Coherently seeded broadband ultrafast fiber amplifiers
dr hab. Mariusz Klimczak, dr Tomasz Stefaniuk
Wydział Fizyki, Uniwersytet Warszawski
The dissertation will be focused on optical, coherently seeded ultrafast fiber amplifiers. Research work shall include building of experimental setups for characterization and spectrotemporal characterization of coherent supercontinuum, as well as building of fiber amplifier setups and their characterization. Specifically, thulium-doped, and synchronized thulium-doped and erbium-doped amplifiers will be investigated, under optical seeding from a common, coherent supercontinuum signal. Research will be therefore conducted using laser sources covering wavelengths around 1560 nm and between 1800 nm and 2100 nm, which correspond to gain bands of erbium-doped and thulium-doped fiber amplifiers. In particular, the latter – amplifiers based on thulium doped active fibers is especially interesting because these devices dispose of the widest gain band among the three main fiber amplifiers (doped with either of Yb3+, Er3+ or Tm3+ ions). It is planned, that during the work, advantage would be taken from seeding one or two amplifiers from a common, spectrally broad, and coherent seed signal. This would specifically include addressing of entire amplification bandwidth of every seeded amplifier, as well as intrinsic synchronization and assuring of the same CEO (carrier-envelope offset) of pulses amplified in each of the seeded amplifiers. This opens entirely new possibilities in generation and synthesis of ultrashort light pulses in all-fiber systems. The first part of dissertation shall include description of measurements and detailed analysis of results obtained in spectro-temporal characterization of group delay in coherent supercontinuum light pulses in all-normal dispersion photonic crystal fibers. This part of work is aimed at experimental verification of temporal structure of spectrally broad pulses and selecting the most suitable fiber for generation of seed signal for seeding of ultrafast amplifiers. Selection criteria shall include dispersion and nonlinear properties, as well as birefringence and feasibility to obtain linearly polarized and spectrally broad seed pulses. In the second part of work, discussion shall be focused on experimental results of broadband seeding of thulium doped fiber amplifiers. The research will include work on setups built using polarization maintaining optical fibers and fiber components. Research methodology will be based on measurements of group delay characteristics using frequency resolved optical gating (FROG) and on measurements of noise characteristics of amplifiers, while the general aim of work will be identification of the compression point, i.e. the shortest obtainable output pulse duration in the investigated systems. Various factors influencing the compression point will be discussed, including seed pulse characteristics, spectral width of the output pulse, uncompensated third-order dispersion. The third part of dissertation shall be dedicated to discussion of results obtained with seeding of thulium-doped fiber amplifiers and erbium-doped amplifiers with a common, broadband and coherent seed signal. Only polarization maintaining fiber-based setups will be investigated. In addition to characterization of group delay profiles and noise performance of the output pulses, the work includes an attempt of nonlinear mixing of the two output pulses from each of the amplifiers and generation of sum frequency signal. The discussion thus includes results of work on group delay matching between the output pules, as well as their spectro-temporal characteristics and measurements of noise characteristics of the obtained sum frequency signal.