Ultrafast high power fiber lasers and their applications

Abstract

In this thesis I report experimental studies toward developing versatile, compact, and reliable ultrafast sources in the 1.5 micron wavelength region, and their power scalability.The first part of the thesis reports on the development of a stable all-fiberized wavelength-tunable frequency-shifted feedback (FSF) picosecond laser. Stability of the passive mode-locking mechanism is achieved by combining the effects of nonlinear polarization evolution and a frequency shifting mechanism carried out by an acousto-optic modulator. The novel configuration generates pulses in the range of ~ 34 to 66 ps, depending on the value of the frequency shift applied in the cavity. The cavity allows for continuous wavelength-tuning over 30 nm of the erbium gain bandwidth via a fiberized tunable filter. The stability of the laser cavity allows pulse analysis as a function of different parameters of the laser cavity. Additional extensive numerical analysis, combined with the experimental results, provide novel insights for understanding the dynamics of FSF lasers in the mode-locking regime, which have not been addressed in the literature before.

The second part of the thesis reports on the development of a versatile, stable, compact mode-locked fibre laser using nonlinear polarization evolution and a semiconductor saturable absorber mirror(SESAM). The novel cavity can generate pulses with widths between ~ 2.7 and 11 ps over 25 nm of erbium gain bandwidth. This is achieved by integrating in the cavity state-of-the-art optical filters. The performance of this laser is compared to that of the FSF laser in terms of pulse energy, amplitude noise, timing jitter and power scaling.

The third part of the thesis reports on the direct amplification of a mode-locked ~ 10 picosecond bandwidth-tunable laser source that I made by means of large-mode area (LMA) erbium-ytterbium co-doped and erbium-doped fibres. While cladding pumping amplification schemes have become a standard option for pulse amplification in the 1.5 µm region, core-pumped amplification in LMA erbium-doped fibres has been less studied. In this thesis, in addition to the amplification of picosecond pulses in an erbium-ytterbium co-doped fibre; I present a novel scheme that uses a hybrid co-propagation core-pumped (1480 nm) and counter-propagation cladding-pumped (980 nm) scheme, which compensates for the low cladding absorption at 980 nm of the erbium-doped fibre. Picosecond pulses are amplified up to 1.5 W with peak powers exceeding 11 kW.

The last part of this thesis reports on the study of a stable operating regime found in passive mode-locked lasers called noise-like pulses, which can generate broadband spectra directly from the main oscillator. Here, I report the record of a 135 nm bandwidth linearly polarized noise-like pulse generation in an erbium-doped fibre laser by exploiting the birefringence of the cavity and the Raman gain of a highly nonlinear fibre (HNLF). Noise characterization of the source is carried out and compared to other commercial broadband sources in order to see its applicability in areas such as optical coherence tomography.

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Identifiers

ORCID for J. Nilsson: orcid.org/0000-0003-1691-7959

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