With the fiber laser developing towards high power, high energy, short pulse and good beam quality, it is urgent to enlarge the mode area of the double cladding fibers for laser amplification. A new effective solution that double cladding fibers based on microstructure techniques is demonstrated.

Wuhan National Laboratory for Optoelectronics fiber laser technology team Professor Li Jinyan, and doctor Wei Huifeng designed and fabricated a new type of all solid double cladding fiber, where the microstructured region acting as pump cladding around the core is composed by periodically arranged low-index Fluorine-doped silica inclusions with an extremely low filling ratio of 0.088. An accurate controlling on cladding index by 1 × 10-5 via our passively doped cladding (PDC) method was achieved. Two fibers with 127μm and 50μm core diameter respectively were fabricated from the same final preform designed by this approach. It is verified that our 50μm core diameter fiber can maintain robust single mode behavior at 1064nm wavelength. The advantage of an all-solid structure along with a much simpler fabrication process makes our approach very suitable for realizing very large mode area fibers for high power fiber laser application.

This work titled “All-solid very large mode area Ytterbium-doped silica microstructured fiber based on accurate control on cladding index” was published in the Optical Society of America (OSA) 's Optics Express (Vol.24, No.8, pp.8978-8987,2016). This work was financially supported by the National Science Foundation of China (Grant No. 61335009) 

Fig.1  Near field mode profile of 400μm cladding fiber at 1064nm under misaligning the launching condition. (a) X direction and (b) Y direction. (c) Beam quality measurement of the 400μm cladding fiber at 1064nm.