Controlling Stimulated Brillouin/ Raman Scattering
Abstract
Project abstract The main goal of this research project is to control stimulated Brillouin and Raman scattering in optical fibers under high power laser operation. Three main tasks will be pursued during the course of this project. 1. Investigate stimulated Brillouin scattering (SBS) in optical fibers for development of high power level single frequency fiber lasers: Currently, stimulated Brillouin scattering (SBS) is the primary power-scaling limitation for single frequency fiber lasers. The state-of-the-art output power level of 811W was recently reported by researchers at AFRL, limited primarily by SBS. We would like to address this challenge in this task. In the first stage, we will improve upon the current SBS limited 811W result by further optimizing the optical fiber design and optimization of the thermal gradient by in-situ SBS gain spectrum monitoring. The optimal thermal gradient may be found by in-situ heterodyne SBS gain spectrum measurement while the high power amplifier is operating. An experimental setup will be built to realize this capability. The Stokes light from the amplifier with be interfered with a sample of the single frequency source used to seed the fiber amplifier. The SBS gain spectrum can then be recorded via high speed RF spectrum analyzer. The thermal gradient condition can then be optimized using this feedback information in order to find the best operating condition for the high power amplifier. 2. Design new large mode area (LMA) photonic crystal gain fibers (PCF) with enhanced SBS threshold: We will investigate new fiber designs in this task to improve the SBS threshold performance. The first approach is to improve upon the current best design by introducing more number of materials used to form the core of the active gain fiber. In particular, we will look into the possibility of using Yb-doped materials instead of un-doped glass in the core of the segmented acoustically tailored PCF to increase the absorption per length of the active fiber. This will enable shorter gain length which will allow higher output power before reaching the onset of SBS. It is also crucial to be able to know the dependence of the SBS gain spectrum on the doping level of the Yb-doped glass. Innovative fiber designs incorporating nano-structures will be also considered in order to better control SBS. 3. Conduct research into understanding stimulated Raman scattering (SRS) in passive and active optical fibers: The goal is to be able to control SRS in high power fiber lasers as well as efficient brightness and wavelength conversion. To achieve this goal we will build an experimental setup for determination of stimulated Raman scattering in short length active and passive optical fibers.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 14, 2016
- Source ID
- FA94511510042
Entities
People
- Khanh Kieu
Organizations
- Air Force Research Laboratory
- United States Air Force
- University of Arizona