Multi-Parameter Characterization ofOptical Fibers for High Power Fiber Lasers

ABSTRACT: This project will demonstrate the feasibility, and determine the performance capabilities, of a laboratory instrument for non-destructively measuring multiple parameters of a high power optical fiber.Firstly the apparatus will measure the fibers refractive index profile and geometry in its short wavelength infrared (SWIR) operating band by multi-wavelength transverse interference microscopy, secondly it will measure the spatial distribution of the fiber's rare-earth dopants by spontaneous emission tomography, and thirdly it will measure the fibers residual stress distribution by polarimetry.Measuring all these parameters in a high power fiber will supplement, and even supersede, existing optical fiber preform measurement technology by providing in-band quantitative data on the actual drawn fiber itself and will therefore facilitate the design, optimization, and commercial manufacture of superior high power fibers and fiber-based components that will serve as the basis for future high energy lasers (HELs) and directed energy (DE) weapons.; BENEFIT: Phase I of this project will demonstrate the feasibility of measuring both the refractive index profile and its wavelength dependence in a high power fiber in its SWIR operating band.It will also demonstrate the possibility of measuring the spatial distribution of the rare earth doping profile and the residual stress distribution in a high power fiber.Additionally, this project will clarify the achievable precision and accuracy of these measurements.The measurement capabilities demonstrated by this project will enable the development of superior high power optical fibers and amplifiers in SWIR bands.The performance of current generation high power optical fibers are constrained by impairments, such as modulation instabilities (MI), that are incompletely understood but would be elucidated by measurements proposed in this SBIR.Demonstrating the feasibility of a multi-parameter measurement platform is anticipated to provide a foundation for a commercial fiber characterization instrument in a later SBIR phase.Such a commercial instrument would be of great value to researchers, designers, and manufacturers of high power optical fibers for high energy lasers (HELs) and directed energy (DE) Weapons.