Cascaded Raman amplifiers based on fluorotellurite fibers

In this letter, we demonstrate efficient cascaded Raman amplification in fluorotellurite fibers pumped by a 1550 nm nanosecond laser. All-solid fluorotellurite fibers with a core diameter of - 5 ??m are fabricated by using a rod-in-tube method. By using a continuous wave (CW) 1765 nm fiber laser as the signal source for first-order Raman amplification, the amplified 1765 nm laser with an average output power of - 190.9 mW and a pulse width of - 3.42 ns is obtained from a 3 m long fluorotellurite fiber for an average pump power of - 519.35 mW and an input signal power of - 1.05 mW, corresponding to a net gain of - 22.6 dB and an optical-to-optical conversion efficiency of 36.76%. Furthermore, a CW 2049.2 nm fiber laser combined with the above 1765 nm laser are used as the signal sources for second-order cascaded Raman amplification. As the power of the 1765 nm and 2049.2 nm lasers are set as 1.05 and 1.00 mW, respectively, the amplified 2049.2 nm laser with an average output power of - 135.35 mW and a pulse width of - 3.36 ns is obtained from the fluorotellurite fiber for an average pump power of - 558.37 mW, corresponding to a net gain of - 21.3 dB and an optical-to-optical conversion efficiency of 24.24%. As the length of the fluorotellurite fiber is increased to 10 m, third-order cascaded Raman amplification is observed by using a 2442.6 nm signal generated by four-wave mixing and the above 1765/2049.2 nm lasers as the signal sources, causing the generation of the amplified 2442.6 nm laser with an average output power of - 18.84 mW. Our results show that fluorotellurite fibers are promising gain media for constructing cascaded Raman fiber amplifiers with a wide range of wavelengths.