Thulium Doped Fiber Lasers At 2μm Region Based On Fiber Nonlinear Effect

In recent years, ultra-short pulsed fiber laser and multiwavelength fiber laser sources operating at 2.0 μm have attracted more and more attention owing to their wide applications in laser medical and environmental monitoring etc, and the series of merits such as compactness, robustness, high flexibility, excellent heat dissipation and convenient intergration. In this dissertation, our study mainly focuses on passively mode-locked and multiwavelength fiber lasers centerd at 2.0 μm based on fiber nonlinear effect, which can be divided into the following three sections:(1) Based on nonlinear Schrodinger equation, the numerical model of describing passively mode-locked thulium doped fiber laser(TDFL) with fiber nonlinear effect is constructed, and the pulse evolution is numerically simulated. Moreover, the transmission function of nonlinear polarization rotation(NPR) based TDFL is solved using the Jones Transfer Matrix method(JTM), and the two different regions of the cavity are also modeled and analyzed theoretically.(2) Firstly, the nonlinear amplified loop mirror(NALM) based passively mode-locked TDFL is realized, which can operate at soliton and noise like pulses(NLP) simultaneously. In soliton regime, the laser can produce stable single pulses with duration of 1.53 ps, repetition rate and pulse energy of 10.34 MHz and 0.21 nJ, respectively. At the highest pump power, the NLP with output power high to 589.52 mW are achieved, which is also the highest power level in NLP. Secondly, based on thulium/holium co-doped silica fiber with high doping, the ultra-short cavity with NPR structure is constructed, which can generate ultra-short soliton pulses with duration of 566 fs, and corresponding energy of 186.68 pJ with repetition rate of 25.98 MHz. Thirdly, using the power dependent transmission method, the saturable absorptions of different single walled carbon nanotubes(SWCNTs) are completed. In addition, by employing SWCNT-C, the stable pulses with repetition rate of 37.3 MHz, pulse energy of 32.4 pJ and pulse duration of 543 fs are gained. Finally, the hybrid mode-locked thulium/holium codoped fiber laser with self-starting and high signal noise ratio single soliton output is also realized with the combination of NPR and SWCNT.(3) Based on JTM mothod, the theoretical model of birefringent fiber filter(BFF) composed of polarization maintaining fiber(PMF), polarization dependent isolation(PDI) and polarization controller(PC) is built and simulated, respectively. And the fiber nonlinear effect based multiwavelength TDFL is constructed based on this model, which can produce the two wavelength laser with central wavelength of 1923.9 nm and 1927.9 nm simultaneously. Besides, the cavity also can operate passively mode-locked regime with fundamental frequency, third harmonic, fifth harmonic or tenth harmonic pulses output. As far as we know, this is also the first multiwavelenth TDFL at 2.0 μm which can operate at continous multi lasing and mode locking pulses state simultaneously.