M. C. Paul

Mode-locked 2 mu m fiber laser with a multi-walled carbon nanotube as a saturable absorber

We propose and demonstrate a passively mode-locked fiber laser operating at 1951.8 nm using a commercial thulium-doped fiber (TDF) laser, a homemade double-clad thulium-ytterbium co-doped fiber (TYDF) as the gain media, and a multi-walled carbon nanotube (MWCNT) based saturable absorber (SA). We prepare the MWCNT composite by mixing a homogeneous solution of MWCNTs with a diluted polyvinyl alcohol (PVA) polymer solution and then drying it at room temperature to form a film. The film is placed between two fiber connectors as a SA before it is integrated into a laser ring cavity. The cavity consists of a 2 m long TDF pumped by a 800 nm laser diode and a 15 m long homemade TYDF pumped by a 905 nm multimode laser diode. A stable mode-locking pulse with a repetition rate of 34.6 MHz and a pulse width of 10.79 ps is obtained when the 905 nm multimode pump power reaches 1.8-2.2 W, while the single-mode 800 nm pump power is fixed at 141.5 mW at all times. To the best of our knowledge, this is the first reported mode-locked fiber laser using a MWCNT-based SA.

The Use of Yttria-Alumino-Silicate Bismuth Doped Fibers for Temperature Sensing

Yttria-alumino-silicate fibers heavily doped with bismuth (BI) are investigated for fluorescence temperature sensing within the interval 25°C...500°C at 750-nm (LED) excitation. High doping with Bi which resulted in a high concentration of Bi active (fluorescing) centers, is shown to permit the use of short pieces of the fibers as “point” sensors, which is advantageous for applications. Theoretical backgrounds of three commonly utilized sensing techniques, based on measuring fluorescence intensity ratio, fluorescence lifetime, and frequency-domain referencing, are developed and compared, aiming for effective temperature sensing using these fibers.

Comparison of cladding shaped of Tm/Yb doped fiber laser for optimum lasing efficiency

A Tm3+/Yb3+ doped fiber laser (TYDFL) using two different types of cladding shapes fiber was demonstrated. The fiber consists of a fabricated D-shaped cladding and circular cladding fiber with a double clad structure. The difference in the ratio of ions concentration between doped ions for both fibers resulted in different lasing output performance. The ring cavity laser setup was used to observe the free running lasers using high-power multimode 931 nm pump sources. It is observed that the D-shaped fiber shows better performances in terms of ASE and lasing compared to a circular shape cladding fiber. The threshold and slope efficiency of a D-shaped fiber were observed to be 1.7 W and 0.82%, respectively.

Development of Nanoengineered Thulium-Doped Fiber Laser With Low Threshold Pump Power and Tunable Operating Wavelength

A tunable and low-threshold thulium (Tm)-doped fiber (TDF) laser is demonstrated using a new silica-based nanoengineered TDF in a linear configuration, in conjunction with 1552-nm pumping. The TDF used in these experiments had a Tm-doped nanoengineering yttrium-alumina-silica glass core with a diameter of 13.43 μm and 0.21 NA, which is surrounded by a pure silica inner cladding with normal acrylate polymer resin coating. The nanoengineered TDF was fabricated using a modified chemical vapor deposition (MCVD) process, in conjunction with a solution-doping technique. The fabricated fiber shows an absorption loss of 165 dB/m at 793 nm. A maximum lasing slope efficiency of 26.2% was obtained at a 1910-nm wavelength using the fabricated fiber with an optimum length of 5 m. The maximum output power of 138 mW was achieved at the maximum pump power of 1100 mW. The lowest pump power threshold of 693 mW for a 1552-nm wavelength was obtained at a TDF length of 7 m. The operating wavelength of the laser could be continuously tuned from 1890 to 1910 nm with an optical signal-to-noise ratio better than 43 dB, whereas the slope efficiency of the laser varies from 16.4% to 19.7%.

Effects of Yb/Tm Concentration and Pump Wavelength on the Performance of Ytterbium-Sensitized Thulium-Doped Fiber Laser

A 1901.6-nm laser is demonstrated using the newly developed double-clad ytterbium-thulium-doped fiber (YTDF) samples in conjunction with 931-nm pumping through the transition of thulium ion from 3F4 to 3H6 with the assistance of ytterbium to thulium-ion energy transfer. The YTDF used was drawn from a D-shape preform, which was fabricated using the modified chemical vapor deposition and solution-doping technique. The laser operates at 1901.6 nm with an efficiency of 2.47% using 2-m-long YTDF in a Fabry-Pérot cavity with two fiber Bragg gratings. It is found that the higher ytterbium-to-thulium concentration ratio contributes to more efficient energy transfer between the sensitizer and acceptor ions in YTDF, which in turn lowers the threshold of the proposed ytterbium-thulium-doped fiber laser (YTFL). The lowest threshold pump power of the proposed YTFL is around 961 mW. The use of multimode pump with a wavelength slightly lower than 931 nm is also observed to improve both the lasers threshold and efficiency of the YTFL.

Wideband spectrum-sliced ASE source operating at 2 micron region based on double clad ytterbium-sensitized thulium-doped fiber

In this paper, we report a wideband spectrum sliced ytterbium sensitized thulium doped fiber at 2 micron wavelength region. This result was achieved using a simple fiber loop mirror formed by a 2.6 m PMF fiber and a directional coupler. The wide-band spectrum sliced ASE is demonstrated using a 915nm multimode pump ytterbium sensitized thulium doped fiber at a room temperature. Result shows that the spectrum threshold was 786mW and the output spectrum will be increased as the pump power was increase up to 1W. The channel spacing of 3.3nm and extinction ratio of 6 dB was achieved within the wavelength region of 200nm when the output power is 1W. The comb spectrum centred at 1888 nm with peak power of around -55 dBm.