title: Mode-converters for rectangular-core fiber amplifiers to achieve diffraction-limited power scaling.
abstract: A rectangular-core (ribbon) fiber that guides and amplifies a single higher-order-mode (HOM) can potentially scale to much higher average powers than what is possible in traditional circular-core large-mode-area fibers. Such an amplifier would require mode-conversion at the input to enable interfacing with seed sources that typically output TEM(00) mode radiation and at the output to generate diffraction-limited radiation for end-user applications. We present the first simulation and experimental results of a mode conversion technique that uses two diffractive-optic-elements in conjugate Fourier planes to convert a diffraction limited TEM(00) mode to the HOM of a ribbon fiber. Mode-conversion-efficiency is approximately 84% and can theoretically approach 100%. We also demonstrate a mode-converter system that converts a single HOM of a ribbon fiber back to a diffraction-limited TEM(00) mode. Conversion efficiency is a record 80.5%.
authors.affiliation: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA. sridharan1@llnl.gov
authors.forename: Arun Kumar
authors.initials: AK
authors.lastname: Sridharan
authors.forename: Paul H
authors.initials: PH
authors.lastname: Pax
authors.forename: John E
authors.initials: JE
authors.lastname: Heebner
authors.forename: Derrek R
authors.initials: DR
authors.lastname: Drachenberg
authors.forename: J Paul
authors.initials: JP
authors.lastname: Armstrong
authors.forename: Jay W
authors.initials: JW
authors.lastname: Dawson
mesh_terms: D000669:Amplifiers, Electronic; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005336:Fiber Optic Technology / Q000295:instrumentation*; D007834:Lasers; D012031:Refractometry / Q000295:instrumentation*