Speaker
Description
In recent years, thulium-doped fibre (TDF) laser systems operating around the 1.9-micrometre region, so-called “eye-safe”, have remarkably performed in various applications, such as medical treatments, remote sensing, scientific research, industrial material processing, etc. Most of these applications are achieved by mode-locked TDF lasers working in the anomalous dispersion that limits the single pulse energy because of its inferior ability to accommodate nonlinear phase compared with normal dispersion operations. Some commercial ultra-high numerical apertures (UHNA) single-mode optical fibres can also compensate for the TDF laser cavity dispersion. However, UHNA fibres have smaller core diameters than SMF to obtain the higher NA, which is unsuitable for high-power laser operation. Besides, the optical gain is still generated in the anomalous dispersion TDF fibres; net normal dispersion operations cannot avoid solitons' pulse breaking.
Here, we fabricated a large-mode-area W-type normal dispersion TDF (NDTDF) that offers normal dispersion at a wavelength above 1650nm to deliver high pulse energy. The presented all-fibre mode-locked TDF laser operated in the net normal dispersion and all-normal-dispersion regimes in the LP02 mode based on an in-house mode selective coupler (MSC). The homemade MSC using a long-period grating (LPG)realized highly efficient mode conversion from LP01 to high-order modes (LP11, LP21, LP02) in the drawn NDTDF.
