Recently, Lili Hu's research group in the Department of Advanced Laser and Optoelectronic Functional Materials, Shanghai Institute of Optics and Precision Machinery (SIPM), Chinese Academy of Sciences (CAS), has proposed a new scheme based on the optimization of field strength of Er-doped silicate fiber as an amplifier to extend the L-band broadband. The related research results were published in Optics Letters under the title of "Er-doped silicate fiber amplifiers in the L-band with flat gain".
The rapid development of big data and artificial intelligence has put forward higher requirements for the capacity of dense wavelength division multiplexers (DWDM) in next-generation optical communication systems. Compared with the maturely developed C-band (1530-1565 nm) erbium-doped fiber amplifier (EDFA), L-band (1565-1625 nm) EDFA has become a new generation of capacity-expanding optical communication products. However, the development of L-band EDFAs faces difficulties and challenges: the gain of Er-doped fibers is limited by the low long-wave emission cross-section and severe excited state absorption, resulting in a small gain at wavelengths greater than 1600 nm. Therefore, how to enhance the long-wavelength gain of Er-doped fiber materials is a key scientific problem that needs to be solved for L-band broadband amplifiers at present.
The research team proposes a new scheme of microscopic ion field strength modulation method for gain enhancement and spectral shaping of Er ions in silicate fiber matrix. The feasibility of silicate fiber as a long-wavelength gain enhancement matrix for Er ions is confirmed both theoretically and experimentally. The scheme obtained the beneficial effects of significant L-band gain enhancement and gain flatness optimization in Er-doped silicate fibers. Meanwhile, by adopting the all-fiber scheme of heterogeneous fiber fusion splicing, using only 1.5 m silicate fiber, the gain coefficient at the longest wavelength of 1625 nm in the L-band is 4.7 dB/m, which is better than that of the quartz fiber of 0.3 dB/m. In addition, the gain flatness of this fiber in the L-band is 0.8 dB, which is better than that of the quartz fiber of 5 dB. Compared with the quartz fiber, the fiber has a high dopant concentration, Compared with quartz fiber, this fiber has high doping concentration, short use length and large gain coefficient, which provides key material support for the new generation of L-band EDFA.
This work is supported by the National Natural Science Foundation of China and National Key Programs.
Fig. 1 L-band gain of Er-doped silicate fiber
