Abstract. We investigate the lasing performance of a new double-clad thulium/ytterbium co-doped octagonal-shaped fibre, basing on a cladding pump technique. The fibre is fabricated with the aid of a modified chemical vapour deposition combined with a solution doping technique. It is characterized by the Tm 3+ -and Yb
3+-cladding absorptions equal to 0.325 and 3.3 dB/m respectively at 790 and 976 nm. A triple-wavelength fibre laser operating at 1914.5, 1934.7 and 1953.6 nm is built that uses a 5 m long fibre in a ring configuration as a gain medium. With the fibre as long as 15 m, the ring laser produces the highest output power of 21.9 mW at the pump power of 3600 mW, with the lowest threshold pump power being equal to 1000 mW. When operating at 1961.4 nm, the maximal efficiency of 0.88 per cent is achieved for the gain medium length fixed at 10 m. We also demonstrate a Q-switched thulium/ytterbium-doped fibre laser that operates at 1977.5 nm and utilizes multi-walled carbon nanotubes as a gain medium. By varying the multimode 905 nm pump power from 1591.3 to 2261.5 mW, one can increase the pulse repetition rate from 18.8 to 50.6 kHz, while the pulse width then decreases from 8.6 to 1.0 µs. The maximum pulse energy 5.71 nJ is obtained at the pump power 2100 mW.
In this paper, we experimentally demonstrate a stable passive Q-switched fiber laser operating at 1543.5 nm using a double clad Erbium-Ytterbium co-doped fiber (EYDF) as the gain medium in conjunction with nonlinear polarization rotation (NPR) technique. An isolator is used in conjunction with a highly nonlinear EYDF to induce intensity dependent loss in a sufficiently-high loss ring cavity to achieve Q-switched operation with a low pump threshold of 300 mW. At 980 nm multimode pump power of 500 mW, the EYDF laser generates an optical pulse train with a repetition rate of 46.95 kHz, pulse width of 5.3 µs and pulse energy of 75.6 nJ. The simple and inexpensive Q-switched NPRbased laser has a big potential for applications in metrology, environmental sensing and biomedical diagnostics.
Simple and low cost passive Q-switched thulium-ytterbium co-doped fibre lasers (TYFL) operating at 1977.5 nm is demonstrated using 905 nm multimode pumping, in conjunction with a multi-walled carbon nanotubes (MWCNTs) saturable absorber. It uses a new octagonal shaped double-clad thulium ytterbium co-doped fibre, manufactured using a modified chemical vapour deposition process and a solution doping. The Tm 3+ and Yb 3+ cladding absorptions of the fibre are 0.325 and 3.3 dB/m at 790 nm and 976 nm, respectively. The MWCNTs composite is prepared by mixing the MWCNTs homogeneous solution with a diluted polyvinyl alcohol polymer solution before it is left to dry at room temperature to produce thin film. The film is sandwiched between two fibre connectors and integrated into the laser cavity for Qswitching pulse generation. The repetition rate of the Q-switching pulse can be tuned from 18.8 to 50.6 kHz while the pulse width reduces from 8.6 to 1.0 µs as the pump power increases from 1.6 to 2.3 W. At the pump power of 2.1 W, the TYFL produces the maximum pulse energy of 5.7 nJ.
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