Ultrafast Fiber Lasers Using Novel Semiconductor Saturable Absorbers and Photonic-Crystal Dispersion Compensators
Isomäki, Antti (2007)
Tampere University of Technology
Arkkitehtuurin osasto - Department of Architecture
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This thesis is concerned with development and demonstration of new techniques for mode-locked fiber lasers using semiconductor saturable absorbers and advanced dispersion compensators. Semiconductor saturable absorber mirrors have been widely used for controlling a large variety of mode-locked lasers since the beginning of 1990s. Several absorber designs have been proposed during these years aiming at optimizing the dynamic properties to achieve reliable start-up and to sustain mode-locking in different types of lasers. In this thesis I present two approaches for semiconductor absorbers a reverse-biased saturable absorber reflector and a saturable absorber used in transmission. While the first, mirror-type absorber was suitable for linear cavity fiber lasers, the transmission-type absorber was conveniently implemented in a ring cavity. The performance of the absorbers in starting the pulse operation and in shaping ultra-short pulses was tested in Er- and Yb-fiber lasers, respectively. Traditionally, the dispersion has been tackled by inserting prisms and diffraction gratings in the laser cavity. However, finding alternatives to these conventional bulk optical components has been of substantial interest in fiber systems. In this thesis I consider two very dissimilar solutions for dispersion management in fiber lasers. A semiconductor Gires-Tournois interferometer can be used to generate a tunable delay within a limited optical bandwidth. The saturable absorption in this structure provides means for controlling the dispersion of the device. Secondly, a method based on solid-core photonic bandgap fibers offers an all-fiber solution. The high anomalous dispersion of this new class of optical fibers can compensate for the normal dispersion of other cavity components at 1 ?m wavelength range. This unique property makes these fibers attractive candidates when looking for methods to produce ultra-short laser pulses at this spectral range.
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