Pulse dynamics of passively mode-locked polarization maintaining fiber lasers
Kothalawala, Veenavee Nipunika (2021)
Kothalawala, Veenavee Nipunika
School of Engineering Science, Laskennallinen tekniikka
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Continuous advancement in understanding the pulse dynamics and characteristics in the development of mode-locking techniques supports accelerating the widespread utilization of ultrafast laser fabrication over a broad range of applications, such as optics, optical communication, and material processing. Also, ultrafast pulsed fiber lasers have acquired an unique attraction among other types of lasers due to their diverse astonishing features such as adaptability, higher reliability, and excellent beam quality. The work devoted in this thesis presents a detailed analysis of passively mode-locked Yb-doped polarization-maintaining fiber lasers operating at 1:04 μm wavelength in all-normal dispersion (ANDi) regime. The focus of this study is to investigate and evaluate the pulse dynamics and characteristics of different mode-locking methods. For this, we examine three fiber cavity configurations (a ring, a figure-eight, and a linear cavity) by exploiting the passive mode-locking approach. Accordingly, the semiconductor saturable absorber mirror (SESAM) and the nonlinear amplifying loop mirror (NALM) are applied to modelock the lasers passively. Experimental results are obtained by employing an optical spectrum analyzer (OSA), radio frequency (RF) spectrum analyzer, frequency-resolved optical grating (FROG) technique, and dispersive Fourier transformation (DFT) method to evaluate the pulse characteristics. The FROG measurements are conducted to determine the primary pulse chirp picture that explains the chirp and the compressibility of the laser. Besides that, we also compared start-up, transition, and build-up mechanisms of these different mode-locked techniques through the time-stretched DFT evaluations.