A kind of large-mode-area (LMA) erbium-doped fiber (EDF) is required to get high output power with good beam quality. This new LMA EDF has a multi-layer-core structure which makes the mode area bigger. The key process is deposition of multi-layer-core structure by using modified MCVD to make every layer of the core with different refractive index. Furthermore, the key optical specifications of the fiber are measured. The absorption peak is 10.6 dB/m at 980 nm and 20 dB/m at 1550 nm. The cutoff wavelength is about 1300 nm. The mode field diameter (MFD) is 12.6 μm and 13.2 μm at 1550 nm according to Petermann-2 and Gaussian definitions, respectively. The core diameter is about 12 μm. The MFD of conventional standard EDFs is in a limited range ~5–8 μm, so the experimental result has made a big progress for MFD. Especially, we can improve the parameters of the multi-layer-core structure to get single mode EDF with larger mode area for high power fiber laser.
Beam quality degradation of signal light in a side pumping coupler with a large-mode-area signal fiber
