Comparison of linear and ring lasers of thulium-ytterbium co-doped fiber

Performance of a double-clad Tm³⁺/Yb³⁺ co-doped yttria-alumino-silicate fiber (TYDF) fiber laser are compared for linear laser and ring laser using 905nm and 931nm pump wavelengths. TYDF used has a D-shaped cross section structure with Tm³⁺ concentration of 5.55×10¹⁹ions/cc and Yb³⁺ concentration is 13.5×10¹⁹ions/cc. Cladding-pumping scheme is applied for this fiber. Linear laser operates at 1901nm which is the operating wavelength of the fiber-Bragg grating used in the configuration. Ring lasers operate at lower pump power threshold of only 0.8W and 1.2W for pump wavelengths of 931nm and 905nm, respectively. Linear lasers have much higher pump power thresholds of 1.2W and 2.2W for the same pump wavelengths used. Maximum output power of 7.03mW was achieved for linear laser pumped 905nm. Efficiency of linear laser using 905nm pump is 0.84% compared to ring laser´s efficiency of only 0.56% using the same pump wavelength. For 931nm pump, linear laser efficiency is 0.70% while ring laser´s efficiency is only 0.40%. It is proven that linear laser gives superior performance in terms of maximum output power and efficiency compared to ring laser. It is also apparent that lasers pumped with 905nm is more efficient compared to 931nm pump.