Experimental demonstration of PPLN-based double ring fiber laser and its application to 40 Gb/s wavelength conversion

摘要

We report a novel double ring fiber laser incorporating a periodically poled LiNbO_3 (PPLN) waveguide. The double ring fiber laser is formed by placing two parallel-arranged tunable filters (TFs) followed by two variable optical attenuators (VOAs) inside the PPLN-based fiber ring cavity. Two continuous-wave (CW) lasing lights can be obtained from the double ring fiber laser with their wavelengths determined by two tunable filters. Using cascaded second-harmonic generation and difference-frequency generation (SHG+DFG), as one of the lasing waves is tuned at the quasi-phase matching (QPM) wavelength of PPLN, the third idler wave is generated. It is easy to perform tunable operation simply by changing the other lasing wavelength. Based on cascaded sum- and difference-frequency generation (SFG+DFG), it is also possible to realize tunable wavelength conversion. Both input signal and converted idler can be tuned by appropriately adjusting two lasing waves. With PPLN-based double ring fiber laser, we first demonstrate stable dual-wavelength generation with minimum wavelength spacing of 0.32 nm. Then we observe SHG+DFG-based tunable triple-wavelength generation. Finally, tunable wavelength conversion at 40 Gb/s based on SFG+DFG is successfully demonstrated in the experiment. No external CW optical waves are needed, which effectively reduces the complexity and cost of the wavelength converter.