Fiber With Comb-Index Core Designed for High-Power Fiber Lasers

A comb-index core fiber (CIF) designed for high-power fiber lasers is proposed, in which the index distribution in the fiber core is comb-like. It is shown that the advantages of the CIFs include few guiding modes, excellent beam quality, large mode area, high optical damage threshold, and high tolerance to fabrication errors. Compared with the conventional single step fiber with the same normalized frequency V , the mode number of CIFs decreases from dozens to only a few ones and single-mode operation is achievable under certain conditions or with the help of fiber bending. The mode profile of LP₀₁ is close to Gaussian shape, which guarantees the beam quality to be of nearly diffraction limit. Meanwhile, the mode area increases by 50%-100% depending on different V values. The maximum power supported by the CIF increases by more than 100%. Finally, 30% fabrication errors on the refractive index and the ring thicknesses have only a little influence on the mode properties of CIFs, which is favorable in practical application.