be realized, and tested at kW powers, that exhibits a 15 dB suppressionin SBS, a 5 dB suppression"" in SRS, is single mode with zero TMI, has < 20 dB/km baseline attenuation, and a bend radius of 10 cm. These designer fibers will b""e compatible with existing fiber draw methods, splicing to conventional HEL pump delivery fibers, and possess favorable active ion s"pectroscopic properties. Careful attention also will be paid to thermal load and robustness of the material both opto-mechanically and from a practical standpoint of manufacturing fiber laser systems. Each Thrust is comprised of sub-tasks and goals to permit both" flexibility and severability.More specifically, previous JTO support to the team has shown nearly 20 dB suppression in SBS, 3 dB s""uppression in SRS, and 3 dB reduction in dn/dT that drives TMI; all through judicious materials selection. As is detailed at length"" herein, binary and ternary glasses, principally based on combinations of Y2O3, B2O3, Al2O3, BaO, BaF2, SrF2, and AlPO4 will be deve""loped into silicaclad optical fibers that exhibit the aforementioned properties. It is known that Al2O3, BaO, and SrO all possess ne""gative p12 photoelasticity values that, when mixed with silica, yield intrinsically low (and possibly zero) Brillouin gain. The high"" refractive indices of these glasses will be reduced by addition of their low index oxides, B2O3, and fluoride analogs, BaF2 and AlF""3 (or more refractory SrF2), affording low NA (ultimately single mode and no TMI), low Brillouin and Raman gain, and n2 oxyfluoride" compositions. Straight-forward solution chemical methods will be employed to purify the raw materials and enable losses below 20 dB/km. Materials modeling will be extended beyond the team~s prior JTO efforts associated with Brillouin gain and thermo-optic effects" to include validation for mixed glass systems (i.e., oxyfluorides) as well as the inclusion of parameters more broadly applicable t""o TMI, such as heat capacity and thermal conductivity.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2017
- Source ID
- N000141712546
Entities
People
- John Ballato
Organizations
- Clemson University
- Office of Naval Research
- United States Navy