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A comparative study of tapered fiber laser configurations

We present a comparative theoretical and experimental study of different schemes of fiber lasers with tapered doubleclad fiber (T-DCF) as an active medium. We have developed a theoretical model for obtaining the distribution of power and power density inside the fiber for the considered laser schemes with different longitudinal shapes of T-DCFs. The slope efficiencies, spectral characteristics, and beam quality deterioration associated with the mode conversion in the TDCF were also studied experimentally for different laser schemes. In addition, a spontaneous transition to a self-pulsing regime under certain conditions, and the associated problems have been investigated. Characteristics of T-DCF lasers constructed in co- and counter-propagating schemes are discussed and compared to those of regular fiber lasers, equivalent in active volume or in brightness.