Broadband Fiber Raman Power-Amplifier for Narrow Linewidth Tunable Seed Lasers Used in Spectroscopic Sensing

We propose an energy and space efficient high power continuous wave (cw) narrow linewidth broadband fiber Raman amplifier (FRA) with spectrally tunable multi-Watt-level average power output in the near and shortwave infrared (1080 – 2000 nm) that can be used in remote sensing systems on both atmospheric and terrestrial space-borne platforms. The all-fiber amplifier design concept for power amplification of a lower power commercially available tunable laser seed source (master oscillator) uses a single gain stage architecture based on germanosilicate (GeO2-SiO2) fibers specifically designed to suppress stimulated Brillouin scattering (SBS), one of the main factors limiting the maximum output power from narrow linewidth cw fiber amplifiers. The amplifier will be pumped by a fiber Raman laser whose spectral output can be tuned by compressive fiber Bragg grating technology. For this proposal TIPD will demonstrate power levels beyond what has been previously demonstrated for this technique, necessary for pumping the SBS suppressed gain fiber amplifier stage to its maximum potential output power. By implementing techniques for suppressing SBS in highly doped germanosilicate fibers it is anticipated that the amplifier wall-plug efficiency will reach 10%. In addition, the single gain stage architecture is compatible with distortion-free amplification of a phase/amplitude modulated seed source, useful for sensors that rely on sophisticated signal processing for detection. During Phase I, we will validate the broadband FRA proof-of-concept through modeling and benchtop demonstrations of both the power amplifier and tunable pump laser stages. Furthermore, appropriate designs for both the tunable laser source and SBS suppressed germanosilicate gain fibers will be formulated and assessed in terms of performance that best meets the target technical specifications for the FRA for a potential Phase II effort.