Wavelength Tunable Thulium-doped Fiber Laser

Since the debut of fiber laser in 1960s, it has kept making progress in either quantity or performance attributing to its characteristics of low threshold, high gain, high efficiency, compact structure, rich output wavelength and easy tuning. Especially the 2μm eye-safe laser, which is produced by Thulium doped fiber, can be widely applied in fields such as remote sensing, optical communication, medical treatment and industrial processes, thus igniting booming international studies on it. Currently, researches on Thulium doped fiber laser concentrates on how to achieve high power and pulse output. In addition, taking the significant advantage of fiber laser featuring wavelength tuning, tunable laser can be greatly employed in fiber sensing, optical device detection, spectral analysis and WDM system. In light of all the advantages, this thesis intends to carry out an experimental study into several novel wavelength tunable Thulium doped fiber laser from the following aspects:Firstly, we propose a switchable and tunable Thulium doped fiber laser pumped by a home-made 1565-nm Erbium doped fiber laser with the Sagnac loop mirror used of polarization-maintaining fiber. The filtering property of Sagnac loop mirror with different length is discussed and its structure parameters are also optimized. By adjusting the PC in the Sagnac loop mirror, the proposed fiber laser can operate around 1860nm at the mode of tunable single-wavelength lasing with a wavelength tuning range of 10nm and also can be switched to the mode of stable dual-wavelength lasing.Secondly, based on the multimode interference theory as well as the pumper of 1565-nm Erbium doped fiber laser, a novel optofluidically tunable Thulium doped fiber laser is proposed in order to expand the range of tuning. In the experiment, a large diameter no-core fiber is adopted to produce a single mode-multimode-single mode (SMS) bandpass filter and the performance of the filter is investigated by adding different refractive index liquids, resulting in optimized structure parameters. By introducing the tunable filter in laser system, single-wavelength lasing tuned in the range of 45nm around 1860nm can be achievedFinally, this experiment proposes a current controlled tunable Thulium doped fiber laser on the basis of multimode interference with magnetic fluids and its pumper is a 793-nm laser diode. By employing general diameter no-core fiber, this experiment makes a filter with SMS structure, whose tunable capacity can be observed once electromagnetic is added when it is put in the capillary with magnetic liquid.4nm shift around 1950nm. By introducing the tunable filter in laser system, lasing around 1950nm can be achieved except for the disadvantage of instability of the output due to the large transmission bandwidth of the filter.